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Types of Neurons: Sensory, Afferent, Motor, Efferent & More

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  • 1:05 Afferent Neurons
  • 2:15 Efferent Neurons
  • 3:11 Interneurons and…
  • 4:00 Sensory Neuron
  • 5:17 Motor Neurons
  • 5:48 Lesson Summary
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Lesson Transcript
Instructor: Artem Cheprasov
There are many types of neurons in your body that help you see, smell, hear, and move. In this lesson, you'll learn more about afferent, efferent, sensory, and motor neurons.

Smelling and Throwing Away Our Dirty Socks

If you've come across a dirty sock, you not only got to experience one of the worst smells in the world, but you probably threw the sock as far away from yourself as possible in order to avoid the smell. What you did, smell the sock and then throw it far away, involved quite a bit more than you probably think about at any given time.

You first had to sense an unpleasant odor through your nose. After your nose guided you to the smelly sock laying on the couch, you were able to visualize it as well. Once you combined your visual stimulation with that of the smell, you realized it was best to get rid of the sock. You initiated a series of hand and leg movements, which then resulted in you throwing the sock as far away as possible.

All of this smelling and moving about involves certain types of special nerve cells that send signals to and from your brain in order to recognize the smelly sock and throw it away.

Afferent Neurons

Afferent neurons sense stimuli and send information to the brain.
Afferent Neurons

When you first smelled the sock, you were able to send signals up to your brain which registered inside of the brain as a certain type of smell. The nerves responsible for sensing a stimulus and sending information about the stimulus to your central nervous system are called afferent neurons. As your stinky sock lay there, it gave off tiny chemical particles that went up into the air around you.

These chemicals then went up your nose and landed on receptors that recognized them. The recognition of the chemical by the receptor triggered it to send signals up to your brain via the afferent neurons. These afferent neurons therefore relayed information about the chemicals, and hence smell, to your brain.

Likewise, when you saw the sock, particles of light hit your eye. The light triggered receptors in your eye to send signals up to your brain via afferent neurons. The brain then collected all the different signals coming from the eye to form a picture of the dirty sock.

Efferent Neurons

Once you smelled the sock and visualized where it was located, it was time to get rid of it as quickly as possible! Your brain was able to process the sight and smell of the sock. Once it was in your sights, it initiated several signals which let your muscles know that you should walk over to the couch, pick up the sock, and throw the sock as far away as possible.

The nerves that carry signals away from the central nervous system in order to initiate an action are called efferent neurons. Hence, when you decided it was time to walk over to the sock to throw it away, the brain sent signals via efferent neurons to your muscles in order to tell them where to walk and how fast to do it. Then, the brain sent signals via efferent neurons to your arms, which were told to get moving to pick up and throw away the sock as quickly as possible!

Interneurons and Association Neurons

The afferent and efferent neurons are usually not long enough to go from, say, your big toe all the way up to your brain. Therefore, afferent and efferent neurons use a neuron which forms a connection between two or more neurons that we synonymously call an interneuron or association neuron. This is the most abundant type of neuron in your body.

An afferent neuron will rely on an association neuron to help transmit signals to the brain.
Association Neuron Diagram

An afferent neuron located in your skin, for example, will use an interneuron to help relay its signal to the brain. Likewise, an efferent neuron leaving your brain will often connect to an interneuron in order to have its signal reach its destination. Many times, interneurons connect an afferent neuron with an efferent neuron as well.

Sensory Neurons

Just like the fact that the word interneuron has a synonym we call an association neuron, so it is the case with afferent and efferent neurons.

Our afferent neurons, if you recall, are the nerves in our body which send signals to the central nervous system about the information they have gathered. Because the afferent neurons sense information, we call them sensory neurons.

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