Difference Between Reflexes And Reflex Arcs
In some cases when receptor organs are stimulated, there is an involuntary muscular contraction or glandular secretion, known as a reflex. The impulse that results from such stimulation is carried to the central nervous system—to the spinal cord or to the brain by way of the spinal cord—and is transmitted to a muscle or a gland. The complete path of the impulse is called the reflex arc.
A reflex arc consists of three parts: (1) the afferent limb or receptor organ (the eye, say, or the ear or the skin) that gives rise to the impulse, and the neuron that carries the impulse to the central nervous system; (2) the reflex center in the gray matter of the central nervous system, made up of the axon of the afferent neuron and its junction with the cell body of the efferent neuron; (3) the efferent limb—the efferent neuron and its branches—which carries impulses from the central nervous system to a muscle or gland.
There are several kinds of reflexes. The knee jerk, a short twitch of the knee extensor muscle, is caused when one taps the tendon at the kneecap. The biceps jerk is produced when the biceps tendon is tapped. Muscle tonus is the continuous partial contraction of the muscles that maintain good posture.
Certain reflexes represent inherited connections and characteristics. These do not depend upon personal experience. They are called unconditioned reflexes. Conditioned reflexes are based in part upon previous experience. For instance, when food enters your mouth, it stimulates various nerve fibers, leading to secretion of saliva from the salivary glands. This secretion represents an unconditioned reflex. There are times, however, when the secretion of saliva is a conditioned reflex: when you see and smell an appetizing dish, for instance. Since you associate the appearance and odor with the food’s taste, you begin to secrete saliva before the food enters your mouth. In this case the secretion represents a conditioned reflex. Conditioned reflexes vary in different individuals.