The thalamus and hypothalamus are complicated subcortical structures. While they both originate from the diencephalon, these two structures have starkly different roles within the central nervous system. The thalamus is a subcortical grey matter structure that acts as a major relay center between the cortex and other subcortical areas while the hypothalamus has many nuclei with various roles; hormone synthesis, temperature regulation, hunger/thirst, etc. The hypothalamic-pituitary axis is an important topic for introductory neuroanatomy courses but is considered low yield for in-service and board examinations. Because of this, the intricacies of this topic will not be covered in-depth in this chapter. The goal of this chapter is to review the complicated roles of the thalamus and associated pathology and briefly review hypothalamic nuclei.

Author: James Eaton, MD
Editor: Brian Hanrahan, MD, Steven Gangloff MD

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Thalamus

  • The thalamus is a collection of subcortical grey matter and part of the diencephalon (along with the hypothalamus) involved in relaying information between different functional regions of the CNS.
  • It borders the dorsal part of the third ventricle and functions as part of the lateral wall of the ventricle.

Thalamic nuclei

  • There are three main types of thalamic nuclei: relay, association, and nonspecific nuclei.
    • Relay nuclei have very distinct inputs and outputs.
    • Association nuclei receive a majority of their input from the cortex and project fibers to other cortical regions.
    • Nonspecific nuclei broadly project to numerous cortical regions.

Relay nuclei

  • Ventral posterior lateral (VPL) nucleus: Relay center for sensory information of the body. The output is to the postcentral (sensory) gyrus.
  • Ventral posterior medial (VPM) nucleus: Relay center for sensory information of the face. The output is to the postcentral (sensory) gyrus.
    • The VPM is also the relay center for taste.
  • Lateral geniculate body/nucleus (LGN): Relay center for vision. Receives input from the retina with output to the primary visual cortex via optic radiations.
    • Optic radiations from the upper visual world travel through the temporal lobe and optic radiations from the lower visual world pass through the parietal lobe.
  • Medial geniculate body/nucleus (MGN): Relay center for hearing. Receives input from the inferior colliculi and projects to the primary auditory cortex.
  • Ventral anterior (VA) nucleus: Conveys motor information from basal ganglia to the premotor cortex. It plays a role in the initiation of movement.
  • Ventral lateral (VL) nucleus: Conveys motor information from both the cerebellum and basal ganglia to the primary motor cortex.
Diagram of Thalamus Anatomy with Nuclei | NOWYOUKNOWNEURO
LP: Lateral posterior. LD: Lateral dorsal. VP: Ventral posterior. VLP: Ventral posterolateral. VPM: Ventral posteromedial. VI: Ventral intermediate. VL: Ventral lateral. VA: Ventral anterior.


 

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