(anatomy) A fan-like, 8-10 mm thick of white matter separating the caudate nucleus and the thalamus from the lentiform nucleus, and bears both afferent and efferent fibers of the cerebral cortex
The internal capsule is a structure comprised of white matter fibers in the brain. It bears the ascending the descending axons. It has the fibers ascending from the thalamus to the cerebral cortex (i.e. visual, auditory, and somatic sensory radiations, etc.) and the fibers descending from the cerebral cortex to the thalamus, subthalamic region, midbrain, hindbrain and spinal cord.
When cut along a transverse plane the internal capsule is V-shaped. The bent or curved part of the internal capsule is called genu. The part in front of the genu is called the anterior limb. The anterior limb of the internal capsule is that part where the fibers running from the thalamus to the frontal lobe and the fibers connecting the lentiform and caudate nuclei are found among others. The posterior limb is the part located posteriorly of the internal capsule. It contains the sensory fibers derived mainly from the thalamus, the fibers of optic radiation, acoustic fibers, and the fibers passing from the occipital and temporal lobes to the nuclei pontis.
The caudal part of the internal capsule is called the retrolenticular portion whereas that part beneath the lenticular nucleus is called the sublenticular portion.