FIGURE 2-3 Initiation and regulation of movements.

Control of movements involves a complex network of connections. Signals commanding the initiation of a movement are generated in the primary motor cortex of the brain. These signals are modulated before they reach the muscle. They are modulated through an intricate circuit in the basal ganglia and thalamus, which regulate the initiation of movements and help coordinate movements. Information from muscle contractions is also transmitted back to the brain through sensory receptors. This information is also used to provide feedback and to modify the movements.

SOURCE: Adapted from Kandel et al., 1991.

Feedback Control of Movements

Critical feedback from sensory nerve endings located on muscles is transferred to the spinal cord via the sensory roots and dorsal horn to the brain, resulting in involuntary modulation of movements. This component of the sensory system is called proprioception. It is responsible for immediately varying the degree of muscle contraction in response to incoming

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