This part concentrated to muscles and how those are controlled. The right movements of muscles need well planned motor system, it consists of all the muscles and the neurons that control them. The muscles consist of hundreds of muscle fibers. Central nervous systems axon branch innervates single fiber. There is somatic musculature which can be controlled voluntary and are innervated by somatic motor neurons that can be called lower motor neurons. There are two types of those neurons, alpha motor neurons and gamma motor neurons.
Alpha motor neurons take care of force generation. Some tasks need more force than others, sometimes fingers need to catch something exact. On the other hand, if you jump over a rock you need explosive force. Alpha motor neuron innervates muscle fibers. Together they formulate component called motor unit. At the same time, all the motor neurons that is connected to one muscle formulates unit called a motor neuron pool. The alpha motor neuron release acetylcholine and makes an action potential. That is the way how it controls muscle fibers. If many action potentials be summed it causes the muscle contraction.
The gamma motor neuron has another mission, it innervates intrafusal fibers. Those fibers are modified skeletal muscle fibers. Those are inside the muscle spindle. Outside the spindle are extrafusual fibers which are innervated by alpha motor neuron.
For muscles to move, the messages must travel to muscles. There are two pathways which carry the messages from the brain to spinal cord: lateral pathways and ventromedial pathways. The distal musculatures are controller via lateral pathways and posture and locomotion control happens via ventromedial pathways.
The planning of different parts of movement happens in different part of cerebral cortex. The motor cortex, Area 4 and 6, is place an area which is specialized for skilled voluntary movement. The input to area 6 comes specially from the ventral lateral nucleus, which is the nucleus of the dorsal thalamus, which in turn gets its input from basal ganglia. Another area of the cerebral cortex is posterior parietal cortex which is central area in creating the awareness of the positions of the body. One part of it, Area 5, gets inputs form primary somatosensory cortical areas and the other part, Area 7, gets inputs from high order visual cortical areas. The prefrontal cortex is involved in representing the most complex part of the motor control, with posterior parietal cortex.
