Final answer:
Motor control involves three levels of neural input: upper motor neurons which initiate movement, lower motor neurons which connect to muscles, and neural circuits for reflexes and automated movements. These systems utilize descending pathways like the corticospinal and corticobulbar tracts for muscle activity and control.
Step-by-step explanation:
The three levels of neural input involved in motor control include the following:
- Upper motor neurons: These neurons originate in the motor region of the cerebral cortex or the brain stem and carry information down to the lower motor neurons. They are involved in the planning, initiating, and directing voluntary movements.
- Lower motor neurons: These neurons extend out of the spinal cord and directly innervate muscles to cause contraction and produce movement. They serve as the direct link between the nervous system and skeletal muscle.
- Neural circuits within the spinal cord: These circuits are responsible for the coordination of reflexes and central pattern generations, such as walking.
Neural control of muscle activities involves three types of contractions: concentric, eccentric, and isometric, as well as muscle fiber recruitment and regulation of muscle tone. The motor system includes not only the pathways that project to the spinal cord, but also nuclei in the brain stem controlling many involuntary functions and reflex arcs that automate certain responses. Ultimately, the motor commands are conveyed via descending motor pathways, such as the corticospinal and corticobulbar tracts, from the higher brain centers to the motor neurons that connect with muscles.