Q. What is meant by the arch reflex?

In some situations the movement of the skeletal striated muscles does not depend upon commands of the superior motor neurons that it is not triggered by volition.

Involuntary movements of those muscles may happen when sensory fibers that make indirect or direct connection with inferior motor neurons are unexpectedly stimulated in situations that suggest danger to the body. This happens, for instance, in the knee jerk reflex or patellar reflex when a sudden percussion on the knee patella (kneecap) triggers an involuntary contraction of the quadriceps (the extension muscle of the thigh). Another instance of the arch reflex occurs when someone steps on a sharp object: one leg retracts and the other by the arch reflex distends to maintain the equilibrium of the body.