Module 1 Communication and homeostasis 1.1.8 Nerve Junctions

Starter Complete memory game - Synapse

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) 3

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.

The structure of the synapse Boardworks A2 Biology The Nervous System The structure of the synapse

What happens at a synapse? Boardworks A2 Biology The Nervous System What happens at a synapse? Teacher notes There are several different types of neurotransmitter. Acetylcholine is found at cholinergic synapses, as shown in the animation. The neurotransmitter noradrenaline is present at adrenergic synapses. Some neurotransmitters and their receptors are excitatory, i.e. they create a new action potential in the postsynaptic neurone. Others are inhibitory, i.e. they make it less likely that a new action potential will be created in the postsynaptic neurone. See the ‘Muscles’ presentation for more information about synapses between motor neurones and a muscle fibre (neuromuscular junction).

Students to use page 18 and 19 and information from the lesson to complete worksheet Using your knowledge of synapses and apply this to drugs

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

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.

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.

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.

What happens at a cholinergic synapse? Stage 4 Sodium channels open. Sodium ions diffuse rapidly along a concenration gradient into the postsynaptic membrane causing depolarisation, which may initiate an action potential.

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

Task Homework - Complete exam question Jan 2010 – Qu 3

Transmission across a synapse - Plenary Boardworks A2 Biology The Nervous System Transmission across a synapse - Plenary

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) 16