Corticospinal tract

The corticospinal tract is a bundle of nerve fibres that carries movement-related signals from the brain to the spinal cord. It is especially important for voluntary control of skeletal muscles, including the precise movements of the hands and fingers.

Most fibres eventually influence motor neurons and interneurons in the spinal cord. These connections help the body organise both fine distal actions and broader movements of the trunk and limbs.

The neurons of the corticospinal tract

The cells that begin the pathway are called upper motor neurons. Their axons arise mainly from movement-related regions of the cerebral cortex and travel downward through the white matter of the brain, the internal capsule, the midbrain, pons, and medulla.

At the spinal cord, upper motor neuron fibres communicate with interneurons and lower motor neurons. Lower motor neurons then carry the final signal out through peripheral nerves to skeletal muscle. This two-level arrangement allows the brain to plan an action while spinal circuits help shape and coordinate its execution.

How does the corticospinal tract communicate with the nervous system?

The tract receives contributions from several connected cortical areas. The primary motor cortex sends many fibres involved in voluntary movement. The premotor cortex and supplementary motor area help prepare, sequence, and organise actions. Somatosensory and posterior parietal regions add information about body position and the surrounding task.

The motor cortex and movement planning

A movement usually depends on more than a single command. The brain combines intention, sensory feedback, posture, and the current position of the limbs. The basal ganglia and cerebellum also contribute to selecting, refining, timing, and correcting movement before signals descend toward the spinal cord.

From the cortex to the medulla

Axons spread through the corona radiata before becoming more compact in the internal capsule. They continue through the cerebral peduncles, pass through the pons, and form prominent bundles called the medullary pyramids. Near the lower medulla, most fibres cross to the opposite side in the pyramidal decussation.

The pathway through the spinal cord

The crossing pattern explains why one side of the brain generally influences voluntary movement on the other side of the body. Fibres that cross descend in the lateral white column, while a smaller group remains nearer the front of the spinal cord before crossing closer to its target level.

The lateral corticospinal tract

The lateral corticospinal tract travels in the lateral funiculus of the spinal cord. It has strong links with circuits controlling distal muscles, particularly those of the arm, hand, and fingers. These connections support skilled, fractionated movements such as reaching, writing, or adjusting the force of a grip.

Spinal motor circuits include alpha motor neurons, which activate contractile muscle fibres, and gamma motor neurons, which help regulate muscle spindle sensitivity. Their coordinated activity supports movement and useful information about muscle length.

The ventral corticospinal tract

The ventral corticospinal tract descends closer to the front of the spinal cord. It is more closely associated with axial and proximal muscles, which help stabilise the trunk, shoulder, and hip during larger movements. Its fibres commonly influence motor circuits on both sides through local spinal connections.

Summary of the role of the corticospinal tract

The corticospinal tract is a major communication route between the cerebral cortex and spinal motor networks. It does not work alone: sensory areas, basal ganglia, cerebellum, brainstem structures, and local spinal circuits all contribute to a useful movement.

• It carries descending signals related to voluntary skeletal-muscle movement.
• Most fibres cross in the pyramidal decussation of the medulla.
• The lateral division is especially important for precise distal movement.
• The ventral division contributes more to control of axial and proximal muscles.
• Interneurons and lower motor neurons help turn the descending plan into muscle activity.

Further reading

Continue with the descending spinal tracts, the spinal cord, the cerebral cortex, or reflex actions.