Thalamus

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Learning objectives

  • What is the thalamus and related structures
  • What does it do and clinical effects of damage
  • What is blood supply and risk of stroke

Subthalamic nuclei

This forms part of the basal ganglia. Damage here can lead to dyskinesias and hemiballismus and associated motor disorders. The thalamus is divided into three sections by the internal medullary lamina. This Y-shaped layer of white matter formed of myelinated fibres divides the thalamus into anterior, medial, and lateral parts.

Thalamus

The thalamus is the largest mass of cell bodies within the nervous system and forms part of the diencephalon. Note that the projection from the thalamus to the cortex uses the internal capsule, both the anterior and posterior limbs. The thalamus may be affected by both haemorrhage and infarction involving the posterior cerebral artery and its branches. It is a large paired egg-shaped structure sitting opposite each other across 3rd ventricle. Contains discrete collections of neuronal cell bodies called nuclei. Separated by a y shaped internal lamina. All but the reticular nucleus send fibres to the cortex. Receives all sensory stimuli (except olfactory) including from the cerebellum, spinal cord and cranial nerves. Bilateral thalamic strokes can cause amnesia as well as hypersomnolence. Others cause hemisensory loss. Thalamic damage can also lead to so-called thalamic pain syndromes where patients experience severe often sharp neuropathic pain in the corresponding contralateral side, and it is notoriously hard to treat satisfactorily and causes much morbidity. It contains several discrete thalamic nuclei

  • Medial dorsal thalamus*Anterior thalamus
  • Back of thalamus
  • Lateral Geniculate body: Fibres from the optic tracts
  • Medial Geniculate body: fibres from inferior colliculus
  • Lateral thalamus
  • Dorsal nucleus
  • Ventral nucleus

Roles of the Thalamus

  • Motor coordination
  • Sensory integration
  • Lateral geniculate nucleus deals with vision
  • Memory Formation and Emotional Expression
  • Controls Sleep and Awake States

Blood supply

  • Primary blood supply of the thalamus is from the posterior cerebral artery.
  • Posterior communicating artery branches also supply the thalamus after passing through the posterior perforated substance.
  • Artery of Percheron is a branch of the PCA which supplies both thalami. Infarction gives a classical clinical syndrome of hypersomnolence. Usually caused by possible cardioembolic events.

References