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The corticospinal tract, one of the most crucial motor pathways in the central nervous system, originates in the precentral gyrus of the cerebral cortex, which is also known as the primary motor cortex. This tract is responsible for carrying voluntary motor commands from the brain to the spinal cord and ultimately to the skeletal muscles.

Key Features:

1. Origin in the Precentral Gyrus:

The precentral gyrus houses the upper motor neurons that initiate voluntary movement.

These neurons give rise to axons that travel downward toward the spinal cord, passing through several critical structures.

2. Passage through the Internal Capsule:

The corticospinal axons pass through the internal capsule, a white matter structure that lies between the thalamus and the basal ganglia. This area is a critical conduit for both sensory and motor pathways.

3. Decussation in the Pyramids:

As the corticospinal fibers descend through the brainstem, the majority cross to the opposite side (decussate) at the medullary pyramids, located in the lower medulla. This is the hallmark of the lateral corticospinal tract.

Approximately 85-90% of the fibers cross over, forming the lateral corticospinal tract, which descends in the lateral white matter of the spinal cord.

4. Lateral Corticospinal Tract:

This division continues downward on the contralateral side of the body (opposite to where it originated in the brain).

These fibers make either monosynaptic connections with motor neurons or synapse on interneurons, which in turn communicate with motor neurons in the ventral horn of the spinal cord. These motor neurons control voluntary movements, especially fine motor control of the limbs.

5. Ventral Corticospinal Tract:

The remaining 10-15% of fibers that do not decussate in the pyramids form the ventral (anterior) corticospinal tract.

These fibers remain ipsilateral (on the same side as their origin) as they descend in the spinal cord.

They cross over at the level of their target spinal segments, synapsing on spinal interneurons that influence motor neurons, particularly for axial and trunk muscles.

Clinical Relevance:

The lateral corticospinal tract, having decussated in the medulla, controls movements on the contralateral side of the body.

Damage to the corticospinal tract above the level of decussation (such as in the brain or brainstem) will result in contralateral motor deficits. However, damage below the decussation (in the spinal cord) leads to ipsilateral motor weakness or paralysis.

The ventral corticospinal tract plays a role in postural control and movement of the axial muscles and is less involved in fine motor control compared to the lateral division.

This is a highly simplified yet representative view of how the corticospinal tract operates, crucial for understanding localization of lesions in motor disorders and spinal cord injury.