Unit 3-Nervous System

Chapter 5

The Central Nervous System

1. General Remarks:

     The value is uncertain, but it seems probable that there are at least 10 billion neurons in the central nervous system along with 100 billion neuroglial cells. Interconnections among the 10 billion neurons make a very complicated system, and one which does not lend itself to easy prediction. Hence, the apparently endless variety of behavior. It is, nevertheless, possible to make some statements about various parts of the central nervous system, and this will be the concern of this chapter.

     The student should recognize that much of our information concerning the central nervous system is obtained by invasive techniques. The invasion of a network--and the central nervous system is basically a network of neurons--destroys the integrity of the network, so many of the conclusions reached about the nature of the network are as fragile as the network itself.

2. Central Nervous System and Autonomic Nervous System:

     The brain and spinal cord, in the bony case provided by the cranium and the vertebrae, receive sensory nerves. Motor nerves issue from the brain and cord. In the cord, the arrangement is relatively simple; one nerve, with its sensory and motor components corresponds to each vertebra. The arrangement in the brain is quite different and will be discussed later.

     The central nervous system is connected to the autonomic nervous system, which controls the function of the internal organs and of the blood vessels and sweat glands of the skin. The term autonomic means self governing, but, in fact, the internal organs are not truly self governing, for their functions can be radically modified by the central nervous system. They are, however, self-sustaining; that is to say, they will survive a destruction of their nerves. Anatomically, however, the autonomic nervous system seems to be a separate entity, and in a sense, its physiology is somewhat different from that of the central nervous system. It will be considered in the next chapter; but its relationship to the central nervous system should always be remembered.

3. Major Subdivisions of the Brain and Spinal Cord:

     The brain and spinal cord, which make up the central nervous system, are divided into six parts recognizable by gross dissection. These are as follows, going from the cord upwards:

     These are illustrated in Figure 99.

4. Membranes of the Brain and Cord:

     Three membranes surround the structures of the central nervous system. Collectively they are called the meninges. The membrane closest to the tissues of the central nervous system is the pia mater. It follows every twist and turn of the brain and cord, bringing small blood vessels to the surfaces. Outside the pia mater is a thin, transparent, gray membrane. It resembles a spider web, hence its name, the arachnoid mater. Unlike the pia mater, the arachnoid is not intimately associated with brain tissue. A space exists between the arachnoid and the pia called the subarachnoid space. The blood vessels of the pia mater, which are derived from the arachnoid mater, course through the sub-arachnoid space. Most cerebral hemorrhages, one of the more common causes of strokes, occur as a result of bleeding of vessels in this space. It is easy to understand this, since these vessels are basically unsupported and course free. Other causes of strokes and some of their effects will be considered at the end of this chapter and in Chapter 16.

     The dura mater is the outermost of the brain linings. It is very closely associated with the arachnoid, and there is not true space between them. The dura mater is very tough and mostly without blood vessels. One can consider it a fibrous skeleton within the bony cranium. The folds of the dura mater keep the parts of the brain in normal position relative to each other. For example, the dura separates the right and left cerebral hemispheres, flax. It separates the cerebellum from the cerebrum (tentorium). These foldings of the dura are shown in Figure 100.

     Although the dura and arachnoid are very closely related to each other, a potential space exists between them, called the subdural space. Blows on the head--even minor ones--sometimes cause hemorrhages into the subdural space. These hemorrhages usually stop quickly, but the blood in the subdural space, sub-dural hematoma, may press against the brain, particularly if hematoma attracts water from the blood, as often happens. Subdural hematomas are more easily treated and usually have less profound effects than sub-arachnoid hemorrhages, provided that they are recognized.

5. Structure of the Spinal Cord:

     The structure of the spinal cord is shown in cross section in Figure 101. The cord is enveloped by the membranes described above and encased in the bony canal of the vertebrae. The neurons of the spinal cord are aggregated in the gray matter, which is shaped somewhat like an "H" within the cord. The white matter of the cord consists of axons, many of them myelinated, which carry nerve impulses up and down the cord. One important group of neurons is outside the cord but inside the bony canal. This is the group of cell bodies involved in the transmission of information from the sense organs to the cord. They make up the dorsal root ganglion.

     A very useful generalization is that sensory information comes to spinal the cord by way of its dorsal root. Motion is controlled by axons which leave the cord by way of its ventral root. The discoveries that sensory information enters the cord by way of the dorsal root and that motor information leaves the cord by way of the ventral root were made almost simultaneously by Bell, an English physician, and Magendie, a French physiologist. It is called the Bell-Magendie Law.

6. Functions of the Spinal Cord:

     Some sensory information is acted upon in the cord, processed there, and appropriate motion produced through activation of spinal motor neurons. For example, a spinal animal, that is to say one in which the brain has been severed from the cord, is still capable of some responses. Spinal men, though they cannot move muscles voluntarily, are quite capable of moving a limb which has been stimulated. Their internal organs function fairly well on the whole. Several functions can be attributed to the cord:

     (1) Sensory information from the body exclusive of the head comes to the cord first through its dorsal root ganglin.

     (2) Such sensory information as is facilitated from above by transmission of impulses through white matter or as is properly summated (in time or in space) results in activation of motor neurons.

     (3) Information is transmitted upwards to the brain; this travels in the white matter.

     (4) The activity of the internal organs and the blood vessels and sweat glands of the skin is controlled, in part, by impulses originating from the cord.

     Figures 101 and 102 show the anatomical basis for some of these functions. The innervation of the internal organs is not shown in these Figures: it will be considered in Chapters 6 and 7.

     It has been found that various types of information travel together in the white mater of the cord. For example, sensory information regarding position and movement (proprioceptive information) travels in the dorsal columns in rather well defined tracts. When these tracts are diseased, as in the disease tabes dorsalis, the afflicted subject, though he can move, does not know exactly how much motion he has performed. His movements become quite awkward because of this sensory loss. The sense of pain travels in two well defined tracts, the lateral and anterior spinothalamics. These are sometimes deliberately interrupted for the relief of pain.

     Information which controls and facilitates voluntary motion is carried downward from the brain by a number of tracts. Some originate in the medulla, some in the cerebellum, and some in the cerebral cortex.

     The most important of the sensory and motor tracts are shown in Figure 103. In this figure, the location of the tract in the cord and the area of the brain connected with the tract are shown together.

7. Spinal Nerves:

     The spinal nerves originate from the spinal cord, exiting between vertebrae. There are seven cervical vertebra and eight nerves derived from the cervical portion of the cord. The extra nerve comes out between the skull and the first cervical vertebra, called the first cervical nerve.

     The eighth cervical nerve lies below the seventh cervical vertebra. From here on, the nerve takes its name from the vertebra above. Thus, the fourth thoracic nerve leaves the spine below the fourth thoracic vertebra. The third lumbar nerve leaves the spine below the third lumbar vertebra.

     The sacrum represents the fusion of five vertebrae, so there are five sacral nerves.

     The coccyx is represented by one spinal nerve, usually quite vestigial.

     The sensory part of each spinal nerve, serves one body segment, called a dermatome. The dermatomes are most clearly understood in an animal which walks on all fours, since they progress quite regularly from the front to back. The vertical position of man makes the distribution of the spinal nerves much harder to understand. A diagram such as Figure 104, by showing a man on all fours, may help.

     The spinal cord is much shorter than the vertebral column. Thus, a spinal nerve which will issue in, say, the lower lumbar region will originate from the cord in mid-chest. Running downward in groups within the spinal column, the spinal nerves, particularly those derived from the lower parts of the cord, are called the cauda eguina, or horse’s tail.

     There is no spinal cord below the second lumbar vertebra. The spinal canal contains some of the membranes of the central nervous system, cerebro-spinal fluid, and the cauda equina. It can, therefore, be entered by a needle with relative safety between the third and fourth lumbar vertebrae, a lumbar puncture.

     The manner in which the spinal nerves fuse, separate and travel is shown in the Table of Nerves (pp. 1-4) and illustrated in Figures 105 to 110.

8. Functions of the Spinal Nerves:

     The fibers of the spinal nerves conduct sensory impulses to the central nervous system. They conduct motor impulses away from the central nervous system. Some of these impulses go to internal organs (Chapter 6), while others go to skin structures such as sweat glands and blood vessels. Others go to skeletal muscle, conveying motor impulses.

     There is no evidence that spinal nerves do anything else whatever. The idea that spinal nerves conduct "vital fluids" to their organs of distribution, that they are "pinched" between the vertebrae, interrupting this flow, and that manipulation of the spine, by relieving such pinching, can restore health, is the basis of a fairly big business but has no scientific merit whatever.

9. Distribution of the Spinal Nerves:

     Plates 7 and 8 of the dissectograph show the spinal nerves as they leave the spine. Their further course in arms, legs and head is shown in Figures 111 to 115. A tabular description is given on the next page.

10. The Brain Stem:

     When the brain is removed, it seems dominated by the cerebral hemispheres and cerebellum. From the superior view, in fact, hardly anything else is seen (Figure 116). From the inferior view, it becomes apparent that the brain is a continuation of the cord and that the cerebral hemispheres and the cerebellum are added to the stem of the brain. (Figure 117). The amiosagittal view of the brain also shows these relationships (Figure 118).

     The brain stem is very clearly seen in fishes and amphibians, where the basic structures are not obscurred by the cerebrum and cerebellum. It consists of the medulla, metencephalon, mesencephalon, diencephalon, and prosencephalon. The structures which develop from the brain stem play very important roles in the adjustment of the animal to its environment, but they are not basic ones in the sense that the animal can survive without them. For example, removal of the cerebral hemispheres does not kill laboratory animals, and the cerebellum can be removed without fatal consequences. In general, the most vital functions are in the lowest parts of the brain stem. The more anterior portions of the brain stem tend to become less involved with the bare necessities of survival and more with finer adjustments.

     In describing the anatomy of the brain stem, it is customary to consider its lower surface ventral and its upper surface dorsal (as they are indeed in a fish). The terms anterior and posterior may be replaced when necessary by rostral and caudal, rostral meaning toward the front end of the brain stem, and caudal toward the hind end.

Table of Spinal Nerves

11. Structures of the Medulla Oblongata:

     When the spinal cord enters the cranium, becoming the medulla oblongata, its organization is changed. The medulla oblongata is thicker than the cord, and the clear separation between gray and white matter is no longer apparent. There are numerous clusters of neurons which control specific activities of the internal organs. For example, there are groups of neurons which control the rate of the heart; others are concerned in respiratory activity. These cell clusters are called centers: those concerned with the heart are the cardiac accelerator center and cardiac depressor center, while those concerned with respiration are called the expiratory and inspirator centers.

     In addition to having these and many other centers, the medulla differs from the cord in two important respects:

     (1) The cord is cylinder-like; there is nervous tissue arranged in a circular manner around a very small central canal. In the medulla, the nervous tissue is arranged in a V-shape. The central canal has expanded. Its roof is made of pia mater lined with ependymal cells. This roof, called the choroid plexus, is ideally suited for the production of fluid and actually does so, making some of the cerebrospinal fluid.

     (2) The nerves of the medulla oblongata and the rest of the brain do not show the characteristic structure of the spinal nerves. Dorsal and ventral roots are absent. Each cranial nerve has a characteristic structure and function, which will be discussed later in this chapter.

     (3) There is a loose network of neurons and their processes which runs through the medulla and the upper parts of the brain, called the reticular system. It connects centers and nuclei of the medulla with sinilar centers and nuclei in the rest of the brain.

     NOTE: Most spinal nerves have anterior and posterior branches which are not the same as the roots. The anterior branches tend to unite to form plexuses. Thus the anterior branches of C1,2,3,4make up the cervical plexus; C5,6,7,8 and T1, the brachial plexus; L1,2,3,4, the lumbar plexus; L4 is also represented along with L5 and S1,2,3,4 in the sacral plexus. The posterior branches of all the spinal nerves run alone; except for T1, the thoracic nerves do not enter nerve plexuses. S5 also runs alone. The coccygeal nerve is rudimentary in man.

     The nerves which come out of the plexuses may be motor, sensory, or mixed. Those nerves may contain components from several segments of the cord. The final sensory distribution shows excellent correlation between the dermatome and the spinal origin of the nerve. The motor distribution is much less regular, since some muscles act across several dermatomes.

12. Functions of the Medulla Oblongata:

     Centers for most of the vital functions are located in the medulla. Besides the cardiac and respiratory centers mentioned previously, there are centers which coordinate the activities of coughing, sneezing, and swallowing. Blood vessels throughout the body are controlled by the vasomotor center of the medulla. Position centers, where information relative to body movement comes to its first synapse, are also located here. A very important center receives information concerning the position and movement of the head. The information is derived primarily from the vestibular apparatus of the inner ear, and the center is called the vestibullar nucleus. It sends facilitating messages to motor neurons throughout the body as well as sensory information to other parts of the brain.

     Though these groups of nerve cells, centers and nuclei, exert dramatic effects when they are stimulated or destroyed, it would be wrong to think of them as truly controlling the activities with which they are associated. These centers are linked with centers further up in the brain, which may control them, and which may in turn be controlled from above; and in the last analysis, any center must be considered to be controlled by the total sensory input. Nevertheless, the medullary centers are the final pathway involved in many types of control. An animal with its respiratory center destroyed will not breathe. Its heart will beat, but its rate cannot be modified by nervous activity. Its muscles, whose motor neuron responses are no longer facilitated by the vestibular nuclei, are in a state of flaccid paralysis. Destruction of the medulla is fatal. Such destruction is achieved when a man is hanged. The sudden backward jerk of the head forces a compression injury of the medulla by parts of the vertebrae which support the skull. Death is not immediate, and the heart beat continues long after respiration stops. The ultimate cause of death is respiratory failure since the respiratory centers have been destroyed.

13. Structure of the Pons and Cerebellar Peduncles:

     The pons, or bridge, connects the ventral surface of the medulla with the midbrain. See Figure 119. Its most prominent anatomical feature is the fact that its fibers run from side to side, up around tissue similar to that of the medulla, and end on top in the cerebellum. There is thus a girdle around the brain stem whose ventral surface is the pons, whose dorsal surface is the cerebellum and whose sides are the cerebellar peduncles.

     There are three pairs of cerebellar peduncles, the anterior, middle, and posterior. They are groups of nerve fibers which convey information to the cerebellum from the body and medulla, and which convey information from the cerebellum to the cerebral hemispheres and back to the cerebellum.

14. Function of the Pons and Cerebellar Peduncles:

     An important respiratory center lies within the pons, called the pneumotaxic center. It exerts some control over the respiratory centers of the medulla (See also Chapter 18). Beyond this, the pons is simply a bridge of fibers going at right angles to the brain stem, conveying information to the cerebellum. The cerebellar peduncles serve as pathways for conveying information to and from the cerebellum and between its two sides.

15. Structure of the Cerebellum:

     The position of the cerebellum is shown in Figure 120. Note that its rostral portion is separated from the cerebral cortex by the tentorium. Its ventral surface overlies the medulla. When seen from above, the cerebellum appears to be divided sagitally by an overlying worm called the vermis into right and left cerebcllar hemispheres. Each hemisphere is further divided by two planes into anterior, middle, and flocculonodular lobes (Figure 121).

     In sagittal sections, the cerebellum shows on its ventral surface an accumulation of white matter which branches through the cerebellum. This stem and its branches are called the arbor vitae, or tree of life. The outside of the cerebellum is made of gray matter. Note that the arrangement of gray and white matter seen in the cord and partially disturbed in the medulla is completely reversed in the cerebellum. There are a number of important nuclei in the cerebellum. The nomenclature is, however, rather inconsistent and the functions of these nuclei are not known with any certainty, so they will therefore not be named here.

16. Function of the Cerebellum:

     It is difficult to localize function exactly within the cerebellum. However, it is clear that the cerebellum is extremely important in the control of motion. Without burdening the student with anatomic detail, we may say about the cerebellum that information concerning position of parts of the body reaches it from receptors in the muscles, tendons, and joints. This information is processed and referred in part to the cerebral cortex and in part to nuclei in the brain stem, which control motion.

     The information sent to the cerebral cortex may indicate that the motion being performed is incorrect or inappropriate. The cerebral cortex may then send information to the cerebellum of such nature as to induce the cerebellum to act on brain stem nuclei to correct the performance. All of these events may occur at a perfectly unconscious level. In walking, in driving a car, or in bringing a spoonful of food to one’s mouth, no conscious effort goes into the action. Yet the muscular movements are enormously complex and must be very finely regulated for proper performance.

     Much of our knowledge of cerebellar function has been gained from study of humans with cerebellar disease. Such persons are not paralyzed. They do show a remarkable breakdown of normal movement. When they walk, they tend to over-step or understep, and when they feed themselves, they have considerable trouble in finding their mouths. They cannot easily put a finger on their own nose, or perform complex movements involving the small muscles of the forearm and hand, such as typing or writing. At the same time, the patient is not particularly aware of sensory disturbance.

     When the flocculonodular lobe, the most posterior of the cerebellar lobes, is diseased, another cerebellar function may be brought to light. This lobe appears to be connected to the systems involved in balancing, particularly the vestibular nuclei. Information goes both ways-from the vestibular nuclei to the cerebellum and from the cerebellum back to the vestibular nuclei. When this system is diseased, balance is maintained only with the greatest difficulty, and there are sometimes persistent dizziness and nausea.

     The cerebellum is probably peculiarly sensitive to alcohol. Almost all of the manifestations of cerebellar disease can be seen in alcohol intoxication. This includes breakdown of normal movement, difficulties in balancing, and dizziness and nausea.

17. Structure of the Midbrain:

     The midbrain connects the cerebellum and pons to the diencephalon. On its dorsal surface are found four hillocks, the colliculi. The two anterior ones contain neurons concerned with the visual reflexes; the two inferior ones are concerned with auditory reflexes. All together, these hillocks are called the corpora quadrigemina, or quadruplet bodies. The ventral surface of the midbrain is covered by the cerebral peduncles. Within the midbrain, just rostral to the boundary between the superior and inferior colliculi, is the red nucleus. Much of the reticular system lies within the midbrain. Figure 122 shows these relationships.

18. Functions of the Midbrain:

     The superior colliculi are involved in the response to the pupil to light. Normally bright light causes the pupils to constrict; so does accomodation for near vision (Chapter 8). However, the pathways are quite different, for the accomodation response does not involve the colliculi at all. Thus, when the colliculi are damaged, as in a form of neurosyphilis, there is reaction of the pupil to accomodation, but not to light.

     The inferior colliculi are believed to act in an analogous manner with respect to hearing, but just what they do has not been established with certainty.

     The red nucleus has long been of interest to physiologists. When the brain stem is cut through the midbrain in such a way that the red nucleus is excluded, the animal develops a rigid paralysis, which appears to be due to facilitation of all stretch reflexes by the vestibular nucleus. This condition, called decrebrate rigidity, can be observed in a man in certain disorders. If the red nucleus is not separated from the vestibular nucleus, decrebrate rigidity does not occur. Presumably the basis for decerebrate rigidity is the faciliation of stretch reflexes by the vestibular nuclei. The vestibular nuclei can however, be kept in check, that is to say inhibited, by the red nuclei.

     Figure 123 illustrates the pathways involved in the production of when a section is made between the red and the vestibular nucleus. It also shows why it does not occur when the section is made rostral to the red nucleus. An important function of the mesencephalon associated with the reticular system will be discussed in detail in Part 27. It should be noted at this time, however that when the reticular substance of the midbrain is stimulated, the cerebral cortex is stimulated. This in turn stimulates the entire brain, including the reticular substance itself.

19. Structure of the Diencephalon:

     The diencephalon, shown in Figures 124 and 125 is made of the thalamus and hypothalamus. Though diencephalic in origin, the thalamus is anatomically very closely related to the cerebral. It consists of a large mass of gray matter which bulges into the cerebral hemispheres in the midfrontal plane. This relationship is shown in Figure 127.

     The hypothalamus, lying on the ventral surface of the diencephalon, is connected to the pituitary gland. The relationships are shown in midsagittal view in Figure 128.

20. Functions of the Diencephalon:

     The thalamus marks the end of most sensory inputs from the body. Here before being relayed to the cerebral cortex, synapses are made. The information conveyed in these synapses is usually lost because it is not facilitated. This is actually very valuable, for were it not so, the cerebral cortex would always have available more information than it could possibly process.

     Facilitation, which makes possible entry of sensory information from the thalamus to cerebral cortex, may occur simply from widespread stimulation--as was discussed under summation of inadequate stimuli in space--or from prolonged stimulation, as in summation of inadequate stimuli in time. The cortex may facilitate the entrance of thalamic information into itself. Thus, fear of or desire for a given type of sensation may disclose the information relative to that sensation which was waiting be be uncovered in the thalamus. For example, most people have occasional pains in the chest, which are disregarded. When, however, a close acquaintance dies of a heart attack, concern for oneself may bring these pains to conscious attention. The pains which one then experiences are no less real than those which attend real heart disease, though they tend not to be as severe or as prolonged.

     In thalamic disease in man, pain is often a symptom. Sometimes the subject cannot localize the pain which carries with it elements of fear; this type of pain has been called protopathic. Localized pain, such as that of a toothache or a surface wound, is said to be epicritic. Protopathic pain is more common than epicritie in thalamic disease.

     The hypothalamus contains a number of centers which dominate the autonomic nervous system. Though these centers can be controlled by the cerebral cortex, their activities are so highly integrated that they can operate in a meaningful way in the absence of cortical control. Among the centers which are known to exist in the hypothalamus are centers for the regulation of water intake and of hunger, centers for the regulation of sexual performance and sexual activity, and centers controlling mood. It was once believed that sleep and wakefulness centers had hypothalamic centers. It is now considered more probable that these are dominated by the reticular formation.

     The relationships between the thalamus and the cerebral cortex are shown in Figure 126. Figure 127 shows the relationships of the thalamus to the basal ganglia. Figure 128 shows the diencephalic structures in relation to the rest of the brain.

     The anatomical relationship between the hypothalamus and the posteric lobe of the pituitary is quite direct, and presumably this gland is directly under hypothalamic control. The connection is by way of a well-defined nerve tract. The anterior lobe of the pituitary, though it is in contact with both the posterior lobe and ventral hypothalamus, makes contact with them only by way of the blood stream. The blood supply of the anterior lobe of the pituitary is entirely by way of a portal system; the blood which reaches the gland is derived from blood which has passed through the hypothalamus or the posterior lobe of the pituitary. The blood supply to the anterior lobe is quite small; thus very slight chemical signals from the posterior lobe or the hypothalamus may represent major signals to the anterior lobe. This will be discussed further in Chapter 21.

21. Structure of the Proencephalon:

     The prosencephalon consists of olfactory blubs, the cerebral cortex and the basal ganglia.

     The olfactory bulbs rest on the nasal roof. They give rise to the olfactory tracts, which terminate in the cerebral cortex. These relationships are best illustrated in Figure X.

     The cerebral cortex surrounds the basal ganglia. The relationship between these ganglia and the cerebral hemispheres is best seen in a transverse section (Figure 129). Lying between the basal ganglia and the cerebral is the internal capsule, through which many cerebral fibers go on their way to the cord. The relationship between the basal ganglia and the internal capsule is also shown in Figure 130.

     The cerebral cortex which makes up the greatest part of the brain is seen in sideview in Figure 131, in sagittal section in Figure 132, from above in Figure 133, and from below in Figure 134. In general, the cortex is deeply convoluted. Its folds, gyri are separated by grooves, or sulci. Grey matter is always outermost, white matter lies below it, and the grey matter of the basal ganglia lies within.

     In the lateral view the lobes of the cerebral cortex are named in accordance with the bones of the skull which lie over them. Thus, there is a frontal lobe behind the frontal bones, a parietal lobe covered by the parietal bones, an occipital lobe, covered by the occipital bones, and a temporal lobe covered by the temporal bones.

     The same lobes may be seen from above. In this view, in which the cerebral hemispheres are separated a little, it is possible to see the corpus callosum which is made up of fibers running between the hemispheres. Figure 140.

     A better view of the corpus callosum is seen in Figure 141, a sagittal section through the head. This view also shows the relationships of the other parts of the brain.

22. Functions of the Proencephalon:

Functions of the olfactory bulb and tract: These are directly concerned with the sense of smell. See Chapter 8.

Functions of the basal ganglia: Because they are so inaccessible, the basal ganglia are not very easily studied.

     The common laboratory animals are able to maintain nearly normal activity with the basal ganglia alone after decortication. Sensation synapsing in the thalamus is presumably referred to both the cortex and the basal ganglia, which coordinate the motor response and the sensory input.

     In man, the cortex seems to be more important than the basal ganglia. Complex motions, particularly those of the fingers and hands, depend on the integrity of the cortex. Nevertheless, the basal ganglia play a very important role. This is shown by the effects of their diseases. These diseases are of two general types, hypokinetic and hyperkinetic. In the hypokinetic condition, also called Parkinson’s Disease, movements ordinarily occuring together lose their connection. For example, the Parkinson patient may smile with his mouth, but not with his eyes. He can walk, but he may not swing his arms. He may also show a peculiar rigidity of the extremities; they are stiff, though they will bend. During rest, there is tremor of the muscles, which disappears with activity.

     The hyperkinetic diseases are chorea, St. Vitus dance; athetosis, a pill-rolling movement; and ballism, a sudden, intense, and violent movement of a large group of muscles.

     Many of the manifestations of disease of the basal ganglin can be treated by selective surgical destruction of a part of the basal ganglion system. Until the function of the basal ganglia is better understood, it seems difficult to choose among the treatments which have been proposed.

Functions of the Cerebral Cortex: The cerebral cortex is immensely complicated and not too well understood. It may help the student if the following generalizations are made:

     These functions will be discussed separately:

23. Cranial Nerves:

     The arrangement of the cranial nerves is not governed by the same law as that which controls the arrangement of the spinal nerves. Sensory nerves may arise ventrally; motor nerves may arise dorsally; some cranial nerves are purely sensory while others are purely motor. Some are mixed motor, sensory, and autonomic.

     A table which summarizes the most important anatomical and physiological facts about the cranial nerves follows:

Table of Cranial Nerves

     The first cranial nerve, the olfactory, extends from the olfactory mucosa, the olfactory lobes, with which it is in very close contact through the olfactory tract, backwards to the olfactory gyri on the medial surface of the brain. It is responsive to exceedingly small chemical chages in the air; it has been estimated that in man, where the sense of smell is not so highly developed, one twenty-five-billionth of a gram of certain substances per milliliter of air will excite the receptors. See also Chapter 8.

     The second cranial nerve, the optic nerve, begins in the retina. Specialized nerve cells here (See Chapter 8) are stimulated by light and conduct information by way of the optic nerves to the optic chiasma. The arrangement of the optic chiasma is such that fibers from the lateral parts of the retina of each eye stay on the same side; fibers from the medial parts cross over to the other side. Crossed fibers from the opposite eye travel together with uncrossed fibers of the same eye through the optic tract. Examination of Figure 144 will show that the right optic tract contains information from the left visual field and vice-versa.

     The optic tract conveys information in two places:

     Three cranial nerves, the third, fourth, and sixth, control the movements of the eye. The third, or oculomotor, nerve controls the muscles of the eye that control its rotation upwards, toward the midline or downwards. It also supplies the muscles of the iris and those of the ciliary body (see Chapter 8). The fourth, or trochlear, nerve supplies the muscle which rotates the eyeball on its axis. The sixth, or abducens, supplies the muscle which turns the eye laterally.

     The fifth, or trigerninal, nerve is the largest of the cranial nerves. It contains afferent and efferent fibers. The afferent fibers are derived from the teeth and the lining of the mouth and nose. Sensory information from the front two-thirds of the tongue other than taste is likewise conveyed by this nerve, as are sensation from the conjunctiva, the cornea and the meninges. The efferent fibers of the nerve supply the muscles of mastication, i. e. the masseters and the temporal muscles. The trigeminal nerve emerges from the brain stem through the pons, the only nerve originating in this area.

     The sixth cranial nerve, the abducens, has already been considered. It arises just caudal of the pons and just rostral (anterior) to the medulla from the ventral surface of the brain.

     The facial nerve, the seventh cranial nerve, is primarily the nerve of facial expression; that is to say, it is the motor nerve for the muscles of the face and scalp. It also contains efferent fibers belonging to the autonomic system (See Chapter 6) which supply the salivary glands. Like the trigeminal nerve, it serves a sensory function to the anterior two-thirds of the tongue. The sensation mediated by the facial nerve is taste; the trigeminal mediates position sense, pain, etc. The facial nerve arises just in front of the eighth nerve.

     The eighth cranial nerve, once called the auditory, is now called the vestibulocochlear nerve. Its root is almost exactly in the vertex of the obtuse angle made between the pons and the cerebellum, when the brain is viewed from its ventral surface. The cochlear branch, serving the function of hearing, comes from the organ of hearing, the cochlea, part of the inner ear. The vestibular branch conies from the organs of balance and motion of the head. These are also derived from the inner ear, but from specialized structures which detect the movement and position of the head. All these structures are discussed in Chapter 8.

     The glossopharyngeal nerve, the ninth cranial nerve, arises adjacent but caudal to the eight cranial nerve. It is almost entirely a sensory nerve, detecting all sensations from the posterior third of the tongue. It is also sensory for the pharynx, the area behind the tongue, above the soft palate, and above the "voice box." In addition, the glossopharyngeal nerve receives sensory input from certain specialized areas in the arteries (Chapter 11). The only known motor function for this nerve is a minor one; it innervates the stylopharyngeus muscle, which aids in the movements of the pharynx (See Chapter 19).

     The vagus, or tenth cranial nerve, is motor and sensory. It begins in the cerebellopontine angle, just behind the glossopharyngeal nerve. Its name means "wanderer", and its course is, in fact a wandering one. It supplies motor information to and probably is supplied with sensory information from the internal organs from the pharynx, trachea, bronchi, lungs (Chapter 18), esophohagus, stomach, liver, pancreas, small intestine, and large intestine (Chapter 20). Certain areas of the arteries supply information concerning the arterial pressure to the vagus or the aortic arch (See Chapter 8).

     The spinal accessory, or eleventh cranial nerve, has several rootlets in the medulla. These fuse and form the nerve, which has a purely motor function. The muscles which are supplied are those which move the head from side to side and the shoulders upwards.

     The twelfth cranial nerve, the hypoglossal, actually begins rostral to most of the eleventh. The ordering results from the fact that the first one or two rootlets of the eleventh nerve are rostral to it. The twelfth is purely motor; the name (from the combining form: hypo- means under, and -lossa means tongue) describes its position. It supplies all the muscles of the tongue.

24. Ventricular System:

     In its development, the brain is originally derived from ectoderm, the outer most layer of the fetus. Two ectodermal ridges appear, which grow upwards and fuse at their tops. Now a separation occurs between the tube formed by this fusion and the ectoderm from which it was derived. The tube, called the neural tube, contains within it a fluid which will in time become the internal fluid system of the brain and cord. This system, which is seen in the spinal cord as the central canal is continuous with the much more complicated system in the brain, the ventricular system. This system, each part of which corresponds to a part of the brain, contains ducts between lakes and is involved in the formation and movement of the cerebro-spinal fluid. (See below). The name ventricular system is also applied to this fluid system because in its widened areas it resembles. small pouches (ventricle means pouch). The ventricular system will be described beginning at the rostral and ending at the caudal end. (See also Figure 145).

     Within each cerebral hemisphere and corresponding roughly to its external shape is a ventricle. Though these are the first two ventricles, they are not referred to by number, but rather as the "lateral ventricles," so called because each side possesses one. Each lateral ventricle connects with the next ventricle, as well as the third ventricle by a small opening called the foramen of Monro. Each lateral ventricle is lined within by a vascular membrane called a choroid plexus. The third ventricle, surrounded by the structures of the diencephalon and covered by a choroid plexus, communicates with the fourth ventricle by way of a narrow passageway, the cerebral aqueduct, which lies in the midbrain.

     The fourth ventricle lies with the medulla as a river in its bed, differing from the latter in the fact that it is covered by a choroid plexus. This choroid plexus is penetrated at three points, one in the center, two at the sides, so that ventricular fluid can go to the outside of the brain and cord.

     Finally, the fourth ventricle is continuous with the cerebrospinal fluid (see below) and the central canal of the spinal cord. The canal is very small and is not always present in the adult.

25. The Cerebro-Spinal Fluid:

     This fluid appears to be formed by blood vessels in the choroid plexuses of the lateral ventricles, third ventricle, and fourth ventricle. It is formed from blood, but differs in important respects from it. Thus, it contains no red cells or proteins. It is rather low in the positive ions, potassium, magnesium, calcium and phosphate, and relative to blood plasma, it is quite high in the negative ion, chloride. From these facts one would expect an immense negative charge, but this does not in fact exist. This is partially due to that fact that there is excess sodium, but more to the fact that, in the blood plasma, proteins are negatively charged, while in the cerebro-spinal fluid there are no proteins. Thus there is electrical neutrality.

     As noted above, the cerebro-spinal fluid formed in the roof of the lateral, third, and fourth ventricles leaks to the outside. The brain and cord are therefore bathed on the outside by fluid formed on the inside. This fluid is easily reached, and samples of it can be taken because the spinal cord is much shorter than the spinal column which encases it. A puncture made between the third and fourth lumbar vertebrae with a long needle always misses the cord, and if performed correctly, it enters the cerebro-spinal fluid. See Figure 146.

     Once outside the brain and spinal cord, the cerebro-spinal fluid is absorbed by the blood vessels of the arachnoid mater. The process here is quite passive, depending on the fact that the cerebro-spinal fluid is devoid of the proteins which are contained in the blood plasma. These protein molecules take up space ordinarily filled by water molecules, so the concentration of water molecules is higher in the cerebrospinal fluid than in the plasma. The separating membrane receives more water from the cerebro-spinal fluid than from the plasma; thus water, along with materials dissolved in it, is returned to the blood.

26. The Cerebral Circulation:

     The arteries which supply the brain are:

     The course of these blood vessels from heart to head will be discussed in more detail in Chapter 11. For the present, we will consider only those parts of the cerebral arterial system which are conveniently seen in the brain itself. The manner in which the arteries supplying the brain connect with each other is best seen from the ventral surface of the brain (Figure 151). Note that all the arteries end in a common circle, the Circuius Arteriosus, which gives rise to the branches which supply the brain. The circulus arteriosus can also be seen at the base of the cranium after removal of the brain. (Figure 152).

     The branches of the circulus arteriosus are shown from the lateral view in Figure 153, and from the medial view in Figure 154.

     The veins which drain the brain are located between the dura mater and the bones of the cranium. They are shown in lateral view in Figure 155. Figure 156 shows the floor of the skull after removal of the brain. It indicates the relationship of the circulus arteriosus to the veins of the brain. The epidural portion of these veins are called sinuses, but they are truly parts of the venous system. It is the fusion of veins which, penetrating the arachnoid and dura, becomes a sinus, and the sinuses empty into the internal jugular and vertebral veins (See Chapter 14).

     The arterial supply to the brain up to the circulus arteriosus is redundant. The circle and the arteries which arise from it can in theory be supplied by any one of the arterial branches which come to the circle. Experimentally, this is quite true in dogs; it is less true in man, where the tying of even one carotid artery sometimes (but not always) severely impairs the cerebral blood flow. The arteries which spring from the circle tend to communicate with each other a little near their beginnings. At their ends any cerebral artery tends to be alone in supplying a given brain area so that each brain area is quite dependent on a particular artery. In many people, however, branches from two or more arteries may supply the same area, though one tends to dominate. The importance of the difference is that persons with end arteries may suffer brain damage when an end artery is blocked; those with multiple arteries usually tolerate blockage of a single end artery quite well, the collateral vessels from other arteries being able to carry the entire blood supply. See Figure 157.

     Both arterial and venous systems show variations from the ideals shown in the figure. Quite often, the circle is incomplete as a result of absence of one or more of the communicating arteries. Arteries arising from the circle follow an almost (but not quite) predictable course. The veins of the brain may show radical differences from the "normal" illustrated.

27. The Reticular Formation, Wakefulness and Sleep:

     The reticular formation is loosely defined as a part of the brain stem in which scattered cells run in all directions, principally longitudinally. It is in physiological relationship to the spinal cord, cerebellum and cerebrum. It receives afferent information from each of these, and it supplies efferent fibers to each. It has been conjectured that the reticular formation is an "activating system" from which messages are sent to the cerebral cortex (arousal). The aroused cerebral cortex now sends messages which further activate the reticular formation, and through it, by way of its efferent pathways, the entire animal. Evidently such a mechanism must result in further activity and presumably in further increase in afferent information to the reticular system. This would result in permanent and ever-increasing wakefulness.

     If on the other hand, the afferents from the body or the fibers from the reticular formation to the cerebral cortex became fatigued one would expect sleep to result. The decreased afferent information would decrease reticular activity, decreasing cerebral activity, etc. Unfortunately, the statement that the "arousal" reaction is quenched by fatigue suffers from the fact that fatigue in the nervous system is not easily measured or even defined. In the absence of such a definition, one might as well summarize the preceding by saying that fatigue induces sleepiness, a concept not new to most, and that a sleeper can be waked by stimulating him, a statement which is hardly startling enough to wake even a mildly sleepy person. It seems preferable at this time to consider sleep and wakefulness as phenomena not fully understood, somehow involving the reticular formation.

28. Electroencephalography:

     It is relatively easy to find electrical potentials at various points over the brain. In a wakeful person, with his eyes open, there is fast irregular rhythm of small amplitude with no characteristic frequency. Relaxation, along with closing the eyes, results in the appearance of a rather regular rhythm (8 - 13 cycles per second at 50 microvolts) of fairly sizable amplitude. In deep sleep large, slow waves appear; they have a frequency of 1 - 3.5 cycles / second and an amplitude of up to 10 microvolts. The transition from sleep to wakefulness is associated with "trains" of 8 - 13 cps waves superimposed on the slower waves of sleep. These trains are short in general, but they increase in duration until they dominate the electroencephalogram. At this point, the waking state may be considered to exist. Opening the eyes now restores the fast irregular rhythm mentioned before. These electroencephalographic changes are believed to originate in the cells of the cerebral cortex. The cells of the thalamus probably contribute to the electrocardiogram also. Some typical patterns seen in the electroencephalogram are shown in Figure 158.

29. Memory:

     Various types of physiological investigations as well as common experience indicate the existence of two types of memory. Remote memories are quite different from recent memories. They tend to be much more stable in the presence of brain disease, brain injury, and senility. Recent memories are quite unstable even in the healthy young brain. For example, a student may be thoroughly prepared for a final examination until it is over, when everything learned is immediately forgotten; on the other hand, it is almost impossible to forget a language which one has spoken fluently, even though it has not been used for many years.

     There are many theories of memory, none of which is quite satisfactory. They range from those which consider memories to be cerebral circuits in which impulses travel a closed path to those in which single neurons or small neuron groups encode and store a whole experience by arrangement of specific complex molecules. There is actually some evidence that learning is associated with the synthesis of proteins and ribose nucleic acids, but none to indicate that the molecules synthesized actually store information.

     An extraordinary report that feeding the ribose nucleic acids of flatworms which had learned to avoid light to other planaria would accelerate their learning of light avoidance received world wide attention. The experiments have not been confirmed and are now considered to have been misleading. At the present time the physiological mechanism of either kind of memory is unknown.

30. Learning:

     Like memory, learning is not well understood. Some learning appears to be cortical; but much learned behavior occurs at subcortical levels. What was believed to be cortical learning was extensively studied by the Russian neurophysiologist Pavlov and his followers using conditioned reflexes. These are bodily responses, ordinarily considered not to be under the control of the conscious will, for example, salivation which can be evoked by stimuli usually perceived through an organ of special sense. Thus, when meat is placed in the mouth, salivation follows. This response is considered an unconditioned relfex. If a bell is sounded before feeding on a number of occasions, the sounding of the bell may itself provoke salivation. The salivary response to the sound is designated the conditioned reflex, the sound being considered the conditioned stimulus. Repetition of the bell-food sequence leads to re-enforcement of the conditioned reflex. If the bell is sounded but not followed by food, the conditioned reflex can be extinguished.

     The use of conditioned reflexes makes possible the examination of the ability of the animal to achieve sensory discrimination. For example, an animal can be conditioned to salivate in response to a sound of 256 cps, but the salivary response can be extinguished by a sound of 300 cps. The animal can, therefore, be considered capable of discriminating between these two pitches. It may, on the other hand, be entirely incapable of distinguishing between a sound of 256 cps and one of 258 cps.

     In the same way the ability of an animal to distinguish one visual stimulus from another may be tested. Such experiments have been carried out in dogs. Dogs can distinguish shapes very well; they can be conditioned to salivate in response to a perfect circle, and the salivary reflex can be extinguished when an ellipse is presented whose major axis differs from its minor axis by only 10%. Despite this visual ability, dogs have been found to be quite color blind.

     The early idea that conditioned reflexes were mediated through the cerebral ortex receives some support from studies on decorticated dogs in which conditioned reflexes are abolished. Unfortunately, bees, octopuses and pigeons can be conditioned quite well, but these animals have little or no cerebral cortex. It is, perhaps, more accurate to say that conditioned reflex formation can occur at any level of the central nervous system, and that animals with a dominant cerebral cortex tend to use it in the formation of these reflexes.

     The effect of selective decortication was studied by Lasley, an American psychologist. His investigations, conducted in many mammalian species, suggested that learned information is not stored in any simple manner in the brain. It seems probable that learning is multiply stored in the cerebral cortex. Removal of one part of the cortex does not abolish learned behavior; the animal simply uses another cortical or sub-cortical area. There is extremely great redundancy in the brain.

     The mechanisms of learning, like those of memory, are basically unknown at this time. There is much data available, but most unifying hypotheses have not been successful.

31. Diseases of the Nervous System:

     Diseases of the nervous system illustrate normal functions very well. To a very large extent, our knowledge of normal nervous function in man is obtained from the correlation of disordered behavior in life and changes in the central nervous system seen after death. In the discussion which follows, no attempt will be made to present a complete discussion of diseases of the nervous system. The interested reader may wish to consult standard textbooks of neurology, neurosurgery, and psychiatry given in the bibliography.

     The order of presentation of diseases corresponds roughly to the order of the anatomical and physiological material.

     The meninges are so closely associated with the brain that their diseases can be considered diseases of the whole central nervous system. The most dreaded, meningitis, is caused by a bacterium called Neisseria meningitidis. Meningitis caused by this organism usually occurs in epidemics. It begins with severe headache, vomiting, and high fever and progresses to delirium and coma. The outlook is quite poor; though the causative organism is sensitive to penicillin, it is protected from it by the "blood brain barrier," which is penetrated slowly by most substances that are not fat soluble. Very large doses of penicillin may be of some use; sulfadiazine is preferred. The tuberculosis bacillus, the colon bacillus, the pneumonococcus, staphylococci, and streptococci can all cause meningitis, as can a variety of viruses.

     The fusion of the vertebrae which make up the spinal canal involves the connection of the vertebral bodies with each other by tough but flexible structures. The toughness results from the connection of the vertebrae with each other by dense fibrous connective tissue which forms a ring connecting any two vertebrae. This ring, the annulus fibrocum, keeps the vertebrae from tearing apart, but it does not prevent them from being squeezed together. This is accomplished by the presence inside the ring of a jelly-like material, the nucleus pulposus. As can easily be imagined, this material is under immense pressure, particularly in the lower part of the body. By the same token, the annulus fibrosus is under considerable strain.

     If the annulus fibrosus tears, the nucleus pulposus may enter the spinal canal through the defect; it may compress the cord or nerves coming to the cord. When the cord is compressed, it may suffer severe damage; more usually herniation of the nucleus pulposus occurs below the second lumbar vertebra so that the cord is spared. Nerve roots may, however, be injured, leading to pain, sciatica, or weakness. Very often this condition requires no treatment other than bed rest. It is sometimes necessary to remove the herniated nucleus pulposus, and rarely, to fuse the affected vertebrae. See Figure 159.

     It has been mentioned that in one form of neurosyphilis the dorsal columns of the cord are affected. Persons with this disease, tabes dorsalis, lose the of position, particularly in the legs. They have serious difficulty in walking, particularly in the dark, when they are unable to watch their feet. Lightening-like pains of agonizing intensity may also occur.

     Anterior poliomyelitis is caused by a virus which enters the body by way of the throat. Outside of the fact that the virus destroys motor neurons, it is impossible to predict where it will strike. The motor neurons supplying the muscles of the legs or arms may be affected. When the motor neurons in the medulla are involved, bulbar poliomyelitis, prolonged use of the "iron long" may be necessary and swallowing may become uncoordinated. There are forms of poliomyelitis in which the cerebellum and specific areas of the cerebral cortex are affected. These usually leave little detectable residue.

     Poliomyelitis was never an important diseases with respect to numbers of cases. In an average year 3000-5000 cases were reported in the United States, and few of these were paralytic. Compared to this there were no less than one hundred times as many deaths from the major forms of heart disease. Today, poliomyelitis is virtually non-existent, largely through concentrated research effort. It is intriguing to speculate what would have happened to heart disease mortality had the same research effort and money been expended per case.

     A nerve fiber degenerates when it is separated from its neuron. Since all the spinal nerves are extensions of neurons, they invariably degenerate when cut. Most such degenerated nerves will, however, regenerate. The sensory and motor functions served by a degenerated nerve are temporarily lost, but they are regained when the nerve regenerates. The cause of regeneration is not clear; but it appears to depend somehow on the nerve sheath. The Schwann cells, which previously lined the nerve on the outside, multiply, making a solid cylinder through which regenerating nerve fibers can grow. These fibers advance at 1 to 2 mm / day, and eventually reinnervate the denervated structures. When the Schwann sheath is interrupted, the regenerating nerve fibers may not find the way. In such a case, they sometimes grow into a little ball, or neuroma, which may be extremely painful. This is best prevented by preparing a guide of nerve tissue through areas where nerve has been widely destroyed. Grafting another nerve into such a gap is often done.

     The most common disorder of nerves today is injury by pressure or by cutting. After such injury the nerve fiber degenerates, but, as has been described, regenerates in most circumstances. Some diseases attack nerves; leprosy is one. Lepers often lose sensation in specific areas where the nerve is involved. A number of poisons, of which lead is the best known, may produce polyneuritis, an inflammatory disease affecting all nerves. Certain vitamin deficiencies may do the same, but this is extremely rare in this country today. Other forms of peripheral nerve disease are quite uncommon. People who account for their ailments by saying "It’s my nerves" would be more accurate if they attributed their sufferings to their central nervous system, though this might not gain as much sympathy.

     The functions of the medulla are so essential to life that serious disease in this area is usually terminal. Breathing, swallowing, heart rate, blood pressure, and equilibrium all have centers here. Disorders in any of these functions may result from altered medullary function. Abnormal breathing patterns (Chapter 18), hiccuping, disorders in swallowing (Chapter 20), high or low heart rates and blood pressures (Chapters 10 and 11), and disturbances in balance and nausea (Chapter 8) may be due to abnormal medullary function. There need not be structural changes in the medulla for such functional alteration; it may result from disorders in the sensory organs that supply information to the medulla; or it may be a consequence of the action of other areas of the nervous system on the medulla.

     Most of our knowledge of cerebellar physiology in man is based on neurological examination of people who are found at autopsy to have had cerebellar disease. Disease of the cerebellar hemispheres takes many forms, almost all associated with disturbance of movement. Voluntary movements may be too strong or too weak, or their sequence may be disorderly. Muscles which should support the body appropriately while a particular movement is being performed may not do so. Learned actions may be forgotten; the patient with cerebellar disease may not be able to ride a bicycle or drive a car; he may experience difficulty in walking or feeding himself. Disease of the flocculonodular lobe are associated with grave disturbances in balance; persistent nausea is common in such cases.

     The midbrain contains the reticular activating system which the entire brain. The reticular activating system is, in turn, aroused when the rest of the brain is aroused. Disease in this area has remarkable consequences. It may result in encephalitis lethargica, sleeping sickness, in which a semi-permanent somnolence is characteristic. It may, on the other hand, result in hyperexcitability which cannot be quenched. It is quite possible that sedative and tranquilizing drugs (barbituates, mepocinate, thorazine) diminish the activity of the midbrain, while stimulating drugs (caffeine, dexedrine) increase it.

     Diseases of the thalamus are characterized by sensory changes. Some of these are distinctly unpleasant, while others are almost enjoyable. When the disease is one-sided, as is usual, the patient may say that half his body feels dread (thalamic fibers are contralateral, so that the side which feels dread is opposite to the side of the disease). He may, on the other hand, relate a state of joy to the side of the body opposite to the disease. (It should be noted here that the joyous aspects of thalamic disease were described first by French neurologists and are not widely believed any more). The unpleasant symptoms have been noted by many authors; one of the most unpleasant things about them is that they are not well localized, so that the patient is quite aware of pain without knowing just where it is. Self-evidently, unlocalized pain excites fear, so thalamic pain has a large and altogether unpleasant emotional overlay. The fact that most sensory impulses pass through the thalamus has lead to thalamic operations for the relief of pain. Since thalamic fibers are contralateral, the thalamus opposite to the painful side is usually operated upon. Unfortunately, a few pain fibers remain ipsilateral, so that the procedure is not perfectly successful, but it is used for the treatment of unbearable pain in the terminal patient.

     The hypothalamus lies just over the pituitary gland and has nervous connections to its posterior lobe. The anterior lobe, receiving its blood supply from the hypothalamus and posterior lobe, is less directly related to the brain stem. Nevertheless, the relationship exists, and the anterior lobe of the pituitary, the source of many important hormones, functions badly when transplanted. It is difficult to say which functions are hypothalamic in origin, which derive from the pituitary, and which depend on the two acting together. In any case, this general area is intimately concerned with such diverse functions as response to infection, lactation, urine output, hunger and satiety, thyroid activity, the sexual cycle in women, growth, child-bearing, and mood. Its activities can be summarized by saying that the hypothlamus is a nearly self-regulating center for autonomic activity.

     Still, the hypothalamus and pituitary are influenced by other parts of the brain. There is a close relationship to the frontal lobes of the cerebral cortex. Psychosomatic diseases may be induced by the cerebral cortex, producing their physical effects by way of hypothalamic and pituitary centers. More will be said about this later (Chapters 6, 25, and 26) In the following, a brief description of some cortical diseases will be given.

     Any part of the brain may either as the result of injury or because of intrinsic factors give rise to slow, large, rhythmic discharges which spread over the entire brain in a rather orderly way, producing disturbances in sensations and motion. Epilepsy is an example of such a disorder. The epileptic seizure is usually preceded by an aura in which the victim is aware of an abnormal sensation, usually disagreeable. This is followed by twitching, at first localized, and later quite widespread. This twitching soon becomes convulsive, and consciousness is lost. After a short time consciousness is regained; it is usually somewhat clouded and often a deep sleep follows. This type of epilepsy (grand mal) probably involves structures in the diencephalon and should be distinguished from focal epilepsy, which appears to originate in the motor areas of the cortex. Both types of epilepsy can be controlled more or less successfully, but the approach to treatment depends on the type and cause. Some forms of epilepsy respond very well to brain surgery, the removal of an irritable focus. Others are best treated at the present time with drugs.

     Though epilepsy is a serious disease of the brain, there is no evidence that it impairs intellectual function. However, despite the number of renowned men who have been epileptics--Dostoevski, Napoleon, Julius Caesar--there is no evidence that epilepsy enhances intellectual function either. Epilepsy is a disease like any other disease, though its victims can get along quite well with it if they recognize their limitation. For example, an untreated epileptic should not swim in deep water, drive a car, or fly an airplane.

     The cerebral cortex in laboratory mammals appears to be the organ where fine adjustments of behavior are made. A dog or cat deprived of its cerebral cortex functions, but in a stereotyped way: the animal responds to stimuli, but it does not seem to be able to make the complex interegations necessary for the best response in view of the whole situation and remembered experiences. In man, the cerebral cortex seems to have assumed some of the roles of the basal ganglia, in addition to making the idiosyncratic adjustments of response to stimulation which characterize individuals. In a sense, the cerebral cortex is the seat of individuality, and diseases of the cerebral cortex are often seen as disorders of the personality. This is not to say that personality is localized in the cerebral cortex, which is very evident when people with hypothalamic disorders are studied, but it can probably be said that the more fragile and delicate aspects of personality are cortical in location.

     Some areas of the cerebral cortex appear to have definitely circumscribed functions. Injury and disease of these areas have relatively predictable effects. Thus, the precentral gyrus appears to control individual voluntary muscles. Injury to this area may result in a flaccid paralysis of a muscle or muscle group. The occipital cortex is closely related to the sense of vision. Some recent work has shown that when the eye of an animal is covered just after birth, the occipital cortex becomes insensitive to stimuli received from that eye after the cover is removed. Some such mechanism may be involved in the blindness of an apparently healthy eye in adults who were cross-eyed as children and learned to suppress information from one eye. When there is disease of both occipital cortexes, blindness may result; when one occipital cortex alone is diseased, the blindness is partial, half of each eye being affected. Examination of Figure 160 will show that right-sided disease of the occipital cortex will produce blindness of the left visual field; that is to say that the right side of the retina in both left and right eyes will have no representation in the cerebral cortex.

     The temporal lobe is concerned with speech and hearing. Disease or injury of this area may lead to disturbances in speech or understanding. Such disturbances are called aphasis, and they may take some very strange forms. For example, a word may not be understood when it is heard, but comprehended fully when read, or the reverse may be true. In other cases, a patient may not be able to pronounce the name of a familiar object when it is shown to him, though he may be able to use its name in speech.

     The temporal lobes are closely related in function as well as anatomy to the occipital lobes. Disease of the temporal lobes is sometimes seen as disordered vision, for example, the loss of the lower right visual field. An occipital lobe lesion would result in the loss of the entire visual field on one side.

     The post central gyrus and the areas posterior to it make up the parietal lobe. It may be regarded as the terminal for sensory information other than that obtained through the organs of special sense: vision, hearing, taste, smell. It must, however, be considered much more than a simple sensory area, for in the parietal lobe many types of sensory input are brought together and co-ordinated. If any part of the cerebral cortex can be regarded as the seat of consciousness, the parietal lobe is perhaps the best candidate.

     In disease of the parietal lobe the patient may lose his "body image." One side of the body, the side opposite to the affected one, may appear to the patient to belong to a stranger. It is not recognized as part of the self. If sufficiently extensive, parietal lobe disease may result in intellectual deterioration.

     The pre-frontal area appears to be concerned with the control of hypothalamic function, and by way of the hypothalamus, influences the internal organs. It may be considered the seat of emotion, but there are undoubtedly other functions as well. Great interest has been attached to the pre-frontal area since the development of the operation of pre-frontal lobotomy in 1935. In this operation, most of the connections between the pre-frontal area and the deeper portions of the brain are cut, but the frontal lobes remain attached to the remainder of the cerebral cortex. Similar operations in animals can reduce "neurotic" behavior induced by contradictory training. The effects in man are difficult to evaluate. The type of personality change depends on the pre-existing personality to a large extent, but overall there seems to be a lessening of anxiety and tension. Along with this, however, there is maybe loss of ambition and responsibility. The operation was at one time used to treat many types of psychotics, and has even been employed to modify criminal behavior. The results are not good. Temporary improvement may be seen but it is often followed by re-institution of the familiar antisocial behavior pattern in a person whose sensibililties may have become coarser.

     There is one use for the operation which is widely recognized. Patients who are dying of painful or distressing diseases who are subjected to this procedure become more resigned to their condition. They may still be aware of pain or discomfort, but somehow they are less concerned about it. Since almost the same effects can be achieved with the new tranquilizing drugs, the surgical procedure seems unwarranted.

     It is almost certain that much of the function of the basal ganglia in animals has been taken over by the cerebral cortex in man. Our knowledge of basal ganglion function in man, therefore, is based almost entirely on observation of the neurological changes during life of people who are found at autopsy to have disease of the basal ganglia. In general, the basal ganglia in man appear to supply a fine control for the background of voluntary motion. Voluntary motions can still be performed when the basal ganglia are diseased, but they are not well coordinated with motions not specifically willed. It is also speculated that the basal ganglia serve to damp out the activities of the motor portions of the cerebral cortex, serving to suppress those movements which are not necessary for the performance of an action. In our present state of knowledge, it must be admitted that the function of the basal ganglia is not known. Nevertheless, destructive injury to parts of the basal ganglia sometimes affords relief to persons suffering from Parkinsonism, and such operations are carried out quite often.

     When a cranial nerve is examined, it is not only the integrity of the nerve but also its cerebral representation that is studied. Brain tumors are very often revealed by abnormal function of the cranial nerves, as are other diseases of the brain. For this reason, a physical examination should always test the function of the cranial nerves. The proper interpretation of such tests depends on knowledge of the peripheral and central connections of the nerves examined as well as their pathways.

     The first cranial nerve, the olfactory, is tested through the sense of smell. Defects in the sense of smell and olfactory hallucinations may signify disorders in the nerve or in the hippocaupal cyrus, where the olfactory trails connect. The sense of smell, perhaps more than any other, is concerned with emotion. The use of perfumes by women testifies to this. Of more medical interest is the fact that persons with schizophrenia psychoses are very often subject to olfactory hallucinations.

     The second cranial nerve, the optic, is concerned with the sense of sight. Unlike most other animals, man has binocular vision; that is to say that objects are seen by both eyes at the same time. This binocular representation is reflected in the distribution of the fibers of the optic nerve (Figure 133) and the optic tracts. Instead of a right eye which sees the right visual field and a left eye which sees the left field, both eyes in man see both right and left. The right visual field is sensed by the lateral (right) half of the left eye and the medial (right) half of the right eye. Objects which are looked at directly are not only seen by both eyes but also have representation on both sides of the cerebral cortex.

     In addition to its function in perceiving visual stimuli, the eyes also regulate the position of the head in part. They control through the iris the amount of light which will be received at the retina, and through shaping of the lens, whether near or distant objects are seen best. These matters will be considered in Chapter 8. For the present, it will suffice to say that the mid-brain, the sunerior colliculi, is a center for some of these responses. Disease of the midbrain may alter these functions.

     A rather rare, but physiologically interesting condition is sometimes associated with neurosyphilis. The Argyll-Robertson pupil reacts to accomodation, indicating that the pathways concerned with vision as such are intact, but persons so afflicted show no pupillary response to light. The lesion is believed to be in the mesencephalon.

     Perhaps the most instructive way to examine the optic nerve is the comparison of the visual field of the examiner with that of the examinee. While both look each other directly in the eye, the examiner moves a finger in a plane between them. Assuming that the examinee is normal, the finger should disappear at the same time for both as it moves up, down and sideways. Blind spots in the examinee should be noted; they may represent serious disease in the retina, optic nerve, or occipital cortex.

     It is quite routine for the physician to look at the retina of the patient. This is done with the aid of an opthalamoscope, which illuminates the subject’s retina. The optical situation is such that enormous magnification is possible. Thus the physician can see the minute blood vessels of the retina, retinal detachments, hemorrhages, the point of entry of the optic nerve, etc. Besides making possible the examination of the retina, the opthalmoscope permits examination of other structures of the eye (Chapter 8). It has been said that the opthalmoscope, properly used, can yield as much information as the stethescope, for many diseases of the whole body are easily revealed in the retina.

     The third, fourth, and sixth cranial nerves are all concerned with the movement of the eyeball in its socket. The third also controls the pupil and the lens; it will be considered separately in Chapters 6 and 8, since many of its fibers are autonomic (Chapter 6) and it is of great importance for vision (Chapter 8).

     Movements of the eye in its socket are controlled by the six eye muscles. The oculomotor nerve controls three of the "rectus" muscles, those which insert on the middle, upper, and lower aspects of the eyeball. The fourth controls the superior oblique muscle, which, in its contraction, rotates the right eye in such a way that both the right and left eye stay in position when one leans to the right. The sixth cranial nerve, abducens, innervating the lateral rectus muscle, rotates the right eye to the right and the left eye to the left. The third and sixth eye muscles and nerves are usually checked together by having the patient look to the right, left, up and down. The superior oblique muscle is not it is checked during most routine examinations except for a neurological examination.

     The fifth cranial nerve, the trigeminal, must be examined with respect to its motor and sensory functions. The motor function is easily examined by feeling the masseter and temporal muscles during a forceful bite. Both should become taut and hard; if they do not, disease of the nerve on the affected side must be considered. The sensory function responds to touch over the facial skin, especially the cornea and conjunctiva. In the normal person, touching the eye causes closure of the eye. This response, called the corneal reflex, is absent when the sensory fibers of the trigeminal nerve concerned with that area are destroyed. Like the motor function, the sensory function of the trigeminal nerve is on the same side, ipsilateral. It may be mentioned here that except for the optic nerve, which has bilateral representation, all the cranial nerves are ipsilateral. In general, motor functions in the cord are represented contralaterally in the brain, that is to say, on the opposite side. Most sensory functions are also contralateral, but there are exceptions for both motion and sensation.

     The fifth cranial nerve is sometimes affected by an agonizing pain of unknown cause, called trigeminal neuralgia. Its victims complain of unbearable facial pain, which they must bear unless fairly radical treatment is undertaken. This treatment usually involves the destruction of the sensory parts of the nerve either by local injection of alcohol or by cutting the sensory part affected. Though such nerve destruction abolishes normal sensation in the area supplied by the nerve as well, patients with the disease experience such intense suffering that they feel the treatment is worth it. Recently, drugs have been found which shorten the attacks and may even cure the disease. At present, however, surgery or alcohol injection seem to be the most reliable treatment.

     The seventh, or facial, nerve is a mixed nerve, containing sensory fibers (taste), parasympathetic fibers (salivary and tear glands--see Chapter 6), and motor fibers (muscles of facial expression) The last predominate since diseases of this nerve are almost invariably one-sided--they produce an asymmetry of facial expression. A patient with facial nerve disease smiles on one side only. His forehead wrinkles on the affected side. Sensation may be disturbed, and one side of the tongue may not be able to detect substances which have strong tastes.

     A not uncommon disease of the facial nerve is fortunately quite temporray. The nerve leaves through a narrow canal. If it becomes inflamed and swollen enough to produce pressure on the nerve, its function is lost (Bell's palsy). The loss may occur over a period of a few hours. If the inflammation subsides rapidly, there is no structural damage to the nerve, and 80% of these patients recover within a few weeks. Inflammations of longer duration damage the nerve structurally; recovery is, correspondly, much delayed. Other causes for Bell's palsy exist, and not all of them have such a good outcome. In any case of Bell’s palsy, the eye on the affected side must be protected since the eyelid is usually paralyzed.

     The eighth cranial nerve serves the organ of hearing (cochlea) and the organs which detect position and motion of the head, the vestibular apparatus. The characteristic finding in disease of the cochlear portion is deafness of the ipsilateral ear, but "ringing" in the ears is often due to cochlear or cochlear nerve disease. Deafness can be tested and usually excites medical interest, but "ringing in the ears," or tinnitus, is difficult to test because the physician must rely on the patient's report, and, though it may represent as serious a condition as deafness, it is very often neglected. It is important to distinguish between deafness due to cochlear nerve and brain disease and the same symptoms resulting from disease of the middle and outer ear. The former, called nerve deafness, is characterized by loss of hearing more marked at some frequencies than others. Hearing aids are not usually of help in this type of deafness. Deafness resulting from disease of the middle or outer ear is characterized by a loss of hearing at all frequencies of sound (See Chapter 8). Hearing through air, which involves the outer and middle ear, is usually more impaired than hearing through bony conduction, which bypasses these. The treatment of conduction deafness is very successful. Sometimes, the simple removal of wax from the outer ear is curative, although delicate surgery on the middle ear may be required. Hearing aids almost always offer some improvement.

     The vestibular branch of the eighth nerve serves an organ concerned in detecting the position of the head and motions of the head. The organ is called the labyrinth and consists of three semicircular canals, which are believed to detect motion and the ritricle and saccule, probably concerned in the detection of position of the head. These will be discussed in more detail in Chapter 8. For the present, it will suffice to say that disease of the vestibular nerve, or its sensory organs, produces dizziness and nausea.

     A most interesting symptom of disease of the vestibular complex has to do with the movement of the eyes. When the body is rotated, the eyes, rather than moving evenly with the body, move in a series of jumps. One point is "fixed" by the eyes; as the body rotates the same point remains fixed through movement of the eyeball, until it is no longer possible for the eyes to see it. At this point the eyes jump to a new point, which is then fixed again as long as possible. Thus there are two types of eye motion during rotation: a slow one, which keeps one point fixed, and a fast one which fixes a new point. These motions are called mystagmus, which has a fast and a slow component.

     In disease of the vestibular apparatus or the vestibular nerve, normal mystagmus may disappear or mystagmus may appear when the body is not rotating. It is often associated with nausea, vomiting, and a staggering gait. Abnormal mystagmic movements may be a consequence of brain tumors as well as of disease of the vestibular apparatus or the vestibular nerve. For reasons which are not understood, streptomycin and dihydrostreptomycin, which have a favorable effect on tuberculosis, sometimes damage both branches of the eighth nerve or their central connections. Faulty adaptation to position and movement of the head may result from the use of these drugs. Vestibular symptoms are more common than cochlear. The effects are dose dependent, and because of them, it has been recommended that the dose originally proposed be reduced to one half.

     The ninth, or glassopharyngeal, nerve serves the posterior third of the tongue and may be tested through the sense of taste or touch in that area. This nerve is rarely diseased, except in conjunction with the tenth and eleventh cranial nerves, all of which may be injured together by a brain tumor. Occasionally, the glossopharyngeal nerve is involved alone. The condition is quite rare, but it resembles trigeminal neuralgia in the intensity of the pain.

     The tenth, or vagus nerve, is the parasympathetic nerve for most but not all of the internal organs. Disease of this nerve is quite rare, but cutting it is usually fatal. It is reported that men can be killed by applying pressure to the vagus nerves in the neck, and some detective stories involve unravelling this method of murder. See also Chapter 6.

     The function of the spinal accessory nerve is best tested through estimation of the strength of the muscles which elevate the shoulders, the trapezius, and turn the head, the sternomastroid.

     The hypoglossal nerve, which supplies motor informaticri to the tongue, is sometimes diseased on one side. When this occurs, the same side of the tongue is paralyzed or weak. A patient with one-sided hypoglossal nerve disease, when asked to stick his tongue out, can only activate the muscles of the normal side. Consequently, the tongue points to the side of the damaged nerve.

     The cerebro-spinal fluid is normally formed in the choroid plexuses of the lateral, third, and fourth ventricles. It escapes from the fourth ventricle through three openings, one in the midline and two at the sides. Once out of the ventricular system, the fluid bathes the outside of the entire central nervous system. It is reabsorbed by arachnoid villi.

     Overproduction of cerebro-spinal fluid, obstruction to its flow, or failure to reabsorb it, can all lead to hydrocephalus. In this condition, the pressure and volume of the cerebro-spinal fluid may be greatly increased. In young children, before the fusion of the bones of the skull, the hydraphalic fluid may lead to enlargement of the head. Destruction of brain tissue may occur, which is more marked in older persons, where the high pressure predominates.

     The commonest cause of hydrocephalus is obstruction of the narrow openings through which the fluid normally moves. This may occur between either of the lateral ventricles and the third ventricle, in the aqueduct in the midbrain or in the openings leading from the fourth ventricle. The treatment, when possible, is surgical; new channels are established for the flow.

     The arterial supply of the brain is by way of four arteries--two internal carotids and two vertebrals. As has been noted above, these arteries usually communicate with each other around the base of the brain, where they form an arterial circle. The two sides of the circle are joined anteriorly by the anterior communicating artery, and the front and back parts of the circle are joined by the posterior communicating arteries. The two vertebral arteries and the artery which make up the back part of the circle are usually fused (See Figures X and Y).

     The brain tissue itself is supplied by arteries which spring from the circle. Thus, in theory, even if one of the carotid arteries was blocked, the other sources of the circle could supply the deficiency.

     The vessels which leave the circle tend to communicate with each other by way of collateral branches when they are close to the circle. Collaterals become more and more sparse as one approaches the terminal branches. At the end of an arterial branch, there is, as it were, an area exclusively dominated by that branch, which has no other blood supply, or at most a very smal one derived from collaterals of an adjoining artery with its own primary domain.

     The cerebral circulation in man is beset by a number of peculiar problems: First, it must be maintained at a high level. The cells of the central nervous system require large quantities of oxygen, one-fifth of the total amount required for the whole body. Second, they have no alternative to oxygen utilization and die within minutes when their oxygen supply is cut off--most other tissues can survive huge reductions in oxygen supply without dying, the heart itself being a notable exception. Third, being an end-arterial system, when an end artery is obstructed, the cells in its domain usually die before collaterals from elsewhere can develop to the point where they deliver significant quantities of blood. Finally, the cerebral arteries, going through tissue which lends them almost nothing in the way of outside support are more prone to rupture than most blood vessels sustaining the high pressures required to achieve the high blood flows required.

     The effects of interruption of arterial blood supply, whether by rupture or obstruction, are sudden and dramatic. They are called cerebrovascular accidents, or strokes. The manifestations of a stroke depend on the area affected. Some strokes involve the entire middle cerebral artery on one side. Since this artery is practically the only source of blood to the lateral and inferior aspects of the frontal lobe--the speech area, the grey and white matter of the parietal lobe, the basal ganglia, and the striate body--its obstruction will be attended by the gravest manifestations, if indeed life is not lost. Spastic paralysis and sensory loss relating to the opposite side of the body are observed almost immediately. Those cranial nerves whose centers or tracts are affected are disturbed ipsilaterally. If the dominant hemisphere is affected, speech and understanding may be lost.

     A common form of stroke due to hemorrhage occurs when there is bleeding from the lenticolostriate artery. This artery goes through the internal capsule which separates the head and tail of the basal ganglia. Important motor fibers from the cerebral cortex course through this area. Hemorrhage of the lenticulostriate artery may obstruct these fibers, kill their neurons or both. In any case, extensive contralateral paralysis develops. It should be noted that this paralysis is one of voluntary motion; the muscles affected continue to show stretch reflexes, and in fact these are often increased.

     Many strokes are obstructive in origin. The arteries supplying the circulus arteriosus may be diseased in the neck; one of the commonest diseases is atherosclerosis. This is a condition in which the normally smooth arterial lining becomes rough, blood which ordinarily slips through such an artery now "churns" through. Small clots form and pass up into the cerebral circulation. Some of these may be totally without effect, others may destroy a few brain cells, and still others, producing obstruction in an end artery may result in clotting in that artery. These clots have a tendency to spread backwards and involve larger arteries; finally a large artery may be obstructed by clotting, with massive brain damage. Such a stroke progresses slowly, over the course of a few days.

     There is also a syndrome of little strokes. Here again the disease is usually atherosclerotic. A few cells are destroyed at a time as the little clots produce their damage, but in time the whole brain is damaged as the number of functional brain cells decreases. Because little strokes are insidious in their progress, they are not a necessary consequence of age. Rather remarkable results have been reported from repair of these accessible cervical vessels. Unfortunately, the diagnosis of little strokes is difficult, and their natural history is not well established. Some have suggested that treatment has no discernible effect on their progression.

     The stroke problem is an important one. It is quite possible that as many deaths are due to strokes as to cancer, but there is a more fatalistic attitude about strokes than cancer. This is unfortunate, because a realistic research approach to stroke is more likely to yield results than the researches now conducted on cancer.

     An aspect of conditioned reflexes not described above may be quite important in disturbed behavior. If an animal is positively conditioned to one kind of stimulus and negatively conditioned to another kind, and the two are applied together, the animal does not know how to respond appropriately. In such a condition, it becomes excitable, bad-tempered, and unstable. This state is sometimes referred to as experimental neurosis. Neurosis in man is not quite the same. It is richer, fuller, and less consistent than the animal counterpart. Neurosis in man has to do with the relationship of the man to his environment. Neurotic behavior generally is discriminatory. A banker who is competent on the job may behave neurotically at a bridge party. People with sensible attitudes in one sphere may appear unreasonable in another. It is a disappointing fact that trained observers are often in disagreement about certain aspects of behavior: some judge them normal others neurotic. Almost all observers are, however, in agreement that there is no intellectual deterioration in the neuroses.

     Psychoses are much graver disorders in personality and behavior. They are attended with so much emotional content that normal thinking becomes difficult. The basic disorder in the psychoses, if indeed there is only one, is quite unclear. Some believe that psychoses are a consequence of faulty training; others hold chemical factors at fault. As in the neuroses, there is little intellectual impairment in most psychoses.

     Most of the major psychoses can be classified as either schizophrenia or manic-depressive psychosis. The importance of schizophrenia, also called dementia praecox, may he indicated by the fact that there are more hospital beds for schizophrenics than all other diseases combined. Yet, the classification of schizophrenics has shown little change since it was first described less than 3 years ago.

     A working definition of schizophrenia is hard to find. In general, schizophrenics seem to avoid emotionally painful situations; each person has his own style of doing so. The classification which has been favored describes four types of response: simple, hebephronic, paranoid, and catatonic. The simple schizophrenic appears to avoid emotional pain by suppressing thoughts which may provoke it. He may appear quite stupid, with interests reduced and social relationships impoverished. The patient tends to be apathetic or indifferent. The hebephrenic schizophrenic appears emotionally shallow. The emotions he does display are inappropriate to the circumstances. He tends to make silly remarks, to dress in a silly manner, to make pointless jokes, to have hallucinations, and behave younger than his years. The paranoid schizophrenic is hostile and aggressive, believing that his importance is so great that he is unrecognized only because of a massive plot against him. He may show considerable ingenuity in fitting the plot he imagines against him into the real circumstances he must recognize. The catatonic schizophrenic is the most dramatic of all. He avoids pain by obliterating the world. He may neglect his own hunger and require force feeding. He may become stuporous and immobile; his immobility sometimes involves his assuming positions for days on end that normal people would find intolerable after a few minutes.

     In the manic-depressive psychoses, the patients may take refuge from their real problems by plunging themselves into the deepest gloom or assuming an attitude of almost violent happiness. Some do both at different times, the gloom and happiness having in common the fact that they are totally irrelevant to any circumstances in the life of the patient. For example, a rich depressed patient may be unwilling to wash his hands because of the cost of soap and water; while a manic patient with medical training may be violently cheerful about an increase or decrease in the value of gold, even though he owns none. There has been a tendency to assume that manic depressives are actually schizophrenics. This may be true, but in general the manic depressive conveys his mood of the moment better than the schizophrenic. When he is happy, the examiner is happier, when he is depressed, the examiner feels gloom. The schizophrenic does not convey his mood very well.

     Both the major psychoses can be treated by drugs that lessen the basic misery of the patient, such as chlogoromazine, meprobanate, or phenothiazine. None, however, approaches a 50% cure rate. Psychotherapy, particularly psychoanalysis, is worthless in the psychoses, and probably detrimental in the neuroses, though it achieves substantial transfers of money.

     The other psychoses, particularly alcoholism, may result in mental deterioration, but they will not be discussed here, primarily because they are so little understood.

     The reader may consider this account of behavioral disorders a depressing one. The fact is that the diagnosis, outlook, and treatment of behavioral disorders is not such as to provoke cheer. Important as these disorders are, we are not in a position to cope with them very well. Imprecision in diagnosis, in ability to evaluate outlook, and unwillingness of those who make their living by treating the behaviorly disturbances to assess the results of the treatment each contribute to the gloomy state of the art.

Continue to Chapter 6.