Diencephalon – Anatomy -Thalamus
The thalamus is a large mass of gray matter situated in the lateral wall of the third ventricle and on the floor of the central part of the lateral the lateral ventricle. It has anterior and posterior ends, superior, inferior, medial and lateral surfaces.
The anterior end with an anterior nucleus is narrow and forms the posterior boundary of the interventricular foramen.
The posterior end is expanded and it is known as the pulvinar. It overhangs the lateral and medial geniculate bodies, and the superior colliculus with its brachium.
The superior surface is divided into a lateral ventricular part which forms the floor of the central part of the lateral ventricle.The inferior surface rests on the subthalamus part of the lateral wall of the third ventricle. The medial surfaces of two thalami are interconnected by an inter thalamic adhesion.
The lateral surface forms the medial boundary of the posterior limb of the internal capsule.
Structure and Nuclei of Thalamus
The Grey matter is divided to from several nuclei.
Anterior nucleus in the anterior part.
Medial nucleus in the medial part. The anterior and medial nuclei together represent the paleo thalamus.
The lateral part of the thalamus is lateral nucleus in the dorsolateral part and the ventral nucleus in the ventromedial part. The ventral nucleus is subdivided into anterior, intermediate and posterior groups. The posterior group is further subdivided into the posterolateral and posteromedial groups.
Intralaminar nuclei including centromedian nucleus (located in the internal medullary lamina) midline nuclei (periventricular grey on the medial surface) and reticular nuclei (on the lateral surface) are also present.
What does the Thalamus do?
The thalamus relays sensory impulses from receptors in various parts of the body to the cerebral cortex. A sensory impulse travels from the body surface towards the thalamus, which receives it as a sensation. This sensation is then passed onto the cerebral cortex for interpretation as touch, pain or temperature.
The prevailing opinion among experts is that the thalamus serves as a kind of “gate,” filtering which information from various channels is allowed to be relayed by it for processing. Detailed research has shown that specific thalamic neurons can modulate informational transfer by employing specific discharge modes.
Furthermore, the thalamus is crucial for perception, with 98% of all sensory input being relayed by it. The only sensory information that is not relayed by the thalamus into the cerebral cortex is information related to smell (olfaction).
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