Afferent vs efferent–If you’ve ever looked up a word in the dictionary only to find that it has more than one meaning, you know the frustration of trying to figure out which definition is appropriate. For instance, a website might say “afferent” means “leading into” and then define it as “being or running towards.” Another site might define afferent as “carrying material inwards,” while another says that an afferent nerve is a nerve from the brain or spinal cord that carries impulses away from the body. For our purposes, however, all that is relevant. We are concerned about the “afferent” meaning: what does it mean when people use it to describe a nerve or a nerve impulse?
And lastly, an afferent nerve impulse travels from one part of the body to another aspect, whereas an efferent nerve impulse goes in the opposite direction.
The internet contains many interesting articles that describe and compare afferent vs efferent nerve impulses. However, we won’t jump directly into all that here. Instead, we’ll explain the nerve impulse first. That’s because some significant pieces of information sometimes get left out of the discussion of afferent vs efferent nerve impulses. Let’s begin by looking at the basic definition of the nerve impulse.
Nerve Impulses
Nerve impulses consist of three parts. The stimulus of the nerve is called the action potential. The substance that conducts the message of the action potential is called a neurotransmitter. And finally, once that neurotransmitter reaches its target, it converts into a chemical that affects an organ or series of organs, namely, its effector organs.
Now, without further ado, let’s find out the difference between afferent vs efferent …
Afferent vs Efferent Impulses
So if the terms “afferent” and “efferent” sound familiar to you, then chances are, you’ve already taken an introductory biology class about afferent vs efferent. And if you haven’t had a basic biology class yet, then perhaps it’s time to do that (for yourself). However, if you’re not a student or if you’ve forgotten what that was all about, then let us first give you a quick and simple overview.
These nerves’ function in the body largely determines the difference between afferent and efferent. Our previous post mentioned that afferent and efferent come from the root word “fer”—which means “to carry” in Latin. So with this in mind, we can easily see the difference between them based on their roles in either sending or receiving messages.
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Afferent vs efferent impulses- Definition
The difference in afferent vs efferent nerves is primarily based on where the nerves originate from. Efferent nerves are motor neurons, while afferent nerves are sensory neurons. The former carries impulses to various body parts from the central nervous system (brain and spinal cord), while the latter maintains impulses to the cerebral cortex (or central nervous system).
So basically, afferent nerves carry impulses from the body as they carry impulses to the cerebral cortex. In comparison, efferent nerves carry impulses towards other parts of the body.
Essentially, afferent nerves carry signals to the central nervous system, while efferent nerves carry signals from the central nervous system. They do this by interconnecting neurons that run between one part of the nervous system and another.
Now for a more in-depth look at each type of nerve…
Afferent vs efferent impulses – Afferent Nerves
Afferent nerves are involved in the receipt and perception of sensory signals. These nerves carry signals from the body to the central nervous system. Their presence in our body is entirely necessary to make sure that we can perceive, recognize, react and respond to our environment. In this regard, they’re called sensory nerves because they rely on sensations, and sensations are the only way humans can recognize their surroundings since we can’t see them.
So when you see a picture, hear a sound, feel pain, smell something good, taste something sweet or feel the cold breeze, your sensory nerves are working for you. Not only that, but they’re also working to connect and communicate with the brain. With its connection to the brain (or central nervous system), it sends signals from the body to the brain and vice versa. This is how the brain can process all of the senses that it receives.
But for the signals to be recognized by both the central nervous system and sensory neurons, they must undergo a process known as transduction. This is when an electrical impulse in one cell causes another cell to release a chemical that’s then absorbed by sensory neurons. This is when the chemical (or neurotransmitter) that was released is converted into an electrical impulse. Then, this impulse is sent to the central nervous system by way of efferent nerves. From there, it undergoes a process known as decapsulation.
Afferent vs efferent impulses – Efferent Nerves
In contrast, efferent nerves carry impulses away from the central nervous system and other parts of the body. They have nerve impulses to muscles for movement, organs for involuntary actions, and glands for hormonal secretions.
So once the central nervous system receives a signal from a sensory neuron, it then sends it to an efferent nerve utilizing transduction. Then, this efferent nerve takes the signal and converts it into an electrical impulse. This is what’s known as decapsulation. This is the process that turns the chemical in the sensory neuron into electrical stimulation.
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So once the signal has been converted into an electrical impulse, it then starts its journey towards organs or motor nerves. The impulses travel from these sensory nerves and finally reach various parts of your body. From there, they’re able to make multiple changes in your muscles or involuntary actions. This is how our muscles and other parts of our body can react to outside stimuli.
Afferent vs efferent impulses- Speed
The speed at which a nerve impulse travels is determined by its length and the number of impulses in that nerve. A longer nerve impulse will travel at a faster speed than a shorter impulse and vice versa. The rate of an efferent nerve is approximately ten times slower than that of an afferent nerve.
Afferent vs efferent impulses- Duration
Nerve impulses are described as being very short or long, measured in milliseconds (ms). There is only a 0.05 ms difference in duration afferent vs efferent nerve impulses; the afferent one lasts for 0.5 ms.
Now, the critical thing to know about afferent vs efferent nerves is that they’re very intertwined. So much so that you can’t talk about one without having to talk about the other. For example, when talking about movement, you can’t mention efferent neurons in your limbs without mentioning sensory neurons since they’re the ones that receive input from outside stimuli. Likewise, sensory neurons without efferent nerves are useless. This is because efferent neurons only begin to work once the sensory signal “to move” is sent to the brain via afferent nerves.
So as you can see, sensory and motor neurons work in tandem with one another. If you can understand the afferent vs efferent nerves, you’ll improve your overall understanding of the nervous system.
