Movement

Movement is the change of the body's position relative to a reference point. It is regulated by the nervous system.

Overview
There are four general systems involved in movement:
 * 1) Upper motor system (a.k.a. Descending System)
 * 2) Brainstem centers
 * 3) Motor cortex
 * 4) Modulatory system of the upper motor system
 * 5) Basal ganglia
 * 6) Cerebellum
 * 7) Brainstem/spinal cord circuits
 * 8) Local circuit neurons
 * 9) Motor neuron pools (a.k.a. Lower Motor System)
 * 10) Skeletal muscles - responsible for physical movement

Upper Motor System
The Upper Motor System consists of brainstem centers and the various motor cortices - the primary localized motor cortex in the prefrontal gyrus, and the prefrontal cortex and the supplementary motor cortex. Has cortical and brainstem systems.

The cortical systems are responsible for planning, initiating, and controlling movements.

The brainstem systems are responsible for posture.

Brainstem/Spinal Cord
The Brainstem/Spinal Cord circuits are comprised of local circuit neurons that are responsible for reflexes and also motor neuron pools - α and γ motor neurons. α-type motor neurons essentially innervate skeletal muscles and relay the brain's commands to the muscles regarding contraction, and are indirectly responsible for movement. γ-type motor neurons also innervate skeletal muscle fibers, but are instead sensory neurons that monitor the length of the muscle fibers and determine the stretch reflex.

Skeletal Muscles
The Skeletal Muscles are directly responsible for movement, contracting on the extensor muscle and releasing on the flexor muscle during normal movement to faciliate motion. Extrafusal muscle fibers are innervated with α-type motor neurons and intrafusal muscle fibers are innerved with γ-type motor neurons. Skeletal muscles are connected with the brainstem/spinal cord circuits.