Human beings respond to their environment in a pretty similar way as other animals do. The nervous system of human beings controls these responses with the outer world. This is a complex system comprising millions of neurons. The function of these neurons can be classified into two major types:
- Bringing the stimuli from the peripheral organ to the central nervous system
- Carrying the responses from the central nervous system to the peripheral organs.
What Goes On Inside the Nervous System?
Before we proceed to the comparison between afferent vs. efferent neurons, it is imperative that we gain some insight into the processing of impulses by the nervous system. This system comprises a closed loop of neurons, which deal with sensation, decision, and reaction. Whenever an impulse or a 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.
Difference Between Afferent and Efferent Neurons
» The axon of afferent neurons extends in both directions, with the peripheral axon directing towards the receptor organ, with the central axon passing into the spinal cord. Although dendrites are structurally and functionally identical to axons, they are myelinated. The cell body in afferent neurons is perfectly rounded and smooth.
» 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.
» Afferent neurons are also called sensory neurons, as they mostly carry impulses from sensory organs. They are classified as pseudounipolar neurons with a single long dendrite and a short axon.
» Efferent neurons are also called motor neurons, as they mostly carry responses to the muscles or glands and bring about movement.
» The aggregation of afferent neurons can be found in a swelling called dorsal root ganglion, which is located just outside the spinal cord.
» The efferent neurons are present in the gray matter of spinal cord as well as medulla oblongata. These neurons form an electrochemical pathway towards the effector organ.
How Are they Different from Interneurons?
Afferent neurons are connected to efferent neurons via multipolar neurons called interneurons. Interneurons are also called relay, association, or local circuit neurons. Similar to efferent neurons, the cell bodies of interneurons are located inside the central nervous system. Interneurons vary greatly in their 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 and efferent neurons is that they perform an exactly contrasting function and follow an opposite electrochemical pathway in the central nervous system loop.