Coupon Accepted Successfully!



  1. Asynaptic reflex e.g. Axon reflex
  2. Monosynaptic reflex e.g. Stretch reflexes (deep tendon reflexes)
  3. Di or Bi-synaptic reflex e.g.
    1.  Inverse stretch reflex.
    2.  Reciprocal innervation.
  4. Polysynaptic reflex e.g.
    1.  Superficial reflexes.
    2.  Withdrawal response
    3.  Flexor
    4.  Crossed – extensor

Which is true about presynaptic inhibition? (AIIMS Nov 08)?

  1. Occurs due to hyperpolarisation of presynaptic membrane
  2. Occurs due to inhibition of release of positive neurotransmitter from presynaptic terminal
  3. Produces action potential
  4. Occurs due to blockage of presynaptic receptor.

B. Occurs due to inhibition of release of positive neurotransmitter from presynaptic terminal

Stretch reflex

It is responsible for contraction of muscle when stretched. Receptor is muscle spindle.Muscles have 2 type of fibres one outside the capsule of muscle spindle called Extrafusal Muscle Fibre.They are contractile, supplied by a ϒMotor neurons from ventral horn, resulting in shortening of muscle proper.


Intrafusal Muscle Fibre

Intrafusal Muscle Fibre are present inside the spindle, they too are contractile supplied by motor neurons. Unlike extrafusal when they contract they lead to activation of muscle spindle as they stretch the centre of muscle spindle.So the function of γ motor discharge is maintaining spindle sensitivity.

  1. There are two types of intrafusal fibers in muscle spindles. The first type contains many nuclei in a dilated central area and is therefore called a nuclear bag fiber.
  2. Typically two nuclear bag fibers occur per spindle: nuclear bag fiber 1 with a low level of myosin ATPase activity and nuclear bag fiber 2 with a high level of myosin ATPase activity. The second fiber type, the nuclear chain fiber, is thinner and shorter and lacks a definite bag.
  3. There are two kinds of sensory endings in each spindle. The primary (annulospiral) endings are the terminations of rapidly conducting group Ia afferent fibers supplying central portion of bothnchain & Bag fibres. The secondary (flower-spray) endings are terminations of group II sensory fibers and are located nearer the ends of the intrafusal fibers but only on nuclear chain fibers.

  4. The nerves from the endings in the nuclear bag region show a dynamic responseQ; ie, they discharge most rapidly while the muscle is being stretched and less rapidly during sustained stretch. 
  5. The nerves from the primary endings on the nuclear chain fibers show a static responseQ; ie, they discharge at an increased rate throughout the period when a muscle is stretched. Thus, the primary endings respond to both changes in length and changes in the rate of stretch.
  6. Stretching of spindle activates the α motor neuron via Ia & II afferents leading to muscle contraction.

Functions of Muscle spindle:

  1. Sensing and Maintaining normal muscle length (By Length servo and Follow up servo mechanism)
  2. Stretch Reflex
  3. Muscle tone (Due to Gamma efferent discharge)
  4. Body Posture (Postural reflex at spinal cord level)
  5. So both stretch and length are functions of muscle spindle but the primary function is maintenance of length.

Test Your Skills Now!
Take a Quiz now
Reviewer Name