Axon Hillock: Definition & Function

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  • 0:00 What is an Axon Hillock?
  • 0:49 The Function of Neurons
  • 3:19 Function of the Axon Hillock
  • 5:49 Lesson Summary
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Lesson Transcript
Instructor: Jay Mallonee

Jay is a wildlife biologist, college professor and writer. His master's degree is in neurobiology and he has studied animal behavior since 1976.

All neurons can produce chemical impulses and have within them an axon hillock that decides if the impulse will be produced or not. Learn how this dynamic processing center uses incoming signals from other neurons to make its decision.

What is an Axon Hillock?

Imagine for a moment that you are one of many departmental managers at a large business. Each department deals with something different, such as payroll or legal issues. The employees under your supervision are responsible for receiving information from other departments and even other businesses and then sending this input to you. Your function is to arrive at a consensus, then decide whether or not to send your decision throughout the business's hierarchy.

Neurons use a similar process to propagate their chemical impulses down the line. As a departmental manager, you would be the axon hillock in this system, since the axon hillock is the area that controls the initiation of the neuron's chemical impulse after processing the incoming signals from other neurons.

The Function of Neurons

Your nervous system is composed of many kinds of nerve cells, which can be grouped into two major classifications: glia and neurons. Glia provide physical support for surrounding nerve cells, along with supplying nutrients and removing waste products. Neurons are specialized nerve cells that have the ability to transmit impulses. They interconnect to form circuitry in your brain that creates memories and allows you to think. In other words, neurons process information based on the impulses they transmit.

A typical neuron has a cell body like any other cell; however, it also has extensions radiating outward from it. Some are called dendrites, and they receive nerve impulses from other neurons. Usually there are many of them, and they allow information (impulses) from numerous neurons to enter the cell body all at once. Now the neuron needs to generate an impulse of its own to continue the 'message' forward throughout the circuitry.

Given all the information it receives, how does the neuron know when to send a signal? The axon hillock decides. It resides in the area of the neuron that connects the cell body with the axon.

Neurons only have one axon, which is the extension that allows nerve impulses to move away from the cell body and toward other nerve cells. The axon then communicates with the dendrites or the cell body of the next neuron. However, axons do not make direct contact with these structures, and instead just get real close. The resulting gap between structures is called the synapse. Synapses are often named by their location. For example, those that only communicate with cell bodies are called axosomatic, meaning 'axo' for axon and 'somatic' for cell body.

When the nerve impulse reaches the end of the axon, it stimulates the release of neurotransmitters. These molecules float across the synapse and are specialized to fit into receptor sites on the dendrites or cell bodies of other neurons. Receptor sites are areas that are shaped to accept only one kind of chemical or molecule - in this case a neurotransmitter. This is similar to a lock that only accepts one kind of key. When the neurotransmitter connects with its appropriate receptor site, this unlocks or sets into motion a new chemical impulse in the next neuron. However, impulses don't occur whenever they want. They're regulated.

Function of the Axon Hillock

The axon hillock is a unique area within neurons because of its ability to process the incoming signals from other cells. To understand how this works, let's look at what a chemical impulse really is.

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