Cortical area · one in each half of the brain

Primary motor cortex

Also called Primary motor cortex, M1, Brodmann area 4

Your brain's movement keyboard: a body map that commands every muscle you move on purpose.

Open in 3D

The precentral gyrus is the ridge just in front of the central groove, and it holds the primary motor cortex. It sends the commands that make your muscles move when you choose to move them. Along it runs a map of the body, called the motor homunculus, where each body part has its own patch. Body parts that need fine control, like the hands, lips and tongue, get huge patches.

Where it is

On the outer surface of each half of the brain, in a strip running from the top of the head down toward the ear, just in front of the central groove.

What it does

Think of it as the control panel of a giant puppet: every body part has its own strings, and the parts that need the finest moves get the most strings.

Works with

• Corticospinal tractIts output fibers gather into this tract to carry movement commands down to the spinal cord.
• Primary somatosensory cortexThe touch map right behind it mirrors its body map and feeds it constant feedback.
• Ventral lateral nucleus of the thalamusThis thalamic relay passes it timing and coordination signals from the cerebellum and basal ganglia.
• PutamenA movement loop through the putamen helps it start and scale actions smoothly.
• Pyramidal neuronIts giant Betz cells are extra-large pyramidal neurons whose long fibers reach down into the spinal cord.
• Superior frontal gyrusThe supplementary motor area in front of it plans movement sequences that it then carries out.

When it goes wrong

For learning only, not medical advice. If you have a health concern, talk to a doctor.

Surprising facts

• Betz cells, named after the 19th-century Ukrainian anatomist Vladimir Betz, live here. They are among the biggest nerve cells in the brain, and their fibers can run all the way down to the lower spinal cord.
• On the body map, the hands and face are enormous while the whole trunk gets only a small strip. Drawn as a figure, the homunculus has giant hands and lips on a tiny body. The real map is messier, with neighboring parts overlapping.
• Under a microscope it looks unusual: it has almost no visible layer 4, the layer that usually receives incoming sensory signals, and instead is packed with big output cells.

Where the name comes from

"Precentral" means "in front of the center": it lies right in front of the central sulcus, the deep groove that divides the frontal and parietal lobes. "Homunculus", the name for its body map, is Latin for "little man".

Learn it in a lesson

• Moving and feelingThe motor and sensory strips. A short guided lesson in 3D.

Sources

1. Neuroanatomy, Precentral Gyrus, StatPearls, NCBI Bookshelf
2. Physiology, Motor Cortex, StatPearls, NCBI Bookshelf
3. Betz cells, Radiopaedia

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