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What Is the Difference between Afferent and Efferent?
The brain is made up of many neurons that communicate with each other. Communication between afferent and efferent neurons occurs in the form of electrochemical signals. The nervous system receives signals from afferent nerve fibers and then sends signals via efferent nerve fibers to either other areas of the nervous system or to organs in the body, such as a gland or muscle. Signaling between afferent and efferent neurons occurs through interneurons.
One of the most common types of neuron in the central nervous system is the multipolar neuron. This type of neuron consists of the soma, or cell body, an axon, and three or more dendrites. The soma is the largest part of the neuron and is where many different processes occur. Attached to the cell body are dendrites, which receive signals from other neurons, and a long axon that separates into a few branches. Located on these branches are terminal buttons which send signals and form synapses with other neurons.
Surrounding the axon of a neuron is a cell membrane that is electrically charged. When the electrical charge of the axon is reversed relative to the outside of the cell membrane, a signal is carried from the cell body, down the axon, to the terminal buttons. This change in electrical charge is called an action potential. Communication between afferent and efferent neurons or nerves fibers is able to occur because of this process.
The neurotransmitter then binds to receptors that are located on the cell membrane of the neighboring neuron called the postsynaptic neuron, which forms a synapse. A synapse is a conjunction between a terminal button on one neuron to the cell membrane of a neighboring neuron. This allows for neurons to communicate with each other. Communication between afferent and efferent neurons occurs in this way via interneurons located entirely in the central nervous system.
Different areas in the nervous system receive signals from afferent neurons. Afferent neurons that are able to respond to physiological changes or that are connected directly with sensory receptors are called sensory neurons. This type of neuron recognizes internal and external environmental changes and sends information about these changes to the central nervous system. Efferent neurons send signals from the central nervous system to either other areas in the nervous system or to muscles or glands. These neurons are called motor neurons and, when an action potential moves down its axon, it results in a muscle twitch.
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![A synapse is a conjunction between a terminal button on one neuron to the cell membrane of a neighboring neuron.]()
By: ThorstenSchmittA synapse is a conjunction between a terminal button on one neuron to the cell membrane of a neighboring neuron. -
![Nerve cells are also called neurons.]()
By: kateryna zakorkoNerve cells are also called neurons. -
![Heat and pain are all transmitted by afferent neurons.]()
By: doble.dHeat and pain are all transmitted by afferent neurons. -
![Our bodies contain trillions of synapse "data" connections, many of which are constantly active.]()
By: rolffimagesOur bodies contain trillions of synapse "data" connections, many of which are constantly active.
Discussion Comments
@burcinc-- That's a great analogy! Another way to remember the difference is to look at the first letter. Afferent starts with A which comes before efferent's first letter E in the alphabet. For our brain to respond to something, first a message has to come to it right? So the afferent neuron comes first. It brings the message and then the brain responds with the efferent neurons which come second.
This is how I studied for my exams and it really helped me remember.
Sometimes I wonder if there is a problem with my afferent neurons. I read somewhere that these two neurons are what allows us to realize that we are hurt and do something about it.
For example, when we touch something hot and it burns our hand, the cells in our hand send a message that we are getting burned to our brain with the help of afferent neurons. Then, the brain sends a message back with efferent neurons to pull our hand away to avoid burning it more.
What happens to me a lot is that I will touch something hot, like the side of the pan when I'm frying foods and realize that I'm getting burned. But the reaction to pull my hand away doesn't seem to come so quickly. I basically stare at my hand getting burned for a couple of seconds until I pull it away. I think that's weird. It seems like my afferent neurons work just fine but the efferent neurons are a little slow.
My professor told me a great simple analogy to explain the difference between afferent and efferent neurons.
He told me to think of both as one way streets in opposite directions. If we imagine our cerebral cortex (central nervous system) to be an urban center, then we can say that efferent neurons are the roads that take you from the urban center to the outskirts of the city and surrounding towns (a.k.a. different body parts). Afferent neurons are the roads that start out from the outskirts and lead to the urban center.
So one takes messages from the cerebral cortex to different organs and one brings back messages from the different organs to the cerebral cortex. So easy right?
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