Reflex Arc Components

Most reflex arcs have five main components: receptors, sensory neurons, interneurons, motor neurons and muscles. Not all reflexes use interneurons. Some connect sensory neurons directly to motor neurons and do not use interneurons.

Neurons have special proteins in their membrane called receptors. Receptors respond to signals in the environment. Some receptors respond to pressure. When the cell is compressed, the receptors are activated, letting your brain know something is pressing on your skin or organs. Other receptors respond to pain or to chemical stimuli, like smells or tastes. Sensory receptors in your ears respond to vibrations in the air that we interpret as sound, and receptors in your eyes respond to light.

Sensory neurons are the cells that contain sensory receptors. They send information from the body to the central nervous system, the brain and spinal cord. These cells are activated when the receptor gets a signal from the environment. The activated sensory neuron extends into the spinal cord, sending an electrical signal all the way to another neuron, the interneuron.

Interneurons are like the middleman of the nervous system. They connect sensory input to other cells that are required for action. In a reflex arc, the sensory neuron sends a signal to the interneuron and activates it. The interneuron then relays that signal to the next neuron, a motor neuron.

Reflex arcs that impact the organs are called autonomic reflex arcs while those that affect the muscles are referred to as somatic reflex arcs.

NEXT: Autonomic Afferent Fibers & Reflex Arcs

USMLE Reviewer (By Subscription)