BMS2-17 Diencephalon Thalamus Hypothalamus PDF

Diencephalon Dr A Aktar Diencephalon – PARTS: • • • • Thalamus Hypothalamus Epithalmus Subthalamus Diencephalon • Accounts for < 2% of brain mass, but extremely important • 4 divisions: • Thalamus • Hypothalamus • Epithalamus • Subthalamus • Epithalamus: Pineal gland, habenucalar nucleus • Su...

Diencephalon Dr A Aktar Diencephalon – PARTS: • • • • Thalamus Hypothalamus Epithalmus Subthalamus Diencephalon • Accounts for < 2% of brain mass, but extremely important • 4 divisions: • Thalamus • Hypothalamus • Epithalamus • Subthalamus • Epithalamus: Pineal gland, habenucalar nucleus • Subthalamus: Involved in basal ganglia circuitry Diencephalon • Only part of diencephalon that can be seen on an intact brain is the inferior surface of the hypothalamus which includes the mammillary bodies and the infundibular stalk • Medial surface of diencephalon can be seen on a hemisected brain • Much of medial surface forms each wall of 3rd ventricle • Laterally is bounded by internal capsule Diencephalon • Caudal boundary of diencephalon is a plane thru post commisure & caudal edge of mamillary bodies • Rostral boundary is plane thru back of ant. commisure & front of optic chiasm • Axis of diencephalon inclined app 80o vs axis of brainstem Diencephalon • Is part of CNS located on both sides of 3rd ventricle • Extends anteriorly from interventricular foramen posteriorly to cerebral aqueduct Thalamus • Located deep in cerebral hemispheres • Shaped like an egg • Composed of gray matter (nuclear mass) & white matter Thalamus • Partly borders 3rd ventricle • Situated btwn cerebral cortex & midbrain • Posteriorly protrudes over most sup. portion of brainstem Relations: Anterior • Head of caudate nucleus & genu of internal capsule • Interventricular foramen Posterior end: Pulvinar of thalamus Thalamus Posterior end: Pulvinar Thalamus Thalamus - Surfaces • Medial surface • Lateral surface • Superior surface • Inferior surface Thalamus – Medial Surface • Forms lateral wall of 3rd ventricle Interthalamic adhesion (massa intermedia) • Area in younger brains • Medial sufaces of R & L thalami fuse – connects R & L thalamus • Absent in many normal older brains Thalamus – Lateral Surface • Related to posterior limb of internal capsule Thalamus - Superior Surface • Has terminal sulcus (superior thalamostriate vein + stria terminalis courses here) Thalamus - Inferior Surface • Anteriorly: • Posteriorly: Separated from hypothalamus by hypothalamic sulcus Tegmentum of mesencephalon Thalamus - Functions • Major sensory relay for ascending tactile, visual, auditory, gustatory info that ultimately reaches cortex • Conveys impulses related to different sensations to cerebral sensory centers (cortex) • Peripheral sensory organs first course to thalamus; modified here and then go to cerebral cortex • Exception: Sense of smell first goes to its center in cortex, then relays in thalamus • Motor control areas such as basal ganglia & cerebellum also synapse in thalamic nuclei • Regulates consciousness, sleep, and alertness Thalamus – Internal Structure • Gray matter: Nuclei • White matter: Internal and external medullary lamina Thalamus – Internal Structure Internal medullary lamina: • Divides most of thalamus into medial & lat. groups of nuclei • Is a thin, curved sheet of myelinated fibers • Splits & encloses an Anterior Group of nuclei, usually referred to collectively as anterior nucleus, which borders on the interventricular foramen Thalamus - Nuclei Medial Group : Lateral Group : Composes bulk of thalamus Thalamus - Nuclei Medial Group : Contains a single large nucleus: dorsomedial (DM) nucleus a.k.a. medial dorsal [MD] nucleus Thalamus - Nuclei Lateral Group : Composes bulk of thalamus • Is further subdivided into a dorsal tier & ventral tier Dorsal Nuclei • Lat. dorsal (LD) nuc • Lat. post. (LP) nuc • Pulvinar • Lat. post. nucleus continuous w/pulvinar • Both nuclei have similar connections, so the 2 together sometimes referred to as the pulvinar- LP complex Ventral Nuclei 3 nuclei arranged in ant-post sequence: • Ventral ant. (VA) nuc • Ventral lat. (VL) nuc • Ventral post. (VP) nuc Metathalamus • Formed by 2 structures: Medial geniculate body + lateral geniculate body • Located posteriorly Medial Geniculate Body • Related to hearing • Is a relay nucleus (intermediate nucleus) • Afferents from inf colliculus & other areas • Efferents to auditory cortex Lateral Geniculate Body • Related to vision • Is a relay nucleus (intermediate nucleus) • Afferent fibers come from retina & sup.colliculus • Efferent fibers go to primary visual cortex (Brodman area 17) Thalamus Hypothalamus // Hypothalamus • Region of brain composed of many small nuclei with diverse functions • Major visceral control center (visceral brain) • Synthesizes & secretes neurohormones, thus act as a conduit btwn nervous system & endocrine systems via the pituitary gland (hypophysis) • Regulates homeostatic functions. E.g. Hunger, thirst, body temperature, circadian rhythms Hypothalamus – Gross Anatomy • Makes up the ventral diencephalon • Inferior to thalamus • Superior to mid-brain Hypothalamus – Gross Anatomy • Is composed of numerous fiber tracts & nuclei situated symmetrically about the third ventricle • In sagittal section, is roughly diamond shaped • Its boundaries are not sharply demarcated, its perimeters can be correlated using neuroanatomic landmarks. Hypothalamus – Gross Anatomy • Separated from thalamus by hypothalamic sulcus in wall of 3rd ventricle • Forms floor of 3rd ventricle • Continuous across the floor of the 3rd ventricle Hypothalamus – Gross Anatomy • On inferior surface : - Infundibular stalk: connection btwn hypothalamus & pituitary gland - Mamillary bodies: 2 rounded protuberances Hypothalamus – Boundaries Rostrally (anterior) Extends from ant. commissure (AC), lamina terminalis (LT), optic chiasm (OC) Caudally (posterior) Extends to periaqueductal gray matter of midbrain, approximated by (from ventral to dorsal) mammillary bodies (MB), interpeduncular fossa, & cerebral peduncles Sagittal section of the hypothalamus, w/ schematic boundary landmarks.. IS: infundibular stalk. TC: tuber cinereum. MT: mammillothalamic tract. PF: postcommissural fornix. PC: posterior commissure. Hypothalamus – Boundaries Inferiorly Tuber cinereum (TC) Inferior surface is continous w/floor of 3rd ventricle Laterally Int capsule Superiorly “ Hypothalamic sulcus Sagittal section of the hypothalamus, w/ schematic boundary landmarks.. IS: infundibular stalk.. MT: mammillothalamic tract. PF: postcommissural fornix. Hypothalamus – Boundaries – Coronal Plane • In coronal plane, boundaries of hypothalamus are more distinct • Superiorly, is divided from thalamus by groove in lateral wall of 3rd ventricle: hypothalamic sulcus • Lateral surface is contiguous w/ thalamus & subthalamus & is bordered by internal capsule & optic tracts • Medially, is bound by ependyma of 3rd ventricle • Inferior surface is continuous w/ floor of 3rd ventricle Specifically Named Areas of the Hypothalamus: Preoptic Area Area posterior to lamina terminalis • Lamina terminalis: Thin sheet of gray matter & pia mater that attaches to upper surface of optic chiasm & stretches upward to fill interval btwn optic chiasm & rostrum of corpus callosum Specifically Named Areas of the Hypothalamus: Tuber Cinereum • A median protuberance (swelling) • Lies btwn optic chiasm (rostrally) & mammillary bodies (caudally) • Is continuous anteriorly w/ lamina terminalis • Continues as the infundibulum, terminating inferiorly on pituitary gland Hypothalamus can be examined 1- Anteroposteriorly 2- Mediolaterally OR Microscopic Anatomy of Hypothalamus: Anteroposteriorly • Supraoptic, a.k.a. chiasmatic region Anterior Lies above optic chiasm • Tuberal a.k.a. infundibulo-tuberal region Middle • Mamillary region Posterior These subdivisions are derived primarily from the hypothalamic blood supply. The anterior hypothalamus is supplied by branches of the anterior cerebral and anterior communicating arteries; the tuberal hypothalamus is supplied by the posterior communicating artery; and the mammillary region is supplied by the posterior communicating, posterior cerebral, and basilar arteries. Parts of Hypothalamus: Mediolaterally • Periventricular • Intermediate (medial) • Lateral zones Using Anteroposterior Classification Supraoptic Region Nuclei • Supraoptic nucleus (ADH) Sends fibers to post. lobe of hypophysis • Paraventricular nucleus (oxytosin) Sends fibers to post. lobe of hypophysis • Ant. hypothalamic nucleus • Preoptic nucleus (medial, lateral) • Suprachiasmatic nucleus Below & lat. to supraoptic nucleus Hypothalamus - Tuberal Region Nuclei • Dorsomedial nucleus • Ventromedial nucleus • Arcuate nucleus Just sup-post to stalk • Lateral hypothalamic area Lateral nucleus Tuberal nuclei • Periventricular nucleus Hypothalamus - Mamillary Region Nuclei • Medial mamillary nucleus • Intermediate (intercalated) mamillary nucleus • Lateral mamillary nucleus • Posterior nucleus • Functionally a component of the limbic system Hypothalamus Suprachiasmatic Nucleus • Lies dorsal to optic chiasm & optic tracts at floor of 3rd ventricle • Positionally can receive afferent input directly from retina, as well as projections from the lateral geniculate nucleus and superior colliculus • Photic afferents  Acts as a dominant regulator of circadian rhythms Hypothalamus – Medial Forebrain Bundle (MFB) • Comprises lateral region of hypothalamus • Is a massive bidirectional fiber pathway - contains both ascending & descending fibers • Connects the hypothalamus to limbic system & brainstem autonomic centers • Through the MFB, signals from brainstem, amygdala, hippocampus, retina & olfactory system are conveyed to hypothalamic nuclei  crucial role of hypothalamus in systemic homeostasis Hypothalamus – Afferent Connections 1) Medial forebrain bundle From olfactory regions (periamygdaloid, septal, basal olfactory regions)  lat hypothalamic area  mid-brain tegmentum 2) Fornix Hippocampal formation  hypothalamus (post commissural fibers of fornix) 3) Stria terminalis Amygdaloid nuclear complex  hypothalamus (to preoptic area) 4) Thalamohypothalamic fibers Hypothalamus – Afferent Connections 5) Dorsal long fasciculus (DLF) and mamillary peduncle From spinal cord and brain stem reticular formation 6) Retino-hypothalamic fibers (tract) Via optic n.  suprachiasmatic nucleus Thru these fibers; control of circadian rhythm (gonadotrophins, adenohypophyseal hormones) 7) From different regions of cerebral cortex Frontal lobe, cingulate gyrus, entorrhinal cortex Hypothalamus Efferent Connections • Mamillo-thalamic tract, mamillo-tegmental tract (together named as fasciculus mamillaris princeps) • MFB • From lateral hypothalamic area  nuclei of diagonal band and septal nuclei • Hypothalamo-spinal fibers • DLF • From medial and perivent. portion  midbrain • Hypothalamo-hypophyseal fibers Hypothalamus – Functions (1) • Anterior region: Parasympathatic • Posterior region: Sympathetic • Ant. & lat. part: Temperature regulation Lesion: Hyperthermia • Post. part: Conservation & increased production of heat Lesion: Hypothermia • Supraoptic nucleus: ADH (maintenance of body water balance) Destruction: diabetes insipidus Hypothalamus – Functions (2) • Hypothal.  ant. lobe of hypophysis • Regulation of sleep • Ant hypothalamus lesions  insomnia • Post hypothalamus lesions  hypersomnia • Regulation of food intake (satiety & hunger) & metabolism • Ventromedial nucleus damage  hyperphagia • Lesion in lateral hypothalamus  hypophagia, aphagia (anorexia nervosa) • Emotional expression • A part of the principal centers concerned with emotional expression Hypothalamus Some of the hormones secreted: • Corticotropin releasing hormone (CRH) • Gonadotropin releasing hormone (GnRH) • Thyrotropin releasing hormone (TRH) • Oxytocin • Antidiuretic hormone (ADH) • Growth hormone releasing hormone (GHRH)