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Primary motor cortex is defined anatomically as the region of cortex that contains large neurons known as Betz cells, which, along with other cortical neurons, send long axons down the spinal cord to synapse onto the interneuron circuitry of the spinal cord and also directly onto the alpha motor neurons in the spinal cord which connect to the ...
Fulton [10] helped to solidify this distinction between a primary motor cortex in area 4 and a premotor cortex in area 6. As Fulton pointed out, and as all subsequent research has confirmed, both primary motor and premotor cortex project directly to the spinal cord and are capable of some direct control of movement.
Cortical stimulation mapping led to the development of a homunculus for the motor and sensory cortices, which is a diagram showing the brain's connections to different areas of the body. An example is the cortical homunculus of the primary motor cortex and the somatosensory cortex, which are separated by the central sulcus.
Topography of the primary motor cortex, showing which zone controls each body part Many of the brain areas defined by Brodmann have their own complex internal structures. In a number of cases, brain areas are organized into topographic maps , where adjoining bits of the cortex correspond to adjoining parts of the body, or of some more abstract ...
A 2-D model of cortical sensory homunculus. A cortical homunculus (from Latin homunculus 'little man, miniature human' [1] [2]) is a distorted representation of the human body, based on a neurological "map" of the areas and portions of the human brain dedicated to processing motor functions, and/ or sensory functions, for different parts of the body.
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.
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.
The primary motor cortex sends its axons through the posterior limb of the internal capsule. Lesions, therefore, result in a contralateral hemiparesis or hemiplegia. While symptoms of weakness due to an isolated lesion of the posterior limb can initially be severe, recovery of motor function is sometimes possible due to spinal projections of ...