It runs from the motor cortex of the precentral gyrus down through the internal capsule, the cerebral peduncles of the midbrain, the pons and the pyramids of the medulla, where most fibres cross, into the spinal cord. It is the main pathway for voluntary movement. [1][2]
A tract has no shape of its own in this atlas; lit: the parts it runs through, in order.
The 3D brain needs JavaScript. The steps below still say where the corticospinal tract runs, in order.
The brain starts seen from the left, a little from the front and below, where the tract runs down the front of the brainstem. Step through lights one step at a time, about 1.2 s each, top to bottom; tap a step below to light it alone. Drag to turn, pinch or scroll to zoom. Step through is off because your device asks for reduced motion; tap each step instead.
The tract itself is not drawn: each step lights the whole part it runs through, not the narrow course of the fibres inside it. At the last step the atlas has only the top of the spinal cord, drawn as its thin central canal, so the tract’s course down the cord's white matter is not drawn either. [3][2]
The route, in 6 steps
The tract starts in the cerebral cortex. About 30% of its neurons start in the primary motor cortex of the precentral gyrus, 30% in the premotor cortex and supplementary motor area in front of it, and 40% in the somatosensory cortex, parietal lobe and cingulate gyrus; only the precentral gyrus is lit. [2][1]Where is the precentral gyrus?
The fibres pass between the caudate nucleus and the putamen as a bundle called the internal capsule, travelling in its posterior limb. [1][2]Where is the internal capsule?
They pass through the midbrain as the cerebral peduncles, entering the cerebral crus at the base of the midbrain, where the corticospinal and corticobulbar fibres run in the middle third of each crus. [1][2][4]Where is the cerebral peduncles?
The tract then burrows through the pons, running down through its basilar (front) part on the way to the medulla. [1][5]Where is the pons?
Entering the medulla, the fibres make up the pyramids, the paired ridges of white matter on its front surface; the tracts that pass through them, the corticospinal and corticobulbar tracts, are named the pyramidal tracts after them. [1][6][7]Where is the medulla oblongata?
Decussation of the pyramids: at the lower end of the medulla, the border with the spinal cord, about 90% of the fibres cross the midline and run on as the lateral corticospinal tract; the other 10% stay on the same side as the anterior corticospinal tract and cross lower down, at the level of the spinal nerve they leave by. This is why each side of the brain moves the opposite side of the body. The atlas has no shape for the crossing, so it is not marked. [1][6][2][8]
The fibres run down the spinal cord and end in its grey matter, on lower motor neurons and interneurons; in the ventral horn they synapse with the lower motor neurons that move the skeletal muscles of the body and limbs. [2][1]Where is the spinal cord?
More about the corticospinal tract
Other names: pyramidal tract, corticospinal pathway [7][2]
The corticospinal tract is one of the two pyramidal tracts; the other, the corticobulbar tract, carries impulses from the brain to the cranial nerves. [2][7]
It holds more than one million axons, which usually become myelinated in the first two years of life. [2][7]
Betz cells, the giant neurons of the primary motor cortex, make up only about 5% of the cells that project to the spinal cord. [2]
Its main job is voluntary control of the body and limbs; some corticospinal neurons synapse directly onto the alpha motor neurons that drive the muscles. [2]
The tract is one of several systems behind movement; the cerebellum and basal ganglia shape movement through loops back to the motor cortex. Every part, lit together with its role: What part of the brain controls movement?
Facts describe anatomy and normal function only. The 3D model is the adult male BodyParts3D brain (credits and licence); it has no shape for tracts, so a pathway is shown by the parts it runs through.