Thalamus Prof. K. Sivapalan

Superior and Medial Relations Large gray matter on either side of the third ventricle The superior surface forms the floor of the central part of the lateral ventricle. The medial surface forms the greater part of the wall of the third ventricle Inter thalamic adhesion [connexus] connect the two thalami Inferiorly, hypothalamus and behind it ventral thalamus are related to thalamus 4/17/2019 Thalamus & hypothalamus

Thalamus & hypothalamus Other Relations Hypothalamic sulcus , running from the inter ventricular foramen to the aqueduct, seperates the hypothalamus. Anterior end lies just behind the inter ventricular foramen Posterior end [called pulvinar] lies just above and lateral to the superior colliculus of the midbrain. Two nuclei, medial and lateral geniculate bodies lie at the posterior end. The lateral surface is related to internal capsule 4/17/2019 Thalamus & hypothalamus

Thalamus & hypothalamus Internal Structure Thalamus is made up of several nuclei. Y shaped sheet of white matter placed vertically divides it into three major portions: anterior, medial and lateral. Each part contains several distinct nuclei 4/17/2019 Thalamus & hypothalamus

Thalamus & hypothalamus Connections Fibers from most parts of the brain converge in thalamus Exteroceptive and proprioceptive impulses in spinothalamic tract and medial leminiscus relay before being projected to sensory cortex Visual impulses go to lateral geniculate body and auditory impulses to medial geniculate body and to respective cortices Taste sensation is conveyed to thalamus through solitariothalamic fibers Olfactory impulses reach thalamus probably through amygdaloid complex Visceral information comes from the hypothalamus All parts of the cerebral cortex, cerebellum and corpus striatum project to thalamus. 4/17/2019 Thalamus & hypothalamus

Thalamus & hypothalamus Connections Ctd. The thalamus projects to all parts of the cerebral cortex through thalamocortical projections Efferent projections from thalamus go to corpus striatum, hypothalamus, and the reticular formation. Function: The thalamus is regarded as a great integrating centre. Integration of all impulses. Some degree of perception exteroceptive sensations- specially pain. 4/17/2019 Thalamus & hypothalamus

Thalamus & hypothalamus Is the ventral portion of the anterior end of diencdephalon. It lies below the hypothalamic sulcus on both sides of the third ventricle. It contains many nuclei. 4/17/2019 Thalamus & hypothalamus

Thalamus & hypothalamus Relations Medially it forms the wall of the third ventricle Laterally it is in contact with internal capsule and posteriorly with the ventral thalamus. Anteriorly extends up to the lamina terminalis and merges with the olfactury structures. Inferiorly, tuber cinereum, infundibulum and mamillary bodies which are considered as parts of hypothalamus. 4/17/2019 Thalamus & hypothalamus

Connections of the Hypothalamus. 4/17/2019 Thalamus & hypothalamus

Functions of theHypothalamus. Temperature regulation- anterior hypothalamus responds to heat, posterior hypothalamus responds to cold. Catecholamine secretion- through limbic function- dorsal and posterior hypothalamus. ADH, Oxitocin- supraoptic and paraventricular nuclei. Other pituitary hormones- paraventricular, preoptic, periventricular, and arcuate nuclei. Thirst- lateral superior hypothalamus. Hunger- venteromedial, arcuate, paraventricular and lateral nuclei. Sexual behavior- [anterior ventral hypothalamus and piriform cortex] and reproduction – GRH, ? puberty Defensive reactions- fear, rage- diffuse. Endocrine and activity rhythms- suprachiasmatic nucleus. 4/17/2019 Thalamus & hypothalamus

Autonomic Nervous System. Visceral function is regulated by autonomic reflexes and endocrines. Many reflexes are coordinated at spinal level- bladder, rectum, and sexual reflexes- input from higher centers also. Blood pressure, respiration, swallowing, coughing, sneezing, gagging and vomiting are coordinated in brain stem- medulla oblongata. Light reflex is coordinated in midbrain. Temperature regulation and many complex mechanisms are coordinated in hypothalamus. 4/17/2019 Thalamus & hypothalamus

Thalamus & hypothalamus 4/17/2019 Thalamus & hypothalamus

Thalamus & hypothalamus 4/17/2019 Thalamus & hypothalamus