Directions, Reference Planes, & Views of the Brain
Structure and Function of the Motor Cortex Areas
- The primary motor cortex (M1, or somatomotor area) occupies a large portion of the precentral gyrus (Brodmann area 4) and typically executes movements that are selected and planned by other areas of the brain.
- A primary motor cortex is present in each hemisphere and both are somatotopically organized. The medial and superior portions control the muscles of the feet and legs, and the lateral portions control the muscles of the thorax, arms and head.
- Each primary motor cortex controls the muscles on the opposite side of the body. Impulses exit the motor cortex via upper level neurons, which cross over at the medulla pyramids. The axons then enter the spinal cord as a part of the corticospinal tracts. Lower level neurons carry impulses from the ventral horns of the spinal cord to the skeletal muscles.
- Directly anterior to the primary motor cortex (Brodmann area 6) are the premotor area (lateral) and supplementary motor area (medial).
- In general, the premotor area anticipates and plans movements based on input from external or sensory cues, such as vision and auditory. In contrast, the supplementary motor area selects and plans complex movements based on internal cues, such as memory.
- Most of the information generated by these areas is passed to the primary motor cortex for execution and the rest travels directly down the spinal cord to the skeletal muscles.
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