Reflex Arc
A reflex arc is a chain of sensory, intercalary and motor neurons along which a nerve impulse passes for a specific reflex.
The reflex arc begins with receptors that perceive a stimulus from the external or internal environment. From the receptors, the nerve impulse travels through sensory neurons to the spinal cord or brain. There, the impulse is switched to interneurons, which carry it further to motor neurons. Through motor neurons, the impulse travels to the effector - muscle or gland, causing their contraction or secretion.
Thus, the reflex arc provides a quick and stereotypical reaction of the body to irritation, which does not require conscious control. This allows the body to quickly respond to changes in the external and internal environment.