Organization Of The Motor Systems
The motor systems are those areas of the nervous system that are primarily responsible for controlling movement. The movement can either be:
• Guided by inputs from the sensory systems (closed-loop or reflex controlled); or
• Triggered by a sensory cue or some internal desire to move (open- loop or volitional movement).
In practice, most motor acts involve both types of movement.
Closed-loop movements predominantly involve the axial or proximal muscles responsible for balance, posture and locomotion, while the open-loop movements are typically associated with the distal musculature concerned with the control of fine skilled movements.
The organization of the motor structures is best viewed in terms of a hierarchy.
A cautionary note
It is important to remember that the division of the central nervous system into motor and sensory functions is a gross simplification as all the motor areas have some sensory input. It is difficult to know the point at which a highly processed sensory input becomes the impulse for the initiation of a movement. It should also be realized that the division of the motor systems into various levels and different motor pools is a convenient but not strictly accurate device for understanding the control of movement and the pathophysiology of disorders of the motor system.