Stimulation of muscle spindles induces a

• A. relaxation of GTOs
• B. relaxation of the stretched muscle
• C. contraction of the stretched muscle
• D. contraction of the reciprocal muscle

Answer: (C)

Stimulation of muscle spindles triggers the stretch reflex, causing the stretched muscle to contract to resist the length change. When a muscle is stretched, the intrafusal fibers within the spindle are pulled, activating Ia afferent neurons that transmit directly to the spinal cord and synapse on the same muscle’s alpha motor neurons. This monosynaptic circuit drives a quick contraction of the stretched muscle, helping maintain posture and prevent overstretch. The Golgi tendon organ, which senses tension, produces an opposite response by inhibiting the same muscle (and often facilitating its antagonist) to protect tendons from excessive force. So, spindle stimulation primarily results in contraction of the stretched muscle.