stretch reflex, it can override the stretch reflex when tension is great, for example, causing a person to drop a very heavy weight. Like the stretch reflex, the tendon reflex is ipsilateral. The sensory receptors for this reflex are called tendon Golgi receptors, which lie within a tendon near its junction with a muscle. In contrast to muscle spindles, which are sensitive to changes in muscle length, tendon organs detect and respond to changes in muscle tension that are caused by muscular contraction, but not passive stretch. Pathology Upper motor neuron lesions which damage the descending pathways down to the spinal cord may cause increase in muscle tone, partly because alpha motoneurons respond more to muscle spindle afferent inputs. This causes increased resistance to passive movement (that the patient doesn't initiate), called spasticity, which is associated with another neurological sign, the clasp-knife response, in which the spastic muscle initially resists passive movement strongly, and then suddenly yieldslike the motion of a pocketknife. The increased initial resistance comes from the stretch reflex hyperactivity, and the sudden collapse may involve the Golgi tendon reflex. The response is also known as the lengthening reaction because of the spastic muscle's reaction to lengthening. See also H-reflex Motor control Reflex action References Other references Reflexes