Thalamus

The thalamus (plural: thalami) is is the largest of the structures making up the diencephalon.

Role

The thalamus acts as a pairedrelay centre, receiving and symmetrical structure indistributing information between the brainperipheries and higher centres such as the cerebral cortices. It contributes to functions such as:

• Consciousness
• Sleep
• Memory
• Sensory and motor functions

Gross Anatomy

Structurally, the thalamus is a large, egg-shaped mass. It is made up of two symmetrical thalami which are usually connected by a band of grey matter called the interthalamic adhesion.

The anterior pole narrows to form the posterior boundary of the interventricular foramen. Posteriorly the thalamus expands to form the pulvinar. On the posteroventral surface of the thalamus lie two rounded projections called the medial and lateral geniculate nuclei.

Relations

Superior

The superior surface is covered by the stratum zonale and is separated from the body of the fornix by the tela choroidea.

More laterally, the superior surface is separated from the head of the caudate nucleus by the stria terminalis and the main partthalamostriate vein.

Lateral

The lateral surface contacts the descending posterior limb of the internal capsule.

Medial

The medial walls, as previously mentioned, are joined in most cases at the interthalamic adhesion. This medial surface also forms the lateral wall of the third ventricle.

Inferior

Inferomedially the thalamus joins the hypothalamus. It is the pathway through which signals are sent fromalso continuous with the cerebrum tolemnisci of the midbrain (brainstem) viategmentum.

Anterior

The anterior pole of the thalamus forms the posterior wall of the interventricular foramen and vice versa.

The thalamus is an eggsurrounded by two thin layers of white matter. On its superior surface it is covered by the stratum zonale and on its lateral surface by the external medullary lamina.

The grey matter of the thalamus is separated by a Y-shaped layer of white matter called the internal medullary lamina. This structure divides the thalamus into anterior, medial and madelateral parts. These three parts contains the larger groups of at least 50 thalamic nuclei. It is in

Other smaller groups are located on the dorsal portionmedial and lateral surfaces of the diencephalonthalamus as well as within the internal medullary lamina.

The thalamus has many functions includingLateral (split into ventral and dorsal):

Ventral:

• translator of prethalamic inputs into readable formVentral anterior
• process and relay of sensory information selectively to various parts of the cerebral cortexVentral lateral
• regulation of sleep and wakefulnessVentral posterior
  • Ventral posterolateral
  • thalamo-cortico-thalamic circuits involved in consciousnessVentral posteromedial
• arousal, the level of awareness, and activityLateral geniculate nucleus
• Medial geniculate nucleus

Blood supply

BloodThe thalamus is main blood supply for the thalamus comes from a number of arteries including polar and paramedian arteries, inferolateral (thalamogeniculate) arteries, and posterior (medial and lateral) choroidal arteries. These are all branches of the posterior cerebral artery. Branches from the posterior communicating artery and basilar artery also contribute.

Related pathology

• thalamic syndrome: contralateral hemianaesthesia, often accompanied by mood swings
• thalamic infarct
• thalamic glioma