Neurones and synapses 6.5 30'

This topic covers neurones and synapses. Get to grips with the structure of a neuron, the propagation of action potentials along a neuron and the transmission of electrical impulses across a synapse. There is also a specific look at cholinergic synapses and neonicotinoid pesticides.

Key words 

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Clean sweep - quick revision through the whole topic

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They contain short explanations in text and images - good revision for all students.

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Video tutorial

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Revision summary list for 6.5 Neurones and synapses

  • Electrical impulses are transmitted in Neurones. (details of neuron types not required)
  • Sodium and potassium ions are pumped across neuron membranes to generate a resting potential.
  • Action potentials are depolarization and repolarization of the neuron which are propagated along the axons of neurons creating nerve impulses. (oscilloscope traces showing resting potential & action potential.)
  • Local currents cause each successive part of the axon to reach the threshold potential.
  • Myelin sheath cells around the axons of nerve fibres allows for saltatory conduction.
  • Synapses (only chemical synapses) join neurons and also join neurons to receptor or effector cells.
  • Depolarized pre-synaptic neurons release a neurotransmitter into the synapse.
  • A nerve impulse is only initiated if the threshold potential is reached.


  • Understand that secretion and reabsorption of acetylcholine by neurons occurs at synapses.
  • Illustrate how blocking of synaptic transmission at cholinergic synapses in insects by the binding of neonicotinoid pesticides to acetylcholine receptors can work as a pesticide.
  • Outline how the workings of neurotransmitters and synapses has led to the development of numerous pharmaceuticals for the treatment of mental disorders.

Revision mind map

This diagram summaries the main sections of topic 6.5.
Test if you can draw something like these concept maps from memory.


Review questions

A quiz containing at least ten questions covering the ten skills outlined in the image above:


How do nerve impulses travel in the nervous system?

Although neurones release chemical neurotransmitters at their endings they actually transmit electrical impulses along their length. This is caused by movement of charged ions across the membrane, but these ions don't move along the neurone.


How is the resting potential created in a neurone?

Sodium potassium pumps are found in the membrane of neurones.
They pump ions across the membrane against a concentration gradient leading to an electrical charge across the membrane called the resting potential.


Which of the following statements is the best description of an action potential?

A nerve impulse is the spreading of an action potential along a neurone. The action potential is the polarization and then depolarization of the nerve cell membrane. This spreads along the axon creating a nerve impuslse.


The diagram shows parts of two neurones at a synapse.

The red dots show a neurotransmitter being released into the synaptic cleft.

Which of the statements below best describes what usually happens to the neurotransmitter molecules after their release?

Neurotransmitters diffuse across the synaptic cleft and bind to receptors in post synaptic neurones.

After this they can be broken down by enzymes before reabsorption by the presynaptic neurone.


Which structure in the nervous system allows the rapid "saltatory conduction" of impulses?

Saltatory conduction is only possible because of the myelination of the nerve axon with its nodes of ranvier.


Curare is used by indigenous peoples of the Americas on their poison darts. It causes muscle relaxation and hunted animals to fall out of trees. Curare is known to inhibit neurotransmitter receptors (acetylcholine) in the nervous system.

Why does this cause relaxation of muscles?

The acetylcholine must be released into the muscle to cause a contraction of the muscle.

Curare inhibits the receptor molecules on muscle cells

This can cause muscle relaxation.


A type of pesticide called "neonicotinoid" interacts with the synapses that use the neurotransmitter acetylcholine.

The diagram illustrates this interaction.

Which of the following statements correctly explains the reason why neonicotinoid pesticides disturb nervous control in insects.

The neonicotinoid molecules bind to the receptor molecules on the post synaptic membrane, this prevents neurotransmitter molecules from binding, it also constantly stimulates the post synaptic neurone.

The neonicotinoid is not broken down by naturally occuring enzymes in the insects so this disturbs the synapses.


The diagram below shows part of the propagation of a nerve impulse.

Which type of protein is the one labelled X which has ions passing through it at this stage?

Depolarisation is caused by sodium (Na+) ions moding across the membrane into the neurone. Repolarisation occurs when the potassium ions move out of the memebrane.


What is the term used to describe the movement of ions which depolarizes and repolarizes a small part of the axon of a neurone during the propagation of an impulse.

Propagation of nerve impulses is the result of local currents of ions.
The movements cause each successive part of the axon to depolarize.


The diagram shows the voltage measured across the neurone membrane during a nerve impulse.

What causes the voltage to return to below -70mV at point 3 on the graph?

The depolarisation occuse when sodium channels open letting Na+ ions into the neurone (2).
The voltage rises to about +50mV.

This causes the opening of potassium channels which allow the K+ ions to leave the neurone (3),
reducing the + charge in the neurone. Called repolarisation.

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Revision fun activity

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