QS Study

Involuntary motor response due to any sensory stimulus is called the reflex action. When a person accidentally touches a hot object, they automatically jerk their hand away without thinking. A reflex does not require any thought input. The function or action occurs immediately, without the involvement of the will or consciousness.

Properties of reflex action

  1. Reflex delay
  2. Summation: Spatial and Temporal,
  3. Subliminal fringe,
  4. Occlusion,
  5. Fatigue,
  6. Facilitation,
  7. Fractionation,
  8. Recruitment,
  9. Reciprocal innervations,
  10. Rebound phenomenon
  11. Irradiation,
  12. Inhibition,
  13. After discharge.


Application of a number of subminimal stimuli produces sufficient Excitatory Postsynaptic Potential (EPSP) to induce the motor neuron to discharge impulse and produce reflex action. This is called summation. It is of two types-

(1) Temporal summation: If rapid and repetitive stimuli are applied to the same pool one after another, adequate EPSP is produced which cause reflex action. This is called temporal summation.

(2) Spatial summation: Here the sub-minimal stimuli are applied simultaneously note on the same spot but at different point of the body.


When a reflex action is produced by the simultaneous stimulation of two afferent nerve, the total tension (T) in the muscle is less than the sumtotal tension (t1 + t2) set up is the same muscle by stimulating two nerves separately i.e., T (t1 + t2).

Here, T = total tension developed due to simultaneous stimulus.

(t1 + t2) – tension developed due to stimulating two nerve separately.

Fig: a and b are separate paths each including several neurons c is the common motor path

Cause: Occurs due to some neurons remain common to both afferent nerve.

Subliminal fringe:

It is opposite to the occlusion, the total tension (t1 + t2) due to separate stimulation is less than the amount of contraction (T) simultaneous stimulation.

Here the stimulus is subthreshold i.e., T > (t1 + t2)

Here, T = total tension developed due to simultaneous stimulation on two afferent nerve.

t1 & t2 = tension developed due to separate stimulation of two afferent nerves.

Fig.: Phenomenon of Subliminal fringe

Cause: During separate stimulation, the impulse becomes adequate for some neurons and inadequate for others. But during simultaneous stimulation, the impulse summated and becomes stronger.