Library · Physiology
Motor control
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Moving a finger on purpose is not the work of a single neuron, but of two lined up in a row. It is a relay of two runners: one comes down from the cortex, the other reaches the muscle. The upper motor neuron begins in the cerebral cortex and travels to the brainstem or the spinal cord. There it hands the message off to the lower motor neuron, which begins in the cord and reaches the muscle.
Each one speaks using a different substance. The upper uses glutamate; the lower, acetylcholine. They are neurotransmitters, the substances one neuron uses to talk to the next. The command starts in the primary motor cortex, which sits in the precentral gyrus, one of the folds of the cortex, and that is where the Betz cells live, huge pyramid-shaped neurons.
And there is a crossing. About 90% of the fibers pass to the other side in the medullary pyramids, an area of the medulla oblongata, and keep heading down in the lateral corticospinal tract, the largest of the descending motor pathways.
In brief
Voluntary movement uses two neurons: the upper begins in the cortex and descends to the brainstem or spinal cord; the lower runs from the cord to the muscle.
A relay of two runners: one comes down from the cortex, the other reaches the muscle.
The upper uses glutamate and the lower acetylcholine; it all starts in the primary motor cortex of the precentral gyrus, with its Betz cells.
About 90% of fibers cross in the medullary pyramids and descend in the lateral corticospinal tract, the largest descending motor pathway.
Sources (1)
- National Center for Biotechnology Information, StatPearls PublishingNeuroanatomy, Motor Neuron, StatPearlsPublished
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