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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.
Posterior limb
  • The portion of internal capsule between the thalamus and the lentiform nucleus.
Retrolenticular limb
  • Lies posterior to the posterior limb, its fibers run posterior to the lentiform nucleus.
Sublenticular limb
  • Runs underneath the lentiform nucleus.
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
  • Prefrontal cortical fibers
    • Predominantly anterior thalamic radiation fibers that connect the frontal cortex with the thalamus and also frontopontine fibers.
Genu and Posterior limb
    • 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
  • Carries auditory fibers from the medial geniculate body.
Sublenticular and retrolenticular limbs
  • Carry visual projection fibers.
PURE MOTOR STROKE
  • Stroke: Internal Capsule - Posterior Limb
    • 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.

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