Final answer:
A sudden stretch to the tendon of a muscle elicits the stretch reflex, an automatic muscle contraction that serves to prevent injury from overstretching. This reflex is also known as the deep tendon reflex.
Step-by-step explanation:
A sudden stretch to the tendon of a muscle results in a muscle contraction response known as the stretch reflex. This reflex is an automatic response to a muscle being stretched, whereby the muscle immediately contracts in response. It functions as a way to prevent muscle and tendon damage from overstretching.
During the stretch reflex, muscle spindles, which are sensory receptors within the muscle, detect the rate and degree of stretch. This information is conveyed to the spinal cord via sensory neurons, where it synapses directly with motor neurons. These motor neurons then transmit signals back to the same muscle, causing it to contract. This protects the muscle from being overstretched by contracting it when a sudden stretch is detected.
The deep tendon reflex is another term for this, as the response is typically elicited by a sharp tap to the tendon, which doctors often perform with a reflex hammer during a physical examination to assess the health of the nervous and muscular systems.