White Matter

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The optic tract is the continuation of the optic nerve that relays information from the optic chiasm to the ipsilateral lateral geniculate nucleus, pretectal nuclei and superior colliculus. 

The lateral geniculate nucleus is a small rounded elevation on the posterior surface of the thalamus.

Contents

Each optic tract contains the fibres from the ipsilateral temporal and contralateral nasal retina.

Course

• Origin: Within the middle cranial fossa, the optic nerves from each eye unite to form the optic chiasm in the suprasellar cistern
• At the optic chiasm;
  • fibres originating from the nasal retina decussate and pass into the optic tract of the opposite side
  • fibres originating from the temporal retina pass directly into the optic tract of the same side
• Each optic tract travels around the cerebral peduncle travels to its corresponding cerebral hemisphere to reach the lateral geniculate nucleus
• Axons from the LGN then carry visual information via the optic radiation to reach the visual cortex
  • Upper optic radiation – axons from the medial part of the LGN carrying visual information from the superior retinal quadrants (corresponding to the inferior visual field quadrant) pass directly through the parietal lobe to reach the superior lip of the calcarine sulcus
  • Lower optic radiation – axons from the lateral part of the LGN carrying visual information from the inferior retinal quadrants (corresponding to the superior visual field quadrant) fan out laterally and inferiorly around the anterior tip of the inferior horn of the lateral ventricle, through the temporal lobe via a pathway known as Meyer’s loop to reach the inferior lip of the calcarine sulcus

Relations

• The optic tract is located lateral to the uncus – the innermost part of the medial temporal lobe parahippocampal gyrus (housing  the primary olfactor cortex)[mfn]Mehra D, Moshirfar M. Neuroanatomy, Optic Tract. [Updated 2020 Jul 31]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK549840/[/mfn]
• The pituitary stalk (infundibulum) and cerebral penduncles of hte midbrain lie medial to the path of the optic tract
• The substantia perforata anterior is immediately superior to the optic tract

Blood supply

• Intracranial part of optic nerve: Anterior cerebral
  • Note: the orbital part of optic nerve is supplied by the ophthalmic artery, and distally by the central artery
• Chiasm: Anterior cerebral artery
• Optic tract: Supplied chiefly by the anterior choroidal and posterior communicating arteries

The internal capsule is deep subcortical white matter structure carrying information past the basal ganglia, separating the caudate nucleus and the thalamus from the putamen and the globus pallidus.

Shape & Location

V-shaped structure when cut horzitontally in a transverse plane. Situated in the inferomedial part of each cerebral hemisphere of the brain

Contents

It contains afferent and efferent white matter projection fibres:

• Afferent fibres: pass from cell bodies of the thalamus to the cortex
• Efferent fibres: pass from cell bodies of the cortex to the cerebral peduncle of the midbrain

Structure

• Anterior limb (anterior crus)
  • Separates the head of the caudae nucleus medially and lentiform nucleus laterally
• Genu
  • Lies medial to the apex of the lentiform nucleus
• Posterior limb (posterior crus)
  • Separates the thalamus medially and lentiform nucleus laterally
• Retrolentiform part
  • Caudal to the lenitform nucleus
  • Carries the optic radiation from the medial part of the lateral geniculate nucleus
• Sublentiform part
  • Beneath the lentiform nucleus
  • Tracts involved in the auditory pathway from the medial genicular nucleus to the primary auditory cortex

Blood supply

• Anterior limb: Mainly by the lenticulostriate branches of the middle cerebral artery and less often branches of the anterior cerebral artery
  • Lenticulostriate arteries are small perforating branches that supply blood to most of the subcortical structures
• Genu: lenticulostriate arteries of the middle cerebral artery
• Posterior limb: lenticulostriate arteries of the middle cerebral artery and anterior choroidal artery of the internal carotid artery