BARR'S The Human Nervous System: An anatomical viewpoint, 9th Edition

Glossary of Neuroanatomical and Related Terms

In this text, the standard Latin forms of anatomical names are anglicized wherever this is possible without loss of euphony. Most anatomical terms have Latin origins, and most names related to diseases are derived from Greek words. Many words are defined and explained (without etymology) in the text. If you cannot find a word in this glossary, try the Index. For eponyms (names of people, applied to structures, syndromes, or diseases) consult the CD-ROM that accompanies the printed book.

Abbreviations

Eng., English; Fr., French; Ger., German; Gr., Greek; L., Latin; O.E., Old English

Abducens.

  1. ab, from + ducens, leading. Abducens (or abducent) nerve supplies the muscle that moves the direction of gaze away from the midline.

Abulia.

Gr. a, without + boule, will. A loss of willpower. (Also spelled aboulia.)

Accumbens.

  1. reclining. The nucleus accumbens is the ventral part of the head of the caudate nucleus, anterior and ventral to the anterior limb of the internal capsule.

Adenohypophysis.

Gr. aden, gland + hypophysis (which see). The part of the pituitary gland derived from the pharyngeal endoderm (Rathke's pouch). Its largest part is the anterior lobe of the pituitary gland.

Adiadochokinesia.

a, neg. + Gr. diadochos, succeeding + kinesis, movement. Inability to perform rapidly alternating movements. Also called dysdiadochokinesia.

Ageusia.

Gr. a, without + geuein, to taste. Loss of the sense of taste.

Agnosia.

a, neg. + Gr. gnosis, knowledge. Lack of ability to recognize the significance of sensory stimuli (auditory, visual, tactile, etc., agnosia).

Agraphia.

a, neg. + Gr. graphein, to write. Inability to express thoughts in writing owing to a central lesion.

Akinesia.

a, neg. + Gr. kinesis, movement. Loss of movement (adjective, akinetic). Often used to mean severe bradykinesia, a feature of advanced Parkinson's disease.

Ala cinerea.

  1. wing + cinereus, ashen-hued. Vagal triangle in floor of fourth ventricle.

Alexia.

a, neg. + Gr. lexis, word. Loss of the power to grasp the meaning of written or printed words and sentences.

Alimentary.

  1. alimentarius, about food. The alimentary canal or tract is the passage extending from the mouth to the anus.

Allocortex.

Gr. allos, other + L. cortex, bark. Phylogenetically older cerebral cortex, usually consisting of three layers. Includes paleocortex and archicortex.

Allodynia.

Gr. allos, other + dynamis, power or force. A condition in which the nervous system misinterprets a sensory stimulus. The word is usually used when a harmless sensation such as touch is consciously felt as pain, which may be excruciating.

Alveus.

  1. trough. Thin layer of white matter covering the ventricular surface of the hippocampus. (The name seems quite inappropriate but has become an accepted part of anatomical terminology.)

Amacrine.

a, neg. + Gr. makros, long + inos, fiber. Amacrine nerve cell of the retina.

Ambiguus.

  1. changeable or doubtful. Nucleus ambiguus (Chs. 7 and 8) occupies an atypically ventral position for a cranial nerve nucleus, and its limits are somewhat indistinct.

Ammon's horn.

Hippocampus, which has an outline in cross section suggestive of a ram's horn. Also known as the cornu Ammonis. Ammon was an Egyptian deity with a ram's head.

Amoeboid.

Gr. amoibe, change. Relating to a cell that continuously changes its shape and looks like an amoeba.

Ampulla.

  1. ampla, full + bulla, vase. A bulge in a tubular structure.

Amygdala.

  1. amygdalum, from Gr. amygdale, almond. Amygdala or amygdaloid body in the temporal lobe of the cerebral hemisphere.

Aneurysm.

Gr. aneurysma, dilation or widening. An abnormal widening of an artery. It can compress nearby structures and may burst.

Anlage.

Ger. arrangement, layout (among other meanings). The grouping of cells in an embryo that is the beginning of an anatomical structure (Plural:anlagen).

Anopia.

(also Anopsia). an, neg. + Gr. opsis, vision. Defect of vision.

Ansa hypoglossi.

  1. ansa, handle + Gr. hypo, under + Gr. glossa, tongue. Loop of nerves containing axons of the first three cervical roots that encircles the common carotid artery and internal jugular vein in the neck. The fibers from C1 pass within the trunk of the hypoglossal nerve before joining the ansa. Also called the ansa cervicalis.

Anterior.

  1. anterior(from ante), before. Nearer to the front or head. In human anatomy, synonymous with ventral. In animals that do not walk upright, anterior and ventral are different directions.

Antidromic.

Gr. anti, against + dromos, racecourse. Of impulses traveling in the opposite direction to what is usual in an axon.

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Aphasia.

a, neg. + Gr. phasis, speech. Defect of the power of expression by speech or of comprehending spoken or written language.

Apraxia.

a, neg. + Gr. prassein, to do. Inability to carry out purposeful movements in the absence of paralysis.

Arachnoid.

Gr. arachne, spider's web + eidos, resemblance. Meningeal layer that forms the outer boundary of the subarachnoid space.

Archicerebellum.

Gr. arche, beginning + diminutive of cerebrum. Phylogenetically old part of the cerebellum, functioning in the maintenance of equilibrium. Also spelled archeocerebellum.

Archicortex.

Gr. arche, beginning + L. cortex, bark. Threelayered cortex included in the limbic system; located mainly in the hippocampus and dentate gyrus of the temporal lobe. Also spelled archeocortex.

Area postrema.

Area in the caudal part of the floor of the fourth ventricle.

Arrector pili.

  1. arrectus, upright + pilus, hair. A cutaneous muscle that moves a hair.

Astereognosis.

a, neg. + stereos, solid + gnosis, knowledge. Loss of ability to recognize objects or to appreciate their form by touching or feeling them.

Astrocyte.

Gr. astron, star + kytos, hollow (cell). Type of neuroglial cell.

Asynergy.

a, neg. + Gr. syn, with + ergon, work. Disturbance of the proper association in the contraction of muscles that ensures that the different components of an act follow in proper sequence, at the proper moment, and of the proper degree, so that the act is executed accurately.

Ataxia.

a, neg. + Gr. taxis, order. Loss of power of muscle coordination, with irregularity of muscle action.

Atheroma.

Gr. athere, porridge. Thickening of the lining of an artery caused by deposition of lipid material.

Athetosis.

Gr. athetos, without position or place. Affliction of the nervous system caused by degenerative changes in the corpus striatum and cerebral cortex and characterized by bizarre, writhing movements of the fingers and toes, especially.

Atlas.

Gr. atlao, I sustain. The first cervical vertebra.

Atresia.

a, neg. + Gr. tresis, perforation. Absence of a passage caused by an error in development.

Atrophy.

a, neg. + Gr. trophe, nourishment. Diminution of size and functional activity; wasting; emaciation.

Autoimmunity.

Gr. auto, self + im, not + munis, serving. A condition in which antibodies or cells of the immune system attack a part of their own body.

Autonomic.

Gr. autos, self + nomos, law. Autonomic system; the efferent or motor innervation of viscera.

Autoradiography.

Gr. autos, self + L. radius, ray + Gr. graphein, to write. Technique that uses a photographic emulsion to detect the location of radioactive isotopes in tissue sections. Also called radioautography.

Axolemma.

Gr. axon, axis + lemma, husk. Plasma membrane of an axon.

Axon.

Gr. axon, axis. Efferent process of a neuron that conducts impulses to other neurons or to muscle fibers (striated and smooth) and gland cells.

Axon hillock.

Region of the nerve cell body from which the axon arises; it contains no Nissl material.

Axon reaction.

Changes in the cell body of a neuron after damage to its axon.

Axoplasm.

Gr. axon, axis + plasm, anything formed or molded. Cytoplasm of the axon.

Ballism.

See hemiballismus.

Baroreceptor.

Gr. baros, weight + receptor, receiver. Sensory nerve terminal that is stimulated by changes in pressure, as in the carotid sinus and aortic arch.

Basis pedunculi.

Ventral part of the cerebral peduncle of the midbrain on each side, separated from the dorsal part by the substantia nigra. Also called the crus cerebri.

Brachium.

  1. from Gr. brachion, arm. As used in the central nervous system, denotes a large bundle of fibers that connects one part with another (e.g., brachia associated with the colliculi of the midbrain).

Bradykinesia.

Gr. brady, slow + kinesis, movement. Abnormal slowness of movements; one of the three major abnormalities resulting from Parkinson's disease.

Brain stem.

In the mature human brain, denotes the medulla, pons, and midbrain. In descriptions of the embryonic brain, the diencephalon is included as well.

Bulb.

Referred at one time to the medulla oblongata, but in the context of “corticobulbar tract,” refers to the brain stem, in which motor nuclei of cranial nerves are located.

Bulbospongiosus muscle.

  1. bulbus, bulb or onion + spongia, sponge. Muscle surrounding the corpus spongiosus, the body of erectile tissue surrounding the urethra at the base of the penis.

Calamus scriptorius.

  1. calamus, a reed, therefore a reed pen. Refers to an area in the caudal part of the floor of the fourth ventricle that is shaped somewhat like a pen point.

Calcaneus.

  1. calcaneum, the heel. Relating to the calcaneum, which is the bone in the heel of the foot. The tendo calcaneus (Achilles' tendon) inserts into the superior surface of the posterior end of the calcaneum.

Calcar.

  1. spur, used to denote any spur-shaped structure. Calcar avis, an elevation on the medial aspects of the lateral ventricles at the junction of occipital and temporal horns. Also calcarine sulcus of occipital lobe, which is responsible for the calcar avis.

Cauda equina.

  1. horse's tail. Lumbar and sacral spinal nerve roots in the lower part of the spinal canal.

Caudal.

  1. cauda, tail. Along the axis of the central nervous system, toward the tail. In human anatomy, approximately equivalent in the brain stem and spinal cord to “inferior” and in the forebrain to “posterior.” Opposite of rostral.

Caudate nucleus.

Part of the corpus striatum, so named because it has a long extension or tail.

Cerebellum.

  1. diminutive of cerebrum, brain. Large part of the brain with motor functions situated in the posterior cranial fossa.

Cerebrum.

  1. brain. Principal portion of the brain, including the diencephalon and cerebral hemispheres but not the brain stem and cerebellum.

Channel.

A protein molecule in a cell membrane that allows the passage of a particular ion, such as sodium, calcium, potassium or chloride, into or out of the cell, following

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a concentration gradient. Channels typically are gated, meaning that they open and close in response to neurotransmitters or local changes in membrane potential.

Cholinergic.

Using acetylcholine as a neurotransmitter.

Chordotomy.

Gr. chorde, cord + tome, a cutting. Division of the spinothalamic and spinoreticular tracts for intractable pain (tractotomy). Also spelled cordotomy.

Chorea.

  1. from Gr. choros, a dance. Disorder characterized by irregular, spasmodic, involuntary movements of the limbs or facial muscles. Attributed to degenerative changes in the neostriatum.

Choroid.

Gr. chorion, a delicate membrane + eidos, form. Choroid or vascular coat of the eye; choroid plexuses in the ventricles of the brain. Also spelled chorioid.

Chromatolysis.

Gr. chroma, color + lysis, dissolution. Dispersal of the Nissl material of neurons after axon section or in viral infections of the nervous system.

Cinereum.

  1. cinereum, ashen-hued, from cinis, ash. Refers to gray matter, but limited in usage. Tuber cinereum (ventral portion of the hypothalamus, from which the neurohypophysis arises); tuberculum cinereum (slight elevation on medulla formed by spinal tract and nucleus of trigeminal nerve); ala cinerea (vagal triangle in floor of fourth ventricle).

Cingulum.

  1. girdle. Bundle of association fibers in the white matter of the cingulate gyrus on the medial surface of the cerebral hemisphere.

Circumventricular organs.

Small regions composed of atypical brain tissue in the walls of the third (see Ch. 11) and fourth (see Ch. 9) ventricles. These structures lack a blood-brain barrier and have chemoreceptor or neurosecretory functions.

Claustrum.

  1. a barrier. Thin sheet of gray matter of unknown function situated between the lentiform nucleus and the insula.

Clinoid processes.

Gr. kline, bed + oides, shape. The anterior and posterior clinoid processes are four bony points at the corners of the diaphragma sellae (q.v.), named from a fancied resemblance to a four-poster bed.

Clivus.

  1. slope. The sloping bone between the pituitary fossa and the foramen magnum, formed from the fused sphenoid and occipital bones.

Cochlea.

  1. cocleaand Gr. kocklias, snail. The spiral cavity of the inner ear and its contents.

Colliculus.

  1. Small elevation or mound. Superior and inferior colliculi composing the tectum of the midbrain; facial colliculus in the floor of the fourth ventricle.

Commissure.

  1. a joining together. Bundle of nerve fibers that passes from one side to the other in the brain or spinal cord. Strictly, this term should be applied to tracts that connect symmetrical structures (cf. decussation).

Conjugate.

  1. con-, together + jugum, a yoke. Relating to coordinated movements of both eyes in the same direction.

Contracture.

Persistent shortening, as in a muscle paralyzed for a long time.

Contralateral.

  1. contra, opposite + laterisof a side. Of the other (left or right) side of the body. Opposite of “ipsilateral.”

Cornu.

  1. horn. See Ammon's horn.Horns of the lateral ventricle and of the spinal gray matter are also formally named as cornua.

Corona.

  1. corona(or Gr. korone), a crown. Corona radiata (fibers radiating from the internal capsule to various parts of the cerebral cortex).

Coronal.

Gr. korone or L. corona, a crown. The coronal suture traverses the top of the head, separating the frontal bone from the parietal bones. A coronal section is one cut in or parallel to the plane of the coronal suture; these planes are sometimes called frontal.

Corpus callosum.

  1. body + hard. L. callumcan also mean a beam or rafter. Main neocortical commissure of the cerebral hemispheres. (In the second century AD, Galen called this structure a beam or rafter. It has a tougher consistency than the cerebral cortex.)

Corpus luteum.

  1. body + luteum, yellow. Progesteronesecreting endocrine tissue that forms in the ovary after ovulation.

Corpus striatum.

  1. body + striatus, furrowed or striped. Mass of gray matter with motor functions at the base of each cerebral hemisphere.

Cortex.

  1. bark. Outer layer of gray matter of the cerebral hemispheres and cerebellum.

Cortical.

  1. corticis, of bark. Of or relating to a cortex.

Corticofugal.

  1. cortico, from bark + fugere.to flee from. Describes efferent axons of neurons in a region of a cortex that terminate somewhere else: in a remote cortical area or in a subcortical nucleus of the cerebrum or cerebellum.

Corticopetal.

  1. cortico, to bark + petere, to seek. Describes axons afferent to a cortex.

Cribriform.

  1. cribrum, sieve + formare, to shape. Perforated by numerous holes. The cribriform plate of the ethmoid bone has about 20 small foramina on each side, accommodating the olfactory nerves.

Crista.

  1. crest. Used in anatomy for various ridge-like structures, including the cristae ampullares of the kinetic labyrinth. The crista galli (L. galli, of a cockerel) is an upward projection of the ethmoid bone in the midline of the anterior cranial fossa.

Crus.

  1. leg. Crus cerebri is the ventral part of the cerebral peduncle of the midbrain on each side, separated from the dorsal part by the substantia nigra. Also called the basis pedunculi. Crus of the fornix.

Cuneus.

  1. wedge. Gyrus on the medial surface of the cerebral hemisphere. Fasciculus cuneatus in the spinal cord and medulla; nucleus cuneatus in the medulla.

Cupula.

  1. diminutive of cupa, tub. A small concave structure. The gelatinous cap of the crista ampullaris. Also applied to the apex of the cochlea.

Cytosol.

Gr. kytos, a hollow vessel + solution. Soluble portion of the cytoplasm, excluding all membranous and particulate components.

Decussation.

  1. decussatio, from decussis, the numeral X. Point of crossing of paired tracts. Decussations of the pyramids, medial lemnisci, and superior cerebellar peduncles are examples. A decussation connects asymmetrical parts of the nervous system.

Dendrite.

Gr. dendrites, related to a tree. Process of a nerve cell on which axons of other neurons terminate. Sometimes also used for the peripheral process of a primary sensory neuron, although this has the histological and physiological properties of an axon.

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Denervation.

Loss of innervation due to transection of axons or death of the somata of the innervating neurons.

Dentate.

  1. dentatus, toothed. Dentate nucleus of the cerebellum; dentate gyrus in the temporal lobe.

Diabetes.

Gr. diabetes, a syphon. Disease with excessive production of urine. In diabetes mellitus (L. mellitus, sweet), the urine contains sugar, whereas in diabetes insipidus (L. in, not + sapor, flavor), the urine is watery and quite tasteless.

Diaphragma sellae.

Gr. dia, across + phragma, wall + L. sellae, of a saddle. The membrane of dura mater that covers the sella turcica and is pierced by the pituitary stalk.

Diencephalon.

Gr. dia, through + enkephalos, brain. Part of the cerebrum, consisting of the thalamus, epithalamus, subthalamus, and hypothalamus; the more caudal and medial part of the prosencephalon of the developing embryo.

Diplopia.

Gr. diploos, double + ops, eye. Double vision.

Dorsal.

  1. dorsum, the back. Toward the back; the direction opposite to ventral. In human anatomy, dorsal is synonymous with posterior when applied to structures in the head and trunk.

Dorsiflexion.

From dorsal and flexor. Movement at the ankle that raises the toes and depresses the heel.

Dorsum sellae.

  1. dorsum, the back + sellae, of a saddle. The part of the ethmoid bone that forms the posterior wall of the sella turcica or pituitary fossa in the base of the skull.

Dura.

  1. dura, hard. Dura mater (the thick external layer of the meninges).

Dyskinesia.

Gr. dys, difficult or disordered + kinesis, movement. Abnormality of motor function characterized by involuntary, purposeless movements.

Dysmetria.

Gr. dys, difficult or disordered + metron, measure. Disturbance of the power to control the range of movement in muscle action.

Ectoderm.

Gr. ektos, outside + derma, skin. Most dorsal layer of cells of the early embryo, which gives rise to the epidermis, neural tube, neural crest, etc.

Edema (oedema).

Gr. oidema, swelling. Abnormal accumulation of fluid in a tissue.

Emboliform.

Gr. embolos, plug + L. forma, form. Emboliform nucleus of the cerebellum.

Embolus.

Gr. embolos, plug. Fragment of a thrombus that breaks loose and eventually obstructs an artery.

Endomysium.

Gr. endo, within + myos (mys), muscle. The delicate connective tissue that surrounds and separates individual contractile fibers of a muscle.

Endoneurium.

Gr. endon, within + neuron, nerve. Delicate connective tissue sheath surrounding an individual nerve fiber of a peripheral nerve. Also called the sheath of Henle.

Endoplasmic reticulum.

Gr. endo, within + a molded form (cytoplasm) + L. reticulum, small net. An array of membranes within a cell. Rough endoplasmic reticulum is associated with ribosomes, where protein molecules are assembled.

Engram.

Gr. en, in + gramma, mark. Used in psychology to mean the lasting trace left in the brain by previous experience; a latent memory picture.

Entorhinal.

Gr. entos, within + rhis (rhin-), nose. The entorhinal area is the anterior part of the parahippocampal gyrus of the temporal lobe adjacent to the uncus. It is included in the lateral olfactory area.

Eosin Y.

Gr. eos, dawn + in (suffix that denotes an organic compound that is not a base) + Y (for yellowish, in contrast to eosin B which has a bluish cast). A red anionic dye of the xanthene series, used as a microscopical stain. It colors cytoplasm and connective tissue components various shades of orange, pink, and red.

Ependyma.

Gr. ependyma, an upper garment. Lining epithelium of the ventricles of the brain and central canal of the spinal cord.

Epineurium.

Gr. epi, upon + neuron, nerve. Connective tissue sheath surrounding a peripheral nerve.

Epithalamus.

Gr. epi, upon + thalamos, inner chamber. Region of the diencephalon above the thalamus; includes the pineal gland.

Epithelium.

Gr. epi, upon + thele, nipple. A layer (or multiple layers) of cells covering any external or internal surface. Originally (1700) this word meant thin skin covering the nipples or lips; later, it was applied to all skin. By the 1870s, the term was being used in its present sense.

Estrogen (oestrogen).

  1. oestrus, gadfly or frenzy + generator, producer. Steroid hormones (estradiol, estrone, estriol) secreted by the ovary that stimulate the secondary sex organs, especially before ovulation.

Ethmoid.

Gr. ethmos, sieve + oides, shape. A bone of the skull that forms the medial part of the floor of the anterior cranial fossa and the upper part of the skeleton of the nasal cavities. The bone includes the cribriform plate.

Euphony.

Gr. eu, well + phone, sound. Agreeable sound or easy pronunciation.

Exteroceptor.

  1. exterus, external + receptor, receiver. Sensory receptor that serves to acquaint the individual with his or her environment (exteroception).

Extrafusal.

  1. extra, outside +fusus, spindle. Relates to the great majority of contractile fibers of a skeletal muscle, which are outside the sensory receptor organs known as neuromuscular spindles.

Extrapyramidal system.

Vague and confusing term applied to motor parts of the central nervous system other than the pyramidal motor system.

Falx.

  1. sickle. Two of the dural partitions in the cranial cavity are the falx cerebri and the small falx cerebelli.

Fasciculus.

  1. diminutive of fascis, bundle. Bundle of nerve fibers.

Fastigial.

  1. fastigium, the top of a gabled roof. Fastigial nucleus of the cerebellum.

Fenestra.

  1. window. A hole. Fenestra rotunda (round) and fenestra ovale (oval) are between the middle and inner ear. Capillary blood vessels are fenestrated when their endothelial cells have pores, each closed by a diaphragm that does not prevent the egress of large molecules. Such vessels typically occur in endocrine organs.

Fimbria.

  1. fimbriae, fringe. Band of nerve fibers along the medial edge of the hippocampus, continuing as the fornix.

Fistula.

  1. pipe. Abnormal communication between two cavities or between a cavity and the surface of the body.

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In an arteriovenous fistula, blood is shunted directly from an artery into a vein or venous sinus.

Flexor.

  1. flexus, bent; flectere, to bend. A muscle that bends a joint.

Foramen

(plural, foramina). L. forare, to pierce. A hole.

Forceps.

  1. a pair of tongs. Used for the U-shaped configuration of fibers that constitute the anterior and posterior portions of the corpus callosum (forceps frontalis and forceps occipitalis).

Fornix.

  1. arch. Efferent tract of the hippocampal formation, arching over the thalamus and terminating mainly in the mamillary body of the hypothalamus.

Fossa.

  1. hole, ditch or grave. An indentation.

Fovea.

  1. a pit or depression. Fovea centralis (depression in the center of the macula lutea of the retina).

Frontal.

  1. frons, forehead. The frontal bone forms the anterior part of the cranium, including the roofs of the orbits, containing the frontal lobes of the cerebral hemispheres.

Fundus.

  1. bottom. Rounded interior of a hollow organ. The ocular fundus is lined by the retina, with its blood vessels, the optic disc, and other landmarks visible through an ophthalmoscope.

Funiculus.

  1. diminutive of funis, cord. Area of white matter that may consist of several functionally different fasciculi, as in the lateral funiculus of white matter of the spinal cord.

Fusiform.

  1. fusus, spindle + forma, shape. Widest in the middle and tapering at both ends. The fusiform gyrus is on the inferior surface of the temporal lobe, lateral to the parahippocampal gyrus.

GABAergic.

Describes a neuron that uses gamma-aminobutyrate (GABA) as its principal synaptic transmitter.

Ganglion.

Gr. knot or subcutaneous tumor. Swelling composed of nerve cells, as in cerebrospinal and sympathetic ganglia. Also used inappropriately for certain regions of gray matter in the brain (e.g., basal ganglia of the cerebral hemisphere).

Gastrocnemius.

Gr. gaster, belly + kneme, leg. The muscle largely responsible for the bulging contour of the calf of the human leg.

Gemmule.

  1. gemmula, diminutive of gemma, bud. Minute projections on dendrites of certain neurons, especially pyramidal cells and Purkinje cells, for synaptic contact with other neurons.

Genu.

  1. genu, knee. Anterior end of corpus callosum; genu of facial nerve. Also geniculate ganglion of facial nerve and geniculate bodies of thalamus.

Glia.

Gr. glue. Neuroglia, the interstitial or accessory cells of the central nervous system.

Glioblast.

Gr. glia, glue + blastos, germ. Embryonic neuroglial cell.

Gliosomes.

Gr. glia, glue + soma, body. Granules seen by light microscopy in neuroglial cells, especially astrocytes. They are probably mitochondria.

Globus pallidus.

  1. ball + pale. Medial part of lentiform nucleus of corpus striatum. Also globose nuclei of cerebellum.

Glomerulus.

Diminutive of L. glomus, ball of yarn. Synaptic glomeruli of the olfactory bulb and cerebellum.

Glomus.

  1. ball of yarn. Applied to various small organs, including the carotid and aortic bodies, and to one of their characteristic cell types.

Glycocalyx.

Gr. glycyx, sweet + kalyx, cup. Outer coating of carbohydrate molecules on the surface of cells.

Golgi apparatus.

An array of membranous compartments within the cytoplasm, where proteins combine with carbohydrates to form glycoproteins.

Gonadotrophic

(also gonadotropic). Gr. gone, generation + trephein, to feed (trophe, food), or trepein, to turn (tropos, a turning). Gonadotrophic hormones are secreted by the anterior lobe of the pituitary gland and in pregnancy by the placenta. They act upon the gonads (ovary or testis) and are essential for the functions of these organs.

Gracilis.

  1. slender. Fasciculus gracilis of the spinal cord and medulla; nucleus gracilis and gracile tubercle of the medulla.

Granule.

  1. granulum, diminutive of granum, grain. Used to denote small neurons, such as granule cells of cerebellar cortex and stellate cells of cerebral cortex. Hence granular cell layers of both cortices.

Habenula.

  1. diminutive of habena, strap or rein. Small swelling in the epithalamus adjacent to the posterior end of the roof of the third ventricle.

Haarscheibe.

Ger. haar, hair + scheibe, disk. Small elevated area of skin that develops in association with specialized hair follicles and serves as a receptor for tactile stimuli.

Helicotrema.

Gr. helix, snail or coil + trema, hole. The communication between the scala tympani and scala vestibuli at the apex of the cochlea.

Hemalum.

From Eng. hematein + alum. A solution containing hematein and aluminum ions, used to stain the nuclei of cells blue. (Hematein is a yellow dye made by oxidation of hematoxylin, which is a colorless compound extracted from the wood of the logwood tree, Hematoxylon campechianum.)Hemalum is frequently used with eosin Y, a dye that colors tissue components other than nuclei pink. The combination (“H & E”) is the most frequently used staining method in pathology laboratories.

Hemianopia.

Gr. hemi, half + an, neg. + opsis, vision. Loss of half of a field of vision. Also called hemianopsia.

Hemiballismus.

Gr. hemi, half + ballismos, jumping. Violent form of motor restlessness that involves one side of the body, caused by a destructive lesion involving the subthalamic nucleus.

Hemiplegia.

Gr. hemi, half + plege, a blow or stroke. Paralysis of one side of the body.

Herpes zoster

Gr. herpein, to creep + zoster, waist-belt. Virus infection of neurons in a sensory ganglion, causing painful inflammation with small blisters in the corresponding area of skin. (Also called shingles; systemic invection with the same virus causes chicken pox.)

Hippocampus.

Gr. hippos, horse + kampos, sea monster; also the zoological name for a genus of small fishes known as sea horses. Rather inappropriate name given to a gyrus that constitutes an important part of the limbic system; produces an elevation on the floor of the temporal horn of the lateral ventricle.

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Homeostasis.

Gr. homois, like + stasis, standing. Tendency toward stability in the internal environment of the organism.

Homonymous.

Gr. homonymos and L. homonymus, having the same name. Applied to defects in the same part (left or right) of the visual field of both eyes, in consequence of transection of the visual pathway posterior to the optic chiasma.

Hormone.

Gr. hormaein, to stir up. A compound secreted into the blood, which exercises a specific physiological function elsewhere in the body.

Hydrocephalus.

Gr. hydror, water + kephale, head. Excessive accumulation of cerebrospinal fluid.

Hyperacusis.

Gr. hyper, over + acacias, a hearing. Abnormal loudness of perceived sounds.

Hypertension.

Gr. hyper, above measure + L. tension, I stretch. (Before 1700, the word tension was incorrectly used as a synonym for pressure.) Abnormally high arterial blood pressure.

Hypophysis.

Gr. from hypo, under + phytin, to grow. The pituitary gland (considered as an attachment underneath the brain).

Hypothalamus.

Gr. hypo, under + thalamus, inner chamber. Region of the diencephalon that serves as the main controlling center of the autonomic nervous system.

Induction.

  1. inducere, to bring in. In embryology, action of one population of cells on the development of another population nearby.

Indusium.

  1. a garment, from induo, to put on. Indusium griseum, thin layer of gray matter on the dorsal surface of the corpus callosum (gray tunic).

Inferior.

  1. comparative of inferus(from infra), lower or below. In human anatomy, nearer to the soles of the feet. In animals that are not bipedal, the equivalent term is posterior.

Infarction.

  1. infarcire, to stuff or fill in. Regional death of tissue caused by loss of blood supply. The resulting piece of nonfunctional material is called aninfarct.In the central nervous system, an infarct replaces axons and/or cell bodies of neurons.

Infundibulum.

  1. funnel. Infundibular stem of the neurohypophysis.

Innervation.

The normal condition in which axons and their presynaptic endings make functional contact with other cells. The associated verb is innervate.

Insula.

  1. island. Cerebral cortex concealed from surface view and lying at the bottom of the lateral sulcus. Also called the island of Reil.

Interoceptor.

  1. inter, between + receptor, receiver. One of the sensory end organs within viscera.

Interstitial.

  1. inter, between + statum, placed. Within spaces. Interstitial cells of the testis are in the spaces between the seminiferous tubules.

Intrafusal.

  1. intra, within + fusus, spindle. Relates to the contractile muscle fibers within the capsule of a neuromuscular spindle.

Ipsilateral.

  1. ipse, itself + laterisof a side. Of the same side (left or right) of the body. Opposite of “contralateral.”

Ischemia.

Gr. ischein, to check + haimos, blood. Condition of tissue that is not adequately perfused with oxygenated blood.

Ischiocavernosus muscle.

Gr. ischion, hip joint + L. caverna, cave or hollow. Paired muscle associated with the bodies of erectile tissue on either side of the base of the penis.

Isocortex.

Gr. isos, equal + L. cortex, bark. Cerebral cortex having six layers (neocortex).

Juxtarestiform body.

  1. juxta, next door to + restis, rope + forma, shape. Vestibulocerebellar fibers, which lie along the medial surface of the restiform body (q.v.).

Kinesthesia.

Gr. kinesis, movement + aisthesis, sensation. Sense of perception of movement.

Koniocortex.

Gr. konis, dust + L. cortex, bark. Areas of cerebral cortex that contain large numbers of small neurons; typical of sensory areas.

Labyrinth.

Gr labyrinthos, building with intricate passages. The cavities and canals of the inner ear within the petrous part of the temporal bone.

Lamella.

Diminutive of L. lamina, plate or leaf. A thin layer or membrane.

Lamina propria.

  1. lamina, plate or leaf + propria, characteristic, one's own. Connective tissue layer underlying an epithelium.

Lateral.

  1. latus, side or flank. Away from the midline.

Lemniscus.

Gr. lemniskos, fillet (a ribbon or band). Used to designate a bundle of nerve fibers in the central nervous system (e.g., medial lemniscus and lateral lemniscus).

Lentiform.

  1. lens (lent-), a lentil (lens) + forma, shape. Lens-shaped. Lentiform nucleus, a component of the corpus striatum. Also called lenticular nucleus.

Leptomeninges.

Gr. leptos, slender + meninx, membrane. Arachnoid and pia mater.

Lesion.

  1. laesum, hurt or wounded. Applied to any abnormality. In the nervous system, a lesion may be destructive (such as an infarct, injury, hemorrhage, or tumor), or it may stimulate neurons (as in epilepsy).

Limbus.

  1. a hem or border. Limbic lobe: C-shaped configuration of cortex on the medial surface of the cerebral hemisphere that consists of the septal area and the cingulate and parahippocampal gyri. Limbic system: limbic lobe, hippocampal formation, and portions of the diencephalon, especially the mamillary body and anterior thalamic nuclei.

Limen.

  1. threshold. Limen insulae: ventral part of the insula; included in the lateral olfactory area.

Locus coeruleus.

  1. place + caeruleus, dark blue. Small dark spot on each side of the floor of the fourth ventricle; marks the position of a group of nerve cells that contain melanin pigment.

Macroglia.

Gr. makros, large + glia, glue. Larger types of neuroglial cells: astrocytes, oligodendrocytes, and ependymal cells.

Macrophage.

Gr. makros, great + phagein, to eat. A type of white blood cell (monocyte) that has entered connective tissue and assumed phagocytic properties.

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Macrosmatic.

Gr. makros, large + osme, smell. Having the sense of smell strongly or acutely developed.

Macula.

  1. a spot. Macula lutea: spot at the posterior pole of the eye that has a yellow color when viewed with red-free light. Maculae sacculi and utriculi: sensory areas in the vestibular portion of the membranous labyrinth.

Mamillary.

  1. mammilla, diminutive of mamma, breast (shaped like a nipple). Mamillary bodies: swellings on the ventral surface of the hypothalamus. Also spelled mammillary.

Massa intermedia.

Bridge of gray matter that connects the thalami of the two sides across the third ventricle; present in 70% of human brains. Also called the interthalamic adhesion.

Mastoid.

Gr. mastos, breast + oeides, shape. The mastoid process is the downwardly projecting part of the temporal bone behind the ear.

Meatus.

  1. passage. The internal acoustic meatus is the bony canal that contains the eighth cranial nerves and the labyrinthine vessels as they pass within the petrous part of the temporal bone.

Medial.

  1. medius, middle. Toward the midline (a relative term).

Median.

  1. medianus, in the middle. Located in the midline.

Medulla.

  1. marrow, from medius, middle. Medulla spinalis: spinal cord. Medulla oblongata: caudal portion of the brain stem. In current usage, “medulla” means the medulla oblongata.

Medulloblastoma.

Malignant tumor of young children, usually in the midline of the cerebellum, enlarging into the fourth ventricle and spreading by way of the subarachnoid space to other parts of the central nervous system.

Mesencephalon.

Gr. mesos, middle + enkephalos, brain. The midbrain; also its embryonic precursor, the part of the neural tube interposed between the forebrain and hindbrain.

Mesoderm.

Gr. mesos, middle + derma, skin. Middle layer of cells of the early embryo, which gives rise to connective tissues, muscle, etc.

Metathalamus.

Gr. meta, after + thalamus, inner chamber. Medial and lateral geniculate bodies (nuclei).

Metencephalon.

Gr. meta, after + enkephalos, brain. Pons and cerebellum; the more rostral of the two divisions of the rhombencephalon or hindbrain.

Microglia.

Gr. mikros, small + glia, glue. Type of neuroglial cell.

Microsmatic.

Gr. mikros, small + osme, smell. Having a sense of smell, but of relatively poor development.

Microvillus.

Gr. mikros, small + L. villus, hair. Hair-like projections of a cell, typically presenting a striated appearance in light microscopy but individually resolved by the electron microscope and seen to be cytoplasmic protrusions.

Mimetic.

Gr. mimetikos, imitative. Muscles of expression supplied by the facial nerve; sometimes referred to as mimetic muscles.

Miotic.

Gr. meiosis, diminution. A drug causing constriction of the pupil of the eye.

Mitochondrion.

Gr. mitos, thread + chondros, granule. A cytoplasmic organelle with distinctive ultrastructure, containing respiratory enzymes.

Mitral.

  1. mitra, a turban; later the tall, cleft hat (miter) of a bishop. Mitral cells of the olfactory bulb.

Mnemonic.

Gr. mneme, memory. Pertaining to memory.

Molecular.

  1. molecula, diminutive of moles, mass. Used in neurohistology to denote tissue that contains large numbers of fine nerve fibers and that, therefore, has a punctate appearance in silver-stained sections. Molecular layers of cerebral and cerebellar cortices.

Mucosa

or mucous membrane. From L. mucus. The moist lining of a cavity or hollow organ, consisting of an epithelium with glands that secrete mucus, the underlying lamina propria, and (in the alimentary tract) the muscularis mucosae.

Muscularis mucosae.

  1. muscle + of mucosa. A thin layer of smooth muscle tissue beneath (external to) the lamina propria in the mucosa of the alimentary tract.

Mutism.

  1. mutus, silent or dumb. Inability to speak.

Myasthenia gravis.

Gr. myos, muscle + a, without + sthenos, strength + L. gravis, heavy (severe). Disease in which there is failure of neuromuscular transmission (see Ch. 3).

Myelencephalon.

Gr. myelos, marrow + enkephalos, brain. Medulla oblongata; the more caudal of the two divisions of the rhombencephalon or hindbrain.

Myelin.

Gr. myelos, marrow. Layers of lipid and protein substances that form a sheath around axons.

Myenteric.

Gr. myos, muscle + enteron, intestine. The myenteric plexus lies between the longitudinal (outer) and circular layers of smooth muscle of the intestine and other parts of the alimentary tract.

Mydriatic.

Gr. mydriasis, enlargement of the pupil. A drug causing dilation of the pupil of the eye.

Myoepithelial cell.

Gr. myos, muscle + epi, upon + thele, nipple. Contractile cell that embraces a secretory unit (acinus or alveolus) of a gland and propels the contents into a duct.

Myotrophic.

Gr. myos, muscle + trephein, to nourish. Responsible for maintaining the structural and functional integrity of muscle (principally by chemical agents from motor neurons, hence the earlier but ambiguous term “neurotrophic”).

Neocerebellum.

Gr. neos, new + diminutive of cerebrum. Phylogenetically newest part of the cerebellum present in mammals and especially well developed in humans. Ensures smooth muscle action in the finer voluntary movements.

Neocortex.

Gr. neos, new + L. cortex, bark. Six-layered cortex, characteristic of mammals and constituting most of the cerebral cortex in humans.

Neostriatum.

Gr. neos, new + L. striatus, striped or grooved. Phylogenetically newer part of the corpus striatum that consists of the caudate nucleus and putamen; the striatum.

Neuralgia.

Gr. neuron, nerve + algein, to suffer. Pain attributed to abnormal stimulation of sensory fibers in the peripheral nervous system.

Neurite.

Gr. neurites, of a nerve. Cytoplasmic processes of neurons. The term embraces both axons and dendrites.

Neurobiotaxis.

Gr. neuron, nerve + bios, life + taxis, arrangement. Tendency of nerve cells to move during

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embryological development toward the area from which they receive the most stimuli.

Neuroblast.

Gr. neuron, a nerve + blastos, germ. Embryonic nerve cell.

Neurofibril.

Gr. neuron, nerve + L. fibrilla, diminutive of fibra, fiber. Filaments in the cytoplasm of neurons (see Ch. 2).

Neuroglia.

Gr. neuron, nerve + glia, glue. Accessory or interstitial cells of the nervous system; includes astrocytes, oligodendrocytes, microglial cells, ependymal cells, satellite cells, and Schwann cells.

Neurohypophysis.

Gr. neuron, nerve + hypophysis. An endocrine organ that is a ventral protuberance of the hypothalamus, comprising the median eminence of the tuber cinereum, the infundibular stem (which is the nervous tissue of the pituitary stalk) and the neural lobe or infundibular process, which is the major part of the posterior lobe of the pituitary gland.

Neurokeratin.

Gr. neuron, nerve + keras (kerat-), horn. Fibrillar material consisting of proteins that remain after lipids have been dissolved from myelin sheaths.

Neurolemma.

Gr. neuron, nerve + lemma, husk. Delicate sheath surrounding a peripheral nerve fiber consisting of a series of neurolemma cells or Schwann cells. Also spelled neurilemma.

Neuroma.

Gr. neuron, nerve + -oma, indicating a tumor. Swelling of a severed or otherwise injured nerve, containing a profusion of axonal sprouts that have failed to regrow usefully.

Neuron.

Gr. a nerve. Morphological unit of the nervous system consisting of the nerve cell body and its processes (dendrites and axon).

Neuropil.

Gr. neuron, nerve + pilos, felt. Complex net of nerve cell processes that occupies the intervals between cell bodies in gray matter.

Neurosecretion.

The activity of a cell that has the signaling properties of a neuron and the secretory properties of an endocrine cell: a neuron that releases a hormone into the blood.

Nociceptive.

  1. noceo, I injure + capio, I take. Responsive to injurious stimuli.

Nucleolus.

Diminutive of nucleus (see below). An inclusion within the nucleus of a cell, composed of protein and RNA.

Nucleus.

  1. nut, kernel. (1) Body in a cell that contains, in the DNA of its chromosomes, the genetic information that encodes the amino acid sequences of proteins. (2) Collection of neuronal cell bodies, which may be large (like the caudate nucleus) or microscopic (like many nuclei in the brain stem).

Nystagmus.

Gr. nystagmos, a nodding, from nystazein, to be sleepy. Involuntary oscillation of the eyes.

Obex.

  1. bar, bolt, or barrier. Small transverse fold overhanging the opening of the fourth ventricle into the central canal of the closed portion of the medulla.

Occipital.

  1. occipitium, back of the head. Pertaining to the back of the head, which can be called the occiput. Occipital bone and occipital lobes of the cerebral hemisphere.

Oligodendrocyte.

Gr. oligos, few + dendron, tree + kytos, hollow (cell). Type of neuroglial cell. Forms the myelin sheath in the central nervous system in the same manner as the Schwann cell in peripheral nerves.

Olive.

  1. oliva.Oval bulging of the lateral area of the medulla. Inferior, accessory, and superior olivary nuclei.

Ontogeny.

Gr. ontos, being + genesis, generation. Development of an individual. The adjective ontogenetic, which means much the same as “embryological” or “developmental,” is used in contrast to “phylogenetic” (which see).

Operculum.

  1. a cover or lid, from L. opertum, covered. Frontal, parietal, and temporal opercula bound the lateral sulcus of the cerebral hemisphere and conceal the insula.

Osseous.

  1. ossis, of bone. Composed of bone: osseous spiral lamina of the cochlea.

Otic.

Gr. otos, of the ear. The otic vesicle is the anlage of the inner ear. The otic ganglion is near the middle ear.

Otolith.

Gr. otos, of the ear + lithos, stone. One of the particles of calcium carbonate associated with the hair cells of the utricle and saccule (otolithic organs) of the inner ear.

Oxytocin.

Gr. oxys, sharp + tokos, birth. An octapeptide hormone of the neurohypophysis that stimulates the smooth muscle of the uterus and the myoepithelial cells of the mammary glands.

Pachymeninx.

Gr. pachys, thick + meninx, membrane. Dura mater.

Paleocerebellum.

Gr. palaios, old + diminutive of cerebrum. Phylogenetically old part of the cerebellum that functions in postural changes and locomotion.

Paleocortex.

Gr. palaios, old + L. cortex, bark. Olfactory cortex consisting of three to five layers.

Paleostriatum.

Gr. palaios, old + L. striatum, striped or grooved. Phylogenetically older and efferent part of the corpus striatum; the globus pallidus or pallidum.

Pallidofugal.

Pallidum (see below) + L. fugere, to flee from. Describes the axons of neurons in the globus pallidus that conduct impulses to other parts of the brain.

Pallidum.

  1. pallidus, (-um), pale. Globus pallidus of the corpus striatum; medial portion of the lentiform nucleus comprising the paleostriatum.

Pallium.

  1. cloak. Cerebral cortex with subjacent white matter but usually used synonymously with cortex.

Paralysis.

Gr. paralysis, secret undoing; from para, beside + lyein, to loosen. Loss of the power of motion.

Paraplegia.

Gr. para, beside or beyond + plege, a stroke or blow. Paralysis of both legs and lower part of trunk.

Paramedian.

Gr. para, beside + L. medianus, in the middle. In a plane parallel to the median or midsagittal plane.

Parasagittal.

Gr. para, beside + L. sagitta, arrow. A word sometimes used instead of sagittal for a sagittal plane or section that is parallel to but not in the midline.

Parenchyma.

Gr. parenchein, to pour in beside. Essential and distinctive tissue of an organ. (The name is from an early notion that internal organs contained material poured in by their blood vessels.)

Paresis.

Gr. parienai, to relax. Partial paralysis.

Parietal.

  1. parietalis, pertaining to walls. The parietal lobes are beneath the parietal bones, which form much of the wall of the top of the cranium.

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Patella.

Diminutive of L. patina, a pan. The kneecap bone embedded in the tendon of the quadriceps group of muscles, which are extensors of the knee joint.

Pathway.

Eng. Route within the central nervous system consisting of interconnected populations of neurons that serve a common function. A pathway often contains one or more tracts.

Perikaryon.

Gr. peri, around + karyon, nut, kernel. Cytoplasm surrounding the nucleus. Sometimes refers to the cell body of a neuron.

Perineum.

Gr. perinaion. Region consisting of the genitalia, the anus, and the immediately surrounding and intervening region.

Perineurium.

Gr. peri, around + neuron, nerve. Cellular and connective tissue sheath surrounding a bundle of nerve fibers in a peripheral nerve.

Pernicious anemia.

  1. per, through + necis, of murder + Gr. an, negative + haimos, blood. Disease caused by failure to absorb vitamin B12 (cyanocobalamin). The vitamin deficiency results in defective production of red blood cells and degeneration in the central nervous system, including subacute combined degeneration in the spinal cord (see Ch. 5).

Pes.

  1. foot. Pes hippocampi: anterior thickened end of the hippocampus that slightly resembles a cat's paw.

Petrous.

  1. petrosus, rocky. The petrous part of the temporal bone, containing the inner ear, has a craggy appearance.

Phagocyte.

Gr. phagein, to eat + kytos, vessel (cell). A cell that can engulf and internalize smaller objects such as bacteria and fragments of dead cells.

Phalangeal.

Gr. phalanx, a formation of soldiers. Phalangeal cells are in lines alongside the sensory cells of the organ of Corti.

Phylogeny.

Gr. phylon, race + genesis, origin. Evolutionary history, typically as deduced from comparative anatomy.

Pia mater.

  1. tender mother. Thin innermost layer of the meninges attached to the surface of the brain and spinal cord; forms the inner boundary of the subarachnoid space.

Pineal.

  1. pineus, relating to the pine. Shaped like a pine cone (pertaining to the pineal gland).

Plantar.

From L. planta, plant; also applied to the foot. An adjective that relates to the sole of the foot (which often treads on small plants). Theplantaris muscle is a small calf muscle that pulls on the sole of the foot. It is very small in the human leg but larger in the legs of quadrupeds.

Plantar flexion

is bending the ankle so that the toes point downward.

Plexus.

  1. plaited, interwoven. Arrangement of interwoven and intercommunicating nerve trunks or fibers or of blood vessels.

Pneumoencephalography.

Gr. pneuma, air + enkephalos, brain + graphe, a writing. Replacement of cerebrospinal fluid by air followed by x-ray examination (pneumoencephalogram); permits visualization of the ventricles and subarachnoid space. This technique has been replaced by computed tomography (CT scan).

Pons.

  1. bridge. Part of the brain stem that lies between the medulla and the midbrain; appears to constitute a bridge between the right and left halves of the cerebellum.

Portal.

  1. porta, gate. A portal vein drains a capillary bed, but instead of joining larger veins that lead to the heart, it ends by branching into capillaries elsewhere.

Positron.

(From positive electron.) Subatomic particle with the same mass as an electron and equal but opposite charge. Positrons emitted by radioactive elements combine with electrons, with elimination of matter and emission of x-rays. Detection of the latter forms the basis of positron emission tomography (PET).

Posterior.

  1. comparative of post, after. Nearer to the back or tail. In human anatomy, synonymous with dorsal when applied to structures in the head and trunk.

Postpartum.

post, after + parturire, to bring forth. Describes the condition of a mother who has recently given birth.

Progesterone.

Steroid hormone secreted by the corpus luteum and the placenta.

Projection.

  1. proiectus, thrown forward. Applied to the axons of a population of neurons and their sites of termination. Often used when the axons do not constitute a circumscribed tract.

Proprioceptor.

  1. proprius, one's own + capere, to take (or receptor, receiver). One of the sensory endings in muscles, tendons, and joints; provides information concerning movement and position of parts of the body (proprioception).

Prosencephalon.

Gr. pros, before + enkephalos, brain. Forebrain, consisting of the telencephalon (cerebral hemispheres) and diencephalon (thalamus and nearby structures).

Prosopagnosia.

Gr. prosopon, person or face + agnosia (q.v.). Inability to recognize previously familiar faces.

Psalterium.

Gr. psalterion, an ancient stringed instrument like a zither. The name is sometimes given to the posterior part of the body of the fornix, including the hippocampal commissure.

Ptosis.

Gr. ptosis, a falling. Drooping of the upper eyelid.

Pulvinar.

  1. a cushioned seat. Posterior projection of the thalamus above the medial and lateral geniculate bodies.

Pump.

A molecular channel in a cell membrane associated with enzymes that enable it to move ions in or out of the cell against a concentration gradient, with expenditure of energy.

Punctate.

  1. punctum, pricked. Apparently composed of dots, as when many axons or dendrites are seen in transverse section.

Putamen.

  1. shell, husk. Larger and lateral part of the lentiform nucleus of the corpus striatum.

Pyramidal system.

Corticospinal and corticobulbar tracts. So-called because the corticospinal tracts occupy the fancifully pyramid-shaped area on the ventral surface of the medulla. The term pyramidal tract refers specifically to the corticospinal tract.

Pyriform.

  1. pyrum, pear + forma, form. Pyriform area is a region of olfactory cortex consisting of the uncus, limen insulae, and entorhinal area; has a pear-shaped outline in animals with a well-developed olfactory system.

Quadriplegia.

  1. quadri, four + Gr. plege, stroke. Paralysis that affects the four limbs. Also called tetraplegia.

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Ramus.

  1. branch. One of the first branches (dorsalventral) of a spinal nerve, or a communicating branch going to (white) or from (gray) a sympathetic ganglion. Some branches of cerebral sulci are named as rami.

Raphe.

Gr. seam. Anatomical structure in the midline. In the brain, several raphe nuclei are in the midline of the medulla, pons, and midbrain. Their names are partly Latinized, as in nucleus raphes magnus (great nucleus of the raphe), etc.

Receptor.

  1. receptus, received. Word used in two ways in neurobiology: (1) Structure of any size or complexity that collects and usually also edits information about conditions inside or outside the body. Examples are the eye, the muscle spindle, and the free ending of the peripheral neurite of a sensory neuron. (2) Protein molecule embedded in the surface of a cell (or sometimes inside the cell) that specifically binds the molecules of hormones, neurotransmitters, drugs, or other substances that can change the activity of the cell.

Restiform.

  1. restis, rope + forma, shape. Restiform body is an old name for the inferior cerebellar peduncle.

Reticular.

  1. reticularis, pertaining to or resembling a net. Reticular formation of the brain stem.

Rhinal.

Gr. rhis, nose, therefore related to the nose. Rhinal sulcus in the temporal lobe indicates the margin of the lateral olfactory area.

Rhinencephalon.

Gr. rhis (rhin-), nose + enkephalos, brain. Obsolete term that referred to components of the olfactory system. In comparative neurology, structures incorporated in the limbic system (especially the hippocampus and dentate gyrus) were included.

Rhombencephalon.

Gr. rhombos, a lozenge-shaped figure + enkephalos, brain. Pons and cerebellum (metencephalon) and medulla (myelencephalon).

Roentgenogram.

After Wilhelm Konrad Roentgen (1845-1923), who discovered x-rays, + Gr. gramma, a letter or record. Picture made with x-rays; more often called an x-ray or a radiograph.

Rostral.

Adjective from L. rostrum, beak, snout. Along the axis of the central nervous system, toward the nose. In human anatomy, approximately equivalent in the brain stem and spinal cord to “superior” and in the forebrain to “anterior.” Opposite of caudal.

Rostrum.

  1. beak. Recurved portion of the corpus callosum, passing backward from the genu to the lamina terminalis.

Rubro-.

  1. ruber, red. Pertaining to the red nucleus (nucleus ruber), as in rubrospinal and corticorubral.

Saccadic.

Fr. saccader, to jerk. Saccadic or quick movements of the eyes in altering direction of gaze.

Sagittal.

  1. sagitta, arrow. The sagittal suture is in the midline of the cranial vault, between the parietal bones. A sagittal section is one cut in or parallel to the median plane.

Satellite.

  1. satteles, attendant. Satellite cells: flattened cells of ectodermal origin that encapsulate nerve cell bodies in ganglia. Also satellite oligodendrocytes adjacent to nerve cell bodies in the central nervous system.

Scala.

  1. flight of steps. The scalae tympani, media and vestibuli mount up to the apex of the cochlea, but they do not include any steps.

Scotoma.

Gr. skotos, darkness. A blind area in the field of vision, due to damage in the retina or central nervous system.

Sella turcica.

  1. Turkish saddle. The pituitary (hypophysial) fossa, a depression in the midline of the sphenoid bone that contains the pituitary gland.

Septal area.

Area ventral to the genu and rostrum of the corpus callosum on the medial aspect of the frontal lobe that is the site of the septal nuclei.

Septum pellucidum.

  1. partition + transparent. Triangular double membrane between the frontal horns of the lateral ventricles; it fills in the interval between the corpus callosum and the fornix.

Sinus.

  1. word applied to various curved, folded, or hollowed-out shapes. Anatomical uses of the word include air cavities in some cranial bones and the large venous channels of the dura mater.

Sinusoid.

  1. sinus(q.v.) + Gr. oeides, shape. A component of a network of thin-walled blood vessels with wider diameter than ordinary capillaries, in the liver, spleen, and some endocrine organs such as the anterior lobe of the pituitary gland.

Soleus.

From L. solea, sole of a foot or sandal, or the flat fish called sole in English. A muscle in the calf of the leg, deep to the gastrocnemius. Its action presses the sole onto the ground.

Somatic.

Gr. somatikos, bodily. Denoting the body, exclusive of the viscera (as in somatic efferent neurons that supply the skeletal musculature).

Somatosensory.

Having to do with somatic sensation. Synonymous with somesthetic.

Somatotopic.

Gr. soma, body + topos, place. Representation of parts of the body in corresponding parts of the brain.

Somesthetic.

Gr. soma, body + aisthesis, perception. Consciousness of having a body. Somesthetic senses are those of pain, temperature, touch, pressure, position, movement, and vibration. Also spelled somaesthetic.

Sphenoid.

Gr. sphen, wedge + oeides, shape. A bone of complex form that extends across the base of the skull. It is interposed (“wedged”) between the cranial vault and the bones of the facial skeleton.

Splenium.

Gr. splenion, bandage. Thickened posterior extremity of the corpus callosum.

Squint.

From Middle English asquint, with the eyes askew. See also strabismus.

Stellate.

  1. stella, star. Stellate neuron has many short dendrites that radiate in all directions.

Stenosis.

Gr. stenos, narrow. Abnormal narrowing of a tube or passage.

Stereotaxic.

Gr. stereos, solid + taxis, arrangement. Relating to a surgical procedure for introducing the tip of an electrode or other instrument into a predetermined position within the brain. The position is calculated from three-dimensional coordinates based on bony landmarks and supplemented by images obtained by CT or MRI.

Strabismus.

Gr. strabismos, a squinting. Constant lack of parallelism of the visual axes of the eyes. Also known as a squint. (This is the only correct usage of the word squint.)

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Stria terminalis.

  1. a furrow, groove + boundary, limit. Slender strand of fibers running along the medial side of the tail of the caudate nucleus. Originating in the amygdaloid body, most of the fibers end in the septal area and hypothalamus.

Striatum.

  1. striatus, furrowed. Phylogenetically more recent part of the corpus striatum (neostriatum) consisting of the caudate nucleus and the putamen or lateral portion of the lentiform nucleus. In comparative anatomy, striatum refers to a region of the brain in fishes, amphibians, and reptiles that is comparable to the corpus striatum of mammals.

Subiculum.

  1. subicere, to bring under or near. An underlying structure. The subiculum hippocampi is the transitional cortex between that of the parahippocampal gyrus and the hippocampus. In a coronal section of the human temporal lobe, the subiculum is beneath the hippocampus.

Submucosal.

  1. sub, under + mucosal (from mucus). In the wall of a hollow organ, the layer that separates mucosa from the external muscular layers; it consists of vascular connective tissue with much collagen and also contains the submucosal (Meissner's) plexus.

Substantia gelatinosa.

Column of small neurons at the apex of the dorsal gray horn throughout the spinal cord.

Substantia nigra.

  1. black substance. Large nucleus with motor functions in the midbrain; many of the constituent cells contain melanin.

Subthalamus.

  1. under + Gr. thalamus, inner chamber. Region of the diencephalon beneath the thalamus, containing fiber tracts and the subthalamic nucleus.

Sudomotor.

  1. sudor, sweat + motor, mover. Applies to sympathetic neurons that stimulate secretion from sweat glands.

Superior.

  1. comparative of superus(from super), above. In human anatomy, nearer to the top of the head. In animals that are not bipedal, the equivalent term is anterior.

Synapse.

Gr. synapsis, junction. Word introduced by Sherrington in 1897 for the site at which one neuron is excited or inhibited by another neuron.

Syndrome.

Gr. syndrome, the act of running together or combining. Collection of concurring clinical symptoms and signs. A syndrome usually is due to a single cause. The word is often used incorrectly as a synonym for “disease.”

Syringomyelia.

Gr. syrinx, pipe, tube + myelos, marrow. Condition characterized by central cavitation of the spinal cord and gliosis around the cavity.

Tangential.

  1. tangens, touching. In the direction of a line or plane that touches a curved surface. Used in anatomy for a plane of section approximately parallel to the surface of an organ.

Tanycyte.

Gr. tanyo, stretch + kytos, hollow (cell). Specialized type of elongated ependymal cell present in the floor of the third ventricle.

Tapetum.

  1. tapete, a carpet. Fibers of the corpus callosum sweeping over the lateral ventricle and forming the lateral wall of its temporal horn.

Tectum.

  1. roof. Roof of the midbrain consisting of the paired superior and inferior colliculi.

Tegmentum.

  1. tegmentum, a covering. Dorsal portion of the pons; also the major portion of the cerebral peduncle of the midbrain, lying between the substantia nigra and the tectum.

Tela choroidea.

  1. a web + Gr. chorioeides, like a membrane. Vascular connective tissue continuous with that of the pia mater that continues into the core of the choroid plexuses.

Telencephalon.

Gr. telos, end + enkephalos, brain. Cerebral hemispheres; the more lateral and rostral of the two divisions of the prosencephalon or forebrain.

Telodendria.

Gr. telos, end + dendrion, tree. Terminal branches of axons.

Temporal.

  1. tempus, time. The temporal lobe is named after the overlying temporal bone of the skull. The bone is named for the overlying skin (the temple), where the hair first goes gray with the ravages of time.

Tendon.

  1. tendo.A cord, band, or sheet of collagen fibers (sinew) that attaches a muscle to a bone or other structure. The tendo calcaneus is shared by the calf muscles (gastrocnemius, plantaris, and soleus), which all insert onto the calcaneus or heel bone to mediate plantar flexion at the ankle joint.

Tentorium.

  1. tent. Tentorium cerebelli is a dural partition between the occipital lobes of the cerebral hemispheres and the cerebellum.

Tetraplegia.

Gr. tetra-, four + plege, a blow or stroke. Paralysis that affects the four limbs. Also called quadriplegia.

Thalamus.

Gr. thalamus, an inner chamber; also meant a bridal couch, so that the pulvinar (q.v.) was its cushion or pillow. Galen made up the word thalamus, and Willis was probably the first to use the word in its modern sense.

Threshold.

O.E. therscwald, a house's door sill or point of entry. In physiology, the point at which a stimulus brings about a response.

Thrombus.

Gr. thrombos, clot. Clotted blood in a living blood vessel. Thrombosis occurs at sites of irregularity, typically due to atheroma in arteries.

Tomography.

Gr. tomos, cutting + graphein, to write. Production of images of sections through a part of the body. Computed tomography with x-rays and nuclear magnetic resonance imaging are valuable diagnostic techniques.

Tone

tonus. Gr. tonos, pitch (sound), or tension. The normal state of firmness and elasticity of muscles caused by partial contraction of some of their fibers.

Tonofibril.

Gr. tonos, or tension + L. fibra, thread. An intracellular filament that contributes to maintaining the shape and position of a cell.

Torcular.

  1. wine press, from torquere, to twist. Confluence of the dural venous sinuses at the internal occipital protuberance was formerly known as the torcular Herophili.

Trabecula.

Diminutive of L. traba or Gr. trapes, a wooden beam. A component of a net-like arrangement of fibrous, muscular or bony structures, such as the connective tissue filaments that bridge the subarachnoid space, or the spicules and lamellae of cancellous bone.

Tract.

  1. tractus, a region or district. Region of the central nervous system largely occupied by a population of axons that all have the same origin and destination (which often form the name, as in “spinothalamic tract”).

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Transducer.

  1. transducere, to lead across. Structure or mechanism for converting one form of energy into another; applied to sensory receptors.

Trapezoid body.

Transverse fibers of the auditory pathway situated at the junction of the dorsal and ventral portions of the pons.

Trigeminal.

  1. born three at a time. Trigeminal nerve has three large branches or divisions.

Trochlear.

  1. trochlea, a pulley. Trochlear nerve supplies the superior oblique muscle, whose tendon passes through a fibrous ring, the trochlea. This ring changes the direction in which the muscle pulls.

Trophic.

Gr. trephein, to feed; trophe, food or nourishment; trophos, a feeder. Relating to nutrition. The term is extended to chemically mediated beneficial interactions among cells and organs. Frequently part of a word, as in thyrotrophic hormone, which stimulates the thyroid gland.

Tropism.

Gr. tropos, a turning. An influence that changes or controls the direction in which a molecule, a cell or an organ moves. Usually encountered as the suffix -tropic or -tropism. Tropisms are important in the embryonic development of the nervous system. As a suffix, -tropic is sometimes interchangeable with -trophic (q.v.). For example, the name thyrotropic hormone signifies that this pituitary hormone passes from the blood into the thyroid gland. The name thyrotrophic hormone indicates its action on the gland.

Uncinate.

  1. hook-shaped. Uncinate fasciculus: association fibers connecting cortex of the ventral surface of the frontal lobe with that of the temporal pole. Also a bundle of fastigiobulbar fibers (uncinate fasciculus of Russell) that curves over the superior cerebellar peduncle in its passage to the inferior cerebellar peduncle.

Uncus.

  1. a hook. Hooked-back portion of the rostral end of the parahippocampal gyrus of the temporal lobe, constituting a landmark for the lateral olfactory area.

Uvula.

  1. little grape. A part of the inferior vermis of the cerebellum.

Vagus.

  1. wandering. Tenth cranial nerve is so named on account of the wide distribution of its branches in the thorax and abdomen.

Vallecula.

  1. diminutive of vallis, valley. Midline depression on the inferior aspect of the cerebellum.

Varicosity.

  1. varix, a varicose vein. In the nervous system, one of many dilations along the course of a neurite.

Vasopressin.

  1. vessel + pressure. An octapeptide hormone of the neurohypophysis. Large doses increase blood pressure by constricting small arteries. The alternative name of antidiuretic hormonedescribes its physiological action on the kidney.

Velate.

  1. velum, sail, curtain, veil. Velate or protoplasmic astrocytes have flattened processes.

Velum.

  1. sail, curtain, veil. Membranous structure. Superior and inferior medullary vela forming the roof of the fourth ventricle.

Ventral.

  1. venter, belly. Opposite of dorsal. In human anatomy, synonymous with anterior when applied to structures in the head and trunk. In animals that do not stand upright, ventral and anterior are different directions.

Ventricle.

  1. ventriculus, diminutive of venter, belly. Lateral, third, and fourth ventricles of the brain.

Vergence.

  1. vergere, to bend or incline. Relating to coordinated movements of both eyes in opposite directions, either medially (convergence) or laterally (divergence).

Vermis.

  1. worm. Midline portion of the cerebellum. Its ventral surface looks a little like a folded earthworm.

Vertigo.

  1. whirling, from vertere, to turn. A false sensation of rotation, either of self or surroundings.

Vestibular.

  1. vestibulum, forecourt or entrance hall. Relating to the equilibratory sense organs of the inner ear, which are connected with a common cavity, the vestibule of the labyrinth.

Zona incerta.

  1. zona, belt + uncertain. Gray matter in the subthalamus representing a rostral extension of the reticular formation of the brain stem.

Zonula occludens.

  1. diminutive of zona, belt + occluding. Also known as a tight junction. Form of continuous close apposition of the membranes of neighboring cells, impermeable to macromolecules.

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