A reflex arc is the basic functional unit of the nervous system which can perform an integrated neural activity. In its simplest form, that is a monosynaptic reflex, it is made up of:
- A receptor e.g. skin
- A sensory or afferent neuron
- A motor or efferent neuron
- An effector e.g. muscle.
The complex forms of reflex arc are polysynaptic due to addition of one or more interneurons in between the afferent and efferent neurons.
An involuntary motor response of the body is called a reflex action. The stretch reflexes (tendon jerks) are the examples of monosynaptic reflexes whereas the withdrawal reflex (response to a painful stimulus) is a polysynaptic reflex.