internal capsule

The internal capsule is a crucial anatomical structure within the brain, primarily composed of white matter. It's described as a fan-shaped band of myelinated nerve fibers that project to and from the cerebral cortex. This structure is divided into an anterior limb and a larger posterior limb, with a curve that points towards the brain's center, forming the genu at its junction.1

The corticospinal tract, vital for skilled voluntary movement, forms a significant part of the internal capsule's posterior limb. Due to its location, passing through nearly every major division of the nervous system, the internal capsule is vulnerable to lesions. A small lesion in its posterior limb can lead to contralateral hemiparesis, characterized by weakness, spasticity, and exaggerated reflexes.2