The stretch reflex (myotatic reflex) is a muscle contraction in response to stretching within the muscle. It is a monosynaptic reflex which provides automatic regulation of skeletal muscle length.
When a muscle lengthens, the muscle spindle is stretched and its nerve activity increases. This increases alpha motor neuron activity, causing the muscle fibers to contract and thus resist the stretching. A secondary set of neurons also causes the opposing muscle to relax. The reflex functions to maintain the muscle at a constant length.
Gamma motoneurons regulate how sensitive the stretch reflex is by tightening or relaxing the fibers within the spindle. There are several theories as to what may trigger gamma motoneurons to increase the reflex's sensitivity. For example, gamma co-activation might keep the spindles taut when a muscle is contracted, preserving their stretch-sensitivity even as the muscle fibers become shorter. Otherwise the spindles would become slack and the reflex would cease to function.
This reflex has the shortest latency of all spinal reflexes including the Golgi tendon reflex and reflexes mediated by pain and cutaneous receptors.
Read more about Stretch Reflex: Examples, Supraspinal Control, Spinal Control, Pathology, See Also
Famous quotes containing the words stretch and/or reflex:
“The city of Washington is in some respects self-contained, and it is easy there to forget what the rest of the United States is thinking about. I count it a fortunate circumstance that almost all the windows of the White House and its offices open upon unoccupied spaces that stretch to the banks of the Potomac ... and that as I sit there I can constantly forget Washington and remember the United States.”
—Woodrow Wilson (1856–1924)
“As a medium of exchange,... worrying regulates intimacy, and it is often an appropriate response to ordinary demands that begin to feel excessive. But from a modernized Freudian view, worrying—as a reflex response to demand—never puts the self or the objects of its interest into question, and that is precisely its function in psychic life. It domesticates self-doubt.”
—Adam Phillips, British child psychoanalyst. “Worrying and Its Discontents,” in On Kissing, Tickling, and Being Bored, p. 58, Harvard University Press (1993)