afferent

(adjective)

The conduction of impulses inwards to the brain or spinal cord.

Related Terms

(noun)

Afferent neurons convey information from tissues and organs into the central nervous system (e.g. sensory neurons).

Related Terms

Examples of afferent in the following topics:

  • Autonomic Reflexes

    • Autonomic reflexes are unconscious motor reflexes relayed from organs and glands to the CNS through visceral afferent signaling.
    • In these cases, the body will interpret the afferent pain stimulus as somatic.
    • General visceral afferent sensations are mostly unconscious visceral motor reflex sensations from hollow organs and glands that are transmitted to the CNS (see for a depiction of a typical nerve fiber, including general visceral afferent fibers).
    • The pain is also usually referred to dermatomes that are at the same spinal nerve level as the visceral afferent synapse.
    • This schematic (but not anatomically correct) depiction of a typical spinal nerve indicates (1) somatic efferent fibers, (2) somatic afferent fibers, (3-5) sympathetic efferent fibers, and (6,7) sympathetic afferent fibers.

  • Vestibulocochlear (VIII) Nerve

    • Processes from the organ of Corti (the receptor organ for hearing) conduct afferent transmission to the spiral ganglia.
    • It is the inner hair cells of the organ of Corti that are responsible for activation of afferent receptors in response to pressure waves reaching the basilar membrane through the transduction of sound.
    • Hair cells of the cristae activate afferent receptors in response to rotational acceleration.
    • Hair cells of the maculae activate afferent receptors in response to linear acceleration.

  • Vagus (X) Nerve

    • Eighty to 90% of the nerve fibers in the vagus nerve are afferent (sensory) nerves communicating the state of the viscera to the brain.
    • The solitary nucleus - Receives afferent taste information and primary afferents from visceral organs.
    • It also has some afferent fibers that innervate the inner (canal) portion of the outer ear, via the auricular branch (also known as Alderman's nerve) and part of the meninges.
    • In addition, 5-HT3 receptor-mediated afferent vagus stimulation in the gut due to gastroenteritis and other insults is a cause of vomiting.

  • Glossopharyngeal (IX) Nerve

    • Visceral sensory (general visceral afferent) - carries visceral sensory information from the carotid sinus and body.
    • General sensory (general somatic afferent) - provides general sensory information from the skin of the external ear, internal surface of the tympanic membrane, upper pharynx, and the posterior 1/3 of the tongue.
    • Special sensory (special afferent) - provides taste sensation from the posterior 1/3 of the tongue.

  • Autonomic Nervous System (ANS)

    • In the gastrointestinal system, an example of an afferent subsystem would be the neurons that detect levels of stomach acid, while an efferent subsystem would be the motor neurons that control the undulation of the intestines.
    • With regard to function, the ANS is usually divided into sensory (afferent) and motor (efferent) subsystems.
    • Numerous afferent sensory fibers innervate the gut.
    • Eighty percent of the fibers in the vagus nerve are afferent and these send signals to the medulla for processing.

  • Classification of Nerves

    • Mixed nerves: contain both afferent and efferent axons, and thus conduct both incoming sensory information and outgoing muscle commands in the same nerve bundle.
    • These nerve fibers are associated with acute pain and therefore constitute the afferent portion of the reflex arc that results in pulling away from noxious stimuli. 
    • Schematic of efferent and afferent nerve transmission to and from peripheral tissue and spinal cord.

  • Pons

    • The alar plate produces sensory neuroblasts, which will give rise to the solitary nucleus and its special visceral afferent column, the cochlear and vestibular nuclei (which form the special somatic afferent fibers of the vestibulocochlear nerve), the spinal and principal trigeminal nerve nuclei (which form the general somatic afferent column of the trigeminal nerve), and the pontine nuclei, which is involved in motor activity.

  • Parasympathetic (Craniosacral) Division

    • The sensory root carries general sensory fibers (general somatic afferent fibers) that also do not synapse in the ganglion.
    • Some ganglia also carry special sensory fibers (special visceral afferent) for taste sensation.

  • Classification of Receptors by Location

    • The sensory endings of a primary (group Ia) afferent and a secondary (group II) afferent coil around the non-contractile central portions of the intrafusal fibers.

  • Glomerular Filtration

    • Blood plasma enters the afferent arteriole and flows into the glomerulus, a cluster of intertwined capillaries.
    • Diagram showing the afferent and efferent arterioles bringing blood in and out of the Bowman's capsule, a cup-like sac at the beginning of the tubular component of a nephron.