Nerve pathway · one in each half of the brain
Corticospinal tract
Also called Pyramidal tract, CST
The main highway for movement, running from your brain all the way down the spinal cord.
The corticospinal tract carries your decisions to move, like wiggling a finger or taking a step, from the brain down to the spinal cord. It starts in the motor strip and nearby areas across the top of the brain, funnels down through the brainstem, and crosses to the other side near the bottom of the brainstem. That crossing is why the left side of your brain moves the right side of your body.
Where it is
From the top and sides of the brain, it funnels down through the deep brain and the front of the brainstem, then runs down inside the spinal cord, all the way to the lower back.
What it does
Voluntary movement
It carries the commands for movements you choose to make, especially precise ones.
Fine finger control
Its most important job in humans is skilled control of the hands and fingers, like writing, buttoning a shirt, or playing an instrument.
Crossing over
Most of its fibers, usually quoted as about 75 to 90 percent, cross at the bottom of the brainstem, so each half of the brain controls the opposite side of the body.
Think of it as an express elevator from the executive office on the top floor straight down to the loading dock where the muscles are.
Works with
- Primary motor cortexMany of its fibers start here in the primary motor cortex, the brain's movement strip.
- Layer V · Internal pyramidalIts fibers come from big output cells in layer V of the cortex.
- Pyramidal neuronIts fibers are the long axons of pyramidal neurons, including giant ones called Betz cells.
- Medulla oblongataIt forms the pyramids on the front of the medulla, where most of its fibers cross to the other side.
- Spinal cordIt runs down the spinal cord and drops off fibers at each level for the arms, trunk, and legs.
- Motor neuronAt the end of the line it hands the command to motor neurons, which send the final signal to the muscles.
When it goes wrong
Stroke
A stroke that damages this tract on one side causes weakness on the opposite side of the body. That is why a stroke in the left brain can weaken the right arm and leg.
The Babinski sign
Stroking the sole of the foot normally curls the toes down. If this tract is damaged, the big toe goes up instead. In babies that is normal, because the tract is still maturing.
ALS and spinal injury
Motor neuron disease (ALS) damages the cells of this tract as well as the nerve cells they talk to. A spinal cord injury can cut it, which is why movement below the injury can be lost.
For learning only, not medical advice. If you have a health concern, talk to a doctor.
Surprising facts
- Some of its fibers are extremely long: a single thread can run from the top of the brain all the way down to the lower spinal cord.
By the numbers
Where the name comes from
Named for where it starts and ends: the cortex (Latin for "bark", the brain's outer layer) and the spinal cord. Its other name, the pyramidal tract, comes from the two pyramid-shaped ridges it forms on the front of the medulla.
Learn it in a lesson
- Moving and feelingThe motor and sensory strips. A short guided lesson in 3D.
Quick quiz
3 questions. Your answers are saved and come back in your daily review.
Which of these is a job of the corticospinal tract?
Show the answer
Voluntary movement. It carries the commands for movements you choose to make, especially precise ones.
Voluntary movement. It carries the commands for movements you choose to make, especially precise ones.
The corticospinal tract is part of which larger structure?
Show the answer
White matter pathways. It belongs to the white matter pathways.
White matter pathways. It belongs to the white matter pathways.
Which part fits this description? "Like an express elevator from the executive office on the top floor straight down to the loading dock where the muscles are."
Show the answer
Corticospinal tract. It is the corticospinal tract. The main highway for movement, running from your brain all the way down the spinal cord.
Corticospinal tract. It is the corticospinal tract. The main highway for movement, running from your brain all the way down the spinal cord.
These parts now come back in your daily review, just before you would forget them.
Practice it and its neighbors in 3DSources
- Neuroscience Online, Chapter 2: Spinal Reflexes and Descending Motor Pathways, McGovern Medical School at UTHealth Houston
- Neuroscience Online, Chapter 3: Motor Cortex, McGovern Medical School at UTHealth Houston
- Neuroanatomy, Corticospinal Cord Tract, StatPearls, NCBI Bookshelf
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Explore the corticospinal tract in 3D
Turn it around, zoom inside and see how it connects to the rest of the brain, then test yourself with quick quizzes.
Open it in 3D