lateral and a mesial branch. The lateral root contains the true visual fibers and these fibers end around cells in three regions, lateral geniculate body, pulvinar, and in the superior colliculus (Fig. 32, 11 and 17). The latter pathway serves to carry impulses (for releasing eye moving reflexes) from the retina to the nuclei of motor nerves (III and IV) whose cells of origin lie near. The cells in the lateral geniculate body and in the pulvinar send axones through the internal capsule to end in the visual cortical area — the gyri about the calcarine fissure of the occipital lobe The olfactory nerve has a very special course. The ganglion cells in the olfactory epithelium in the nose send axones (first order) to end around the mitral cells in the olfactory bulb (relay PSYCHOLOGY station). The mitral cells there send axones known as the olfac- tory tract (second order) to enter the hippocampal gyrus in the region of the uncus (Fig. 31, 20). The system is shown in Fig. 41.
Summary. — Schematically at any rate, the architecture we have been studying is simple enough. All of the tracts in the cord bearing cutaneous impulses (occupying ventro-lateral col- umns) and kinaesthetic impulses (occupying posterior columns) from the body are gathered together in the medial lemniscus, which ever increases in size from its beginning in the medulla due to the addition of fibers coming from reception nuclei of the afferent cranial nerves. It is soon joined by the axones from the reception nuclei of the auditory nerve (lateral lemniscus). All of these axones, including the optic, terminate in nuclei lying in the corpora quadrigemina or thalamus. These nuclei send axones di- rectly (or by addition of a short central neurone) to the sensory projection areas in the cortex, for example, the somassthetic, visual and auditory. In this summary we neglect only the olfac- tory, which does not appear in any of these levels, and the gusta- tory, about whose central connections we know little or nothing.
Connection of Sensory Projection Areas with the Motor Area in the Cortex. — From our study of behavior we have found that many objects can stimulate more than one sense organ, and that when we have learned to respond in a certain way to that object, the same response may be initiated by stimulation of any one of the sense organs: for example, the stimulation of vision, smell, taste or touch effected by an apple may lead to the same final movement, the reaching out and grasping of the apple and the carrying of it to the mouth. If the formation of habit (ac- quired forms of reaction) involves the cortex, then we should expect to find that the cortical reception area of each sense organ should be in close connection with the cortical motor area. En- tirely apart from behavior studies it was early established by Fritsch while operating upon a wounded soldier in the Francovsian War, that if the galvanic-electric current is applied to n parts of the brain, movement of the limbs occurs Careful experiments during recent years have shown that the pre^central gyrus is the main cortical motor area. Stimulation there is fol- NEURO-PHYSIOLOGICAL BASIS OF ACTION 149 lowed by the contraction of a particular group of muscles on the opposite side of the body. The diagrammatic sketch (Fig. 42) shows what motor parts are moved. Since we know that the peripheral, spinal and cerebral motor neurones run to these muscles and directly control them, we may be sure even before we examine the architecture that the motor area is connected with the cell bodies which give rise to the lower motor neurones. Be- tween the motor area or motor projection " center" and the sen- sory projection areas lie the so-called association "centers." These areas do not directly receive the final neurones from sense organs nor does a weak electrical stimulation arouse muscular FIG. 42. — The human cerebral hemisphere seen from the left side, upon which the func- tional areas of the cortex are indicated. The area marked "motor speech" is Broca's convo- lution. (Starr, " Nervous Diseases," Lea & Febiger.)
movement. They are the * ' silent areas. ' ' Entirely too much has been made of them (and of the whole localization of function as well, page 154). Try to look upon them as more or less non-spe- cialized brain areas which contain interconnecting neurones. It may be safe to say — it is often said — that every gyrus is con- nected with every other gyrus on the same side by association neurones and with every gyrus on the opposite side by commis- sural neurones (corpus callosum).
Connection of Cortex with Lower Centers. — Histological examination shows that in the precentral gyrus (motor area) there exist a large number of giant pyramidal cell bodies on each side. The cells are shown in Fig. 43. It has been shown PSYCHOLOGY Small pyramidal cells that these giant cells give rise to axones whlfch without relay pass to all levels of the spinal cord. Other cells located there send axones to the nuclei of origin of the cranial motor nerves. This vast system is schematically shown in Fig. 44 and can be followed there pass- ing through the cor- ona radiata, through the striate body and through the thala- mus; it takes up a ventral position on the cerebral peduncle and passes through the transverse fibers of the pons to the medulla oblongata, where it forms the right and left pyra- mid on its ventral surface. This system is called the pyram- idal tract (fascic- ulus aerebronspin- and 26). The fur- ther course of these fibers is continued in the next paragraph. In addition to this prc,S«:¥^ system of descending neurones, the cortex the frontal lobe sends a direct system of axones to the red nucleus (nucleus ruber) in the cerebral peduncle (this nucleus m the tegmentum above the peduncles and just ventral to the >ra quadngemina)— the cortico rubro tract (the red nucleus turn probably sends up an ascending system of neurones which end in the frontal region). We know, furthermore, that Large pyramidal '>,- cells, Polymorphic cells NEURO-PHYSIOLOGICAL BASIS OF ACTION 151 axones from cells in the frontal, parietal and occipital association regions form descending pathways to the cells in the pons — the cortico-pontile tracts. Many of the descending pathways are far too complicated to study without neurological material.
FIG. 44. — Coronal section through cerebral hemispheres and brain stem. 1, pyramidal decussation (decussatio pyramidum); 2, nucleus olivaris inferior; 3, n. vagus; 4, n. glosso- pharyngeus; 5, nn. facialis et acusticus; 6, n. trigeminus; 7, n. oculo-motorius; 8, corpus mammillare; 9, optic tract (tractus opticus); 10, globuspallidus (part of nucleus lentiformis); 11, insula; 12, putamen (part of nucleus lentiformis); 13, head of nucleus caudatus (caput nuclei caudati); 14, corpus callosum; 15, longitudinal fissure (fissura longitudinalis cerebri); 16, corona radiata; 17, septum pellucidum; 18, thalamus; 19, third ventricle (ventriculus tertius); 20, internal capsule (capsula interna); 21, cerebral peduncle (penduculus cerebri); 22, superficial fibers of the pons; 23, middle cerebellar peduncle (brachium pontis); 24, pyra- midal tract passing through pqns (fasciculi longitudinales pontis); 25, cerebellum; 26, pyra- midal tract in medulla (pyramis medullse oblongatse). (Modified from Toldt.)
Descending Tracts in the Spinal Cord. — The pyramidal tract is the most conspicuous tract in the cord. At the lower end of the medulla the fibers begin to decussate (Fig. 44, 1). After PSYCHOLOGY decussation they take up two positions in the cord. A part of the fibers from one motor cortex continue down to the ventral fuuiculus of the same side, the direct pyramidal tract (fasciculus cerebro-spinalis anterior) (Fig. 45, 16). The majority of the fibers swing over to the opposite side and descend in the lateral funiculus, forming the lateral pyramidal tract (fasciculis cere- bro-spinalis lateralis) (Fig. 45, 11). The direct pyramidal tract is soon exhausted. The fibers reach a certain level and turn at right angles to end around motor cells in the ventral horn. The . 45.— Diagram of cross-section of spinal cord through mid-cervical region to e arrangement of the fiber tracts. 16, tractus cortico-spinalis ventralis, the direct ict (fasciculus cerebro-spinalis anterior); 11, tractus cortico-spinalis lateralis, \ i/ pyramidal tract (fasciculus cerebro-spinalis lateralis)- 15 tractus vestibules rubro-spinalis.
lateral or crossed pyramidal tract can be identified down to the lowest level of the cord. As the tract descends it gets smaller and smaller, due to the fact that some of the fibers turn at right angles to end around motor cells at each successive level. The pyramidal neurones and the peripheral motor neurones thus together form a very direct path between the motor area in the brain and the muscle.
There are several other descending tracts in the cord. The NEUROPHYSIOLOGICAL BASIS OF ACTION 153 most important ones only are here mentioned. A. Tractus-rubro spinalis (von Monakow's tract) (Fig. 45, 12). This is a tract running from the mid-brain (nucleus ruber) to the cord. Its fibers terminate in the dorsal portion of the ventral horn. It is a joint cerebellar and thalamic system. Axones of cells in the cerebellar cortex run to the nucleus dentatus in the cerebellum: cells from this nucleus send axones to end in the nucleus ruber; this nucleus in turn sends axones to form the rubro-spinal tract. It brings the motor cell in the cord under the influence of the thalamus and the cerebellum. B. Traetus vestibulo-spinalis (Fig. 45, 15). This tract originates in the reception nuclei of the vestibular nerve lying in the medulla — Deiter's nucleus. It was pointed out that this nucleus receives impulses both from the cerebellum and from the semicircular canals. The axones in this tract also terminate around the ventral horn cell. We thus see that there are adequate connections both ascending and descend- ing by means of which the cerebellum can serve as an equilibrat- ing and toning organ for the muscles.
A General Caution. — This short sketch of the cerebro-spinal system should teach us that every sensory structure studied in our last chapter can, when stimulated, excite a segmental reflex, a reflex involving neighboring segments, or a reflex involving practically the whole of the central nervous system. All of this complexity is needed to serve as a neural basis for the complex types of reflex, instinctive and habitual acts man performs. We shall see when we come to study the motor side of the organism that sustained integrated acts such as are involved in eye-hand or ear-hand, such as those involved in walking or swimming, require that the peripheral motor neurones should be under the influence of many distant parts of the central nervous system. While we wish to emphasize the importance of the central nervous system, we do not wish to make a fetish of it. Due to the studies on the localization of function and of the disturbances which occur when injury is done to the sensory projection centers in the cortex, there has grown up in neurological circles a kind of scientific phrenology. The main fact about the central nervous system is that it affords a system of connection between sense organs and 154 PSYCHOLOGY 154 PSYCHOLOGY glands and muscles. Interrupt the pathway in any place and the organism no longer acts as a whole; some phase of the be- havior pattern will drop out. Nor should the nervous system be overemphasized. The whole motor and glandular systems in each and every part do the reacting. A sudden stooping or rotation of the head, or a loud noise, probably changes the tonus of every muscle in the body, striped and unstriped, and starts a wealth of glandular activity. But action cannot take place without the participation of the bones. Action again means an increased food supply, an increased strain upon the heart, and the elim- ination of waste product. A simple eye-hand coordination, the picking up of a pin from the ground, brings about a well-ordered and integrated response of the organism as a whole. Such a well- ordered response will not take placet without a central jnervous system, but it must be said with equal truth that it will not take place without a heart, without bones, and without glands and muscles.
THE SYMPATHETIC NERVOUS SYSTEM.
Introduction. — So far in our discussion of the nervous sys- tem we have neglected the sympathetic system, but we have spoken of the peripheral motor neurones. The sympathetic sys- tem must be looked upon as an extension of the peripheral motor nervous system. The peripheral motor nerves1 belonging to the cord and brain are distributed to the striped muscles of the body (page 160). But the striped musculature of the skeleton repre- sents only a part of the efferent organs. The viscera in the thoracic, abdominal and pelvic cavities and certain structures in the head region contain unstriped or smooth muscle tissue and glands. The sympathetic system which in nearly every case is under the dominion of the motor nerves of the cord and brain controls the smooth muscles of the viscera and glands. The sympathetic is thus wholly motor. Afferent neurones are distributed to the tissue which the sympathetic controls, but these afferent neurones belong to the afferent peripheral cerelro-spinal system which we have already studied — the organic sense organ. There is no sub- stantial evidence to show that the sympathetic system has an afferent supply of its own. It may be true from an evolutionary NEURO-PHYSIOLOGICAL BASIS OF ACTION 155 point of view that the cerebro-spinal system, is an adjunct to the sympathetic, but the development of the former has reached such a point that it now is the "tail that wags the dog." There has been a tendency in recent years to exploit the sympathetic system at the expense of the cerebro-spinal. This has been done largely in the interest of giving a iieurophysiological basis to certain psychoanalytic principles. When one considers the enormous development of language habits and of the vast system of integra- tions existing among the reflex arcs controlling the striped muscu- lature of the body as a whole, one cannot take such a view seri- ously, even though he himself is prepared to yield an ever-in- creasing importance to the system. Emotional activity is impor- tant, hunger, thirst, micturition, defecation are also important factors, as we have tried to show — especially when disturbances in those mechanisms occur. But after all the sympathetic mechanisms which underlie such functions are simply a part of the body as a whole. To overemphasize it is to neglect our facts in the interest of theory.
The Ganglia of the Sympathetic (or Autonomic) System. — Fig. 27 shows (in black, on right side only) (1) a chain of sym- pathetic ganglia that run parallel on each side of the spinal cord. The ganglia appear on each of these trunks at fairly regular in- tervals. Each trunk runs from the second cervical vertebra to the first piece of coccyx. The two trunks unite in one ganglion at the coccyx — the ganglion coccygeum impar. It will be under- stood that these ganglia, as do all other sympathetic ganglia, lie wholly outside of the central nervous system. (2) The cephalic or brain portion of the sympathetic consists of four main ganglia on each side, but not appearing in regular segments as do those considered above — the ciliary ganglion (ciliary muscle in the eye, sphincter of the iris, etc.), sphenopalatine (vaso-motor, secre- tory), the optic (vaso-motor, etc.) and the submaxillary ( glands of mouth, etc.). There are also numerous other small ganglia. These ganglia are not shown. (3) Ganglia scattered through the visceral organs, in the cavities of the thorax, abdomen and pelvis — the heart, lungs, liver, alimentary tract, pancreas and sex organs. The most important of these ganglia are found in 156 PSYCHOLOGY 156 PSYCHOLOGY connection with the cardiac plexus, cceliac (Solar) plexus and the hypogastric plexus (abdominal and pelvic). None of these is shown in our drawings.
Structure of the Sympathetic Ganglia. — The ganglia consist of gray matter, cell bodies giving rise to axones, and of ends of axones coming from other neurones. The axones of the sympa- thetic are rarely myelinated throughout their course, but they are occasionally myelinated for a short distance after leaving the cell body. Most of the axones are covered with a sheath of Schwann. The dendrites are numerous and similar in structure to those we have studied in the central nervous system.
Distribution of Sympathetic Neurones. — The axones of sympathetic neurones, after a shorter or longer course, end finally in the glandular tissue, in the heart muscle, in the blood- vessels, and in the non-striated muscular tissue of the body wherever it is found. We see the system in action in the bristling of hairs, dilatation and constriction of the pupil, secretion of saliva, inhibition and acceleration of the heart, flushing, goose- flesh, peristalsis, defecation, urination, tumescence in the sex organs, etc. Sympathetic neurones thus are motor and control the so-called vegetative functions.
The Control of the Central Nervous System Over the Sym- pathetic System. — The neural connection of the central nervous system with sympathetic ganglia is shown in Fig. 46. It is seen there that cell bodies in the gray matter of the cord (lateral horn), and this is true also of the brain, send out axones through the motor roots, which end in a near or distant sym- pathetic ganglion. The synaptical connection is like that in the central nervous system. The axone breaks up into an end brush and ends around the dendrites of the sympathetic neurone. The neurone (Fig. 46, 8) running from the spinal cord or brain to the sympathetic ganglia and ending there is called the pre-gan- glionic neurone (the axone is also called the pre-ganglionic axone or fiber). This pre-ganglionic neurone is myelinated and is similar in all respects to motor neurones with the possible excep- tion of its size; in general it is slightly smaller. The sympathetic neurone (Fig. 46, 5) running from the ganglion cell to end in the NEURO-PHYSIOLOGICAL BASIS OF ACTION 157 gland or smooth muscle tissue is called usually the post-ganglionic neurone. We thus see that the whole sympathetic nervous sys- tem is under the control of the central nervous system by means of the pre-ganglionic neurone.
(The white ramus communicans consists of pre-ganglionic axones on their way to enter a sympathetic ganglion. There is also a gray ramus communicans consisting largely of axones of FIG. 46. — Diagrammatic cross-section of the cord to show control of sympathetic by cerebro-spinal system. In addition the diagram shows the reflex arc from skin to striped muscle. 6, spinal afferent neurone with peripheral ending and sensory structures 1 and 2 with central ending in the cord; a collateral from this neurone ends around the central cell marked 7, whose axone in turn ends around motor neurone 9, whose axone ends in the striped muscle 3; neurone 8 has its cell body in the lateral horn of the gray matter; the axone, however, ends in a sympathetic ganglion, in the drawing around 5, a sympathetic neurone; the sympathetic neurone ends in smooth muscle cell 4.
sympathetic neurones which must get out of the visceral cavity in order to run to the sweat glands of the skin, the muscles of the hairs and blood-vessels. These post-ganglionic fibers join the spinal nerves and run a common course with them. ) The Afferent or Return Connections of the Sympathetic. — Notwithstanding the work of Dogiel and Huber and others, more recent investigations show that the sympathetic1 has no afferent system of its own. The peripheral afferent system of the brain and cord (spinal and cranial ganglia) affords the sensory inner- vation for the tissues controlled by the sympathetic. The periph- eral process from a spinal or cerebral ganglion cell, instead of running towards the skin or kinaBsthetic structures, turns to enter 158 PSYCHOLOGY 158 PSYCHOLOGY the white ramus and pass along with the* pre-ganglionic fiber. But instead of ending in a sympathetic ganglion, where the pre- ganglionic fiber ends, it passes through or alongside of the gan- glion without making functional connections and ends in the motor or glandular tissue that is under the control of the post- ganglionic or sympathetic fiber. This is the usual relation. Pos- sibly an illustration will make; this clearer. The sweetheart of a boy comes suddenly into the room. His face flushes. The neural situation in outline is as follows: The optic impulses pass back over the optic tract and upon reaching the central system arouse an impulse in pre-ganglionic neurones. These neurones carry the impulse to the sympathetic neurones which dilate the blood- vessels of the face. But this sudden change in the1 temperature of the face arouses the ordinary nerve endings in the skin which are sensitive to warmth, etc. In the viscera the conditions are probably not at all different.
Divisions of the Sympathetic System. — Most authors divide the sympathetic as a whole into two divisions, oftentimes into more. The most recent and satisfactory division seems to be as fol- lows (Ranson): (1) The thoracico-lumbar autonomic system is that division of the sympathetic the pre-ganglionic fibers of which make their exit from the spinal cord through the thoracic and upper lumbar nerves. (2) The craniosacral autmomic system is that division of the sympathetic system the pre-ganglionic fibers of which make their exit from the cerebro-spinal axis (brain and :;ord) through the III, VII, IX, X, XI cranial nerves and the II, III and IV sacral nerves. Most of the structures innervated by the autonomic system receive a double supply, a portion from part 1 above and a portion from part 2. When this occurs the two sets possess opposite functions; for example: autonomic system 1 dilates the pupil, while autonomic system 2 contracts it; again, autonomic 1 increases secretion in the submaxillary gland, auto- nomic 2 decreases it. Finally, autonomic 1 accelerates the heart, autonomic 2 inhibits it.
Concluding Statements.— Although the material presented in this chapter has possibly seemed detailed we have done little more than present the elementary conduction systems which connect NEURO-PHYSIOLOGICAL BASIS OF ACTION 159 the sense organs with the central nervous system and the latter with the muscles and glands. We have had to leave out of account all discussion of the special functions of the cerebral cortex, thal- amus, caudate nucleus, nucleus lentiformis, the cerebellum, and the gray cellular masses in the brain stem. If what has been pre- sented has been followed, the student should carry away with him an increased knowledge of what kinaesthetic motor responses, visual-motor responses, and organic-motor responses are, and what is meant by the integration or tying together of long and short reflex arcs in such a way that concerted, controlled and sus- tained action in the muscles may be obtained. This knowledge is fundamental if the factors underlying human behavior are sought. The sympathetic system should not be confusing. Every sense organ is the beginning of an arc which ends in a muscle. The organic sense organ is no exception. The afferent portion of this system is similar in all respects to that of the kinassthetic or cutaneous, but on the motor side it takes both the pre-ganglionic neurone and the post-ganglionic (sympathetic) neurone to estab- lish connections with the effectors. In other words, the pre-gan- glionic neurone belonging to the central system has to be "lengthened" or "supplemented" in order to reach and stimu- late the motor organs belonging to the organic system. This is, of course, an oversimplification in the interest of making the ana- tomical relation clear. Whether neural action in neurones be- longing to the sympathetic system is in all respects similar to neural action elsewhere is a problem which we need not attempt to study here.
CHAPTER V THE ORGANS OF RESPONSE: MUSCLES AND GLANDS Introduction. — In order to complete our sketch of the mechan- isms involved in human response, it remains for us to study the effectors. So far we have studied receptors or sense organs and their stimuli, and the system of conductors stretching out between receptors and the effectors, or acting organs. The motor neurones of the cord and brain end directly in skeletal muscle or indirectly (through the intermediation of a sympathetic post-ganglionic neurone, page 157) in the smooth muscles of the body and the glands. Our sketch would be incomplete if we failed to get a good working notion of action in skeletal muscles, smooth muscles, and glands. In the sketch which follows we have omitted all details and have summarized only the most important features of such action, and the features with which psychology has most to do. We can study the effector system under three general divisions: I, the striped muscles; II, the smooth muscles; III, the glands.
I. STRIPED MUSCLES.
I. STRIPED MUSCLES.
Structure of the Striped Muscles. — The skeletal or striped muscles constitute the principal mass of the body as a whole. Each muscle is more or less of an organic whole, which can assume various shapes and sizes. The morphological unit of a muscle, however, is a muscle fiber or muscle cell. Each muscle consists of a large number of thread-like cells which usually lie parallel to the long axis of the muscle. At one or both ends, the muscle tapers down and forms a junction with a tendon. The tendons in turn are attached to the bone. The fibers of the muscles are grouped into larger and smaller bundles, each bundle being bound with connective tissue. A sheath, or perimysium, surrounds the muscle as a whole.
The individual muscle fibers vary greatly in diameter and length. They are rarely longer than 36 nun., and the diameter varies from 0.1 to 0.01 mm. The fibers are cylindrical in shape ORGANS OF RESPONSE Each fiber is inclosed in a thin homogeneous elastic membrane called the sarcolemma. The material inside the fiber is striated. It is supposed to be of a semi-viscous consistency. This material is the muscle plasma. The muscle plasma is made up of fibrils which run the whole length of the intervening sarcoplasm. The fibrils seem to be made up of alternating dim and light discs.
Neural Endings in Muscles. — The peripheral motor and sen- sory neurones end in the muscles. We have already spoken of the .End- "plate FIG. 47. — Ending of motor nerves in striped muscle. The axones pierce the perimysium, lose their medullary sheath and end in a plate-like formation on the individual muscle fibers. (Piersol's Anatomy.)
sensory endings in muscles on page 59. The axones of the motor nerves upon reaching the muscle lose their medullary sheath and break up into numerous fine fibrils. These fibrils spread out in plate form (motor end plates) and pass to each muscle fiber. Fig. 47 shows the ending in striped muscle fibers of axones of efferent neurones.
In addition to the afferent and efferent supply coining from the central nervous system, the muscles receive sympathetic fibers, i.e., the axones of post-ganglionic neurones end in the 11 162 PSYCHOLOGY muscle. The function of the sympathetic "neurones there, how- ever, seems to be that of controlling the blood supply to the muscles.1 Relations of Muscles to Bones and Tendons, etc. — The bones of the body, about 200 in number, are the passive organs in reac- tion. The muscles are the active organs. The bones are more or less rigid structures, well adapted to their function, combining the maximum amount of rigidity with the least amount of weight. All of the long bones are hollow and filled with a substance rich in fat. The bones are united rigidly, as those of the skull, or else in a way to permit movement the one upon the other. The bones united by cartilages are semi-mobile, for example, the bones of the pelvis, ribs and vertebras. The bones united by articular cap- sules are semi-mobile, mobile or very mobile, as the elbow, knee, shoulder and hip. In the true articulations the heads of the bones are covered with a large cartilage to which is attached the •fibrous articular capsule which connects the two bones. External to the capsule lie the strong protective ligaments. In each cap- sule there are epithelial cells which secrete the synovia, a trans- parent viscous mass which lubricates the articular surfaces. Most skeletal muscles have tendons at each end. The tendons end in two contiguous bones. The majority of the muscles thus cross one joint. Whenever this condition is met we have a lever.