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Afferent—Carrying impulses toward the central nervous system, or toward the cortex. Agraphia—Loss of the power of writing. Ala cinerue—An area of gray matter in the floor of the fourth ventricle. It marks the common nucleus of the ninth and tenth cranial nerves. Alexia—Loss of the power to read. Amygdaloid (almost shaped)—A. tubercle, a swelling in the floor of the posterior horn of the lateral ventricle, produced by a thickening of cortex. It is a part of the rhinencephalon. Angular gyrus—The gyrus which closes the posterior end of the superior temporal sulcus. It lies in the area of visual overflow, and is occupied by visual associations, conscious or unconscious. Ansa—A loop. A. lenticularis, a bundle of fibers connecting the lenticular nucleus with the cortex, the upper lamina of the internal capsule. A. peduncularis, a bundle of fibers connecting the thalamus with the cortex, the lower lamina of the internal capsule. Aphasia—Loss of the power of speech. Aqueduct of the cerebrum—A channel which connects the third ventricle with the fourth ventricle. It is about an inch long. Arbor vitae—The treelike appearance of the cerebellum on section. It is caused by the infolding of the cortical gray matter upon the white core. Archipallium—The primitive brain; the part of the hemispheres first developed; the rhinencephalon. Arcuate fibers—Fibers following the course of part of a circle; internal arcuate fibers, those from the nucleus gracilis and nucleus cuneatus passing into the fillet; external arcuate fibers, those which surround the olivary nucleus externally. They include fibers from several sources. Arterial circle (circle of Willis)—An arterial anastomosis composed of the posterior communicating arteries, the anterior cerebral arteries, and the anterior communicating arteries, all derived from the basilar and the internal carotid arteries. Association—A term applied to those neurons, tracts or centers which are concerned in relating the parts of the nervous system at different levels. Axon—The emissive prolongation of the neuron. It is characterized by the absence of tigroid substance; its origin from an implantation cone; its constant diameter, the right or recurrent angle of its branchings, and sometimes its great length. Axon hillock—The implantation cone, an area of the protoplasm of a neuron from which the axon arises. It contains no tigroid substance. Axis cylinder—The axon; the nervous part of the peripheral nerve. Basis pedunculi—The crusts of the cerebral peduncle, the part of the peduncle ventral to the substantia nigra. Brachium—An arm. B. conjunctivum, the bundle of fibers which connects the cerebellum and midbrain, the superior cerebellar peduncle. B. pontis, the bundle of fibers which connects the cerebellum and pons, the middle cerebellar peduncle. Superior B., the bundle of fibers which connects the superior quadrigeminate with the lateral geniculate body. Inferior B., the bundle of fibers which connects the inferior quadrigeminate body to the medial geniculate body. Calamus scriptorius (the writing pen)—The gray matter at the inferior angle of the floor of the fourth ventricle. Calcar avis—A swelling along the inner wall of the posterior horn of the lateral ventricle produced by a thickening of the infolded calcarine fissure. Calcarine fissure—A fissure in the inferior and median aspect of the occipital lobes. It is partly occupied by the visual area. Capsule—The sheets of white fibers beneath the cerebral cortex. Internal C., the sheet of fibers between the thalamus and the striate body. External C., the sheet of fibers between the striate body and the cortex. Cauda equina—The inferior continuation of the spinal cord and membranes. It includes the filum terminale with the roots of the lumber and sacral nerves. Chiasma opticum (optic chiasm)—The partial decussation of the optic tracts. The fibers of the chiasm include (a) fibers from the temporal halves of both retinae, which do not decussate, (b) fibers from the nasal halves of both retinae, which decussate, (c) fibers from the medial geniculate body of each side as they pass to the same contra-lateral body. The last fiber group is not concerned in the visual path. Chromophilic—Havaing an affinity for stains. C. cells, those capable of being deeply stained. C. masses, the tigroid masses, or Nissl’s substance, masses of deutoplasmic particles in the protoplasm of the normal resting neuron which take certain stains with especial avidity. They are supposed to represent the stored potential energy of the neuron. Ciaglinski’s tract—A long sensory tract lying in the posterior commissure of the spinal cord. Its existence and relations are not certainly known. Cilio-spinal—Pertaining to the eye centers and the spinal cord. C. center, a group of nerve cells in the upper thoracic cord which is concerned in the control of the orbital structures. Caudate nucleus—That part of the striate body which lies under the floor of the lateral ventricle, and which curves from an anterior headlike swelling to a posterior narrow taillike termination continuous with the amygdaloid nucleus. Cellulifugal—Carrying impulses from the cell body. Cellulipetal—Carrying impulses toward the cell body. Center—A group of nerve cells in which the nerve impulses controlling any function are coordinated. C. of origin, a group of nerve cells whose axons make up a motor nerve. C. of termination, a group of nerve cells among which the axons of a sensory nerve terminate. Cephalization—The headward tendency of parts in phylogenetic development; the tendency of the centers to move forward, and of organs to become innervated from centers more anteriorly placed. Cerebellum (little brain)—The mass of nerve matter developed from the metencephalon; the chief organ for the coordination of muscular movements. Cerebrum—The brain, the nervous matter included in the skull anterior to the tentorium cerebelli; commonly, the two hemispheres. Cingulum (girdle)—A bundle of fibers in the gyrus fornicatus which encircles the corpus callosum. It is concerned in associating the olfactory areas. Circle of Willis—See Arterial circle. Clarke, column of—See Nucleus dorsalis. Collaterals—Branches from axons. These are usually of about the same caliber as the axon, and are given off at a right or recurrent angle. Claustrum—A layer of gray matter lying beneath the insula and lateral to the external capsule. It resembles the deeper layers of the cortex in structure. Its specific function is not known. Colliculus—(a yoke)—Anterior C., the anterior pair of quadrigeminate bodies concerned in the control of the movements of the intrinsic and extrinsic eye muscles. Posterior C., the posterior pair of quadrigeminate bodies concerned in the control of the intrinsic and extrinsic ear muscles and in the transmission of auditory impulses cephalad. Column, of the spinal cord—Cells arranged vertically through the gray matter; originally applied to the curving surfaces of the external aspect of the cord. Comma tract—A bundle of short descending fibers of the spinal cord, the descending branches of the incoming fibers of the posterior roots of the cord, passing to levels one or two segments lower. Cortex (bark)—The outermost layer of any structure; applied to the layer of gray matter upon the outer aspect of the cerebrum and the cerebellum. Cuneus—A wedge-shaped gyrus upon the inner aspect of the occipital lobe. It is occupied in part by the visual overflow. Cuneate tubercle—The swelling on the floor of the fourth ventricle, produced by the nucleus cuneatus. Cuneatus—See Nucleus cuneatus. Corpora albicantia—See C. mammillaria. Corpora mammillaria—Two bodies situated beneath the crura cerebri. These receive the descending fornix fibers, and send fibers to different parts of the thalamus, midbrain and pons. The bodies are part of the olfacto-somatic reflex arcs. Corpora geniculata—These bodies include two pairs. C. G. medialis, or the median geniculate body, lies upon the postero-median aspect of the thalamus. It is concerned in carrying the impulses for hearing toward the acustic area of the cortex. C. G. laterals, or the lateral geniculate body, lies on the posterior aspect of the thalamus, lateral to the body just mentioned. It is concerned in transmitting the impulses for seeing to the visual area of the cortex. Corpora quadrigemina—See Colliculus. Corpora striata—This body lies within the cerebral hemisphere. It includes the caudate nucleus and the lenticular nucleus, q.v. Chromatolysis—The destruction of the tigroid masses. C. occurs during excessive overstimulation of the neurons, or in the presence of poisons, increased heat, etc. Corpus callosum—A thick sheet of fibers which connects the two hemispheres. Corpus dentatum—A mass of gray matter in each cerebellar hemisphere. Its folded appearance gives it the name. Corpus pineale—(the pineal body)—A structure, reminiscent of the medial eye, lying in the midline just anteriorly to the superior colliculus. Corpus restiforme (the restiform body)—A large bundle of fibers which passes into the cerebellum; the inferior cerebellar peduncle. Corpus trapezoideum—A mass of fibers from the auditory nuclei which form a trapezoidal outline in section through the upper medulla. It is part of the auditory conduction path. Degeneration—Retrogressive metabolic changes, associated with abnormal conditions of structure or environment. D., Wallerian, the degeneration which occurs in the part of a nerve fiber dissociated from the cell body. D., Nissl’s, the atrophy which occurs in a neuron which fails to receive its normal stimulation, or whose celulifugal impulses are impeded for a long time. Decussation—A crossing of fibers. Qualifying terms are self-explanatory, as decussation of the fillet, of the pyramids, etc. Dieter’s cell—See Golgi. Dendrites--Protoplasmic prolongations of the nerve cell. Dendrites are characterized by their treelike branching, their decreasing caliber, the tigroid masses with their protoplasm, usually their short length, and their cellulipetal function. Dentate nucleus—See Corpus dentatum. Diencephalon—The midbrain. Dieter’s nucleus—Nucleus of termination of the vestibular nerve. Direct cerebellar tract (cerebello-spinal)—See Table II. Direct pyramidal tract—See cerebro-spinal, Table II. Dorsal nucleus (Clarke’s column)—A mass of cells at the base of the posterior horn of the cord, chiefly in the thoracic region. Efferent—Carrying impulses away from the central nervous system. Epiphysis—See Corpus pineale. Epistriatum—An area of gray matter above the corpus striatum in lower vertebrates It probably is the anlage of the cortical parts of the rhinencephalon. Eminentia cinerea—A swelling on the floor of the fourth ventricle in the region of the ala cinerae, due to the presence of the vagus nucleus. Encephalon (the brain)—The term is applied to the hemispheres particularly. Ependyma—The layer of cells lining the cerebral and spinal ventricles. It is derived from the infolded epiblastic cells, and is ciliated in certain parts of the neural cavities. External arcuate fibers—See Arcuate. External capsule—See Capsule. Falx cerebri—A double fold of the inner layer of the dura mater which dips between the cerebral hemispheres. It includes within its layer in the lower part the inferior sagittal sinus, and in the triangular space between its two layers and the outer layer of the dura, lining the skull, the superior sagittal sinus. Fascia dentate—An infolded part of the cerebral cortex, anterior to the hippocampus. It is absent in anosmatics, is poorly developed in hyposmatics, and is concerned in the olfactory sense. Fasciculus (a bundle of fagots)—A bundle of nerve fibers having a common course, and usually a common origin or destination, or both. See Table II. Fillet (ribbon or band)—A bandlike bundle of fibers. Lateral F., or lemniscus, a tract from the auditory centers, terminating in the posterior colliculus, and in the medial geniculate body. It carries auditory impulses. Medial F., a tract composed of axons of the nucleus gracilis, nucleus cuneatus, and the nuclei of common sensation and taste in the medulla; it terminates in the lateral nucleus of the thalamus, after giving off certain branches during its course. Filum terminale—A bundle composed mostly of connective tissue, with a small amount of nervous matter, representing the lower prolongation of the spinal cord. Fissure—A furrow in the brain, either produced by clefts between the embryonic vesicles, or of such depth and structure as to involve the entire wall of the hemispheres, or to produce eminences upon the walls of the lateral ventricles. Fornix—A bundle of fibers which associates the anterior and the posterior parts of the rhinencephalon. It includes fibers from several sources and of several destinations, all of them concerned in the transmission of impulses ultimately olfactory. Funiculus (a little rope)—One of the rounded aspects of the spinal cord, resembling a column. Three funiculi are found on each side of the cord. The term is applied also to bundles of fibers, as a synonym of fasciculus. Ganglion—A collection of nerve cells associated for the performance of some particular function, but not necessarily capable of coordinating nerve impulses. The term is an anatomical one, and no physiological significance is implied in its use. Gasserian ganglia—See Semilunar ganglion. Gelatinosa—A substance found around the neural canal and over the head of the posterior horn in the cord, also in other situations in smaller amounts. It is composed of neuroglia, with small nerve cells interspersed within it. Genetic—Giving origin to. G. nucleus, a group of nerve cells whose axons make up a motor nerve. Geniculate—See Corpora geniculata. Globus pallidus—Two ganglionic masses of gray matter lying beneath the cortex of the hemispheres. These are the inner part of the lenticular nucleus, and are so called because they are rather poorly supplied with blood, and also because the cells of which they are composed contain no pigment. Their function is not well known. Golgi cells—The term is often applied to the cells which Golgi called Type II. These cells have a single short axon, which exhausts itself by frequent branching in the immediate neighborhood of the cell body. Golgi’s Type I cell gives off a long axon, which passes out of the gray matter, or at any rate reaches to a great distance from the cell body. Later authors call the Type I of Golgi the "Dieter’s" cell. Gol (tract or column of)—See Fasciculus gracilis, Table II. Gower’s tract—See Cerebello-spinal, Table II. Gyrus—An infolding of the cerebral cortex not produced by the embryonic vesicles, and not so deep as to produce indentations upon the walls of the cerebral ventricles. Helwig’s tract—See Olivo-spinal, Table II. Hippocampus—A swelling upon the floor of the posterior horn of the lateral ventricle, produced by the hippocampal fissure. The infolding of the cortex of the hippocampal fissure produces the structure known as the "horn of Ammon." Hypophyris—The pituitary body, a structure arising in part from the pharyngeal membrane and in part from the floor of the third ventricle. It includes nervous matter of unknown function and also glandular matter, which elaborates an internal secretion, which is of great importance, but of whose nature very little is known. Hypothalamus—The masses of gray matter lying beneath the thalamus, including the zona incerta, the nucleus hypothalamicus (Luy’s body), and the stratum dorsale. The hypothalamic region seems to be concerned in the instinctive and emotional reactions. Infundibulum—A depression in the floor of the third ventricle which leads into the hypophysis. It does not remain open after a very early period of embryonic development. Insula (the island of Reill)—A part of the cerebral cortex which became infolded during embryonic development as a result of the deepening of the lateral cerebral fissures (of Sylvius). It can be seen only by separating the lips of the fissure, or by cutting away the operculum which overhangs it. The insula is an association area of whose function little is known. Innervation—The act or process of transmitting nerve impulses to, as to a muscle or gland. The term is applied to structures external to the nervous system, and is used in relation to the source of the nerve impulses to any structure. Intumescentia—A swelling. I. Cervicalis, the cervical enlargement of the spinal cord. I. Lumborum, the lumbar enlargement of the cord. Internal capsule—See Capsule, internal. Island of Reill—See Insula. Interbrain—The thalamencephalon, the region of the thalamus, hypothalamus, and part of the walls of the third ventricle. It is developed from the posterior portion of the first primitive vesicle. Iter a tertio ad quarium ventriculum—See Aqueduct of the cerebrum. Koryochrome—A nerve cell whose nucleus occupies almost the entire cell. Lemniscus—See Fillet. Limbic lobe—A part of the cortex which lies on its median aspect above the corpus callosum, and on the inner inferior aspect of the hemisphere. It is part of the rhinencephalon and is rudimentary in the human brain. Limen—A threshold. L. insulae, the line at which the insula is continuous with the anterior perforated space. Liminol value—The amount of stimulation necessary to cause the initiation of a nerve impulse by a neuron; the efficient stimulus of any cell or cell structure. Localization—The recognition of the function of any particular area, particularly applied to the cortical areas. Locus ceruleus—An area in the floor of the fourth ventricle, which is of a grayish blue color, because of the pigment of its cells. Lyra, or Lyre—Commissural fibers between the diverging crura of the splenium, supposed to resemble the strings of that instrument. Mammillary bodies—See Corpora mammillaria. Medullation—The process of becoming medullated, or covered with the medullary sheath, the white substance of Schwann. Medullary sheath—The myelin sheath, the white substance, fatty and homogeneous, which is formed around the fibers of the cerebro-spinal nerves (except the olfactory) in the order of their assumption of function. Meninges—The membranes which surround the brain and cord. The outer is the dura mater, the middle layer is the arrachnoid, and the innermost, lying next the brain or cord, is the pia mater. Metathalamus (upon the thalamus)—The geniculate bodies, which lie upon the posterior aspect of the thalamus. Moss fibers—The incoming fibers of the cerebellum, which terminate in mossllike branchings in relation to similar terminations of the dendrites of the small multipolar cells of the cerebellar cortex. Moss cells (the term is rather indiscriminately used by different authors)—Neuroglia cells whose branches are fine and mossy in appearance; nerve cells whose dendrites are of mossy appearance. Myelin—The white substance of Schwann, the medullary sheath. Myelinization—The process of becoming invested with myelin; medullation. Neopalliium (new brain mantle)—That part of the cerebral cortex not included in the archipallium or rhinencephalon; the part concerned in cerebral functions exclusive of smell. Neural—Pertaining to the nervous system. N. canal, the canal through the spinal cord; the sixth ventricle. Neuraxone—The axon. Neuroblast—The cells of early embryonic life which become developed into neurons. Neuroglia (nerve glue)—Cells descended from the same epiglastic cells which give origin to the neurons, but which have been developed with the power of reproduction, but no marked irritability. Neuroglia is functionally the connective tissue of the central nervous system; it supports and confines the neurons, the fibers, and the various vessels which nourish these. Neurilemma—The thin connective sheath which surrounds the nerve fibers outside of the central nervous system. It surrounds both sympathetic and cerebro-spinal nerve fibers, and at the roots of the nerves is continuous with the pia mater. Neuron—A nerve cell with all of its branches, including the nerve endings in neurons of the first order. Nissl—See Degeneration and Tigroid. Nucleus—The nutritive center of a cell; (a) a collection of nerve cells whose fibers form a tract or nerve; hence, the nutritive center of a tract or nerve. Nucleolus—A small body of deeply-staining substances found within the nucleus of nerve cells and of other cells. Nucleur ruber (red nucleus)—A mass of cells lying beneath the aqueduct and the third ventricle. It is associated with the cortex and the basal ganglia, and with the lower centers. It appears to be concerned in the coordination of the instinctive and emotional reactions. Node(a knot)—A joint or lump. N. of Ranvier, those points in the course of a nerve fiber at which the myelin sheath is interrupted and the neurilemma is in contact with the nerve fiber. Operculum—That part of the cortex, chiefly of the parietal lobe, which overhangs the insula. The operculum properly includes also a part of the temporal and the frontal lobes. Overflow—Cortical area adjacent to areas of specific function; concerned in associational process which may or may not be conscious. Perikaryon (around the kernel)—the part of the neuron which immediately surrounds the nucleus; the cell body, exclusive of the long prolongations. Prevertebral—Anterior to the vertebrae. P. ganglia, those sympathetic ganglia which are located anterior to the lateral chain of ganglia, as the semilunar ganglion, the ganglia of the cardiac and pulmonary plexuses, etc. Prosencephalon—That part of the nervous system developed from the first cerebral vesicle, the hemispheres with the corpora striata and the optic thalamus and the adjacent structures. Psychic—Pertaining to consciousness. Pulvinar (a pillow)—A swelling upon the median aspect of the thalamus. It receives a large proportion of the optic tract fibers, and is a way station in the path of the impulses concerned in vision. Putamen—The outer mass of gray matter of the lenticular nucleus. Quadrigeminate—See Colliculus. Radix, root—The groups of fibers leaving the central nervous system, as the anterior or posterior roots of the cord, the roots of the cranial nerves, etc. Red nucleus—See Nucleus rubber. Reflex ("turned back")—The action which results from the stimulation of sensory neurons, affecting efferent neurons, without the intermediation of consciousness. It is not essential that the action be unconscious, but only that consciousness, or volition, shall not affect the action. Restiform body ("rope-shaped")—The inferior cerebellar peduncle. See Table II. Rhinencephalon—The part of the brain concerned in the sense of smell. It is the part of the brain first to become functional in phylogenetic development. Rhombencephalon—The part of the brain developed from the posterior vesicle. It includes the metencephalon and the myeloncephalon, the cerebellum, pons and medulla. Rubro-spinal tract—See Table II. Schwann—Sheath of, the neurilemma. Substance of, the myelin sheath which surrounds the nerve fibers of the central nervous system. Semilunar ganglion—The Gasserian ganglion, the sensory ganglion of the trigeminal or fifth cranial nerve. Septum pellucidum—The membrane which separates the laterala ventricles. Somethetic—Pertaining to the body sensations; that part of the cerebral cortex in which the sensations of the body are registered; the Rolandic area, the area lying about the central fissure. Stereognosis—The sense of appreciating the elements of the external cortex in which the sensations of the body are registered; the Rolandic area, the area lying about the central fissure. Strand cells—Those cells in the cord whose axons enter into the spinal tracts. Also called Dieter’s cells and Golgi Type I cells. Subiculum—The lower wall of the hippocampus. Sulcus—A groove upon the surface of the cortex, not deep enough to indent the ventricular wall, nor developed from the deep furrows between the embryonic vesicles. Sensorium—The cortical areas concerned in consciousness of sensations. Somatic—Pertaining to the body wall. Somato-motor—Controlling the skeletal muscles. Somato-visceral—A term applied to those reflex actions which are initiated by somatic sensory impulses, affecting the visceral structures. Stimulus—The agent which acts upon nerve or other tissues in such a manner as to change their activity. Stimulation—The process of changing the activity of nerve or other tissues. Tegmentum—The part of the cerebral peduncles which lies between the aqueduct and the substantia nigra. Telencephalon—The endbrain, that part of the nervous system developed from the anterior portion of the anterior vesicle; it includes the hemispheres, corpus callosum, fornix, etc., to the optic thalamus, but not including it. Tentorium, "roof"—T. cerebelli, the fold of dura mater which roofs the cerebellum. Telodendria—The terminal branchings of the dendrites. Tigroid masses (Nissl substance)—Dentoplasmic bodies in the nerve cell which have especial affinity for certain stains. Tuber—A swelling, as t. cinerum; a swelling in the floor of the fourth ventricle of a gray color. Uncinate—Hook-shaped. U. fasciculus—See Table II. Velum, "a veil"—A fold of the pia mater such as is found in the lateral ventricles and in the fourth ventricle. Ventral—Pertaining to the anterior aspect of the body. Ventricle—A cavity; one of the cavities of the central nervous system. The first ventricle is found within the right cerebral hemisphere; the second, within the left hemisphere; the third, between the hemispheres; the fourth, between the pons and medulla and the cerebellum; the fifth, between the folds of the septum pelucidum; the sixth, the canal of the spinal cord. All of the ventricles except the fifth are continuous. Vaso-motor—A term applied to the nerves which control the size of the blood vessels. Viscero-motor—A term applied to the nerves controlling the visceral muscles and glands. Viscero-somatic—A term applied to reflex actions by sensory impulses from viscera affecting somatic motor nerves. Wallerian—See Degeneration. Zona incerto—The upward extension of the reticular formation beneath the thalamus. |