Afferent nerve
Encyclopedia
In the nervous system
, afferent neurons (otherwise known as sensory
or receptor neuron
s), carry nerve impulses
from receptor
s or sense organs towards the central nervous system
. This term can also be used to describe relative connections between structures. Afferent neurons communicate with specialized interneuron
s. The opposite activity of direction or flow is efferent.
In the nervous system there is a "closed loop" system of sensation, decision, and reactions. This process is carried out through the activity of afferent neurons, interneurons, and efferent neurons.
A touch or pain
ful stimulus
, for example, creates a sensation in the brain only after information about the stimulus travels there via afferent nerve pathways. Afferent neurons are pseudounipolar neurons, that have a single long dendrite
and a short axon
, and a smooth and rounded cell body
. The dendrite is structurally and functionally similar to an axon, and is myelin
ated; it is these axon-like dendrites that make up the afferent nerves. Just outside the spinal cord
, thousands of afferent neuronal cell bodies are aggregated in a swelling in the dorsal root
known as the dorsal root ganglion
.
participle afferentem (af- = ad- : to + ferre : bear, carry), meaning carrying into.
Ad and ex give an easy mnemonic device for remembering the relationship between afferent and efferent : afferent connection arrives and an efferent connection exits.
Another mnemonic device is SAME DAVE. Sensory Afferent Motor Efferent, Dorsal Afferent Ventral Efferent.
Nervous system
The nervous system is an organ system containing a network of specialized cells called neurons that coordinate the actions of an animal and transmit signals between different parts of its body. In most animals the nervous system consists of two parts, central and peripheral. The central nervous...
, afferent neurons (otherwise known as sensory
Sensory neuron
Sensory neurons are typically classified as the neurons responsible for converting external stimuli from the environment into internal stimuli. They are activated by sensory input , and send projections into the central nervous system that convey sensory information to the brain or spinal cord...
or receptor neuron
Neuron
A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...
s), carry nerve impulses
Action potential
In physiology, an action potential is a short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls, following a consistent trajectory. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and...
from receptor
Receptor (biochemistry)
In biochemistry, a receptor is a molecule found on the surface of a cell, which receives specific chemical signals from neighbouring cells or the wider environment within an organism...
s or sense organs towards the central nervous system
Central nervous system
The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...
. This term can also be used to describe relative connections between structures. Afferent neurons communicate with specialized interneuron
Interneuron
An interneuron is a multipolar neuron which connects afferent neurons and efferent neurons in neural pathways...
s. The opposite activity of direction or flow is efferent.
In the nervous system there is a "closed loop" system of sensation, decision, and reactions. This process is carried out through the activity of afferent neurons, interneurons, and efferent neurons.
A touch or pain
Pain
Pain is an unpleasant sensation often caused by intense or damaging stimuli such as stubbing a toe, burning a finger, putting iodine on a cut, and bumping the "funny bone."...
ful stimulus
Stimulus (physiology)
In physiology, a stimulus is a detectable change in the internal or external environment. The ability of an organism or organ to respond to external stimuli is called sensitivity....
, for example, creates a sensation in the brain only after information about the stimulus travels there via afferent nerve pathways. Afferent neurons are pseudounipolar neurons, that have a single long dendrite
Dendrite
Dendrites are the branched projections of a neuron that act to conduct the electrochemical stimulation received from other neural cells to the cell body, or soma, of the neuron from which the dendrites project...
and a short axon
Axon
An axon is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neuron's cell body or soma....
, and a smooth and rounded cell body
Soma (biology)
The soma , or perikaryon , or cyton, is the bulbous end of a neuron, containing the cell nucleus. The word "soma" comes from the Greek σῶμα, meaning "body"; the soma of a neuron is often called the "cell body"...
. The dendrite is structurally and functionally similar to an axon, and is myelin
Myelin
Myelin is a dielectric material that forms a layer, the myelin sheath, usually around only the axon of a neuron. It is essential for the proper functioning of the nervous system. Myelin is an outgrowth of a type of glial cell. The production of the myelin sheath is called myelination...
ated; it is these axon-like dendrites that make up the afferent nerves. Just outside the spinal cord
Spinal cord
The spinal cord is a long, thin, tubular bundle of nervous tissue and support cells that extends from the brain . The brain and spinal cord together make up the central nervous system...
, thousands of afferent neuronal cell bodies are aggregated in a swelling in the dorsal root
Dorsal root
In anatomy and neurology, the dorsal root is the afferentsensory root of a spinal nerve.At the distal end of the dorsal root is the dorsal root ganglion, which contains the neuron cell bodies of the nerve fibres conveyed by the root.If the dorsal root of a spinal nerve were severed it would lead...
known as the dorsal root ganglion
Dorsal root ganglion
In anatomy and neuroscience, a dorsal root ganglion is a nodule on a dorsal root that contains cell bodies of neurons in afferent spinal nerves.-Unique unipolar structure:...
.
Etymology and mnemonics
Afferent is derived from LatinLatin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
participle afferentem (af- = ad- : to + ferre : bear, carry), meaning carrying into.
Ad and ex give an easy mnemonic device for remembering the relationship between afferent and efferent : afferent connection arrives and an efferent connection exits.
Another mnemonic device is SAME DAVE. Sensory Afferent Motor Efferent, Dorsal Afferent Ventral Efferent.
External links
- Sensory receptor neurons, a dynamic list of Petilla convention aligned sensory neurons at NeuroLexNeuroLexNeuroLex is a dynamic lexicon of neuroscience concepts. It is a structured as a semantic wiki, using Semantic MediaWiki. NeuroLex is supported by the Neuroscience Information Framework project.- Overview :...
.