During deep tendon reflex testing, what is observed when the tendon is struck?

During deep tendon reflex testing, what is observed when the tendon is struck?

• A. No contraction observed.
• B. Only sensory changes noted.
• C. Muscle contraction and joint movement bilaterally.
• D. Increased muscle tone at rest.

Answer: (C)

When the tendon is struck, it stretches the muscle and triggers a monosynaptic stretch reflex. Sensory fibers (Ia afferents) carry this signal to the spinal cord and directly activate the same muscle’s alpha motor neurons, causing a quick, involuntary contraction of that muscle. This reflex often produces a brief movement at the joint of the tested limb—the classic “jerk” you can observe. So the observed action is a muscle contraction accompanied by a brief joint movement in the limb being tested. It’s not just sensory change, it’s not absent, and it’s not a resting increase in tone.

When the tendon is struck, it stretches the muscle and triggers a monosynaptic stretch reflex. Sensory fibers (Ia afferents) carry this signal to the spinal cord and directly activate the same muscle’s alpha motor neurons, causing a quick, involuntary contraction of that muscle. This reflex often produces a brief movement at the joint of the tested limb—the classic “jerk” you can observe.

So the observed action is a muscle contraction accompanied by a brief joint movement in the limb being tested. It’s not just sensory change, it’s not absent, and it’s not a resting increase in tone.