Organ
Internal capsule
A compact route between cortex and deeper structures
High-yield
Corticospinal fibers occupy the posterior limb. Corticobulbar fibers are classically taught near the genu, but human mapping shows that their position is more variable and may extend into the posterior limb. Small lesions can therefore affect several motor functions.
Overview
Many ascending and descending cortical connections converge in the internal capsule. It lies between the caudate and thalamus medially and the lentiform nucleus laterally. Its anterior and posterior limbs meet at the genu, while additional fibers pass behind and below the lentiform nucleus. Above this region, fibers spread through the corona radiata; descending motor pathways continue toward the brainstem.
Reference facts
- Location
- Between caudate head and lentiform nucleus anteriorly, and between thalamus and lentiform nucleus posteriorly
- Parts
- Anterior limb: thalamic and frontal projections; genu and posterior limb: descending motor and sensory connections; retrolenticular and sublenticular portions: visual, auditory and other posterior cortical projections
- Blood supply
- Perforators from MCA lenticulostriate arteries, ACA/Heubner branches and the anterior choroidal artery, with overlapping and variable territories
- Relations
- Continuous with the corona radiata above; descending fibers continue toward the cerebral peduncle and brainstem, while other fibers terminate in subcortical targets
- Function
- Conveys major motor, somatosensory and thalamocortical pathways, together with other cortical projections; it does not contain every connection of the cortex
Clinical correlation
A small capsular infarct can produce marked weakness of the opposite face, arm and leg, sometimes without obvious cortical signs. The severity need not be equal in all three. Lesions involving sensory or visual pathways can instead produce additional deficits, including a homonymous visual-field loss.
Frequently asked questions
Where is the internal capsule located?
Between caudate head and lentiform nucleus anteriorly, and between thalamus and lentiform nucleus posteriorly.
What does the internal capsule do?
Conveys major motor, somatosensory and thalamocortical pathways, together with other cortical projections; it does not contain every connection of the cortex.
What are the parts of the internal capsule?
Anterior limb: thalamic and frontal projections; genu and posterior limb: descending motor and sensory connections; retrolenticular and sublenticular portions: visual, auditory and other posterior cortical projections.
What is the blood supply of the internal capsule?
Perforators from MCA lenticulostriate arteries, ACA/Heubner branches and the anterior choroidal artery, with overlapping and variable territories.