Internal Capsule

Internal Capsule

Question 1. Describe the internal capsule under the following headings:

1. Definition and location,
2. Gross anatomy,
3. Fibres,
4. Arterial supply and
5. Applied anatomy.
   

Answer:

Internal Capsule Definition and Location The internal capsule is a compact bundle of projection fibres lying in the inferomedial part of the cerebral hemisphere. Hence, it lies in a narrow space between the lentiform nucleus laterally and the caudate nucleus and thalamus medially.

The internal capsule connects the cerebral cortex to the brainstem and spinal cord.

Internal capsule

It contains important fibres belonging to the pyramidal tract and sensory fibres from the opposite half of the body.

Internal Capsule Gross Anatomy

Shape: In horizontal section, it appears as a ‘V’-shaped mass of white fibres.

Internal Capsule Parts: It consists of five parts:

Internal capsule anatomy

• Anterior limb: Lies between the lentiform nucleus and the caudate nucleus.
• Genu (bend of internal capsule): Lies in the angle between the caudate nucleus, thalamus and lentiform nucleus.
• Posterior limb: Lies between the lentiform nucleus and the thalamus.

Internal capsule stroke

• Retrolentiform part: Lies behind the lentiform nucleus.
• Sublentiform part: Lies deep to the lentiform nucleus.

Internal Capsule Fibres: The constituent fibres in the different parts of the internal capsule.

Posterior limb of the internal capsule

Constituent Fibres in the Different Parts of the Internal Capsule

Internal Capsule Arterial Supply The arterial supply of different parts of the internal capsule is as follows:

• The anterior limb is supplied by the middle and anterior cerebral arteries.
• Genu is supplied by the middle cerebral artery and the recurrent artery of Heubner.
• The posterior limb is supplied by the Charcot’s artery of cerebral haemorrhage and the anterior choroidal artery.
• The sublentiform part is supplied by the anterior choroidal artery.
• The retrolentiform part is supplied by the posterior cerebral artery.

Internal Capsule Applied Anatomy

• A small lesion in the internal capsule results in widespread paralysis and sensory loss because a huge number of motor and sensory fibres are packed densely in the internal capsule.
• The commonest lesion in the internal capsule occurs due to cerebral haemorrhage or cerebral thrombosis. It causes complete hemiplegia on the opposite side (i.e. contralateral hemiplegia).
• The most common cause of cerebral haemorrhage is the rupture of Charcot’s artery of cerebral haemorrhage and it usually involves the posterior limb of the internal capsule, leading to contralateral hemiplegia.