Diencephalon PDF

Diencephalon  Diencephalon A mass of gray matter (nuclei). The diencephalon is situated where the cerebrum joins the brainstem. It consists of thalamus, hypothalamus, epithalamus, subthalamus and metathalamus.  Thalamus It is a large mass...

Diencephalon  Diencephalon A mass of gray matter (nuclei). The diencephalon is situated where the cerebrum joins the brainstem. It consists of thalamus, hypothalamus, epithalamus, subthalamus and metathalamus.  Thalamus It is a large mass of gray matter. The thalamus is as a synaptic relay for pathways projecting to the cerebral cortex. - It has: Two ends : Anterior and posterior. Four surfaces : Superior, inferior, medial and lateral. 4 5 Relations of thalamus - Anterior end: forms the posterior boundary of the interventricular foramen of Monro. - Posterior end: broad and is called Pulvinar. It overlies medial and lateral geniculate bodies. - Inferior surface: is related to the subthalamus, hypothalamus and tegmentum of the midbrain. Relations of thalamus - Superior surface : related to the following structures : 1. Body of caudate nucleus. 2. Body of lateral ventricle. 3. Thalamostriate vein. 4. Stria terminalis. 8 Relations of thalamus - Lateral surface: is related to the posterior limb of the internal capsule and lentiform nucleus. - Medial surface: is related to the third ventricle. It is connected to the thalamus of the opposite side by the interthalamic adhesion.  Internal structure of thalamus The thalamus (grey matter) has white matter as: 1- External medullary lamina: covers the lateral and superior surfaces. 2- Internal medullary lamina: Y- shaped bundle that divides the thalamus into : anterior, medial, lateral nuclear groups. Each group is subdivided into a number of nuclei.  Thalamic nuclei I. Anterior group: between the anterior two limbs of the Y- shaped internal medullary lamina. II. Medial group: medial to the internal medullary lamina..  Thalamic nuclei III. Lateral group: lateral to the internal medullary lamina. It is divided into : 1- Nucleus lateralis dorsalis (LD). 2- Nucleus lateralis posterior (LP). 3- Pulvinar nucleus (P).  Thalamic nuclei IV. Ventral group : 1- Nucleus ventralis anterior (VA). 2- Nucleus ventralis lateralis (VL). 3- Nucleus ventralis intermedius (VI). 4- Nucleus ventralis posterior which is further subdivided into: a. Nucleus ventralis posterior medialis (VPM). b. Nucleus ventralis posterior lateralis (VPL). Thalamic radiations 14  Thalamic radiations Anterior thalamic radiation : connects the frontal lobe with the medial and anterior nuclei. Superior thalamic radiation : connects the ventral and lateral nuclei with the precentral and post central gyri.  Thalamic radiations Posterior thalamic radiation : connects the pulvinar with the occipital lobe. It includes the connection between the lateral geniculate body and the occipital lobe (optic radiation). Inferior thalamic radiation : connects the pulvinar with the temporal lobe. It includes the connection between the medial geniculate body and the temporal lobe (auditory radiation).  Blood supply of the thalamus - It is supplied by branches of posterior communicating, posterior cerebral, posterior choroidal and basilar arteries.  Hypothalamus - It includes structures that lie in the floor and lateral wall of third ventricle. Parts Optic chiasma region Tuber cinerium and stalk of pituitary gland Mammillary bodies 19  Epithalamus It consists of : 1. Pineal body (gland). 2. Habenular nuclei. 3. Habenular commissure. 4. Posterior commissure. - It lies between the midbrain Subthalamus and thalamus. - It contains mainly the subthalamic nucleus which lies above the sustantia nigra. - It has connections with GRS Metathalamus 22  Metathalamus - It consists of the medial and lateral geniculate bodies which lie on the inferior surface of the pulvinar of the thalamus. - Medial geniculate body : - It is situated lateral to the superior colliculus of the midbrain. - It is connected with the inferior colliculus by the inferior brachium. - It is a relay nucleus in the auditory pathway.  Metathalamus - Lateral geniculate body : - It is situated lateral to the medial geniculate body. - It is connected with the superior colliculus by the superior brachium. - It receives fibers of the optic tract carrying visual impulses and sends efferent fibers ( optic radiation) to the visual area.  Test your self - True or false : - Anterior end of the thalamus is called pulvinar. - Body of caudate nucleus is related to the superior surface of thalamus. - Inferior thalamic radiation includes optic radiation. - Pineal body is a part of the epithalamus.  Test your self - Which structure is included in the metathalamus? A. Mammillary body. B. Substantia nigra. C. Lateral geniculate body. D. Pineal body.