Reflexes Health Article

Definition

Reflexes are the body's automatic reaction to some type of sensory stimuli. They involve nerve impulses passing from a receptor to a nerve center and then outward to, for example, a nerve or a gland.

Description

Reflexes are classified as unconditioned and conditioned.

Unconditioned reflexes

Unlike most human behaviors, unconditioned reflexes occur without specific learning or experience. They are considered involuntary acts, because a response occurs automatically when a stimulus (for example, a pinprick) takes place.

Unconditioned reflexes that protect us from harm are called nociceptive reflexes. For example, sneezing, coughing, and gagging are automatic responses to foreign bodies in the nose and throat. Eye blinking or winking helps protect the eye from harm. Reacting quickly to touching a hot stove is yet another example of a nociceptive reflex.

Most reflex acts are very complicated. However, in simple reflexes four events are involved: reception, conduction, transmission, and response. The stimulation is received by receptors, or sensitive nerve endings. These may be in the eye, ear, nose, tongue, or skin. Energy from the stimulus is changed into nerve impulses and conducted from the receptor to the central nervous system. From there, the nerve impulses are transmitted to the motor nerves, which control muscle action. The motor nerves conduct the impulses to the muscles and glands, causing them to respond or act. For example, touching a hot stove stimulates receptors in the skin of the finger. This creates a nerve impulse that travels along a sensory nerve to the spinal cord. In the spinal cord, the sensory nerve fibers interlace with motor nerve fibers. The nerve impulse passes from the sensory fibers to the motor fibers, which relay it to the muscles, causing them to contract. When the muscles contract, the person's hand jerks back.

People have many reflex reactions to such emotional stimuli as anger or fear, including changes in blood pressure and respiration. Lie detectors measure specific physical reactions to emotional stimuli.