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Types of Neurons and Their Structure and Function

Anne Kamiya, Karen Schweitzer, Amanda Robb
  • Author
    Anne Kamiya

    Anne has experience in science research and writing. She has a graduate degree in nutrition (gut microbiome & nutritional microbiology) and undergraduate degrees in microbiology (immunology & medical microbiology) and English (myth & folklore). She has also worked as an ocean & Earth science educator.

  • Instructor
    Karen Schweitzer
  • Expert Contributor
    Amanda Robb

    Amanda has taught high school science for over 10 years. She has a Master's Degree in Cellular and Molecular Physiology from Tufts Medical School and a Master's of Teaching from Simmons College. She is also certified in secondary special education, biology, and physics in Massachusetts.

Learn about neurons and their parts. Explore the structure, function, and types of neurons, and discover how neurons transmit and receive information. Updated: 03/22/2022

What is a Neuron?

What is a neuron? The nervous system includes motor cells and sensory nerve cells called neurons that carry electrical signals back and forth from the body to the brain and within the brain. The nervous system includes the peripheral nervous system (PNS) which picks up sensory information from the environment, and the central nervous system (CNS), which is the brain and the spinal cord. The brain is made largely of neurons that store, receive, and transmit information. Neurons are so abundant that at birth a baby has more than 100 billion neurons in its brain and at least 100 trillion connections between those neurons develop as that baby grows into an adult. Neural impulses that travel along the axons of neurons in the form of electrical signals are called action potentials.

Neurotransmitters

Neurons are nerve cells that are constantly sending signals to your brain, muscles and glands. You have over 100 billion neurons in your brain sending signals. The signals help the different parts of your body communicate with each other. Thanks to neurons, you're able to swat a mosquito if you feel it land on your arm or wave to a friend if you see her walking towards you. Neurons send chemical signals called neurotransmitters, and they work quickly to help you react to everything going on around you.

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  • 0:00 Neurotransmitters
  • 0:36 Neuron Parts
  • 1:34 Action Potential
  • 3:05 Synaptic Gap
  • 3:56 Refractory Period
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What are the Parts of the Neuron?

The parts of a neuron include three major structures that allow it to receive, process, and transmit electrical signals. Neuron structure is very important for its function because neurons are specifically designed to transmit electrical signals from cell to cell.

  • The soma is the body of the neuron and is also sometimes called its cell body; this structure is where the cell's organelles and nucleus are located.
  • The dendrites are numerous branch-like structures that extend from the soma in different directions, picking up signals from other neurons.
  • The axon is a long, skinny stalk covered in a fatty insulator called myelin. The axon acts like a highway that charges and carries action potentials to the terminal end of the neuron where it can transmit that signal to the next neuron.


Structure of a neuron showing its dendrites, cell body (soma), nucleus, and axon. The far end of the axon is called the terminal end of the axon.

Structure of a neuron including soma, dendrites, and axon.


Dendrites Receive Input

Dendrites function to help a neuron receive chemical or electrical inputs from another neuron. If the inputs reach a certain threshold, an electrical signal is created and sent to the axon for transmission as an action potential.

Axons Transmit Output

Normal neuron function would not be possible without axons to transmit output. When an action potential is sent to the axon, it carries that signal to the terminal end of the axon, where the action potential is converted to outputs that communicate with dendrites on the next neuron.

How Does a Neuron Work?

Introduction: Neuron Network Structure

Neurons positioned next to each other form a complex network of interconnected cells. Action potentials are transmitted from one neuron to another in a chain-link of communicating neurons. The terminal end of one neuron's axon is called the pre-synaptic neuron. The dendrites sticking out of the next neuron are called the post-synaptic neurons. The pre-synaptic and post-synaptic neurons are positioned very close to each other but do not connect. Because this near connection means the two neurons do not actually touch each other, there is a small gap between them, which is called a synapse. There are two types of synapses in neurons: chemical synapses and electrical synapses.

  • Chemical synapse: There is a gap between the two neurons that cannot transmit an electrical signal. Communication between the two neurons takes place with chemical communication molecules called neurotransmitters. Neurotransmitters in a chemical synapse can tell the next neuron to fire or not fire an electrical signal. Most synapses are chemical synapses.
  • Electrical synapse: There is a gap between the two neurons, but gap junction proteins create tunnel-like structures that physically link the neurons together. An electrical synapse can only transmit an electrical signal and tell the next neuron to fire a signal.


Between two adjacent neurons is a small space where the two neurons do not touch each other, called a synapse.

Structure of a neuron next to another neuron and a space labeled a synapse.


Part I: Chemical Signal Input Received by the Post-synaptic Neuron (Dendrites)

Pre-synaptic neurons (terminal axons) release neurotransmitters into the synapse, which bind to receptors on the post-synaptic neurons (dendrites). If the chemical signals are excitatory and able to trigger a response, they are converted into electrical signals. Neurotransmitters function to either excite or inhibit the firing of the neuron. Some common neurotransmitters are serotonin, dopamine, and acetylcholine.

Part II: Firing Thresholds and the All-or-None Law

Before a neuron receives a chemical signal, it is at rest. A resting neuron is defined as one that is electrically polarized, with the inside of the cell more negatively charged (by -70mV) than the outside of the cell. In order for an action potential to be generated, the neuron must first depolarize, meaning the voltage difference must go down. Depolarization does not always cause a neuron to fire an action potential, because there is a certain degree of depolarization, called a threshold, required to trigger firing. In most cases, the threshold is -55mV. Whether or not a neuron fires when a signal is received all depends on whether the threshold is met. There is no in-between. The all-or-none law describes this binary outcome, where the neuron either fires or does not fire, depending on whether the threshold for firing an action potential is met.

Part III: Depolarization and the Refractory Period

So, how does depolarization occur? The post-synaptic neuron (dendrite) is covered in ion channels. These channels open or close depending on whether a neurotransmitter binds to them. For example, one type of neurotransmitter may bind to sodium ion channels in the post-synaptic neuron, causing the sodium ion channels to open. Sodium ions rush into the neuron, causing it to depolarize, meeting and then exceeding the threshold for firing an action potential. After the neuron fires, it goes through a rest period called the refractory period. During the refractory period, sodium ions that flooded the neuron during depolarization are pumped out into the extracellular space until the voltage difference is returned to the neuron's resting potential.

Neuron Parts

Think of these neurons as little baseball players throwing balls to each other. The baseballs are the chemical signals called neurotransmitters. So, when you see a ball flying through the air towards you, sensory neurons send signals to your brain. This sets off a chain reaction of signals, which are fired off to motor neurons that cause your muscles to react so you can catch the ball.

Now, let's take a journey inside the human body to see what happens when we see, hear or touch something. Neuron Garciaparra is warming up. He has dendrites, like catching arms, that receive signals. He also has a pitching arm that fires off signals. This pitching arm is called an axon. Like a pitcher's power sleeve, a myelin sheath covers the axon, or pitching arm, and boosts the speed at which Neuron can fire off signals. The terminal branches at the end of the axon make up the pitching hand. This is where Neuron fires off signals.

Action Potential

Here's how it works. When the signal (ball) comes in, it excites Neuron into action. Positively charged sodium ions begin to enter the cell membrane. There are sodium ions in sports drinks, so think of this process as Neuron drinking a sports drink to increase electrolytes like sodium ions. A neural impulse, or electric current, travels from the dendrites (catching arms) through the axon (pitching arm) to the terminal branches (pitching hand) to be fired off to another neuron. This process is called the action potential. Then he winds up his pitch and...BAM!...fires off the signal.

The all-or-none law states that, once the neuron receives the signal, it has to fire it off. Like a pitcher who winds up and starts delivering the pitch, the neuron can't balk. There's no stopping once the nerve impulse has been activated. But, if your neurons don't get the signal, they don't fire. So, you'll swat a mosquito only if you feel it land on your arm. Either you feel it and the neurons deliver the signals so you can react, or you don't.

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Video Transcript

Neurotransmitters

Neurons are nerve cells that are constantly sending signals to your brain, muscles and glands. You have over 100 billion neurons in your brain sending signals. The signals help the different parts of your body communicate with each other. Thanks to neurons, you're able to swat a mosquito if you feel it land on your arm or wave to a friend if you see her walking towards you. Neurons send chemical signals called neurotransmitters, and they work quickly to help you react to everything going on around you.

Neuron Parts

Think of these neurons as little baseball players throwing balls to each other. The baseballs are the chemical signals called neurotransmitters. So, when you see a ball flying through the air towards you, sensory neurons send signals to your brain. This sets off a chain reaction of signals, which are fired off to motor neurons that cause your muscles to react so you can catch the ball.

Now, let's take a journey inside the human body to see what happens when we see, hear or touch something. Neuron Garciaparra is warming up. He has dendrites, like catching arms, that receive signals. He also has a pitching arm that fires off signals. This pitching arm is called an axon. Like a pitcher's power sleeve, a myelin sheath covers the axon, or pitching arm, and boosts the speed at which Neuron can fire off signals. The terminal branches at the end of the axon make up the pitching hand. This is where Neuron fires off signals.

Action Potential

Here's how it works. When the signal (ball) comes in, it excites Neuron into action. Positively charged sodium ions begin to enter the cell membrane. There are sodium ions in sports drinks, so think of this process as Neuron drinking a sports drink to increase electrolytes like sodium ions. A neural impulse, or electric current, travels from the dendrites (catching arms) through the axon (pitching arm) to the terminal branches (pitching hand) to be fired off to another neuron. This process is called the action potential. Then he winds up his pitch and...BAM!...fires off the signal.

The all-or-none law states that, once the neuron receives the signal, it has to fire it off. Like a pitcher who winds up and starts delivering the pitch, the neuron can't balk. There's no stopping once the nerve impulse has been activated. But, if your neurons don't get the signal, they don't fire. So, you'll swat a mosquito only if you feel it land on your arm. Either you feel it and the neurons deliver the signals so you can react, or you don't.

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  • Activities
  • FAQs

Modeling Neurons

In this activity, students will be building their own model of a neuron that has all of the parts that were explained in the lesson. To complete this activity, it's best to have a good selection of craft supplies, such as pipe cleaners, clay, straws, glue, cardboard, beads, bottle caps, corks, glitter, or anything else you can imagine. The more materials students have to choose from the more creative they can be. For example,students might choose to use pipe cleaners to represent the dendrites of the neuron, and thick straws to create a long axon. To help students create their model, you can use academic sources for images of neurons, such as those from an encyclopedia or university.

Directions

In this activity, you'll be building a model of a neuron. Your neuron should use at least three different materials and have all of the parts described in the lesson:

  • Dendrites
  • Axon
  • Myelin
  • Synaptic gap
  • Neurotransmitters

Use the criteria for success below to ensure that your neuron has everything it needs. When you're done, show your model off to a friend and educate them about the parts of a neuron.

Criteria for Success

  • Model uses at least three different materials
  • Model includes all of the important parts of a neuron described in the lesson as listed above
  • Student can explain the parts of a neuron using their model

What are the parts of a neuron?

A neuron's main cell body is called a soma, which contains a nucleus, and other organelles like mitochondria. Dendrites are branchy extensions that come out of the soma and receive signal inputs from other neurons. The axon looks like a long stalk and transmits action potentials received by the dendrites along the neuron. When the terminal end of the axon is reached, a signal output is sent to the next connecting neuron via the synapse.

What are the three types of neurons?

The first type of neuron is a sensory neuron, which transmits sensory input from the environment, such as touch and taste, to the brain. The second type of neuron is a motor neuron, which send signals from the brain to the muscles, telling the muscles what to do. Interneurons are the third type of neurons, which connect to other neurons.

What is a simple definition of a neuron?

Nerve cells in the brain and body that transmit electrical signals are called neurons. There are billions of neurons in both the central nervous system (CNS) and peripheral nervous system (PNS).

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