Difference Between Afferent and Efferent

Main Difference – Afferent vs Efferent

Afferent and efferent neurons connect the central nervous system (CNS) to produce a signal transmission pathway, which coordinates functions in the body. The CNS is composed of the brain and the spinal cord. Both afferent and efferent neurons belong to the peripheral nervous system (PNS). Afferent neurons are also known as sensory neurons, and efferent neurons are also known as motor neurons. However, the effect (stimuli and the responses) of sensory and motor neurons are slightly different from that of afferent and efferent neurons. Sensual perceptions of the body are eye, nose, ear, tongue, and skin. The information gathered from these sensory perceptions are respectively light, smell, noise, taste, and touch. The effector organs can be various groups of muscles and fibers, glands, and organs. The main difference between afferent and efferent is that afferent refers to the neurons carrying signals from sensory perceptions towards the CNS while efferent refers to the neurons carrying signals from the CNS to the effector organs.

Key Areas Covered

1. What is Afferent Neuron
      – Definition, Features, Function
2. What is Efferent Neuron
      – Definition, Types, Features, Function
3. What are the Similarities Between Afferent and Efferent
      – Outline Of Common Features
4. What is the Difference Between Afferent and Efferent
      – Comparison of Key Differences

Key Terms: Afferent Neurons, Axon, Cell Body, Central Nervous System (CNS), Dendron, Efferent Neurons, Motor Neurons, Peripheral Nervous System (PNS), Sensory Neurons

What is Afferent Neuron

The neurons, which carry sensory impulses towards the CNS are referred to as afferent neurons. The afferent neurons convert external stimuli into internal electrical impulse. The nerve impulse travels along the afferent nerve fibers to the CNS. The cell body of the afferent neuron is located in the dorsal ganglia of the spinal cord.

The afferent neurons gather information from sensory perceptions such as light, smell, taste, touch, and hearing, respectively, from the eye, nose, tongue, skin, and ear. The sensory signals of light are gathered from the rod and cone cells in the retina of the eye, and those nerve impulses are carried to the brain by the afferent neurons of the eye. The afferent neurons in the nose are stimulated by different odors, and nerve impulses are sent to the brain. The taste buds in the tongue gather sensory information about different tastes and the nerve impulses are carried to the brain by the afferent nerves of the tongue. The mechanical stimuli such as touch, pressure, stretch, and temperature are detected by the skin, and the nerve signals are sent to the brain by the afferent neurons. The afferent neurons of the ear are stimulated by different wavelengths within the sensible range to each animal, and the nerve impulses are carried to the brain. All sensory signals are processed in the brain, and the brain coordinates the relevant organs for a specific response. The structure of the afferent and efferent neurons are shown in figure 1.

Figure 1: Afferent and Efferent Neurons

What is Efferent Neuron

The neurons which carry motor impulses away from the CNS are referred to as efferent neurons. The efferent neurons carry information from the CNS to the effector organs, facilitating muscle contraction and secretion of substances from glands. The cell body of the efferent neuron is connected to a single large axon, which forms neuromuscular junctions with the effector organs. Two types of motor neurons are found: upper motor neurons and lower motor neurons. There are also three types of efferent neurons known as somatic efferent neurons, general visceral efferent neurons, and special visceral efferent neurons. The two types of somatic efferent neurons are alpha motor neurons and beta motor neurons. The involvement of afferent, efferent, sensory, and motor neurons in the exterior digitorium reflex is shown in figure 2.

Figure 2: Exterior Digitorium Reflex

Similarities Between Afferent and Efferent

• Afferent and efferent neurons belong to the peripheral nervous system.
• Both neurons help the brain in the coordination of sensory stimuli with their responses.
• Both neurons are composed of a cell body, dendrons, and dendrites.

Difference Between Afferent and Efferent

Definition

Afferent: Afferent neurons are the neurons that carry sensory impulses towards the CNS.

Efferent: Efferent neurons are the neurons that carry motor impulses away from the CNS.

Known as

Afferent: Afferent neurons are also known as sensory neurons.

Efferent: Efferent neurons are also known as motor neurons.

Function

Afferent: Afferent neurons carry signal from sensory organs to the CNS.

Efferent: Efferent neurons carry signal from the CNS to effector organs and tissues.

Axon

Afferent: Afferent neurons consist of a short axon.

Efferent: Efferent neurons consist of a long axon.

Receptor

Afferent: Afferent neurons consist of a receptor.

Efferent: Efferent neurons lack a receptor.

Cell Body

Afferent: Cell body of the afferent neuron is situated in the dorsal root ganglion of the spinal cord and no dendrites are found in it.

Efferent: Cell body of the efferent neuron is situated in the ventral root ganglion of the spinal cord and consists of dendrites.

Dendrons

Afferent: Afferent neuron consists of one long dendron.

Efferent: Efferent neuron consists of many short dendrons.

Function

Afferent: Afferent neurons carry signals from the outer part of the body into the central nervous system.

Efferent: Efferent neurons carry signals from the central nervous system to the outer parts of the body.

Multipolar/Unipolar

Afferent: Afferent neurons are unipolar.

Efferent: Efferent neurons are multipolar.

Found in

Afferent: Afferent neurons are found in skin, eyes, ears, tongue, and nose.

Efferent: Efferent neurons are mainly found in muscles and glands.   

Conclusion

Afferent and efferent neurons are two components of the peripheral nervous system. Afferent neurons carry information from sensory organs towards the CNS. CNS coordinates the stimuli with relevant responses. The response of the CNS to a particular stimulus is sent to the effector organs such as glands, organs, and tissues by efferent neurons. Thus, the main difference between afferent and efferent neurons is their role in coordinating stimuli and responses in the body.

Reference:

1.” Afferent Neurons.” Afferent Neurons definition | Psychology Glossary. N.p., n.d. Web.Available here. 02 July 2017. 
2. “Efferent Neurons.” Psychology Glossary. N.p., n.d. Web. Available here. 02 July 2017. 
3. “Types of Neurons: Sensory, Afferent, Motor, Efferent & More.” Study.com. N.p., n.d. Web. Available here. 02 July 2017.

Image Courtesy:

1. “Afferent (PSF)” By Pearson Scott Foresman – Archives of Pearson Scott Foresman. This file has been extracted from another file: Afferent (PSF).jpg ( Public Domain) via Commons Wikimedia
2. “The extensor digitorum reflex” By Zhang MJ, Zhu CZ, Duan ZM, Niu X.Department of Cardiology, Second Affiliated Hospital, School of Medicine, Xi’an Jiao Tong University, China. [email protected] – (CC BY-SA 4.0) via Commons Wikimedia

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