Neuroanatomy Transcriptions - Cerebrum Part II

LOBES OF THE CEREBRAL HEMISPHERE
Superolateral Surface of the Hemisphere
	frontal lobe
	-occupies area anterior to central sulcus and superior to the lateral sulcus
	-superolateral surface of the frontal lobe is divided by 3 sulci into 4 gyri:
		-precentral sulcus - runs parallel to central sulcus
		-superior frontal sulcus - extends anteriorly from precentral sulcus
		-inferior frontal sulcus - same direction as superior frontal sulcus
		-precentral gyrus - lies bet. precentral sulcus and central sulcus
		-superior frontal gyrus - lies superior to the superior frontal sulcus
		-middle frontal gyrus - lies bet. superior & inferior sulci
		-inferior frontal gyrus - lies inferior to the inferior frontal sulcus;
			invaded by the anterior and ascending rami of the lateral sulcus
	parietal lobe
	-occupies area posterior to central sulcus and superior to the lateral sulcus
	-extends posteriorly as far as the parieto-occipital sulcus
	-lateral surface of the parietal lobe is divided by 2 sulci into 3 gyri:
		-postcentral sulcus - runs parallel to central sulcus
		-intraparietal sulcus - runs posteriorly from the middle of the post central sulcus
		-postcentral gyrus - lies bet. postcentral sulcus & central sulcus
		-superior parietal lobule (gyrus) - lies superior to intraparietal sulcus
		-inferior parietal lobule (gyrus) - lies inferior to intraparietal sulcus
	temporal lobe
	-occupies area inferior to the lateral sulcus
	-lateral surface of the temporal lobe is divided by 2 sulci into 3 gyri
		-superior temporal sulcus - runs parallel to the posterior rami of the lateral sulcus;
			divides temporal lobe into superior, middle, & inferior temporal gyri
		-middle temporal sulcus - same as superior temporal sulcus
	occipital lobe
	-occupies the small area behind the parieto-occipital sulcus
Medial and Inferior Surfaces of the Hemisphere
	- the lobes of the cerebral hemisphere are not clearly defined on these surfaces, though many important
		areas should be recognized
	corpus callosum
	-largest commissure of the brain, forms a striking feature on this surface
	cingulate gyrus - begins under the anterior end of the corpus callosum 'til it reaches the posterior end
	callosal sulcus - separates cingulate gyrus from corpus callosum
	cingulate sulcus - separates cingulate gyrus from superior frontal gyrus
	paracentral lobule
	-area of the cerebral cortex that surrounds the indentation produced by the central sulcus on the
		superior border; anterior part of this lobule is a continuation of the precentral gyrus on the
		superior lateral surface; the posterior part is continuous with the postcentral gyrus
	precuneus
	-area of cortex bounded anteriorly by the upturned posterior end of the cingulate sulcus and posteriorly
		by the parieto-occipital sulcus
	cuneus
	-a triangular area of the cortex bounded superiorly by the parieto-occipital sulcus, inferiorly by the
		by the calcarine sulcus, and posteriorly by the superior medial margin
	collateral sulcus
	-situated on the inferior surface of the hemisphere; runs anteriorly below the calcarine sulcus
	lingual gyrus - lies between the the collateral sulcus and calcarine sulcus
	parahippocampal gyrus - lies anterior to the lingual gyrus; ends in front as the hooklike uncus
	medial occipitotemporal gyrus
	-extends from occipital pole to the temporal pole; bounded medially by the collateral sulcus and
		rhinal sulcus and laterally by the occipitotemporal sulcus
	occipitotemporal gyrus - lies lateral to the occipitotemporal sulcus; continuous with inferior
		temporal gyrus
	olfactory sulcus - on the inferior surface of the frontal lobe, where the olfactory bulb and tract
		and tract lie
	gyrus rectus - lies medial to the olfactory sulcus
	orbital gyri - numerous; lie lateral to the olfactory sulcus
INTERNAL STRUCTURE OF THE CEREBRAL HEMISPHERES
	The cerebral hemispheres are covered with a layer of gray matter - the cerbral cortex. Located
	in the interior of the cerebral hemispheres are the lateral ventricles, masses of gray matter-
	known as the basal nuclei, and nerve fibers (embedded in neuroglia -white matter)
Lateral Ventricles
	-there are 2 lateral ventricles in each cerebral hemisphere;
	-each is a roughly C-shaped cavity lined with ependyma and filled with CSF
	-may be divided into a body (occupies parietal lobe), anterior horn(extends into frontal lobe),
		posterior horn (occipital lobe) and inferior horn (into temporal lobe)
	-communicates with third ventricle through the interventricular foramen (of Monro) – this
		opening (@ anterior part of the medial wall of the lateral ventricle) is bounded
		anteriorly by the anterior column of fornix and posteriorly by the anterior end of thalamus
Basal Nuclei
	-a collection of mases of gray matter in each cerebral hemisphere
	-composed of the corpus striatum, amygdaloid nucleus and claustrum
	Corpus Striatum
		-situated lateral to the thalamus; almost completely divided by the internal capsule into
			the caudate nucleus and lentiform nucleus
		caudate nucleus - large C-shaped mass of gray matter; closely related to the lateral ventricle
			& lies lateral to the thalamus; its lateral surface is related to the internal capsule, w/c
			separates it from the lentiform nucleus
		lentiform nucleus - wedge-shaped mass of gray matter; its broad convex base is directed
			laterally and its blade medially; buried deep in the white matter of the cerebral hemisphere;
			related medially to internal capsule and laterally to the external capsule, separating it
			from the claustrum, which in turn separates the external capsule from the insula
			inferiorly, at its anterior end the lentiform nucleus is continuous with the caudate nucleus
	Corpus Striatum (cont'd)
		-the corpus striatum receives afferent fibers from different areas of the cerebral cortex,
			the thalamus and brainstem. Efferent fibers then travel back to the same areas of the NS.
		-function of the corpus striatum is concerned with muscular movement, brought about by
			controlling the cerebral cortex rather than through direct descending pathways to
			the brainstem and spinal cord
	Amygdaloid Nucleus
		-situated in the temporal lobe close to the uncus; is considered part of the limbic system
	Claustrum
		-a thin sheet of gray matter separated from the lateral surface of the lentiform nucleus
			by the external capsule; lateral to it is the subcortical white matter of the insula;
		-its function is unknown
White Matter of the Cerebral Hemispheres
	-white matter is composed of myelinated nerve fibers of different diameters supported by neuroglia
	-may be classified into 3 groups according to their connections: (1) commisural fibers,
		(2) association fibers, and (3) projection fibers
	Commissure Fibers
		-these fibers essentially connect corresponding regions of the 2 hemispheres
		-these are: the corpus callosum, anterior commissure, posterior commissure, fornix and
			habenular commissure
		corpus callosum - largest commissure; connects the 2 cerebral hemispheres; lies at the bottom
			of the longitudinal fissure; divided into rostrum, genu, body and splenium
			rostrum - thin part of the anterior end of the corpus callosum, which is prolonged posteriorly
				to be the continuous with the upper end of the lamina terminalis
			genu - curved anterior end; bends inferiorly in front of septum pellucidum
			body - arches posteriorly to to become the splenium
			splenium - the continuation of the body; thickened posterior portion
			Traced laterally, fibers of the genu curve forward into the frontal lobes and
				form the forceps minor
			Fibers of the body extend laterally as the radiation of the corpus callosum
				intersect with bundles of association and projection fibers as they pass the cerebral cortex
				tapetum - fibers which form the roof and lateral wall of the posterior horn of the lateral
				ventricle, as well as the lateral wall of the inferior horn
			Traced laterally, fibers of the splenium arch backward into the occipital lobe
				and form the forceps major
		anterior commissure - small bundle of nerve fibers that cross the midline in the lamina terminalis
			-traced laterally, a smaller or anterior bundle curves forward on each side toward the anterior
				perforated substance of the olfactory tract
			-a larger bundle curves posteriorly on each side and grooves the inferior surface of the lentiform
				nucleus to reach the temporal lobes
		posterior commissure - bundle of nerve fibers that cross the midline immediately above the
			opening of the cerebral aqueduct into the third ventricle
			-related to the inferior part of the stalk of the pineal gland;
			-various collections of nerve cells are situated along its length; destinations and funct'l.
				significance of these fibers are unknown, except for the pretectal nuclei fibers involved
				in pupillary light reflex, which crosses this commissure towards the parasympathetic part
				of the oculomotor nuclei
		fornix - composed of myelinated nerve fibers; constitutes the efferent system of the hippocampus
			that passes to the mamillary bodies of the hypothalamus
			-Nerve fibers first form the alveus, a thin layer of white matter covering the ventricular surface
				of the hippocampus, and then converge to form the fimbria. The fimbriae increase in thickness
				and upon reaching the posterior end of the hippocampus, they arch forward above the
				thalamus and below the corpus callosum to form the posterior columns of the fornix.
				The two columns then come together in the midline to form the body of the fornix.
				commissure of the fornix - consists of transverse fibers that cross the midline
				from one column to another just before the formation of the body of the fornix
				Function of the commissure of the fornix is to connect the hippocampal formations of the
				two sides
		habenular commissure - small bundle of nerve fibers that cross the midline in the superior part
			of the root of the pineal stalk
			-associated with the habenular nuclei, which are situated on either side of the midline in this
				region
			-receives many afferents from the amygdaloid nuclei and hippocampus - these pass to the
				habenular nuclei in the stria medullaris thalami
			-some fibers cross the midline to reach the contralateral nucleus through the habenular
				commissure
			-function and connection in humans is unknown
	Association Fibers
		-these fibers essentially connect various cortical regions within the same hemisphere
		-may be divided into short and long groups
		Short association fibers - lie immediately beneath the cortex and connect adjacent gyri
			Run transversely to the long axis of the sulci.
		long association fibers - collected into named bundles that can be dissected in a formalin-
			hardened brain
			uncinate fasciculus - connects motor-speech area and the gyri on the inferior surface of the
				frontal lobe with the cortex of the pole of the teporal lobe
			cingulum - long, curved fasciculus lying w/in the white matter of the cingulate gyrus; connects
				frontal and parietal lobes with parahippocampal and adjacent temporal cortical regions
			superior longitudinal fasciculus - largest bundle of nerve fibers; connects the anterior part
				of the frontal lobe to the occipital and temporal lobes
			inferior longitudinal fasciculus - runs anteriorly from the occipital lobe, passing lateral to
				the optic radiation, and is distributed to the temporal lobe
			fronto-occipital fasciculus - connects the frontal lobe to the occipital and temporal lobes;
				situated deep within the cerebral hemisphere and is related to the lateral border of the
				caudate nucleus
	Projection Fibers
		-afferent and efferent nerve fibers passing to and from the brainstemto the entire cerebral cortex
			must travel between large nuclear masses of gray matter w/in the cerebral hemisphere.
			at the upper part of the brainstem these fibers form a compact band known as the internal capsule,
			flanked medially by the caudate nucleus and the thalamus, and laterally by the lentiform nucleus.
			Because of the wedge shape of the lentiform nucleus, the internal capsule is bent to form an
			anterior limb and a posterior limb, w/c are continuous with each other at the genu.
			Once the nerve fibers emerge superiorly from bet. The nuclear masses, they radiate in all directions
			to the cerebral cortex. These radiating projection fibers are known as corona radiata.
			Most of the projection fibers lie medial to the association fibers, but they intersect commissural
			fibers of the corpus callosum and the anterior commissure. The nerve fibers w/in the most
			posterior part of the posterior limb of the internal capsul radiate toward the calcarine sulcus
			And are known as optic radiation.
Septum Pellucidum
	-thin vertical sheet of nervous tissue conssisting of white and gray matter covered on either side
		with ependyma
	-stretches bet. Fornix and corpus callosum
	-anteriorly, it occupies the interval bet. body of corpus callosum and rostrum
	-essentially a double membrane with a closed, slit-like cavity bet. membranes
	-forms partition bet. The anterior horns of the lateral ventricles
Tela Choroidea
	- a two-layered fold of pia mater
	- situated between the fornix superiorly and the roof of the 3rd ventricle and upper surfaces of the 2
		thalami inferiorly
	-seen from above, anterior end is situated @ the interventricular foramina
	-lateral edges are irregular and project laterally into the body of the lateral ventricles, covered w/
		ependyma and form the choroid plexuses of the lateral ventricle
	-posteriorly, the lateral edges continue into the inferior horn of the lateral ventricle and are covered
		with ependyma so that the choroid plexus projects through the choroidal fissure
	-on either side of the midline the tela choroidea projects down through the roof of the 3rd ventricle
		to form the choroid plexuses of the 3rd ventricle
	-blood supply of the tela choroidea and the choroid plexuses of the lateral and 3rd ventricles are
		derived from the choroidal branches of the internal carotid and basilar arteries
	-venous drainage is into the internal cerebral veins, w/c unite to form the great cerebral vein
		the great vein joins the inferior sagittal sinus to form the straight sinus
CLINICAL NOTES
Lesions of the Thalamus
	-usually result from thrombosis or hemorrhage of one of the arteries that supply the thalamus
	-since the thalamus receives sensory impulses from the opposite side of the body, disability from a lesion
		w/in it will be confined to the contralateral side of the body - there may be impairment of all forms of
		sensation: light touch, tactile localization & discrimination, & loss of appreciation of joint movements.
	Subthalamic Lesions
		-the subthalamus should be regarded as one of the extrapyramidal motor nuclei and has a large
			connection with the globus pallidus
		-lesions result in sudden, forceful involuntary movements in a contralateral extremity - movements
			may be jerky (choreiform) or violent (ballistic)
	Pineal Gland
		-consists of essentially pinealocytes and glial cells supported by a connective tissue framework
		-regressive changes that occur with age cause accumulation of calcareous concretions w/in
			the glial cells and connective tissue of the gland - these deposits are useful to the radiologist
			since they serve as a landmark - assists in assesment of pineal gland displacement by a lesion
			w/in the skull.
		-functions are mainly inhibitory; influences the pituitary gland, Islets of Langerhans, parathyroids,
			adrenals, and gonads
		-patients with pineal tumors that press against the pineal gland have been observed to have
			severe alteration of reproductive function
	Hypothalamus
		-area of the NS that is of great functional importance; not only controls emotional states but
			assists in regulation of fat, carbohydrate and water metabolism
		-influences body temerature, genital functions, sleep, and food intake
		-it and the pituitary gland constitute a closely integrated unit; hypothalamus plays a role in
			the release of pituitary hormones
	Syndromes of the Hypothalamus
		-lesions may result from infection, trauma or vascular disorders
		-craniopharyngioma, chromophobe adenoma of the pituitary and pineal tumors
			(different tumors) may interfere with th function of the hypothalamus
		-most common abnormalities: genital hypoplasia or atrophy, diabetes insipidus, obesity,
			disturbance of sleep, irregular pyrexia and emanciation
		-some disorders above may occur together, i.e. in adiposogenital dystrophy syndrome
	Cerebral Cortex, Sulci and Lobes of the Cerebral Hemisphere
		-composed of gray matter, only about 1/3 lieson the exposed convexity of the gyri; remaining 2/3
			form the walls of the sulci
		-different areas of the cortex have different functions; anatomical division into lobes and by gyri
			and sulci enables the physician to localize loss of function or accurately place a brain lesion. Examples:
			-focal lesions of the precentral gyrus = contralateral hemiparesis;
			-lesions of the postcentral gyrus = contralateral hemisensory loss
			-widespread lesions of the frontal lobe = loss of attention span or change in social behavior
			-widespread degeneration of cerebral cortex = dementia