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

Artem has a doctor of veterinary medicine degree.

Expert Contributor
Amanda Robb

Amanda holds a Masters in Science from Tufts Medical School in Cellular and Molecular Physiology. She has taught high school Biology and Physics for 8 years.

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.

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Additional Activities

A Neuron Comic Strip

In this activity, students will draw a short comic strip that shows the pathway of information for carrying out an activity of their choice, such as kicking a ball, or reading a word on a page. To help students choose an activity, point them towards something where you need to sense your environment, then carry out an action. This is called a sensory motor pathway and will use all the types of neurons they read about. Each box in their comic should have a picture and a short description.

Example:

For example, a student might choose kicking a ball. They can draw the first box with a sensory neurons, because sensory neurons in your eyes must see the ball. The second box would have the sensory neuron connecting to an interneuron to send the information to the brain. Then, another interneuron might connect to a motor neuron. In the fourth box, the motor neuron would connect to the muscle. Then, in the last box the action is carried out, which is to kick the ball.

Student Directions:

In this activity you will be drawing a comic strip that shows the steps of an activity where you sense the environment, then carry out an action. Each box in your comic strip should have a picture and a description. Some activities you might choose are smelling a juicy hamburger and lifting it to take a bite, seeing a ball and kicking it, or hearing music and dancing. The activity you choose should start with sensory neurons and end with the action.

To help, check out this checklist for each one of the boxes in your comic.

Criteria For Success

  • Overall the comic includes all three types of neurons described in the lesson: sensory, interneurons and motor neurons.
  • Each comic box has a description and a picture.
  • Box 1: Describes the role of sensory neurons in detecting the environment.
  • Box 2: Describes sensory neurons connecting to interneurons.
  • Box 3: Describes interneurons connecting to motor neurons.
  • Box 4: Describes motor neurons connecting to muscle.
  • Box 5: Shows the action carried out by the muscle.

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