KEY POINTS

1. The muscle spindle stretch receptor is an encapsulated organ of specialized muscle fibers with separate motor and sensory innervations.

2. The muscle spindle conveys information about muscle length to the central nervous system.

3. Muscle stretch and action potentials along spindle sensory neurons lead to reflex contraction of the extrafusal muscle fibers.

4. The central nervous system can control spindle sensitivity directly through the gamma (γ) motor neurons.

5. The Golgi tendon organ lies in series between muscle and tendon and detects muscle tension.