Internal capsule

Internal Capsule

Brain Atlas: Internal Capsule

ANATOMY

Anterior limb

The anterior portion, between the head of the caudate and the lentiform nucleus.

Genu The middle (bend) of the internal capsule, which occurs along the medial-lateral plane of the anterior thalamus.

Retrolenticular limb

Lies posterior to the posterior limb, its fibers run posterior to the lentiform nucleus.

Sublenticular limb

Retrolenticular vs Sublenticular Limbs

The relative anterior-posterior positions of the sublenticular and retrolenticular limbs are inconsistently defined. They are most easliy thought of as lying posterior to the posterior limb.

Superior/Inferior Plane

Note - The internal capsule gradually dips down along the anterior-posterior course of the anterior limb and then rises again along the anterior-posterior course of the posterior limb.

FUNCTION

Anterior limb

Predominantly anterior thalamic radiation fibers that connect the frontal cortex with the thalamus and also frontopontine fibers.

Comprise the motor fibers as follows - the facial fibers begin in the anterior limb, descend through the genu, and enter the posterior limb; the arm fibers descend through the anterior portion of the posterior limb; the leg fibers originate posterior to the arm fibers and pass anteriorly during their descent through the posterior limb.

Sublenticular limb

Sublenticular and retrolenticular limbs

PURE MOTOR STROKE

Infarction of the genu and posterior limb of the internal capsule is one cause of this classic and common stroke syndrome.
The motor fibers are arranged somatotopically - the facial fibers pass through the genu, the arm fibers lie posterior to the facial fibers in the anterior portion of the posterior limb, and the leg fibers descend posterior to the arm fibers in the posterior portion of the posterior limb.
The motor fibers crowd together inferiorly within the internal capsule; therefore, the more inferior the infarct, the broader the motor deficit.