Synapses Bill Indge Synapses What happens at a

Synapses Bill Indge

Synapses What happens at a synapse? Impulse travels down the presynaptic neurone Neurotransmitter diffuses across synaptic cleft Action potential produced in postsynaptic neurone

Synapses Presynaptic neurone Vesicle containing neurotransmitter Voltage-gated calcium channel Synaptic cleft Postsynaptic neurone

Synapses 1 Action potential passes down presynaptic neurone 2 Calcium channels open and allow calcium ions to diffuse into the neurone

Synapses 3 Some of the vesicles fuse with the presynaptic membrane and release the neurotransmitter, acetylcholine, into the synaptic cleft

Synapses 4 Acetylcholine diffuses across synaptic cleft and binds to a ligand -gated sodium channel on the postsynaptic membrane

Synapses 5 Action potential initiated in postsynaptic neurone

Synapses 6 Neurotransmitter is broken down by enzymes. Inactive products are taken up by reuptake transporters into the presynaptic neurone

Synapses Summary 1 An action potential passes down the presynaptic neurone. 2 Calcium channels open and allow calcium ions to diffuse into the neurone. 3 Some of the vesicles fuse with the presynaptic membrane and release the neurotransmitter, acetylcholine, into the synaptic cleft. 4 Acetylcholine diffuses across the synaptic cleft and binds to a ligand-gated sodium channel on the postsynaptic membrane. 5 An action potential is initiated in the postsynaptic neurone. 6 The neurotransmitter is broken down by enzymes. Inactive products are taken up by reuptake transporters into the presynaptic neurone.

Red back spider Synapses A bite from a red-back spider results in the uncontrolled release of acetylcholine. One of the symptoms of being bitten by this spider is severe sweating. Explain why.

Synapses Remember what happens at a synapse: Impulse travels down the presynaptic neurone Neurotransmitter diffuses across synaptic cleft Action potential produced in postsynaptic neurone

Synapses A sting from a cone shell prevents calcium ions crossing the presynaptic membrane. One of the symptoms of being stung by a cone shell is paralysis. Explain why.

Synapses Remember what happens at a synapse: Impulse travels down the presynaptic neurone Calcium channels open and allow calcium ions to diffuse into the neurone Neurotransmitter diffuses across synaptic cleft Action potential produced in postsynaptic neurone

Synapses The following slides refer to the worksheet on synapses. • Look at the instructions: Read the following passage. Use the information in the passage and your own biological knowledge to answer the questions. • Start by reading the passage through quickly. • Pick out the key ideas in each paragraph. This will provide you with some signposts so that you can find what you want quickly.

Synapses Here is a section from the passage. Pick out the key ideas in each paragraph: Benzodiazepines are drugs that are widely used to treat anxiety and insomnia. They work by affecting the activity of a neurotransmitter called GABA is the most common inhibitory neurotransmitter in the brain.

Synapses Signpost You now have a set of signposts. In this passage, the three paragraphs cover the following topics: • Benzodiazepines, drugs that affect inhibitory synapses • Ethanol and its effect on GABA • Ethanol and its effect on glutamate This should enable you to find your way round the passage quickly.

Synapses • Unless there is a good reason to do something different, the order of the questions reflects the order of the topics in the passage. • Line references are there to help you. Make sure that you use them. 1 GABA receptors are examples of transmembrane ligand-gated ion channels (lines 5– 6). Explain why. (3 marks) • This question is testing your understanding of technical terms.

Synapses 1 GABA receptors are examples of transmembrane ligand-gated ion channels (lines 5– 6). Explain why. (3 marks) • (Transmembrane means that) the receptor spans the cell surface membrane; • (Ligand-gated means that) the channel is opened by the binding of a specific substance, in this case GABA; • (Ion channel means that) there is a pore running through the molecule through which ions such as chloride can pass;

Synapses 2 (a) Explain the part played by sodium ions and potassium ions in establishing the resting potential in a neurone. (4 marks) This is the first part of a three-part question. It is a straightforward recall question. The main points that you need to make in your answer are shown on the next slide.

Synapses • A lot of positive potassium ions diffuse out; • Few positive sodium ions diffuse in; • Therefore there are fewer positive ions inside the neurone; K+ Na+ Resting potential of – 60 m. V • In other words, the inside of the neurone is now negative with respect to the outside; This is the resting potential.

Synapses 2 (b) An increased influx of chloride ions makes the resting potential of the neurone more negative (lines 7– 8). Explain how. (2 marks) To be really useful, recall must be based on understanding. This question is designed to test understanding of the information required in part (a) of this question. • Chloride ions have a negative charge; • This makes the resting potential more negative;

Synapses 2 (c) A larger difference between the resting potential and the threshold results in a neurone being less likely to generate an action potential. Explain why. (3 marks) The final part of Question 2 completes the story linking benzodiazepines with the behaviour patterns associated with worry, stress and anxiety. • The same number of sodium ions entering; • Will not reach threshold; • Must reach threshold to generate action potential;

Synapses 3 Explain how the effects of ethanol on the presynaptic side of the synapse (lines 15– 16) may affect GABA release. (2 marks) You need to refer to lines 15– 16 here to find out the effects of ethanol on the postsynaptic side of a synapse. • GABA-containing vesicles are more likely to fuse the presynaptic membrane; • More GABA will be released; The first step in this question is to locate the relevant material in the passage. It is better to express this idea in your own words rather than simply copying it out.

Synapses 4 Memory loss can occur after drinking large amounts of alcohol. Use information in the passage to suggest an explanation for this memory loss. (2 marks) This question wants you to use information from the passage. You will have to search for the answer here as there are no line references. This is where your signposts will come in useful. • (The passage says that) ethanol prevents glutamate binding to receptors; • No excitation of neurones associated with memory;