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| Question | Answer |
| What is a synapse? | A synapse is the junction between a neurone and another neurone, or between a neurone and an effector cell (e.g. a muscle or gland cell) |
| Describe the structure of a synapse | Synaptic cleft = the tiny gap between the cells at a synapse The presynaptic neurone has a swelling called a synaptic knob, which contains synaptic vesicles filled with neurotransmitters |
| Complete the sentences: There are different types of synapses, each with a slightly different __________ that relates to their function. A _________ synapse uses the neurotransmitter _________________ (ACh) which binds to cholinergic receptors. | There are different types of synapses, each with a slightly different STRUCTURE that relates to their function. A CHOLINERGIC synapse uses the neurotransmitter ACETYLCHOLINE (ACh) which binds to cholinergic receptors. |
| Outline the method of synaptic transmission | 1. An action potential arrives at the synaptic knob of the presynaptic neurone 2. The action potential stimulates voltage-gated Ca²⁺ channels in the presynaptic neurone to open 3. Ca²⁺ diffuse into the synaptic knob (they're pumped out afterwards by active transport) 4. The influx of Ca²⁺ into the synaptic knob causes the synaptic vesicles to move to the presynaptic membrane 5. Synaptic vesicles fuse with the presynaptic membrane 6. The vesicles release ACh into the synaptic cleft by exocytosis 7. ACh diffuses across the synaptic cleft and binds to specific cholinergic receptors on the postsynaptic membrane 8. This causes Na⁺ channels in the postsynaptic neurone to open 9. The influx of Na⁺ into the postsynaptic neurone causes depolarisation 10. An action potential on the postsynaptic membrane is generated if the threshold is reached 11. ACh is removed from the synaptic cleft so the response doesn't keep happening - it's broken down by an enzyme called acetylcholinesterase (AChE) and the products are re-absorbed by the presynaptic neurone and used to make more ACh |
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| Synaptic transmission can be affected by chemicals like... | Drugs Toxins Poisons |
| How do chemicals affect synaptic transmission? | Some chemicals... 1. Are the same shape as neurotransmitters - they mimic their action at receptors (these drugs are called agonists) 2. Block receptors so they can't be activated by neurotransmitters 3. Inhibit the enzyme that breaks down neurotransmitters - more neurotransmitters in the synaptic cleft to bind to receptors 4. Inhibit the release of neurotransmitters from the presynaptic neurone |
| Give an example of a chemical that has the same shape as neurotransmitters (agonists) | Nicotine mimics acetylcholine (it binds to certain types of cholinergic receptors in the brain) |
| Give an example of a chemical that blocks receptors (so they can't be activated by neurotransmitters) | Curare blocks the effects of acetylcholine by blocking certain cholinergic receptors at neuromuscular junctions, so muscle cells can't be stimulated (muscles become paralysed) |
| Give an example of a chemical that inhibits the enzyme that breaks down neurotransmitters | Nerve gases stop acetylcholine from being broken down in the synaptic cleft (can lead to loss of muscle control) |
| Give an example of a chemical that inhibits the release of neurotransmitters from the presynaptic neurone | Opioids block Ca²⁺ channels in the presynaptic neurone (fewer vesicles fuse with the presynaptic membrane so less neurotransmitter is released) |
| What is synaptic divergence? | When one neurone connects to many neurones, information can be dispersed to different parts of the body |
| What is synaptic convergence? | When many neurones connect to one neurone, information can be amplified |
| What is spatial summation? | Where two or more presynaptic neurones converge and release their neurotransmitters at the same time onto the same postsynaptic neurone. |
| Complete the sentences: In spatial summation, the small amount of ____________________ released from each of these neurones can be enough altogether to reach the __________ in the postsynaptic neurone and trigger an _________ potential. Stimuli might arrive from different sources, but spatial summation allows signals from multiple __________ to be coordinated into a single response. | The small amount of NEUROTRANSMITTER released from each of these neurones can be enough altogether to reach the THRESHOLD in the postsynaptic neurone and trigger an ACTION potential. Stimuli might arrive from different sources, but spatial summation allows signals from multiple STIMULI to be coordinated into a single response. |
| What is temporal summation? | Where two more more nerve impulses arrive in quick succession from the same presynaptic neurone |
| TRUE OR FALSE: Temporal summation makes an action potential more likely | TRUE More neurotransmitter is released into the synaptic cleft |
| Synapses make sure impulses are unidirectional. What does this mean? | The nervous impulse can only travel in one direction |
| How do synapses make sure that nerve impulses are unidirectional? | Neurotransmitters are only released from the presynaptic neurones and receptors for neurotransmitters are only on the postsynaptic membranes |
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