THALAMUS

About 3 cm long and making up 80% of the diencephalon, the thalamus is made up of two paired, ovulated masses of grey matter that are arranged into nuclei and contain tracts of white matter. 

Usually, a gray matter connection called the mass intermedia (interthalamic adhesion) joins the right and left parts of the thalamus. 

The anterior end of each thalamus presents an eminence, the anterior tubercle of the thalamus, which participates in the delimitation of the interventricular foramen. 

The pulvinar, a sizable eminence that projects over the lateral and medial geniculate bodies, is present on the posterior end, which is significantly larger than the anterior. 

The medial geniculate body is part of the auditory pathway, and the lateral part of the optic pathway, and both are considered by some authors as a division of the diencephalon called the metathalamus.

The lateral portion of the upper surface of the thalamus forms part of the floor of the lateral ventricle and is lined by ependymal epithelium (the epithelium that lines this part of the thalamus and is called the fixed lamina). The medial portion of the thalamus forms the lateral wall of the III ventricle, whose roof is constituted by the fornix and the corpus callosum, telencephalic formations. The transverse fissure is occupied by a cul-de-sac of the pia mater, which then enters the fabric of the choroid.The internal capsule, a small bundle of fibres linking the cerebral cortex to subcortical nerve centres, separates the lateral surface of the thalamus from the telencephalon. The hypothalamus and subthalamus continue down the inferior surface of the thalamus. 

Structural Parts

The thalamus is located in a central region of the brain called the diencephalon, and this position allows it to act by transmitting and integrating various motor and sensory impulses between the central nervous system and the periphery.

Parts 

• Anterior, medial, and lateral parts, separated by the internal medullary lamina. 

• Interthalamic adhesion, connecting the thalamus on each side. 

• Medial and lateral geniculate bodies. 

Relations 

• Anteriorly: interventricular foramen of Monro and internal cerebral vein 

• Medially: third ventricle 

• Posteriorly: stria terminalis, the third ventricle's choroid plexus, the body of the fornix, the internal cerebral vein, the thalamostriate vein, the caudate nucleus, the internal capsule, the quadrigeminal bodies, and the corpus callosum are all located posteriorly. 

• Inferiorly: hypothalamus, mesencephalic aqueduct, mesencephalic tegmentum

Cores 

1. Anterior group: anterior nuclei 

2. Posterior group: 

Posterior subgroup (pulvinar, medial geniculate body, lateral geniculate body) 

Dorsal subgroup (dorsal lateral nucleus and posterior lateral nucleus) 

Ventral subgroup (anterior ventral nucleus, lateral ventral nucleus, lateral ventral posterior nucleus, medial ventral posterior nucleus) 

3. Medial group: intralaminar nuclei, dorsomedial nucleus 

4. Reticular nucleus 

5. Median group

Some nuclei transmit impulses to the sensory areas of the brain: 

• Body (nucleus) Medial Geniculate – transmits auditory impulses; 

• Body (nucleus) Lateral Geniculate – transmits visual impulses; 

• Body (core) Ventral Posterior – transmits impulses for taste and for somatic sensations, such as touch, pressure, vibration, heat, cold and pain.

The thalamus serves as a way station for most of the fibers that travel from the lower part of the brain and spinal cord to the sensory areas of the brain. The thalamus sorts the information, giving us an idea of ​​the sensation we are experiencing, and directs it to specific areas of the brain for more accurate interpretation.

FUNCTIONS OF THE THALAMUS: 

• Sensitivity; 

• Motricity; 

• Emotional Behavior; 

• Cortex activation; 

• It plays some role in the wakefulness mechanism, or state of alertness.