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Neurotransmitters and Synapses

Neurotransmitters and Synapses

Description:

This lesson will define neurotransmitter, synapse, and receptor sites and explain their functions in neural impulses and types of neurotransmitters,

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Tutorial

What's Covered

The nervous system is essentially the body's communication system.  It allows information to be sent to and from the brain and allows us to control the rest of our body.    Basically, it allows us to send all all messages that allow us to do all the thing that constitute our mind and behavior.

In this tutorial you will learn about neurons, neurotransmitters, and synapses. Specifically you will focus on:

  1. Neurons
  2. Dendrites
  3. Axons

1. NEURONS

The nervous system is comprised of your brain and neurons, and all the nerves that extend throughout the body, acting as the body's communication system. It sends information to and from the brain, and allows you to control the rest of your body in different kinds of ways.

Think About It

How do those individual neurons-- the cells that make up your nervous system-- transmit that information, and create this kind of communication?

There are two different ways that a neuron communicates:

    • Within the neuron itself-- within one individual neuron
    • Between different neurons.

This tutorial will focus on the message being sent inside of one neuron.


2. DENDRITES

The process starts at the dendrites, which are the long, tree-like branches that extend from the cell body itself. What these dendrites do is they collect different kinds of messages from other neurons surrounding it.

However, it doesn't necessarily do anything until it reaches a certain level of messages. So one message doesn't cause it to communicate its information; iit has to be a combination of lots of them. This is what we call the "Threshold of Excitation." Which is to say, the level, or the point at which the neuron is caused to fire, or a neural impulse is triggered.


Term to Know

    • Threshold of Excitation
    • The level or point at which a neuron fires, or a neural impulse is triggered.

3. AXONS

Looking more closely at the axon, which is that tail like structure that extends off of the cell body, and acts as a sender or a transmitter of information.

You can see below that the axon is actually covered in all these tiny little holes or tunnels, or what are called "ion channels”.

What the ion channel does is allow the cell to control or pump the amount of ions, either inside of the cell, or outside of the cell. An ion is a positively or negatively charged atom.

Example When the cell pumps a certain amount of sodium (Na), outside of the cell, and potassium inside of the cell, these electrically charged ions create a charge across the entire axon. And at a resting potential, which is when a cell is not firing-- in other words, when it's sitting and it's waiting to fire, to send a message-- the sodium is generally concentrated outside of the cell. And at this point there is more potassium inside of the cell.


Term to Know

    • Resting Potential
    • The state in which a neuron is not firing or sending a neural impulse and when there is a negative electrical charge inside the neuron.

Step by Step

    1. A neuron receives a message from the dendrites-- enough to reach that threshold of excitation
    2. When it reaches that point at which it's going to fire, then the cell switches from a resting potential to an action potential.
    3. The neural impulse fires.
    4. Ion channels open, and sodium (NA), comes rushing inside of the cell
    5. Potassium comes outside of the cell afterwards.

The result is a positive charge inside the cell, and a negative charge outside of the cell. A domino effect happens, where these ion channels open up and create that switch of electrical charges. And then the ones next to it also throw themselves open, and send sodium and potassium outside and inside of the cells.

This domino effect continues to go all the way down the axon, until it reaches that axon terminal, that button at the very end of the cell (the end of the neurotransmitter below with circles and dots!).


When an axon fires (the neuron as a whole fires) it is an all-or-nothing reaction. Either it fires completely and throws open all of these ion channels, or doesn't fire at all.

Hint

The axon is like a light switch. On or off.

These neural impulses, these action potentials, can move very quickly. They are fast, but they're not necessarily instantaneous. This is why it takes a split second for us to react to something in our environment.

Between the axon and the dendrites of other neurons there is this space.  This space is called a '''synapse'''. There's an actual gap that occurs right between these different cells, which prevents the electrical impulse from jumping over to other cells.

Another way to communicate with those cells is needed. So instead, when that electrical impulse reaches the axon
terminal, it releases what are called neurotransmitters. And neurotransmitters are chemical messengers that
attach themselves to other dendrites of other neurons surrounding them. And this is helpful because it allows one
neuron to communicate with lots of different neurons by sending out all of these different chemical messengers.
So it's not just one-to-one, it could be one to potentially hundreds of neurons. 

Terms to Know

    • Action Potential
    • The state in which a neuron reaches its Threshold of Excitation and fires, or sends an electrical impulse down the axon.
    • Ion Channels
    • Small tunnels along a neuron that to pump ions from one side of the cellular membrane to the other, which creates an electrical charge.
    • Synapse
    • The small space between the axon terminal of one neuron and the dendrites of other neurons.

After this occurs, after all of this exciting action potential happens, the cell resets. Essentially the ion channels pump the potassium back inside the cell, and the sodium back outside of the cell. And it resets itself, and gets ready to fire again.

So it goes back to a resting potential, and that is how the information is sent. That electrical charge is created that goes all the way across a neuron, and gets ready to send information to other areas and other neurons that are attached to.


Summary

This tutorial discussed how messages are sent inside of one neuron. The nervous system is comprised of your brain and neurons, and dendrites collect different kinds of messages from other neurons surrounding it. You learned that axons act as a sender or a transmitter of information.

Good luck!

Source: This work is adapted from Sophia author Erick Taggart.

TERMS TO KNOW
  • Threshold of Excitation

    The level or point at which a neuron fires, or a neural impulse is triggered.

  • Neuropeptides

    A special class of neurotransmitters that regulate the activity of neurons and systems in the brain.

  • Acetylcholine

    The most common neurotransmitter, which is used in movement in the peripheral nervous system and related to attention and memory in the brain.

  • Receptor Sites

    Areas on neurons that connect and respond to neurotransmitters.

  • Neurotransmitter

    Chemical messengers that allow neurons to communicate with other neurons across the synapse.

  • Synapse

    The small space between the axon terminal of one neuron and the dendrites of other neurons.

  • Action Potential

    The state in which a neuron reaches its Threshold of Excitation and fires, or sends an electrical impulse down the axon.

  • Resting Potential

    The state in which a neuron is not firing or sending a neural impulse and when there is a negative electrical charge inside the neuron.