Difference Between Efferent and Afferent

source: http://www.buzzle.com/articles/afferent-vs-efferent.html
Human beings respond to their environment in pretty similar way as other animals. Human nervous system controls these responses with the outer world. Human nervous system is a complex system comprising of millions of neurons. The function of these neurons can be classified into two major types, firstly bringing the stimuli from the peripheral organ to the central nervous system and second carrying the responses from the central nervous system to the peripheral organs. Afferent and efferent neurons are the two types of nerve fibers which perform these functions. Let us understand in detail the comparison between afferent vs efferent neurons. More on central nervous system function.

Difference Between Afferent and Efferent Neurons

Before we proceed to the comparison between afferent vs efferent neurons it is imperative that we gain some insight upon the processing of impulses by the nervous system. Nervous system comprises of a closed loop of neurons which deal which sensation, decision and reaction. Whenever an impulse or stimuli is received by a receptor organ, it is carried to the brain for processing. A decision is made regarding the impulse which is again carried back to the receptor organ. Depending upon this decision a reaction to the impulse is produced by the receptor organ. Three types of neurons take part in this entire cycle, namely afferent, interneurons and efferent neurons. Afferent neurons are concerned with carrying the impulse from the receptor organ towards the brain, whereas efferent neurons carry the response of the brain back to the receptor organ. Both these neurons communicate with each other through the medium of interneurons. More on organs of the nervous system.

Afferent neurons are also called as sensory neurons as they mostly carry impulses from sensory organs. Afferent neurons are classified as pseudounipolar neurons with a single long dendrite and a short axon. The axon extends in both directions, with peripheral axon directing towards the receptor organ, whereas central axon passing into the spinal cord. Although, dendrites are structurally and functionally identically to axons, they are myelinated. The cell body in afferent neurons is perfectly rounded and smooth. The aggregation of afferent neurons can be found in a swelling called dorsal root ganglion, which is located just outside the spinal cord. More on anatomy of central nervous system.

Efferent neurons are also called as motor neurons as they mostly carry responses to the muscles or glands and bring about movement. Efferent neurons are bipolar with dendrite on one end and axon on the other. The cell body is connected at one end to a single long axon while several dendrites form the other end of the cell body. The cell body in efferent neurons is satellite shaped. The impulse enters the cell body via several dendrites and then leaves it through the single axon at the other end. The efferent neurons are present in the gray matter of spinal cord as well as medulla oblongata. The efferent neuron forms an electrochemical pathway towards the effector organ.

Afferent neurons are connected to efferent neurons via multipolar neurons called interneurons. Interneurons are also called as relay neuron, association neuron or local circuit neuron. Similar to efferent neurons, the cell bodies of interneurons are located inside the central nervous system. Interneurons vary greatly in structure and function. Hence, it is impossible to predict the types of interneurons present in the central nervous system. It is estimated that human brain contains about 100 billion interneurons with an average of 1000 synapses, on each interneuron.

The most important point of comparison between afferent vs efferent neurons is that they perform an exactly opposite function and follow an opposite electrochemical pathway in the central nervous system loop.
By Florentyna K
Published: 5/26/2010

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