Neurons and Synaptic Transmissions

What are neurones?

• neurones are nerve cells

• There are at least 100 billion neurones in the human nervous system

• 80% of neurones are located in the brain

What do neurones do?

* Transmit signals both electrically and chemically
* Provide the nervous system with it's primary means of communication
* Allow us to connect and communicate with our environment.

What are the different parts of a neurone and their jobs?

1. Dendrites - contain receptors, which receive signals
2. Cell body (soma) - includes the nucleus
3. Nucleus - contains the DNA of the cell
4. Axon - carries impulses away from the cell body, down the length of the neurone
5. Nodes of Ranvier - force electrical signals down the gaps along the axon
6. Myelin Sheath - membrane that covers and protects the axon. Aalso speeds up the electrical impulse
7. Schwann cell- maintains the PNS
8. Axon terminal buttons - communicate with the next neurone across the synapse and send the signal to another neurone, muscle or organ

Label each part of the neurone:

1. dendrites

2. cell body (soma)

3. axon

4. axon terminals

5. nucleus

6. nodes of fancier

7. myelin sheath

8. Schwann cell

What are the differences between dendrites and axon terminal buttons?

• Dendrites only contain receptors, so they can only receive signals

• Axon terminal buttons do not have receptors and only have terminals, so therefore, they can only send/release impulses

What are motor neurones?

Motor neurones carry signals from the Central Nervous System and send them to muscles, glands and organs

What are relay (interconnecting) neurones?

Relay neurones carry messages from one part of the CNS to another. They connect to motor and sensory neurones, passing messages between them. They only exist in the eyes, brain and spinal cord.

What are sensory neurones?

Sensory neurones receive information from the environment through one of the 5 senses, and relay it by sending the signal up to the CNS.

Identify the different neurons:

1. motor neuron

2. relay (interconnecting neuron)

3. sensory neuron

What is a synapse?

When two neurones connect with each other, it lives a synaptic gap known as a synapse.

Name the parts of the synapse

1. synaptic vesicles

2. axon terminal buttons

3. neurotransmitters

4. pre-synaptic terminal

5. synapse/synaptic gap

6. dendrites

7. receptor

8. post-synaptic receptor site

What are the 3 stages of synaptic transmission?

1. Pre-synaptic transmission

2. The synapse

3. Post-synaptic transmission

What occurs during pre-synaptic transmission?

In the pre-synaptic terminal, vesicles containing neurotransmitters are carried towards the axon terminal buttons to be released into the synapse. At this point the single is electrical

What occurs in the synapse?

Here, the vesicles are diffused into he synaptic gap and neurotransmitters are released into the synapse. At this point, the signal is converted into a chemical impulse.

What occurs during post-synaptic transmission?

During post-synaptic transmission, the dendrites containing receptors receive the signal. It is converted back into an electrical impulse, vesicles reform and the process of transmission starts again

What activates the neutron?

• when a neurone is in a resting state, the inside of the cell is negatively charged compared to the outside.

• when a neurone is activated by a stimulus, the inside of the cell becomes positively charged for a split second, causing an action potential to occur

• this causes an electrical impulse that travels down the axon towards the pre-synaptic terminal

What is excitatory transmission?

• neurotransmitters have either an excitatory or inhibitory effect on the neighbouring neurones.

• excitatory transmission occurs when a neurotransmitter increases the positive charge of the post-synaptic neurone.

• this increases the likelihood that the neurone will fire and pass on the electrical response.

What is inhibitory transmission?

• this occurs when a neurotransmitter increases the negative charge of the post-synaptic neurone.

• this then decreases the likelihood that the neurone will fire and pass on the electrical response.

What is summation?

• excitatory and inhibitory influences are summed and must reach a certain threshold in order for the action potential of the post-synaptic neurone to be triggered.

• if the net effect of the neurotransmitters is inhibitory then the post-synaptic neurone is less likely to fire

• it is more likely to fire if the net effect is excitatory

Excitation vs inhibition stimuli