Question:medium
Identify the type of the fibre marked in the image of the internal capsule.
Identify the type of the fibre marked in the image of the internal capsule.
Show Hint
The internal capsule carries cortex-to-cord axons, which are projection fibres.
Updated On: Jun 23, 2026
- Projection fibres
- Short association fibres
- Long association fibres
- Commissural fibres
Show Solution
The Correct Option is A
Solution and Explanation
Step 1: Identify the structure. The dense white-matter band wedged between the basal ganglia and thalamus is the internal capsule.
Step 2: Classify its traffic. It carries cortico-spinal, cortico-bulbar, and thalamo-cortical axons, all of which travel between the cortex and distant structures below it, the definition of projection fibres.
Step 3: Use the shape clue. On a horizontal cut it forms a V with a genu, anterior limb, posterior limb, plus retrolenticular and sublenticular parts that carry optic and auditory radiations.
Step 4: Eliminate the others. Association fibres stay within a hemisphere and commissural fibres cross between hemispheres, neither of which describes the internal capsule.
$cortex \leftrightarrow subcortical\ targets = projection\ fibres$
\[\boxed{Projection\ fibres}\]
Step 2: Classify its traffic. It carries cortico-spinal, cortico-bulbar, and thalamo-cortical axons, all of which travel between the cortex and distant structures below it, the definition of projection fibres.
Step 3: Use the shape clue. On a horizontal cut it forms a V with a genu, anterior limb, posterior limb, plus retrolenticular and sublenticular parts that carry optic and auditory radiations.
Step 4: Eliminate the others. Association fibres stay within a hemisphere and commissural fibres cross between hemispheres, neither of which describes the internal capsule.
$cortex \leftrightarrow subcortical\ targets = projection\ fibres$
\[\boxed{Projection\ fibres}\]
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