Image Based Question – 73111

Identify the type of the fibre marked in the image of internal capsule:

A. Projection fibres

B. Short association fibres

C. Long association fibres

D. Commissural fibres

Correct Answer » A Explanation

Answer A. Projection fibres

Internal capsule

• Area of white matter in the brain that separates the caudate nucleus and the thalamus from the putamen and the globus pallidus.
• The internal capsule contains both ascending and descending axons.
• It consists of axonal fibres that run between the cerebral cortex and the pyramids of the medulla.

Components

• The internal capsule is V-shaped when cut transversely (horizontally).
• When cut horizontally:
• the bend in the V is called the genu
• Anterior limb of the internal capsule.
• the posterior limb or crus posterius is the part behind the genu, between the thalamus and lenticular nucleus.
• the retrolenticular portion is caudal to the lenticular nucleus and carries optic tracts including the geniculocalcarine radiations.
• the sublenticular portion is beneath the lenticular nucleus and are tracts involved in the auditory pathway from medial geniculate nucleus to the primary auditory cortex (Brodmann Area 41).
• Gross motor strength is impaired with ischemia of the internal capsule.