Charles Scott Sherrington

“ Just as in a nerve fibre, when excited by a localized stimulus, the excited state spreads from the excited point to the adjacent unexcited ones, so in muscle the “contraction,” when excited at a point, spreads to the adjacent uncontracted parts. Both in muscle and in nerve this spread is termed conduction. It is propagated along the muscle fibres of the skeletal muscles at a rate of about 3 metres per second. In the heart muscle it travels much more slowly. ”

“ Each neuron or nerve cell is a morphologically distinct and discrete unit connected functionally but not structurally with its neighbours, and leading its own life independently of the destiny of its neighbours. Among the properties of the neuron is conductivity in all directions. But when neurons are linked together it is found that nerve impulses will only pass from neuron A to neuron B, and not from neuron B to neuron A ”

“ Coincidently with the persistence of the tonic contraction, the higher and volitional centres seem to lie under a spell of inhibition; their action, which would complete or cut short the posture-spasm, rests in abeyance. Suspension of cerebral influence exists even more markedly, of course, when the cerebral hemispheres have been ablated.
But a potent—according to some, the most potent—factor in hypnotism, namely, suggestion, is unrepresented in the production of so-called animal hypnotism. We know that one idea suggests another, and that volitional movements are the outcome of ideation. ”

“ A tendency to rhythmic contraction seems discoverable in almost all muscles. In some it is very marked, for example in some viscera, the spleen, the bladder, the ureter, the uterus, the intestine, and especially in the heart. In several of these it appears not unlikely that the recurrent explosive liberations of energy in the muscle tissue are not secondary to recurrent explosions in nerve cells, but are attributable to decompositions arising sua sponte in the chemical substances of the muscle cells themselves in the course of their living. ”

“ A prominent and practically important illustration of neural tonus is given by the skeletal muscles. These muscles exhibit a certain constant condition of slight contraction, which disappears on severance of the nerve that innervates the muscle. It is a muscular tonus of central source consequent on the continual glow of excitement in the spinal motor neuron, whose outgoing end plays upon the muscle cells, whose ingoing end is played upon by other neurons—spinal, cerebral and cerebellar. ”

“ The neuron is described as having a cell body or perikaryon from which the cell branches—dendrites and axon—extend, and it is this perikaryon which, as its name implies, contains the nucleus. It forms the trophic centre of the cell, just as the nucleus-containing part of every cell is the trophic centre of the whole cell. ”

“ The motor field of the cortex is, taken altogether, relatively to the size of the lower parts of the brain, larger in the anthropoid than in the inferior monkey brains. But in the anthropoid brain still more increased even than the motor field are the great regions of the cortex outside that field, which yield no definite movements under electric excitation, and are for that reason known as “silent.” The motor field, therefore, though absolutely larger, forms a smaller fraction of the whole cortex of the brain than in the lower forms. ”

“ The second factor inducing the assimilative change is the withdrawal of the nervous system from sensual stimulation. The eyes are closed, the maintenance of posture by active contraction is replaced by the recumbent pose which can be maintained by static action and the mere mechanical consistence of the body, the ears are screened from noise in the quiet chamber, the skin from localized pressure by a soft, yielding couch. The effect of thus reducing the excitant action of the environment is to give consciousness over more to mere revivals by memory, and gradually consciousness lapses. ”

“ In sleep the jerk is diminished, in deep sleep quite abolished. Extreme bodily fatigue diminishes it. Conversely, a cold bath increases it. The turning of attention towards the knee interferes with the jerk; hence the device of directing the person to perform vigorously some movement, which does not involve the muscles of the lower limb, at the moment when the light blow is dealt upon the tendon. A slight degree of contraction of muscle seems the substratum of all attention. ”

“ They dwindle in size; they do not, however, die. Similarly, when the axons of the motor spinal cells are by severance of the nerve trunk of a muscle broken through, the muscle cells undergo “degeneration”—dwindle, become fatty, and alter almost beyond recognition. This trophic influence which one neuron exerts upon others, or upon the cells of an extrinsic tissue, such as muscle, is exerted in that direction which is the one normally taken by the natural nerve impulses. ”

“ Hence during the day the assimilatory processes of these cells are overbalanced by their wear and tear, and the end-result is that the cell attains an atomic condition less favourable to further disintegration than to reintegration. That phase of cell life which we are accustomed to call “active” is accompanied always by disintegration. When in the cell the assimilative processes exceed dissimilative, the external manifestations of energy are liable to cease or diminish. ”

“ The nerve cells of the higher vertebrata, unlike their blood cells, their connective tissue cells, and even their muscle cells, early, and indeed in embryonic life, lose power of multiplication. The number of them formed is definitely closed at an early period of the individual life. Although, unlike so many other cells, thus early sterile for Growth in Nervous System. reproduction of their kind, they retain for longer than most cells a high power of individual growth. ”

“ In the dog it has been proved that after removal from the animal of every vestige of its cortex cerebri, it still executes habitual acts of great motor complexity requiring extraordinarily delicate adjustment of muscular contraction. It can walk, run and feed; such an animal, on wounding its foot, will run on three legs, as will a normal dog under similar mischance. ”

“ The Muscle. mechanical work is obtained by movement resulting from a change, it is supposed, in the elastic tension of the framework of the living cell. In the fibrils existing in the cell a sudden alteration of elasticity occurs, resulting in an increased tension on the points of attachment of the cell to the neighbouring elements of the tissue in which the cell is placed. These yield under the strain, and the cell shortens between those points of its attachment. This shortening is called contraction. ”

“ It is this relatively huge development of cortex cerebri which is the pre-eminent structural character of man. This means that the number of “longest routes” in man is, as compared with lower animals, disproportionately great. In the lower animal forms there is no such nervous structure at all as the cortex cerebri. In the frog, lizard, and even bird, it is thin and poorly developed. In the marsupials it is more evident, and its excitation by electric currents evokes movements in the musculature of the crossed side of the body. ”

“ Stretching of the muscles antagonistic to the extensors—namely, of the flexor muscles—reduces the jerk by inhibiting the extensor spinal nerve cells through the nervous impulses generated by the tense flexor muscles. Hence a favourable posture of the limb for eliciting the jerk is one ensuring relaxation of the hamstring muscles, as when the leg has been crossed upon the other. ”

“ But in the decapitated animal we have good arguments for belief that we get the reflex movement alone as response; the psychical touch drops out. Could we assume that there is in the adult man reflex machinery which is of higher order than the merely spinal, which employs much more complex motor mechanisms than they, and is connected with a much wider range of sense organs ”

“ In the heart muscle during a brief period after each beat, that is, after each single contraction of the rhythmic series, the muscle becomes inexcitable. It cannot then be excited to contract by any agent, though the inexcitable period is more brief for strong than for weak stimuli. ”

“ To take one’s watch from the pocket and look at it when from a familiar clock-tower a familiar bell strikes a familiar hour, is an instance of a habitual action initiated by a sense perception outside attentive consciousness. We may suddenly remember dimly afterwards that we have done so, and we quite fail to recall the difference between the watch time and the clock time. In many instances hypnotism seems to establish quickly reactions similar to such as usually result only from long and closely attentive practice. ”

“ There is close interconnexion between the two aspects of the double activity that in physiological theory constitute the chemical life of protoplasm, between dissimilation and assimilation. Hering has long insisted on a self-regulative adjustment of the cell metabolism, so that action involves reaction, increased catabolism necessitates after-increase of anabolism. The long-continued incitement to catabolism of the waking day thus of itself predisposes the nerve cells towards rebound into the opposite phase ”

“ The ship’s engineer, engaged in conversation with some visitor to the engine-room, talks apparently undisturbed by all the multifold noise and rattle of the machinery, but let the noise alter in some item which, though unnoticeable to the visitor, betokens importance to the trained ear, and his passive attention is in a moment caught. ”

“ It is a brief extension of the limb at the knee-joint, due to a simple contraction of the extensor muscle, elicited by a tap or other short mechanical stimulus applied to the muscle fibres through the tendon of the muscle. The jerk is obtainable only from muscle fibres possessed of neural tonus. If the sensory nerves of the extensor muscle be severed, the “jerk” is lost. The brevity of the interval between the tap on the knee and the beginning of the resultant contraction of the muscle seems such as to exclude the possibility of reflex development. ”

“ Larger and thicker in the rabbit, when excited it gives rise in that animal to movements of the eyes and of the fore-limbs and neck; but it is only in much higher types, such as the dog, that the cortex yields, under experimental excitation, definitely localized foci, whence can be evoked movements of the fore-limb, hind-limb, neck, eyes, ears and face. ”

“ These include, besides ocular squint, many spatial positions and movements unwonted to the body: the looking from a height, the gliding over ice, sea-travel, to some persons even travelling by train, or the covering of one eye. Common to all these conditions is the synchronous rise of perceptions of spatial relations between the self and the environment which have not, or have rarely, before arisen in synchronous combination. ”

“ Injuries of the cerebellum, if large, derange the power of executing movements, without producing any detectable derangement of sensation. The derangement gradually disappears, unless the damage to the organ be very wide. A reeling gait, oscillations of the body which impart a zigzag direction to the walk, difficulty in standing, owing to unsteadiness of limb, are common in cerebellar disease. ”

“ They lower the external activities of the cells, but do they not at the same time lower the internal, reparative, assimilative activity of the cell that in natural sleep goes vigorously forward preparing the system for the next day’s drain on energy? In most cases they, seem to Narcotics. lower both the internal and the external activity of the nerve cells, to lessen the cell’s entire metabolism, to reduce the speed of its whole chemical movement and life. ”

“ The tactual organs of the soles, and the muscular sense organs of limbs and trunk, are originating perceptions that indicate that the self is standing on the solid earth, yet the eyes are at the same time originating perceptions that indicate that the solid earth is far away below the standing self. ”

“ They continue to grow, and to thrust out new branches and to lengthen existing branches, for many years far into adult life. They similarly possess power to repair and to regenerate their cell branches where these are injured or destroyed by trauma or disease. This is the, explanation of the repair of nerve trunks that have been severed, with consequent degeneration of the peripheral nerve fibres. As a rule, a longer time is required to restore the motor than the sensory functions of a nerve trunk. ”

“ Such a drugging of tissue by its own excreta is known Theories of Sleep. in muscular fatigue, but the fact that the depth of sleep progressively increases for an hour and more after its onset prevents complete explanation of sleep on similar lines. It has been urged that the neurons retract during sleep, and that thus at the synapses the gap between nerve cell and nerve cell becomes wider, or that the supporting cells expand between the nerve cells and tend to isolate the latter one from the other. ”

“ In the diagram there is indicated the situation of the cortical centres for movement of the vocal cords. Their situation is at the lower end of the motor field. That they should lie there is interesting, because that place is close to one known in man to be associated with management of the movements concerned in speech. ”

“ Akin to this condition is that in which the power of maintaining muscular effort is increased; the individual may lie stiff with merely head and feet supported on two chairs; the limbs can be held outstretched for hours at a time. ”