Complete Text (Part 13)

the paths of the upper sensory neurons (vide supra). In multiple sclerosis the nodules are scattered through the tracts, effecting a partial and diffuse interruption of sensory impulses, the result being a partial form of ataxaia which is now understood to be the explanation of intention tremor. In lateral amyotrophic sclerosis, on the contrary, the process is always sharply limited and the cere- bellar tract left intact; hence, amid all the havoc wrought by this formidable disease, co-ordination is Myelitis, in which all the tracts are involved, gives ataxia, but the motor paralysis masks it. In a hereditary form of locomotor ataxia, known as Friedreich's Disease, the inco-ordination extends to the muscles of speech, anfl the muscles of the FUNCTIONAL DIAGNOSIS 163 trunk are involved, making it difficult to maintain static as well as dynamic equilibrium. That the sense of vision plays an important part in co-ordination is proved by the fact that in all the ataxia diseases referred to the inco-ordination becomes more marked when the eyes are closed (Komberg's symptom). "V •m -m Mechanism of Co-ordination. — By just what means the cerebellum exerts its co-ordinating influence on the motor impulses is not known. Possibly by im- pulses sent to the motor area of the cerebrum which instruct the latter in the distribution of its motor currents; possibly by inhibitory impulses given to the motor fibres on their way down through the pons; possibly by direct neurons of its own to the muscles concerned (comma tract?). Degeneration or atrophy of the cerebellum pro- duces complete ataxia, including the facial muscles. This condition is seen in a rare disease known as hereditary cerebellar ataxia. Motor power is intact. Muscular sense and general sensibility are unim- paired, as are also the cutaneous reflexes; but the tendon reflexes are exaggerated because the ten- dons are under the influence of the cerebellum. The facial movements are noticeably purposeless and ab- surd. Relation of Cerebrum to Cerebellum.— It may be said that in removal or injury of the cerebellum, al- though it produces temporary ataxia and inco-ordi- 164 FUNCTIONAL DIAGNOSIS nation, without any impairment of motor power, the ataxia and inco-ordination in man, are largely re- gained after a time, provided the cerebrum is in- tact. This physiological fact coincides with the ana- tomical fact that a goodly proportion of neurons which convey muscle-sense are distributed to the cerebrum, and affords another instance of the domi- nant capacity of the cerebrum, which is able to as- sume a great many functions in the absence of their customary centres. A notable exception to this is found in the case of the disease just mentioned, hereditary cerebellar ataxia. In this trouble the cerebrum does not com- pensate for the cerebellum, doubtless because there has been no conscious education in co-ordination, and the cerebrum therefore has no experience to fall back upon. FUNCTIONAL DIAGNOSIS 165 THE CEREBRUM. The cerebrum is, both topographically and func- tionally, the highest part of the nervous system. Its function is but little understood, its activity being dependent upon consciousness — that unknown and unknowable factor in the physiologic equation. "We are only able to state, in a general way, that it is the seat of intelligent and voluntary function. More- over, it seems that it only becomes so after repeated impressions and experiments, for the brain of an in- fant can hardly be regarded as a seat of intelligence or volition; and this trial and error process (even the passive part of it) is only possible in the pres- ence of consciousness, for no impression can be made on the cerebrum during unconsciousness. Psychical Functions. — Of the higher operations of the brain, commonly called psychical, including the phenomenon of consciousness, nothing can be predi- cated by physiology. They are generally supposed to be functionated in the outermost layer of the cortex (molecular layer), the axoms of whose neu- rons do not pass out of that layer, but communicate freely and completely with each other. This, how- ever, is a purely histological hypothesis. Cortical Region. — The pyramidal and polymor- phous layers of the cerebrum, consisting chiefly of gray matter (non-medullated), send axons both up- ward into the molecular layer and downward into the medulla of the brain. 166 FUNCTIONAL DIAGNOSIS The Cerebral Medulla.— The medulla of the brain consists almost entirely of white matter (medullat- ed), representing axons from neuron-cells in the upper layers and in the spinal cord. The fibers com- posing the medulla are classified according to their anatomy and function. (1) Association Fibers, connecting one part of the cortex with another. (2) Commissural Fibers, connecting the two hemispheres, cerebellum, and pons. (3) Projection Fibers, which come from or go to the medulla oblongata and cord, and from the great sensory and motor tracts. These fibers, after leav- ing the cortex, sweep backward, in the form of an arc (corona radiata), getting closer together the lower they are traced, and pass in a very compact bundle on each side, through the capsule (the mo- tor fiber through the auterior and for part of the posterior limb, the sensory through the back part of the posterior limb) down to the medulla oblongata, where they decussate, and into the cord. Cerebral Motor Paralysis. — Trauma or disease of the great sensory and motor tracts during their pas- sage through the capsule and pons, where the fibers are compressed into a very small sectional area, nat- urally includes all of the neurons in the injury, and produces a paralysis of all the parts supplied by the tract — partial or complete according to the extent of the injury or compression. If the lesion is above the FUNCTIONAL DIAGNOSIS 167 cranial nerve roots (as it usually is), the result is a crossed paralysis involving the same side of the head and neck and the opposite side of the body. If it is below the cranial nerve nuclei, the paralysis in- volves the opposite side of the body. Hemorrhages into the capsule are very common, as are also embolisms of the middle cerebral artery, tumors, gummata and abscesses involving the cap- sule. The first two lesions usually cause a sudden and complete paralysis ; the other three lesions usu- ally produce gradually progressive hemiplegia. . si "y Cerebral Localization. — Experiment and observa- tion have demonstrated that certain areas of the cor- tex, being stimulated, functionate various parts of the body ; one area, for example, always moving the leg, another the arm; and still smaller points are found in these areas which influence detailed sec- tions of the parts in question, as the foot and toes, hands and fingers. The same is true of special func- tions, such as speech, hearing, etc. Hence we con- clude that every part of the body is represented, afferently and efferently, by a certain definite area in the cortex, although the sensory areas, naturally, cannot be mapped out with the definiteness of the motor areas. Monoplegias. — Inasmuch as the motor centres of the cortex are separated from each other by a more or less measurable distance, traumata and degener- 168 FUNCTIONAL DIAGNOSIS ative processes of the cortex, unless extraordinarily extensive, do not involve more than one or two of these centres. Hence the paralyses produced by cor- tical lesions do not as a rule involve more than one group of muscles, and are known as monoplegias. Conversely a monoplegia may as a rule be diagnosed as due to a cortical lesion, for in no other part of the cerebro-spinal course are peripheral groups rep- resented by neurons sufficiently isolated to incur separate injury. In certain types of cortical epilepsy the central irritation starts in one of these cortical centres, and the fit begins with a corresponding disturbance in the group of muscles controlled by that centre ( Jack- sonian Epilepsy). •• *k -m Location of Motor Areas. — The motor areas are for the most part situated along the fissures of Ro- lando and sylvius, and a description of the probable location of the centres for the most important parts of the body will be found in the accompanying ta- ble. The location of special senses centres will be indicated in discussing those senses : It will be readily seen from the table and illustra- tion that the arrangement of the centres facilitates the occurrence of monoplegias. These are quite fre- quent in practice and it is usually a simple matter to diagnose the exact spot in the brain at which the lesion exists. Frequently, too, the lesion will include two adjoining centres, such as those of the face and FUNCTIONAL DIAGNOSIS 169 170 FUNCTIONAL DIAGNOSIS arm, or of the arm and leg, and a paralysis of these two regions is then produced which is called an as- sociated plegia. But it is apparent that an associ- ated cortical paralysis of the leg and face, without paralysis of the arm cannot occur as the result of a single cortical lesion. The greatest care must be exercised in differen- tiating between the various centres concerned in the functions of speech, hearing, and writing, and the effects of injury to these foci. Each of these func- tions is made up of two distinct operations of the brain, performed by two distinct and separate cen- tres, which may be classified as follows : Hearing. — (1) Perception of sound; (2) Storing of Sounds (auditory memory). Sight. — (1) Perception of images; (2) Storing of Images (visual memory). Speech. — (1) Recognition of stored sounds (spoken words) ; (2) Motor Speech. Writing. — (1) Recognition of Stored Images (written words) ; (2) Motor Writing. It will be readily apparent that the function of speech depends upon that of hearing since sounds cannot be reproduced which have not first been per- ceived and memorized. In like manner the function of writing depends upon that of sight, since the images cannot be reproduced which have not been first perceived and memorized. Psychologically the acts of storing and reproducing an impression are FUNCTIONAL DIAGNOSIS 171 identical ("there can be no impression apart from expression"). It will be further seen that the centres for these intradependent functions are situated immediately above each other in the brain as follows : Motor Speech, Memory of Spoken Words, Hearing, Arm and Hand, Memory of Written Words, Vision. Pure Deafness. — A lesion of the auditory cen- tre, or centre of pure hearing, produces inability to perceive sound. The current conveyed by the audi- tory nerve produces no effect upon it. This lesion is not necessarily fatal to speech, in these days of modern resource and patience, as the patient may be taught by sight, and, in the absence of sight, even by thought, to recognize and reproduce motions of the mouth and tongue. This form of deafness is called pure deafness. Word Deafness. — A lesion of the centre of sound memory produces inability to store sounds, and therefore to recall them. This form of deafness is called word deafness, and is fatal to intelligent speech, because the word desired to be spoken can- not be thought of. In regard to speech this is known as amnesic aphasia. Pur© Blindness. — A lesion of the visual centre 172 FUNCTIONAL DIAGNOSIS produces inability to perceive an image. The cur- rent conveyed by the optic nerve makes no impres- sion upon it. This form of blindness is called pure blindness and can be overcome by patient education so far as the ability to write is concerned. Word Blindness. — A lesion of the visual memory centre produces inability to store and hence to recall images. This form of blindness is called word blind- ness and is fatal to intelligent writing because the word desired to be written cannot be recalled. In regard to writing this is called amnesic agraphia. Aphasia. — The form of aphasia dependent upon injury to the sound memory centre (amnesic apha- sia) has already been described. The other form of aphasia is that which results from injury to the mo- tor mechanism of speech and is called motor or pure aphasia. Agraphia. — The form of agraphia resulting from injury to the centre of visual memory (amnesic agraphia), has been described. That form which comes of injury to the motor mechanism of the arm and hand is called motor or pure agraphia. Soul Blindness and Deafness. — There is still an- other form of word blindness and deafness in which sounds are heard and images seen, and both are stored and reproduced, but no connection is per- ceived between the sound or the image and any con- ception of the mind. This is known as soul blindness and deafness. It depends on no special centre, but upon a general dissociation of the cerebral areas. FUNCTIONAL DIAGNOSIS 173 REACTION OF DEGENERATION. Reaction of Degeneration. — A similar process of degeneration occurs in a neuron which is cut off from its cell by pathological lesions in the interven- ing axon, such as new growths, sclerosis, inflamma- tory congestions, etc. The process is then known as secondary degeneration, ascending or descending as the case may be, and is clinically detected and meas- ured by certain abnormal ways in which the neuron and the muscles it supplies react to electrical cur- rents. This is known as the Reaction of Degenera- tion and may be briefly stated as follows : In health, both nerve and muscle react to the fara- dic current by contracting sharply upon application of the needle, and to the galvanic current by a con- traction at the closing and opening of the circuit, but not during the passage of the current, the Ka- thode contraction being more vigorous than the anode. In complete reaction of degeneration neither nerve nor muscle reacts to faradic current ; the nerve does not react to galvanic; the muscle contracts slowly and undulatingly to the galvanic, and exhibits as good a reaction to the kathode as to the anode. In incomplete reaction of degeneration the reac- tions exhibit intermediate between normal and com- plete degeneration. Reaction of degeneration enables us to locate the lesion in the lower neuron or in the root-cells, i. e., 174 FUNCTIONAL DIAGNOSIS between the periphery and the trophic ganglia ; and the persistence or improvement of the abnormal re- action indicates a grave or favorable prognosis of the restitution of the integrity of the neuron. Reaction of degeneration is generally associated with muscular atrophy, because the trophic influence of the ganglion is also exerted upon the nutrition of the muscle. It does not occur in diseases involving only the cord tracts or upper neurons, or in cerebral lesion. Multiple neuritis, involving inflammation of the lower neuraxons ; poliomyelitis, inflammation of the anterior horns; and Progressive muscular atrophy, involving both lower neuraxons and anterior roots; all give reaction of degeneration. Amyotrophic la- teral sclerosis gives reaction of degeneration in its later stages, when it attacks the motor roots. FUNCTIONAL DIAGNOSIS 175 SPECIAL FUNCTIONS. Vision. Ocular Movements are performed by means of the extrinsic muscles of the eye, the movements exe- cuted by each pair being as follows : Superior Bec- tus, upward and inward ; Inferior Eectus, downward and inward; External Eectus, outward on vertical axis ; Internal Eectus, inward on vertical axis ;. Su- perior Oblique, outward on antero-posterior axis; Inferior Oblique, correcting the inward deviation of the recti. These muscles are in a constant condition of to- nicity and oppose each other. Muscular Imbalance is the result of inadequacy on the part of one of the extrinsic muscles, causing a deviation of the eyeball in the direction of the opposing muscle or muscles. This condition may be overcome for a time by excessive innervation of the faulty muscles, but eventually this gives way, and strabismus ensues. The inadequate muscle is com- monly one of the recti, since these bear the brunt of the work. Inadequacy of the external rectus causes convergent strabismus; internal rectus causes di- vergent strabismus. ■b "m 'm Muscular Innervation. — All the extrinsic muscles are innervated by the third cranial nerve, except two, namely, the external rectus supplied by the sixth, and the superior oblique by the fourth cranial. 176 FUNCTIONAL DIAGNOSIS Muscular Imbalance. — It is due to the fact that the external and internal recti are supplied by separate nerves that imbalance occurs between these two muscles. The inadequacy of one of them, due to op- tical defects, is compensated for a time by excessive innervation of the other, until the overworked nerve gives way and becomes paralyzed. The sound nerve continues to innervate the opposite muscle which pulls the eye in its own direction. Paralysis of the third nerve causes divergent, of the sixth convergent, strabismus. Paralysis of the fourth nerve causes inability to turn the eye downward and outward. Lucitas. — When the third nerve is paralyzed, not only dies it produce divergent squint, but inasmuch as all other muscles which might move the eyeball are controlled by the same nerve complete immo- bility of the eyeball results. This is known as lucitas. ■v 'm n. Accommodation is the faculty of increasing the convexity of the lens. It is accomplished by contrac- tion of the ciliary muscle, which draws the choroid forward, thus releasing the suspensory ligaments and allowing the lens by its elasticity to assume a more convex form. Accommodation takes place for the purpose of focussing divergent rays, i. e., for sighting near objects, and is relaxed to focus parallel rays, i. e., for sighting distant objects. The exercise of this faculty belongs to the province of optics, and will not be further discussed here. FUNCTIONAL DIAGNOSIS 177 Presbyopia. — In persons over forty-five and in younger persons under certain pathological condi- tions, the lens becomes hard and inelastic, and ac- commodation is greatly limited. ■V *m *m Innervation of Accommodation. — The faculty of accommodation is innervated by the third nerve, through its branches to the ciliary muscle, known as the ciliary nerve.