Primary motor cortex

The primary motor cortex (Brodmann area 4) is a brain region that in humans is located in the dorsal portion of the frontal lobe.The location of the primary motor cortex is most obvious on histological examination due to the presence of the distinctive Betz cells.[3] As the primary motor axons travel down through the cerebral white matter, they move closer together and form part of the posterior limb of the internal capsule.After crossing over to the contralateral side in the medulla oblongata (pyramidal decussation), the axons travel down the spinal cord as the lateral corticospinal tract.In addition to the main corticospinal tract, Motor cortex projects to other cortical and subcortical areas, including the striatum, hypothalamus, midbrain and hindbrain, as well as the thalamus, basal ganglia, midbrain and medulla[4] Corticomotorneurons are neurons in the primary cortex which project directly to motor neurons in the ventral horn of the spinal cord.The lateral, convex side of the primary motor cortex is arranged from top to bottom in areas that correspond to the buttocks, torso, shoulder, elbow, wrist, fingers, thumb, eyelids, lips, and jaw.[10] A second modification of the classical somatotopic ordering of body parts is a double representation of the digits and wrist studied mainly in the human motor cortex.Researchers who addressed this issue found that the map of the hand, arm, and shoulder contained extensive overlap.Instead, in this second view, the so-called primary motor and lateral premotor strips together composed a single cortical area termed M1.Strictly speaking M1 refers to the single map that, according to some previous researchers, encompassed both the primary motor and the lateral premotor cortex.If the primary motor cortex with its Betz cells is damaged, a temporary paralysis results and other cortical areas can evidently take over some of the lost function.Lesions of the precentral gyrus result in paralysis of the contralateral side of the body (facial palsy, arm-/leg monoparesis, hemiparesis) - see upper motor neuron.On this basis they suggested that neurons in motor cortex, by "voting" or pooling their influences into a "population code", could precisely specify a direction of reach.Scott and Kalaska[35] showed that each motor cortex neuron was better correlated with the details of joint movement and muscle force than with the direction of the reach.Strick and colleagues[37] found that some neurons in motor cortex were active in association with muscle force and some with the spatial direction of movement.[39][41][42] Neurons in this region project to a specific subcortical nucleus in which a pattern generator coordinates the cyclic rhythm of the whiskers.