Types of Neurons

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Neurons are the cells in our body that are responsible for transmitting electrical signals through the nervous system. The ability to move or feel the world around us all starts as an impulse sent by a neuron. This process helps us see, taste, touch, and move. In order to instantly facilitate these bodily processes, highly specialized neurons are used to transmit these signals and coordinate the body.

Read on to learn about the different types of neurons in the body and how they help us function.

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Types of Neurons

There are many different types of neurons, and they all have special functions in the brain, spinal cord, and muscles that control our body. These different types of neurons are highly specialized. Some neurons are responsible for taste while others sense pain.

Traditionally, scientists classify neurons based on function into three broad types:

  • Sensory
  • Motor
  • Interneurons

Scientists also classify neurons into four groups based on structural differences:

  • Multipolar
  • Unipolar
  • Bipolar
  • Pseudo-unipolar

Although almost any neuron falls into one of these broad categories, these seven groups are only a subset of all the neurons within the nervous system. Categorizing neurons helps us to simplify how they work and better understand their role in the body.

Sensory Neurons

Sensory neurons help us feel and explore the world around us. Major senses such as touch and pain can help us to move safely through the world.

Pain is an example of an important sensory neuron. When you feel pain from a hot pan or a sharp pin, you are sending sensory information via sensory neurons up to the brain. The flow of electrical impulses is directed from the source of the pain along nerve fibers that connect to sensory neurons.

Sensory neurons are critical for informing our body about the environment around us. They can relay information on temperature and teach us when to avoid a hot items. Sensory neurons can also support complex movements like picking up utensils.

The sensory neurons provide feedback to our muscles and joints to enable precise and carefully choreographed movements.

Motor Neurons

Motor neurons control the movement of the body. These neurons coordinate our muscles and ensure that our arms and legs move together.

Motor neurons can be subdivided into lower motor neurons and upper motor neurons located in the brain and spinal cord. The differences between upper and lower motor neurons involve the level of control each exerts over functions of the body.

Differentiating movements based on upper and lower neurons is commonly used by healthcare providers to describe types of neurological disorders.

How Motor Neurons Work in Practice

Think of the process of standing up from a chair. Your brain tells the motor neurons in your legs to activate. Next your motor neurons send instructions to the muscles controlling your legs to rise up. Finally, you might press your arms against the arms of the chair to provide an additional lift.

This series of movements is entirely controlled by the activity of motor neurons. Impressively, it can all happen without much thought at all. The motor neurons work in concert with your muscles to move the body seamlessly through space.

Interneurons

Interneurons are the most abundant neurons in the body. They act as the signal controllers within the body, relaying important information from one end of the nervous system to the other.

The interneurons sit in the middle of other neurons, such as motor or sensory neurons. They are responsible for relaying electrical signals.

Interneurons can also serve to regulate the signals from neurons. They can control what is sent along and what isn't. They have a multipolar structure that allows them to receive multiple signals and then send a unified command to another neuron. In this way, you can think of interneurons as traffic controllers, sitting in the middle of the neurologic pathway and coordinating the flow of information.

Interneurons and Depression

Interneurons are thought to play an important role in signal transmission in the brain, where they have been linked to depression.

Neuronal Anatomy

Neurons are the basic cellular unit of the nervous system. Neurons have different components that play integral roles in their ability to receive and transmit signals through the body.

The most important components of the neuron are:

  • Cell body: In the cell body, neurons store genetic material and produce energy to function.
  • Axon: Axons are responsible for conducting electrical signals. They need to respond and provide information quickly. However, they can stretch for meters and meters. To overcome this issue, the body has developed clever ways to produce rapid electrical transmission via a specialized structure called myelin. Myelinated neurons can communicate rapidly and are 10 times faster than neurons without myelin.
  • Synapse: The synapse is the portion of the neuron where information is received. The synapse is composed of small receivers, called dendrites, that pick up signals and then relay them to the axon.

In addition to the billions of neurons within the nervous system, there are a host of supportive cells, called glial cells, that regulate neuronal activity. The glia are responsible for cleaning out waste and debris from neurons, as well as responding to inflammation and invaders like viruses and bacteria.

While glia do not directly regulate signal transmission in the nervous system, increasing research has shown that they play an important role in healthy nervous system function.

Types of neurons based on structure include:

  • Unipolar neurons: These neurons have a single long axon that is responsible for sending electrical signals. The axon in unipolar neurons is myelinated, which allows for rapid signal transmission.
  • Multipolar neurons: These neurons are able to receive impulses from multiple neurons via dendrites. The dendrites transmit the signals through the neuron via an electrical signal that is spread down the axon.
  • Bipolar neurons: These neurons send signals and receive information from the world. Examples include the neurons in the eye that receive light and then transmit signals to the brain.
  • Pseudo-unipolar neurons: These neurons relay signals from the skin and muscles to the spinal cord. They are the primary neurons responsible for coordinating movement of the arms and legs using input from the brain.

Summary

Neurons are responsible for transmitting signals throughout the body, a process that allows us to move and exist in the world around us. Different types of neurons include sensory, motor, and interneurons, as well as structurally-based neurons, which include unipolar, multipolar, bipolar, and pseudo-unipolar neurons. These cells coordinate bodily functions and movement so quickly, we don't even notice it happening.

A Word From Verywell

Neurons and their various complexities can seem like a daunting topic to understand. However, knowing that distinct types of neurons play different roles within the body can help you develop a basic understanding of the nervous system's structure. Understanding the types of neurons and how they affect the body can provide an explanation for different disorders of the nervous system, from traumatic spinal cord injuries to neurodegenerative diseases.

Frequently Asked Questions

  • What are the most common types of neurons?

    The most common neuron types are sensory neurons, motor neurons, and interneurons. Of these, the interneurons are the most abundant neuron.

  • Which neurons carry impulses away from the central nervous system?

    Efferent neurons help carry signals from the brain and central nervous system (CNS) to the muscles and skin. The efferent neurons are responsible for control of the body.

  • Are neurons replaced throughout life?

    Some neurons, such as those located in the peripheral nervous system, can slowly regenerate and repair themselves. However, neurons located in the brain and spinal cord are not able to heal or regenerate. For this reason, specific injuries to the nervous system are permanent, such as spinal cord injuries. In some cases, neuronal plasticity within the brain can lead to healthy neurons picking up the job or function of other neurons that have been damaged.

  • Which neurons are myelinated?

    Most neurons that carry signals regarding movement and higher-level functions, such as thinking and reading, are myelinated. In contrast, the neurons that control the feelings of pain and temperature are sometimes myelinated and sometimes not. Non-myelinated neurons transmit electrical signals more slowly than the myelinated nerves in the body.

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