How does the stretch reflex cause the quadriceps femoris muscle group to contract?

Stretch reflex causes muscle fiber to stretch. This situation sends sensory signals to the spinal cord and the response is a muscle contraction, in this case, the femoral quadriceps contraction.

Explanation:

The stretch reflex occurs at the muscle level and for it to occur it is important to emphasize a structure wrapped deep in the muscle fibers of the central region of the muscle. This structure is called muscle spindle or neuromuscular spindle and is very sensitive to stretching (stretching) of muscle fibers.

When muscle fiber stretching occurs, the spindle sends sensory signals to the spinal cord and the response is a contraction of the same muscle to prevent its fibers from rupturing, generating a protective response. This is how the stretch reflex causes the femoral quadriceps muscle group to contract.

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