Diencephalon.docx

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Department
Anatomy and Cell Biology
Course
Anatomy and Cell Biology 3319
Professor
Kem Rogers
Semester
Fall

Description
Diencephalon • Forms the central core of forebrain & surrounded by cerebral hemispheres • Consists largely of three paired structure – thalamus, hypothalamus, epithalamus & subthalamus (includes subthalamic nucleus) • Border the third ventricle & consist primarily gray matter Thalamus • Paired structure that makes up 80% of the diencephalon • Forms the superolateral walls of the third ventricle – inferior to corpus colosum • Right & left parts are joined by small midline connection: interthalamic adhesion (intermediate mass) • Contains 12 major nuclei – each sends axons to a particular portion of the cerebral cortex • Bilateral distribution of all nuclei • Y-shaped sheet of white matter • 3 ventricle separates two halves of thalamus • Categories of thalamic nuclei o Modality specific (to primary cortical, sensory areas or motor areas) o Association (anterior, LD, LP, MD & pulvinar) o Non-specific (reticular to thalamic for arousal & intralaminar group to all areas for cortical arousal) • Internal medullary lamina – divides the thalamic nuclei into 3 groups: o Anterior nuclei o Medial group including medial dorsal nucleus o Large lateral nuclear groups • Afferent impulses from all senses except olfaction converge on thalamus & synapse in at least 1 nuclei • All ascending fibers from subcortical regions, including basal ganglia and retina (CN II), must synapse in a thalamic nucleus before reaching the cortex – relay station (except for olfactory) • Descending tract passes lateral to thalamus as internal capsule • Relays information to cerebral cortex but also processes the information as it passes through • Nuclei organize & then either amplify or tone down signals headed for cerebral cortex Thalamic Nuclei Reticular Nuclei – neurons with short axons that project into nuclei & set arousal level for thalamic nuclei • • No connection between two cerebral hemispheres • Look at the dot – point to female face but say it’s a male face • Female face is on right occipital cortex - spatial perception is on right side • Left side sees male face - Language is on left side Hypothalamus • Inferior portion of the diencephalon • Forms the inferolateral walls of the third ventricle • On the underside of the brain • Lies between optic chiasma (point of crossover of cranial nerves II, optic nerves) & posterior border of the mammillary bodies (rounded bumps that bulge from hypothalamic floor) • Projecting inferiorly from hypothalamus is the pituitary gland o Contains about a dozen brain nuclei of gray matter o Main visceral control center of the body o Regulating many activities of the visceral organs • Control of autonomic nervous system o Composed of peripheral motor neurons that regulate contraction of smooth & cardiac muscle & secretion of glands o Directing autonomic neurons o Regulates heart rate, blood pressure, digestive tract activity, sweat glands, salivary glands etc. o Relay instruction through periaqueductal gray matter of midbrain & reticular formation of brain stem • Regulation of body temperature o Body’s thermostat is in the hypothalamus o Monitor blood temperature & receives input from peripheral thermoreceptors o Initiates body’s cooling or heating mechanisms (sweating or shivering) & induces fever • Regulation of hunger & thirst sensations o Sensing c
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