QS Study

Internal capsule is a large band of nerve fibers, situated in the inferomedial part of each cerebral hemisphere. It is a deep subcortical structure that contains a concentration of white matter projection fibers. It contains both ascending and descending axons, going to and coming from the cerebral cortex.

Boundary –

  • Superiorly – Cerebral hemisphere.
  • Medially – Head of caudate nucleus & thalamus
  • Laterally – Lentiform nucleus.
  • Contents: Ascending & descending tracts from the cerebral cortex.

Location: It is located between the lentiform nucleus laterally and the thalamus and caudate nucleus medially.

Parts of Internal Capsule –

(i) Anterior limb: Lies between the head of the caudate nucleus and the lentiform nucleus. It is the part of the internal capsule that lies between the anterior part of lentiform nucleus laterally and head of caudate nucleus medially.

(ii) Posterior limb: Lies between the thalamus & the lentiform nucleus. It is that part of the internal capsule which lies between the thalamus medially and the posterior part of lentiform nucleus laterally.

(iii) Genu: Is the bend between the anterior & posterior limbs. It is the bend between the anterior and posterior limb of the internal capsule. The concavity of the bend faces laterally.

(iv) Retrolentiform part: Lies behind the lentiform nucleus. It is located posterior to the lentiform nucleus.

(v) The sublentiform part: Lies below the lentiform nucleus. It is located inferior to the lentiform nucleus.

Internal Capsule 1

Fig: Internal Capsule parts

Blood supply: The blood supply of the internal capsule is variable but is commonly from small perforating branches of the middle cerebral artery and anterior cerebral artery.

Arterial supply –

Central branches of:

  1. The middle cerebral artery.
  2. The anterior cerebral artery.
  3. The posterior communicating arteries.
  4. The anterior choroidal artery.

Fibers in the internal capsule –

(1) Anterior limb:

  • Ascending Tract: Anterior thalamic radiation.
  • Descending Tract: Fronto pontine fibers.

(2) Genu:

  • Ascending Tract: Anterior part of superior thalamic radiation.
  • Descending Tract: Cortico nuclear fibers.

(3) Posterior limb:

Ascending Tract:

  • Superior thalamic radiation
  • Fibers from globus pallidus to subthalamic nucleus.

Descending Tract:

  • Corticospinal tract
  • Corticopontine fibers
  • Corticorubral fibers

(4) Retrolentiform part:

Ascending Tract: Posterior thalamic radiation

Descending Tract:

  • Parietopontine & occipitopontine fibers
  • Fibers from occipital cortex to superior coliculus & pretectal region.

(5) Sublentiform part:

Ascending Tract: Auditory radiation

Descending Tract:

  • Parietopontine & temporopontine fibers
  • Interconnection b/w temporal lobe & thalamus.
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