Diencephalon: Epithalamus, Subthalamus, Hypothalamus

Epithalamus

• Smaller than the other parts of the diencephalon.
• Dorsal and caudal aspect of the midline.
• Located rostral to the superior colliculus.
• Includes the pineal gland and habenular nuclei.

Subthalamus

• Difficult to observe.
• Located beneath the thalamus.
• Dorsolateral to the hypothalamus.
• Found immediately medial to the internal capsule.
• Important to consider it with the basal ganglia because it helps regulate movement.

Hypothalamus

• Ventral aspect of the wall and floor of the third ventricle.
• Controls the neuroendocrine system, limbic system, and autonomic nervous system.
• Influences the pituitary gland

Thalamus

• It makes up 80% of the diencephalon.
• It is composed of two oval masses, roughly the size of a small hen's egg.
• It is organized into nuclei, connected via the massa intermedia, and interspersed with white matter.
• General and special sensory information is transmitted to the sensory cortex.
• Receives info from the cerebellum and basal ganglia, and sends it to motor regions in the frontal lobe.
• Connected to the association and limbic areas of the brain.

Thalamus External Structures

• Forms the lateral wall of the third ventricle.
• Features an interthalamic adhesion, also know as the massa intermedia.
• Anterior pole extends as far as the interventricular foramen.
• Posterior limb of the internal capsule occurs laterally.
• Head of caudate nucleus is anterolaterally.
• The internal capsule is located laterally.
• The caudate nucleus is located anterolaterally.
• The floor of the lateral ventricle is located dorsally.
• The subthalamic nucleus is located ventrally.
• The hypothalamus is located inferiorly.

Thalamus Internal Structure

• It contains an internal medullary lamina.
• The internal medullary lamina is a Y-shaped thin layer of white fibers carrying afferent and efferent.
• Divides the thalamus into three nuclear masses.
• Intralaminar nuclei are embedded in the laminar.
• It contains the anterior nuclear group.
• It contains the medial nuclear group.
• It contains a lateral section, which is further subdivided.

Thalamus Functional Structure

• Projects to the ipsilateral cortex.
• All nuclei receive information from the cortex.
• Some specific connections exist between thalamic nuclei and cortical areas.
• These connections have well-defined sensory and motor functions, which are located in the ventral part of the lateral group of nuclei.
• Nonspecific nuclei have less functionally distinct connections with the wider cortex, including association cortices and the limbic system.
• It is a major relay station for sensory and motor impulses.
• Information from the spinal cord, brain stem, and midbrain is relayed via the thalamus to create the primary sensory cortex.
• Crude perception of pain, temperature, and pressure arises in the thalamus
  • More precise location is dependent on the primary sensory cortex
• Information projects from the cerebellum and basal ganglia via the thalamus to the primary motor cortex.
• Connections between the thalamus and association and limbic areas facilitates autonomic activities and maintenance of consciousness.