Basal Ganglia

BASAL GANGLIA

Introduction: -subcortical, intracerebral masses of grey matter forming important parts of extrapyramidal system. They include followings: 1) Corpus striatum- is partially divided by internal capsule into two nuclei they are a) Caudate nucleus b) Lentiform nucleus.(further divided into lateral part putamen & medial part globus pallidus.Caudate nucleus & putamen are often grouped as striatum & globus pallidus is pallium. 2) Amygdaloid body forms a part of limbic system 3) Claustrum

Corpus Striatum -corpus striatum comprises caudate nucleus & lentiform nucleus. Caudate nucleus -C shaped or comma shaped nucleus which is surrounded by lateral ventricle.- Concavity of C encloses thalamus & internal capsule -it has head, body & tail -head forms floor of anterior horn of lateral ventricle and medial wall of anterior limb of internal capsule- band of grey matter connect it to putamen across the ant. limb of internal capsule near anterior perforated substance.

-body forms floor of central part of lateral ventricles and lies medial to posterior limb of internal capsule.- separated from thalamus by stria terminalis & thalamostriate vein. -superiorly, related to frontooccipital bundle & corpus callosum -tail forms roof of inferior horn of lateral ventricle & ends by joining amygdaloid body at temporal pole -medially, related to stria terminalis,laterally to tapetum & superiorly to sublentiform part of internal capsule & globus pallidus.

Lentiform Nucleus: -large lens-shaped(biconvex) nucleus forming lateral boundary of internal capsule -lies beneath insula & claustrum. It has 3 surfaces: -lateral suface is convex & related to external capsule, claustrum, outermost capsule, insula & is grooved by lateral striate arteries. -medial surface is more convexrelated to internal capsule, caudate nucleus & thalamus.

-inferior surface is related to sublentiform part of internal capsule which separates it from optic tract, tail of caudate nucleus & inferior horn of lateral ventricle.-it is grooved by anterior commisure just behind anterior perforated substance. -lentiform nucleus is divided into two parts by a thin lamina of white matter. * larger lateral part is putamen * smaller medial part is called globus pallidus. Made up of large motor cells.

Morphological Divisions of Corpus Striatum: -paleostriatum is older & primitive part- is represented by globus pallidus (pallium) -neostriatum is more recent in development.-is represented by caudate nucleus & putamen of lentiform nucleus. -neostriatum is often called striatum.

Connections of Corpus Striatum: Caudate nucleus & putamen are afferent nuclei whlie globus pallidus is efferent nucleus. Connections are shown below.

Functions of Corpus Striatum: -regulates muscles tone & thus helps in smoothening voluntary movements. -controls automatic associated movements like swinging of arms during walking –controls coordintated movements of different parts of body for emotional expression. -influences precentral motor cortex which is supposed to control extrapyramidal activities of body

Clinical Anatomy -lesion of corpus striatum result in parkinsonism. Rigidity & tremor. This disease can be controlled by both medically & surgically *Medically: Use of Dopamin antagonist.(L-dopa) *Surgically: Pallidotomy & thalamotomy -hypertonicity or lead pipe like muscular rigidity. -bradykinesia -involuntary movement like tremor & other types abnormal movements like chorea, hemiballismus, asthetosis.

Amygdaloid Body: -nuclear mass of temporal lobe, lying anterosuperior to inferior horn of lateral ventricle. – is continuous with tail of caudate nucleus -part of limbic system. -continuous with cortex of uncus, limen insulae & anterior perforated substances * afferents: from olfactory tract * efferent: gives rise to stria terminalis ends in anterior commissure, anterior perforated substance & hypothalamic nuclei.

Claustrum -saucer-shaped nucleus situated between putamen & insula.- it is the thickest & continuous with anterior perforated substance.- function is claustrum is unknown.

White Matter of Cerebrum -consists chiefly of myelinated fibers which connect various parts of cortex to one another & also to other parts of CNS -classified into 3 groups *association fibers. *projections fibers. *commissural fibers.

Association (Arcuate) Fibers: -fibers connects different cortical areas of same hemisphere to one another. Subdivided into two types: *short association fibers connect gyri to one another *long association fibers connect more widely separated to on another eg. #uncinate fasciculus connects temporal pole to motor area & orbital cortex. #cingulum connects cingulate gyrus & to parahippocampal gyrus #sup.longitudinal fasciculus connects frontal lobe to occipital & temporal lobs #inf. Longitudinal fasciculus connects occipital & temporal lobes.

Projections Fibers: -connects cerebral cortex to other part of CNS eg. brain stem & spinal cord, many important tracts like corticospinal & coticopontine are made up of this fibers.

Commissural Fibers: -connects corresponding parts of two hemispheresconstitute commissures of cerebrum they are as follows: *corpus callosum connecting cerebral cortex of two sides *anterior commissure connecting archipallia (olfactory bulbs, piriform area & anterior part of temporal lobe) *posterior commissure connects sup. colliculi & also transmitting corticotectal fibers from pretectal nucleus to EW nucleus of opposite side.

*the commissure of fornix (hippocampal commisure): connects crura of fornix & thus hippocampal formations of two sides *habenular commissure connects habenular nuclei *hypothalamic commissures including anterior hypothalamic commissure (of Ganser), ventral supraoptic commissure (of Gudden) & dorsal supraoptic commissure (of Meynert)

Corpus Callosum: -largest commissure of brain.connects two cerebral hemispheres. Since it is neopallial commissure attains great size in man (10 cm long) -connects all parts of cerebral cortex of two sides except lower & anterior parts of temporal lobes which are connected by anterior commissure.

Parts of Corpus Callosum: -anterior end is genu- lies 4 cm behind frontal pole – related aneriorly to anterior cerebral arteries & posteriorly to anterior horn of lateral ventricle. -rostrum is directed downwards & backwards from genu & ends by joining lamina terminalis. –in front of anterior commissure, it is related to anterior horn of lateral ventricle & inferiorly to indusium griseum & longitudinal striae.

-trunk or body is middle part, between genu & spleniumsuperior surface is convex from backward & concave from side to side. –related to anterior cerebral arteries & to lower border of falx cerebri.overlapped by cingulate gyrus & covered by indusium griseum & longitudinal striae. inferior surface is concave from backwards & convex from side to side.- provides attachment to septum pellucidum & fornix, & forms central part of roof of lateral ventricles.

-splenium is posterior end forming thickest part of it.-lies 6cm front of occipital pole.inferior surface is related to tela choroidea of 3rd ventricle pulvinar, pineal body & tectum of midbrain.- sup. Surface is related to inf. Saggital sinus & falx cerebri. –posteriorly related to great cerebral vein, straight sinus & free margin on tentorium cerebelli.

Fibers of Corpus Callosum: -rostrum connects orbital surfaces of two frontal lobes -forceps minor is made up of fibers of genu that connect two frontal lobes] -forceps major is made up of fibers of genu that connects two occipital lobes -tapetum is formed by some fibers from the trunk & spelnium of corpus callosum.-tapetum forms roof and lateral wall of posterior horn & lateral wall of inferior horn of lateral ventricle. -corpus callosum helps to coordinate activities of two hemispheres.

Internal Capsule -large band of fibers situated in inferomedial part of each cerebral hemisphere -in horizontal sections of brain it appears V-shaped with its concavity directed laterally & concavity is occupied by lentiform nucleus. -it contains fibers going to & coming from cerebral cortex. -when traced upwards, fibers of capsule diverge continuous with corona radiata. When traced downwards its fibers converge & many of them are continous with crus cerebri of mid brain.

-internal capsule is divided into following parts: * ant. Limb lies between head of caudate nucleus & lentiform nuclues. * post. limb lies between thalamus & lentiform nucleus. *retrolentiform part lies behind lentiform nucleus *sublentiform part lies below the lentiform nucleus

Blood Supply

Fibers of the internal capsule

Clinical Anatomy.