efferent

Efferent is a term used in biology to describe something that carries signals, substances, or flow away from a central point, typically away from the brain or spinal cord. It contrasts with afferent, which describes information or materials moving toward a central structure. The word has broad application across anatomy and physiology, including nervous, circulatory, and lymphatic systems.

In neuroanatomy, efferent pathways convey motor commands from the central nervous system to effectors such as muscles and glands. Efferent neurons include somatic motor neurons that control skeletal muscle and autonomic (visceral) efferents that regulate cardiac muscle, smooth muscle, and glandular activity. Autonomic efferents are organized into sympathetic and parasympathetic divisions, each employing distinct neurotransmitters and receptors to influence target organs.

In the circulatory system of the kidney, the term efferent arteriole refers to the small vessel that carries filtered blood away from the glomerulus toward peritubular capillaries and, in the loop of Henle, the vasa recta. The efferent arteriole helps determine filtration pressure and the kidney’s ability to concentrate urine. Similarly, in the lymphatic system, efferent lymphatic vessels drain lymph away from lymph nodes toward the venous circulation, in contrast to afferent vessels that bring lymph into nodes.

Other uses include concepts such as efference copy (or corollary discharge), a neural signal that predicts the sensory consequences of one’s own actions, aiding in motor control and perception. Overall, efferent emphasizes outward or outbound conveyance from a central source, complementing the inward pathway denoted by afferent.