The Thalamus

An egg shaped mass whose extent is:

  • Foramina of Monroe to the posterior commissures.
  • The third ventricle to the posterior limb of internal capsule.

The posterior enlarged part (pulvinar) overlies the midbrain.

Structures related to its dorsal surface include:

  • Striae terminalis
  • Terminal vein
  • Striae medullaris

It is joined with the opposite medially by interthalamic adhesion.

The internal medullary lamina divides the thalamus into nuclear groups:

  • Anterior
  • Medial
  • Lateral
  • Ventral
  • Nuclei within the he lamina are termed intralaminar.
 
Connections  

Functions:

  • Relay/processing/filtering center for sensory information
  • Distribution of most afferent input to cortex.
  • Control of electrocortical activity of the cortex (attention, alertness, consciousness).
  • Integration of motor functions (relays inputs to cerebellum, striatum etc).
 
Functions of specific nuclei:
  • Anterior group: part of limbic system (mamillothalamo-cortical sytem).
  • Medial group: integrate sensory data for projection to frontal lobe.
  • Ventral group: integrate sensory data for projection to primary sensory cortex (VPL, VPM).
  • Posterior LGB project visual information to occipital cortex.
  • Posterior MGB project auditory information to auditory cortex.
  • Intralaminar/midline receive from brainstem reticular formation and project diffusely to cortex.