The simplest type of reflex, involving only two neurons, characterized by a quick contraction of a muscle (with a normal latency of 15–25 milliseconds), triggered by a signal from a muscle spindle in response to a sudden stretch induced by a sharp tap on the muscle tendon. Absence of the reflex indicates damage to the muscle, nerves, or spinal cord, and a hyperactive reflex suggests hyperthyroidism or a lesion in the pyramidal tract. The most important deep tendon reflexes are the Achilles tendon reflex, biceps reflex, patellar reflex, and triceps reflex. Also called a myostatic reflex, or tendon reflex. See also monosynaptic reflex, reflex, stretch reflex. DTR abbrev.