Module 5 Communication, homeostasis & energy

1. Module 5 Communication, homeostasis & energy Block 2A – 5.3 Neuronal communication 5.3.5 Transmission across a synapse

2. Spec

3. Starter • Complete memory game - Synapse

4. Learning Objectives Success Criteria • To understand how information is transmitted across a synapse • Describe (with the aid of diagrams) the structure of a cholinergic synapse (Grade E - D) • Explain the role of neurotransmitters in transferring action potentials (Grade C –B) • Apply understanding of synapses to explain how drugs work (Grade B – A)

5. Cholinergic Synapses • Acetylcholine is a common transmitter. • Synapses that have acetylcholine transmitter are called cholinergic synapses. • Cholinergic synapses are common in vertebrates, where they occur in the CNS and at neuromuscular junctions • This is an electron micrograph of synapses between nerve fibres and a neurone cell body.

6. What happens at a synapse?

7. Students to use page 54 and 55 and information from the lesson to complete worksheet • Using your knowledge of synapses and apply this to drugs

8. Effects of drugs on synapses • Drugs which have molecules of similar shape to transmitter substances can affect protein receptors in postsynaptic membranes. • Agonists – mimic the effect of neurotransmitters 1) Stimulating the release of more neurotransmitter 2) Inhibiting the enzyme that breaks down the neurotransmitter Stimulates the nervous system by creating more APs in postsynaptic neurones. • Nicotine, caffine, amphetamines, ecstacy • Antagonists – block the effects of neurotransmitters 1) Inhibiting the release of neurotransmitter 2) Blocking the receptors on the Na/K ion channels on the postsynaptic membrane Reduce the bodies response to impulses • Beta blockers

9. What happens at a cholinergic synapse? Stage 1 • An action potential arrives at presynaptic membrane. Voltage gated calcium channels in the presynaptic membrane open, calcium ions enter the presynaptic neurone along a concentration gradient. • Afterwards these are pumped out using ATP.

10. What happens at a cholinergic synapse? Stage 2 • Calcium ions cause synaptic vesicles to fuse with the presynaptic membrane, releasing acetylcholine into the synaptic cleft (exocytosis). • This also requires ATP as it is an active process.

11. What happens at a cholinergic synapse? Stage 3 • Acetylcholine diffuses cross the synaptic cleft and binds to specific neuroreceptor sites in the post synaptic membrane.

12. What happens at a cholinergic synapse? Stage 4 • Sodium channels open. Sodium ions diffuse rapidly along a concentration gradient into the postsynaptic membrane causing a generator potential or excitatory postsynaptic potential (EPSP). • If sufficient generator potentials combine then the potential across the membrane reaches a threshold potential • A new action potential is created

13. What happens at a cholinergic synapse? Stage 5 • The enzyme acetylcholinesterase hydrolyses acetylcholine into choline and ethanoic acid (acetyl). • The products diffuse back into the presynaptic neurone where acetycholine is resynthesised using ATP from the mitochondria. • The break down of acetylcholine prevents it prevents it from continuously generating a new action potential

14. The structure of the synapse

15. Task • Homework - Complete exam question Jan 2010 – Qu 3

16. SA

19. Plenary

20. Learning Objectives Success Criteria • To understand how information is transmitted across a synapse • Describe (with the aid of diagrams) the structure of a cholinergic synapse (Grade E - D) • Explain the role of neurotransmitters in transferring action potentials (Grade C –B) • Apply understanding of synapses to explain how drugs work (Grade B – A)