afferent

Afferent is an anatomical term describing structures or pathways that carry toward a central location, most commonly toward the central nervous system. The word derives from Latin ad- “toward” and ferre “to bear.” The term is commonly contrasted with efferent, which describes pathways that carry signals away from the CNS or a central structure.

In neuroscience, afferent refers to neurons and nerve fibers that convey sensory information from peripheral receptors to the CNS. Afferent neurons are typically sensory neurons with cell bodies in dorsal root ganglia (for spinal nerves) or in cranial nerve ganglia. Peripheral receptors include mechanoreceptors, nociceptors, thermoreceptors, chemoreceptors, and specialized receptors for vision and audition. Signals undergo transduction at the receptor and are transmitted via peripheral nerves to the spinal cord and brain, where they are processed and integrated.

Afferent information can be somatic, arising from skin, muscles, and joints, or visceral, arising from internal organs. Visceral afferents also convey physiologic status such as blood pressure and gut stretch, and some pathways convey pain through networks that may overlap with somatic routes in the CNS.

In other organ systems, the term afferent is used similarly. For example, in the kidney the afferent arteriole delivers blood to the glomerulus for filtration; changes in its diameter influence the glomerular filtration rate. In the lymphatic system, afferent lymphatics transport lymph toward lymph nodes.

Efferent denotes signals and fibers that exit the CNS or a structure to affectors like muscles or glands.