Effector

Peripheral tissue at the outer end of an efferent neural path (one leading away from the central nervous system).

An effector acts in special ways in response to a nerve impulse. In humans, effectors may either be muscles, which contract in response to neural stimuli, or glands, which produce secretions. The muscles are generally divided into two groupings: somatic effectors, which are the body's striated muscles (such as those found in the arm and back), and autonomic effectors, which are smooth muscles (such as the iris of the eye).

Both types of effectors are linked to the gray matter of the spinal cord, but each system originates in a different portion of it. The somatic effectors, which are responsible for powerful motor movements, are linked to the ventral horn cell, a large neuron in the ventral portion of the gray matter. The autonomic effectors receive impulses from the lateral part of the gray matter. The smooth muscles that are supplied by these effectors maintain the tone of blood vessels walls, thus helping to regulate blood pressure. Glandular secretions controlled by autonomic effectors include external secretions, such as sweat, and internal ones, such as the hormone epinephrine secreted by the adrenal medulla of the brain . Some nerve fibers that connect with autonomic effectors also pass through the ventral roots of the spinal nerves by way of a ganglion located outside the spinal cord and are then distributed to smooth muscles and glands.

Further Reading

ABC's of the Human Mind. Pleasantville, NY: Reader's Digest Association, 1990.

effector (inducer) In the operon theory of gene regulation, a chemical substance that is able to render a repressor inactive by combining with it, thus permitting the messenger-RNA for a particular enzyme to be produced.

effector Any structure (e.g. gland, muscle, electric organ, stinging cell, or pigment cell) that responds to a stimulus directly or indirectly. The nervous system controls most effectors.

effector (i-fek-ter) n. any structure or agent that brings about activity in a muscle or gland. The term is also used for the muscle or gland itself.

effector A cell or organ that produces a physiological response when stimulated by a nerve impulse. Examples include muscles and glands.