Module 5 Communication, homeostasis & energy Block 2A – 5.3 Neuronal communication 5.3.6 Summation

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Starter What are neurotransmitters and where do they act? (3 marks) 2. Explain the importance of acetylcholinesterase at the neuromuscular junction (3 marks) Are chemical substances that act as signalling molecules, released from the pre-synaptic bulge (1) to diffuse across the symapse (1). It breaks down acetylcholine so that no further APs are triggered on the post-synaptic membrane (1) If acetylcholinesterase was not present, this would lead to it not being broken down (1) Continued stimulation of the muscle may lead to permanent contraction and possible paralysis

Learning Objectives Success Criteria To understand what affects the transmissions of action potentials Outline the role of synapses (Grade E - D) Outline the significance of the frequency of impulse transmission (Grade C –B) Understand the importance of synapses in summation and control (Grade A) 4

Roles of synapses Divergence and convergence Synaptic divergence – when one neurone connects to many neurones information can be dispersed to different parts of the body Synaptic convergence – when many neurones connect to one neurone information can be amplified. Divergence – info. from one neurone divides Convergence – info from many neurones comes together

TASK – use page 56 – draw diagrams explaining summation The amount of neurotransmitter from impulse may not be sufficient to cause depolarisation. This is an excitatory post-synaptic potential (EPSP) Due to the neurotransmitter being removed almost as quick as its released. To produce depolarisation several EPSPs combine together to to overcome threshold of post-synaptic membrane. This is called summation. Spatial Summation A number of different pre-synaptic neurones all release enough neurotransmitter to exceed the threshold and trigger an action potential in the next neurone. Temporal Summation One pre-synaptic neurone releases neurotransmitter many times over a short period of time to exceed the threshold and trigger an action potential in the next neurone. TASK – use page 56 – draw diagrams explaining summation

In addition some pre-synaptic neurones can produce inhibitory post-synaptic potentials (IPSP). These can reduce the effect of summation and prevent action potentials in the post-synaptic neurone. Unidirectionality = Synapses can only pass in one direction – from the presynaptic to the postsynaptic neurone. Produce a mind map to describe the control of communication Complete exam question

Exam questions Excitatory synapse Inhibitory synapse Action potential Ion channel Membrane potential Example Complete the table above (4 marks) How does summation improve the chances of initiating a nerve impulse? Explain the differences between temporal and spatial summation (5 marks)

PA Excitatory synapses Inhibitory synapses Action potential   Excitatory synapses Inhibitory synapses Action potential Increase the chance of an action potential Decrease the chance of an action potential Ion channels Cause sodium channels to open Cause chloride channels to open Membrane potential Cause postsynaptic membrane potential to become less negative — increase the potential Cause postsynaptic membrane potential to become more negative Example Acetylcholine or glutamic acid GABA (gamma- aminobutyric acid)

PA 2. Summation is the effect of adding together all impulses received by synapses in order to generate an action potential in the next neurone. Temporal summation: when a single neurone has many impulses passing through very frequently and collectively building up enough neurotransmitter to generate an action potential in the postsynaptic membrane. Spatial summation: where several synapses that signal to the same postsynaptic membrane transmit impulses at the same time and so collectively produce enough neurotransmitter to generate an action potential in the postsynaptic membrane.

Plenary What happens next? One students starts the 1st event of the synapse and students take it in turns recounting the next event. Can be done as a class or in groups Card sort

Learning Objectives Success Criteria To understand what affects the transmissions of action potentials Outline the role of synapses (Grade E - D) Outline the significance of the frequency of impulse transmission (Grade C –B) 14