QS Study

Definition – Stretching of a muscle lead of discharge of muscle spindle afferent nerve which causes the reflex contraction of that muscle, this is called stretch reflex. It helps sustain appropriate posturing because a slight lean to either side causes a stretch in the spinal, hip and leg muscles to the other side, which is rapidly countered by the stretch reflex. This reflex has the straight latency of all spinal reflexes including the Golgi tendon reflex and reflexes mediated by pain and cutaneous receptors.

Fig: Stretch Reflex features

Salient features

It is caused by a stretch in the muscle spindle. When the stretch impulse is received a rapid sequence of events follows. The motor neuron is activated and the stretched muscles and its supporting muscles are contracted while its antagonist’s muscles are inhibited.

  1. Occurs in antigravity extensor muscles only.
  2. The stimulus arises by the stretch of the muscle & is received by the kinaesthetic receptor in it.
  3. Does not undergo rapid adaptation.
  4. The rate of discharge of motor neurons is slow about 9/sec.
  5. Mediated by a monosynaptic reflex arc.
  6. No irradiation takes place.

Importance

  • Production of muscle tone
  • Maintenance of posture Description of a stretch reflex.