5.1.3 Neuronal Communication Signals and messages

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) 2

Starter Complete card sort

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. Unidirectionality How do synapses ensure that APs only travel in one direction? Divergence – info. from one neurone divides Convergence – info from many neurones comes together Unidirectionality – acetylcholine vesicles only released from presynaptic neurone. Receptors only on postsynaptic membrane

TASK – use page 56 – draw diagrams explaining summation Each stimulus from the presynaptic neurone causes the same amount of neurotransmitter to be released into the synaptic cleft. In some synapses the amount of neurotransmitter from impulse may not be sufficient to cause depolarisation. - Threshold is not reached. If the neurotransmitter can build up – then threshold can be reached – this is known as summation and can be achieved in either of two ways: Spatial Summation A number of different presynaptic 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.

Keyword check – What are these words with the vowels missing?! myln schwnn vltg gtd n chnnl xn dndrn ctn ptntl dplrstn smmtn synps ctylchlnstrs

Keyword check – What are these words with the vowels missing?! myelin schwann voltage gated ion channel axon dendron action potential depolarisation summation synapse acetylcholinesterase

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

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) 12