Lab 8 - Higher Motor Function

Axial Sections (continued)

View and identify the structures in the illustration.

In Fig. 1, Layer A, the most superior slice, note how the axons of the cortex are collecting to form the corona radiata. Notice the optic radiations passing through the retrolenticular segment of the internal capsule. Remember that the anterior limb of the internal capsule divides the caudate head from the lenticular nucleus (putamen + globus pallidus), and the posterior limb divides the thalamus from the lenticular nucleus. (The lenticular nucleus is sometimes called the lentiform nucleus).

Note the compact fiber density in the posterior limb. From a clinical perspective a small lesion in the posterior limb of the internal capsule can affect motor and/or sensory functions on the entire contralateral body and face. The arterial supply to this part of the internal capsule is the lateral striate (also called lenticulostriate) branch of the middle cerebral artery.

Trace the course of the corticofugal axons as they travel through the internal capsule to emerge at the diencephalic/mesencephalic junction as the crus cerebri.

In Fig. 1, Layer C locate the substantia nigra, the largest nuclear mass in the midbrain. It contains pigmented neurons (melanin) that give it its characteristic color in unstained sections such as the one seen here. This area is invariably the site of pathological changes associated with Parkinson's disease.