A motor neuron is a neuron whose cell body is located in the motor cortex, brainstem or the spinal cord, and whose axon (fiber) projects to the spinal cord or outside of the spinal cord to directly or indirectly control effector organs, mainly muscles and glands. There are two types of motor neuron – upper motor neurons and lower motor neurons. Axons from upper motor neurons synapse onto interneurons in the spinal cord and occasionally directly onto lower motor neurons. The axons from the lower motor neurons are efferent nerve fibers that carry signals from the spinal cord to the effectors. Types of lower motor neurons are alpha motor neurons, beta motor neurons, and gamma motor neurons.
Micrograph of the hypoglossal nucleus showing motor neurons with their characteristic coarse Nissl substance ("tigroid" cytoplasm). H&E-LFB stain.
The motor cortex is the region of the cerebral cortex involved in the planning, control, and execution of voluntary movements.
The motor cortex is an area of the frontal lobe located in the posterior precentral gyrus immediately anterior to the central sulcus.
Topography of human motor cortex. Supplementary motor area labelled SMA.
Motor cortex controls different muscle groups
Some commonly accepted divisions of the cortical motor system of the monkey
A biophysically realistic model of the mouse primary motor cortex microcircuit representing a cylindrical volume of 300 μm diameter: 3D visualization, connectivity, dimensions, and neuronal densities, classes, and morphologies