Stretch reflex


Stretch reflex

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.

Contents

Examples

A person standing upright begins to lean to one side. The postural muscles that are closely connected to the vertebral column on the side will stretch. Because of this, stretch receptors in those muscles contract to correct posture.

Other examples (followed by involved spinal nerves) are responses to stretch created by a blow upon a muscle tendon:

Another example is the group of fibers in the calf muscle, which synapse with motor neurons supplying muscle fibers in the same muscle. A sudden stretch, such as tapping the Achilles' tendon, causes a reflex contraction in the muscle as the spindles sense the stretch and send an action potential to the motor neurons which then cause the muscle to contract; this particular reflex causes a contraction in the soleus-gastrocnemius group of muscles. Like the patellar reflex, this reflex can be enhanced by the Jendrassik maneuver.

Supraspinal control

The central nervous system can influence the stretch reflex via the gamma motoneurons, which as described above control the sensitivity of the reflex.

Inhibitory signals arrive at gamma neurons through the lateral reticulospinal tract from Brodmann area 6, the paleocerebellum and the red nucleus. Facilitatory signals arrive through the ventral reticulospinal tract from Brodmann area 4, the neocerebellum and the vestibular nucleus.

Spinal control

  • Withdrawer reflex
  • Damping & Loading reflex
  • Jendrassik manoeuvre

Pathology

The clasp-knife response is a stretch reflex with a rapid decrease in resistance when attempting to flex a joint. It is one of the characteristic responses of an upper motor neuron lesion.

See also

External links



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Look at other dictionaries:

  • stretch reflex — n a spinal reflex involving reflex contraction of a muscle in response to stretching called also myotatic reflex * * * (myotatic reflex) the reflex contraction of a muscle in response to its being stretched. * * * reflex contraction of a muscle… …   Medical dictionary

  • stretch reflex — noun reflex contraction of a muscle when an attached tendon is pulled; important in maintaining erect posture • Syn: ↑myotactic reflex • Hypernyms: ↑reflex, ↑reflex response, ↑reflex action, ↑instinctive reflex, ↑innate reflex …   Useful english dictionary

  • stretch reflex — myotatic reflex the reflex contraction of a muscle in response to its being stretched …   The new mediacal dictionary

  • РЕФЛЕКС РАСТЯЖЕНИЯ (STRETCH REFLEX), РЕФЛЕКС РАСТЯЖЕНИЯ МЫШЦЫ — (myotatic reflex) рефлекс, вызывающий сокращение мышцы в ответ на ее растяжение …   Толковый словарь по медицине

  • Рефлекс Растяжения (Stretch Reflex}, Рефлекс Растяжения Мышцы (Myotatic Reflex) — рефлекс, вызывающий сокращение мышцы в ответ на ее растяжение. Источник: Медицинский словарь …   Медицинские термины

  • reflex action — noun an automatic instinctive unlearned reaction to a stimulus • Syn: ↑reflex, ↑reflex response, ↑instinctive reflex, ↑innate reflex, ↑inborn reflex, ↑unconditioned reflex, ↑physiological reaction …   Useful english dictionary

  • reflex response — noun an automatic instinctive unlearned reaction to a stimulus • Syn: ↑reflex, ↑reflex action, ↑instinctive reflex, ↑innate reflex, ↑inborn reflex, ↑unconditioned reflex, ↑physiological reaction …   Useful english dictionary

  • Reflex — A reaction that is involuntary. The corneal reflex is the blink that occurs with irritation of the eye. The nasal reflex is a sneeze. * * * 1. An involuntary reaction in response to a stimulus applied to the periphery and transmitted to the… …   Medical dictionary

  • Reflex — For other uses, see Reflex (disambiguation). A reflex action, also known as a reflex, is an involuntary and nearly instantaneous movement in response to a stimulus.[1] A true reflex is a behavior which is mediated via the reflex arc; this does… …   Wikipedia

  • Tendon reflex — (or T reflex) may refer to: A stretch reflex, when the stretch is created by a blow upon a muscle tendon. This is the usual definition of the term.[1][2] Deep tendon reflex also usually refers to this sense.[3] The Golgi tendon reflex, motivated… …   Wikipedia


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