The gray matter predominantly occupied in the diencephalon is the thalamus. It constitutes various nuclei, each serving different roles ranging from relaying information to regulating alertness and consciousness. The thalamus constitutes the right half and the left half, each of which is oval-shaped forming the walls of the third ventricle.
Placed at the core of the diencephalon, the thalamus serves as a central hub. It is responsible for relaying and integrating numerous motor and sensory impulses between the higher structures of the peripheries and the brain. Hence, the prime function that the thalamus is actively involved in is the relaying of sensory and motor signals to the cerebral cortex.
Mostly, the thalamus is a cell body of nerve cells (gray matter) in addition to some regions with axons (white matter). The internal and external medullary lamina constitute the white matter surfaces of the thalamus. The internal medullary lamina segregates the thalamic nuclei into medial, anterior and lateral groups while the external medullary lamina surrounds the lateral surface of the thalamus.
This paired structure of the diencephalon situated near the centre of the brain is found overlying the mesencephalon. It enables nerve fiber connections in all directions to the cerebral cortex. Each of the thalamus links to the other through the interthalamic adhesion.
The thalamus comprises a series of nuclei crucial to replay sensory signals. The nature of these nuclei mainly is inhibitory and excitatory. The thalamocortical neurons pick up the motor or sensory information from all over the body and offer selected information through thalamocortical radiations to the cerebral cortex.
Also, the thalamus is connected with mammillary bodies, hippocampus, and the fornix through the mammillothalamic tract. The thalamic function of episodic memory and learning is offered by the connection of the limbic system structures to the anterior nuclei of the thalamus. Additionally, it also regulates the activity of wakefulness and sleeping.
As stated, it serves as an effective relay station filtering impulses between the body and the brain. A thalamic nucleus is found in every sensory system (except olfaction) that receives, processes and transmits information to a connected cortical area. The thalamus consists of the lateral geniculate nucleus which receives visual sensory impulses from the retina to direct to the visual cortex of the occipital lobe. The ventral posterior nucleus of the thalamus, on the other hand, is further categorized into the spinothalamic tract, ventral posteromedial nucleus and the ventral intermediate nucleus.
5 important functional components of the thalamus are:
- Sensory nuclei responsible for all sensory domains (olfaction is an exception)
- Intralaminar and reticular nuclei handling arousal and pain sensation
- Associative nuclei implying cognitive roles
- Limbic nuclei comprehending motivation and mood
- Effector nuclei administering motor language functions
The thalamus has several connections to different sections of the brain hence undertakes many functionalities. It is deemed to be the structure of the limbic system along with being part of the CNS (central nervous system). This is because it connects many portions of the cerebral cortex to different parts of the spinal cord and the brain that regulates the processing of sensory movement and information. Precisely, the thalamus serves to pass neuronal transmissions for the regulation of the Circadian rhythm to the brain, so as to subdue the response to sensation such as sound while asleep.
It takes part in motor control by rendering positive reinforcements of movements arising in the motor cortex. The thalamic functionalities of motor control involve three particular nuclei –
- Ventroanterior – initiation and planning of movement
- Ventrolateral – cadence and coordination of movement
- Ventrointermedial – coordination of movement
This was a brief on the functions of the thalamus. For more related information important for NEET, visit us at NEET BYJU’S.