Thalamus: Anatomy & Function

ThalamusAnatomy and function of the thalamus. Thalamic nuclei and connections
~ 5 min

In this note, we are going to discuss the anatomy and function of the thalamus.

Together with the epithalamus and hypothalamus, it is a part of the diencephalon.

Parts and location

The thalamus is a paired egg-shaped structure made up of numerous nuclei.

Its posterior part is called the pulvinar.

The left and the right thalami are connected by the interthalamic adhesion, also known as the intermediate mass.

Basically, the thalamic nuclei act as a relay station for the multiple pathways, which run through the thalamus.

It allows some signals to get into the cerebral cortex, while other signals are blocked or slowed down. In general, the thalamus is a kind of “bouncer” in the brain.

The medial part of the thalamus serves as the lateral wall of the third ventricle.

Thalamic nuclei

The thalamus is subdivided into 5 groups of nuclei by a Y-shaped bundle of white matter called the internal medullary lamina.

Anterior group

Medial group

Lateral group

Intralaminar group

Midline group

Each group is made up of one or several nuclei.

The specific information about the most significant nuclei you can see in the table (next page), each of them has multiple functions and connections. But the key point here, that you really need to remember, is that all sensory pathways run through the thalamus except the olfactory pathway.

So, the thalamus is a kind of subcortical sensory center, that provides integration of nearly all sensory information.

Geniculate bodies

And now let’s talk about the geniculate bodies, that are also the thalamic nuclei, but perform a very specific function. The lateral geniculate body is a relay center for the visual pathway

and the medial geniculate body – for the auditory pathway.

Previously, these nuclei were considered as a separate structure, called metathalamus, but now this term is outdated.

Functional classification

The thalamic nuclei have multiple connections with various structures of the nervous system. All these connections, for a better understanding, are classified into four functional groups.

Relay nuclei or specific nuclei. They receive information from a few sources, so this information is very specific and well-defined. And they project it to a very specific, functionally discrete cortical area. Most of the thalamus consists predominantly of such nuclei.
Diffuse projection, or nonspecific nuclei. They receive information from a large number of sources and project it to several cortical areas and subcortical structures. Their action spectrum is broader than that of the relay nuclei.
Association nuclei, which receive information from the cerebral cortex, and then project it back to the cerebral cortex specifically to the association areas.
And the fourth group, or rather one nucleus – is the reticular nucleus. It is unique because its projections don’t run into the cortex. The reticular nucleus has two-way connections with other thalamic nuclei. So it serves to regulate the activity of the thalamus.

The reticular nucleus is not only a functional formation: as an anatomical structure, it is located more lateral to the other groups and is separated from them by a thin layer of white matter called the external medullary lamina.

Subthalamus

Below the thalamus, we can find the subthalamus, and its main structure is called the subthalamic nucleus. It is a component of the basal ganglia system, so for more information about it, check out the corresponding topic.

Golosary