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The primary motor cortex alone has been shown to have as many as 116 different types of cells differentiated in their morphology, electrophysiological properties (including firing patterns) and gene expression profile (for example, by type of neurotransmitter released (GABA, glutamate etc.).
His reasons were largely based on cytoarchitectonics, or the study of the appearance of the cortex under a microscope. The primary motor cortex contains cells with giant cell bodies known as "Betz cells". These cells were mistakenly thought to be the main outputs from the cortex, sending fibers to the spinal cord. [1]
A simple example of this type of correspondence is the primary motor cortex, a strip of tissue running along the anterior edge of the central sulcus. Motor areas innervating each part of the body arise from a distinct zone, with neighboring body parts represented by neighboring zones.
That is, the legs and trunk fold over the midline; the arms and hands are along the middle of the area shown here; and the face is near the bottom of the figure. Because Brodmann area 4 is in the same general location as primary motor cortex, the homunculus here is called the motor homunculus.
Fibres arise from the primary motor cortex (about 30%), supplementary motor area and the premotor cortex (together also about 30%), and the somatosensory cortex, parietal lobe, and cingulate gyrus supplies the rest. [2] The cells have their bodies in the cerebral cortex, and the axons form the bulk of the pyramidal tracts. [4]
The corticospinal tract originates in several parts of the brain, including not just the motor areas, but also the primary somatosensory cortex and premotor areas. [1] Most of the neurons originate in either the primary motor cortex (precentral gyrus, Brodmann area 4) or the premotor frontal areas.
Upper motor neurons represent the largest pyramidal cells in the motor regions of the cerebral cortex. The major cell type of the UMNs is the Betz cells residing in layer V of the primary motor cortex, located on the precentral gyrus in the posterior frontal lobe.
Cortex Primary motor cortex (Precentral gyrus, M1) Premotor cortex; Supplementary motor cortex; Prefrontal cortex. Orbitofrontal cortex; Dorsolateral prefrontal cortex; Ventrolateral prefrontal cortex; Dorsomedial prefrontal cortex; Ventromedial prefrontal cortex; Gyri. Superior frontal gyrus; Middle frontal gyrus; Inferior frontal gyrus