Final answer:
Stretching of a muscle spindle causes reflexive contraction of the muscle the spindle resides in.
Therefore, the correct answer is option 3
Step-by-step explanation:
A muscle spindle is a sensory receptor located within the muscle that detects changes in muscle length and sends signals to the central nervous system. When a muscle spindle is stretched, it initiates a reflexive contraction of the muscle it is located in. This reflexive contraction is known as the stretch reflex.
The stretch reflex is a protective mechanism that helps maintain muscle tone and stabilize joints. When a muscle is stretched, the muscle spindle detects the change in length and sends sensory signals to the spinal cord. These signals then activate motor neurons, which in turn cause the muscle to contract.
For example, if you were to tap your knee with a reflex hammer, it would stretch the quadriceps muscle in your thigh. The muscle spindle within the quadriceps detects this stretch and triggers a reflexive contraction, causing your leg to kick forward.
The other options listed in the question are not correct in relation to the stretching of a muscle spindle. Stretching of the muscle spindle does not cause reflexive inhibition of the muscle, stretching of the tendon, or activation of antagonistic muscles. The reflexive contraction of the muscle the spindle resides in is the primary response associated with the stretching of a muscle spindle.
Therefore, the correct answer is option 3) reflexive contraction of the muscle the spindle resides in.