5.7 Neurotransmitters

Introduction

Neurons communicate with each other at junctions called synapses. But how does a signal cross the gap between two neurons? This is where neurotransmitters come in. Neurotransmitters are chemical messengers that carry signals from one neuron to the next. This topic explains what neurotransmitters are, how they work, and why they are important.

Definition

Neurotransmitters are chemical messengers. Their function is to carry chemical signals or "messages" from one neuron to the next target cell.

Main Idea

• Neurotransmitters are located in the axon terminal.
• They are stored within thin-walled sacs called synaptic vesicles.
• Each vesicle can contain thousands of neurotransmitter molecules.
• As a message or signal travels along a nerve cell, the electrical charge of the signal causes the vesicles of neurotransmitters to fuse with the nerve cell membrane at the very edge of the cell.
• The neurotransmitters, which now carry the message, are then released from the axon terminal into a fluid-filled space that's between one nerve cell and the next target cell.
• Each type of neurotransmitter lands on and binds to a specific receptor on the target cell.
• After binding, the neurotransmitter then triggers a change or action in the target cell, like an electrical signal in another nerve cell, a muscle contraction or the release of hormones from a cell in a gland.
• Examples of neurotransmitters are: epinephrine and norepinephrine, glycine and serotonin.

Core Concept

How Neurotransmitters Work

Detailed Explanation

1. What are Neurotransmitters?

Neurotransmitters are chemical messengers. Their function is to carry chemical signals or "messages" from one neuron to the next target cell.

Simple explanation: Neurotransmitters are like chemical letters that carry messages from one neuron to another.

Why they are important:

• They allow communication between neurons.
• They allow communication between neurons and muscles.
• They allow communication between neurons and glands.

2. Location of Neurotransmitters

Neurotransmitters are located in the axon terminal.

They are stored within thin-walled sacs called synaptic vesicles.

Each vesicle can contain thousands of neurotransmitter molecules.

Simple explanation: Neurotransmitters are stored in tiny bags called synaptic vesicles at the end of the axon.

3. Release of Neurotransmitters

As a message or signal travels along a nerve cell, the electrical charge of the signal causes the vesicles of neurotransmitters to fuse with the nerve cell membrane at the very edge of the cell.

The neurotransmitters, which now carry the message, are then released from the axon terminal into a fluid-filled space that's between one nerve cell and the next target cell.

Simple explanation: When the nerve impulse reaches the end of the axon, it causes the vesicles to burst open and release neurotransmitters into the gap (synaptic cleft).

4. Binding to Receptors

Each type of neurotransmitter lands on and binds to a specific receptor on the target cell.

After binding, the neurotransmitter then triggers a change or action in the target cell.

Examples of changes or actions:

• An electrical signal in another nerve cell.
• A muscle contraction.
• The release of hormones from a cell in a gland.

Simple explanation: Neurotransmitters are like keys that fit into specific locks (receptors) on the target cell. When they bind, they cause a response.

5. Examples of Neurotransmitters

Examples of neurotransmitters are:

• Epinephrine (adrenaline)
• Norepinephrine (noradrenaline)
• Glycine
• Serotonin

Simple explanation: These are some of the chemicals that carry messages in the nervous system.

6. Do You Know?

After neurotransmitters deliver their message, the molecules must be cleared from the synaptic cleft. They do this in one of three ways:

Simple explanation: After neurotransmitters deliver their message, they are removed from the synapse. This prevents continuous stimulation.

Why this is important:

• It allows the synapse to reset.
• It prevents overstimulation of the target cell.

Intermediate Level

Neurotransmitters are chemical messengers that carry signals from one neuron to the next target cell.

Key points:

• Neurotransmitters are stored in synaptic vesicles.
• Each vesicle contains thousands of neurotransmitter molecules.
• Neurotransmitters are released into the synaptic cleft.
• They bind to specific receptors on the target cell.
• Binding triggers a change or action in the target cell.
• After delivery, neurotransmitters are cleared from the synaptic cleft.

Important Points

• - Neurotransmitters are chemical messengers.
• - Their function is to carry chemical signals or "messages" from one neuron to the next target cell.
• - Neurotransmitters are located in the axon terminal.
• - They are stored within thin-walled sacs called synaptic vesicles.
• - Each vesicle can contain thousands of neurotransmitter molecules.
• - As a message or signal travels along a nerve cell, the electrical charge of the signal causes the vesicles of neurotransmitters to fuse with the nerve cell membrane.
• - The neurotransmitters are then released from the axon terminal into a fluid-filled space between one nerve cell and the next target cell.
• - Each type of neurotransmitter lands on and binds to a specific receptor on the target cell.
• - After binding, the neurotransmitter triggers a change or action in the target cell.
• - Examples of neurotransmitters are: epinephrine and norepinephrine, glycine and serotonin.
• - After neurotransmitters deliver their message, the molecules must be cleared from the synaptic cleft.
• - They do this in one of three ways: diffusion, reuptake, or degradation.

Remember

• - Neurotransmitters = chemical messengers
• - Location = axon terminal
• - Storage = synaptic vesicles
• - Release = fuse with presynaptic membrane
• - Action = bind to receptors on postsynaptic membrane
• - Examples = epinephrine, norepinephrine, glycine, serotonin
• - Removal = diffusion, reuptake, degradation
• - Function = carry signals from one neuron to the next target cell

Common Mistakes

• 1. Thinking neurotransmitters are electrical signals.
• - Neurotransmitters are chemical messengers. The signal becomes electrical again in the postsynaptic neuron.
• 2. Confusing synaptic vesicles and neurotransmitters.
• - Synaptic vesicles = sacs that store neurotransmitters.
• - Neurotransmitters = chemical messengers.
• 3. Forgetting the role of receptors.
• - Neurotransmitters bind to specific receptors on the target cell.
• 4. Mixing up the methods of removal.
• - Diffusion = fade away.
• - Reuptake = reabsorbed by presynaptic neuron.
• - Degradation = broken down by enzymes.
• 5. Thinking neurotransmitters act on all cells.
• - Neurotransmitters bind only to specific receptors on target cells.
• 6. Believing neurotransmitters stay in the synaptic cleft forever.
• - Neurotransmitters are removed by diffusion, reuptake, or degradation.
• 7. Confusing excitatory and inhibitory neurotransmitters.
• - Excitatory = stimulate the postsynaptic neuron.
• - Inhibitory = inhibit the postsynaptic neuron.

Quick Revision

60-Second Revision

• Neurotransmitters = chemical messengers
• Location = axon terminal
• Storage = synaptic vesicles
• Release = fuse with presynaptic membrane
• Action = bind to receptors on postsynaptic membrane
• Examples = epinephrine, norepinephrine, glycine, serotonin
• Removal = diffusion, reuptake, degradation
• Function = carry signals from one neuron to the next target cell
• Warning: Do not confuse neurotransmitters (chemical messengers) with nerve impulses (electrical signals). Neurotransmitters carry the signal across the synapse.