1. Some Most All Synapses WAL: An overview of the synapse
How is information transmitted across a synapse?
Some
What functions do synapses perform?
What is a synapse?
Starter – (10.30)

2. Today we are covering from the specification:
Pages of your textbook

3. Synapses Synapses are gaps between neurones
Information is sent between neurones by chemical transmission
Neurotransmitters pass across the synaptic cleft (a small gap 20-30nm wide between neurones) from the presynaptic neurone
A new action potential will be triggered in the post synaptic neurone

4. Functions of a synapse
Synapses act as junctions between neurones allowing:
A single impulse to be transmitted to a number of different neurones creating simultaneous responses.
A number of impulses to be combined at a synapse allowing stimuli from different receptors to interact for a single response.

5. Explain to your partner the function of a synapse
Understanding checkpoint!
An overview of synapses
WAL:
What is a synapse?
All
Explain to your partner the function of a synapse

7. Postsynaptic Neurone Presynaptic Neurone Synaptic Cleft
Smooth Endoplasmic Reticulum
Incoming
Action Potential
Calcium ion channel
Mitochondrion
Synaptic
Knob
Membrane of postsynaptic neurone
Synaptic vesicle containing neurotransmitter
Synaptic
Cleft
Sodium ion channels
Postsynaptic Neurone

8. Incoming Action Potential Neurotransmitter New action Potential
The basic process (GCSE level)
Neurotransmitter
New action Potential

9. Give students 2 minutes to add as many labels as they can

10. Step 1 – Calcium Channels Open
The incoming action potential causes depolarisation in the synaptic knob
This causes calcium channels to open
Calcium ions (Ca2+) flood into the synaptic knob

11. Incoming
Action Potential
Ca2+
Ca2+
Ca2+
Ca2+

12. Step 2 – Neurotransmitter Release
The influx of calcium ions causes synaptic vesicles to fuse with the presynaptic membrane
This releases neurotransmitter in to the cleft
 So calcium ions cause the release of neurotransmitter

13. Incoming
Action Potential
Ca2+
Ca2+
Ca2+
Ca2+

14. Step 3 – Sodium Channels
Neurotransmitter (acetylcholine) is released into the synaptic cleft.
Acetylcholine binds to the receptor site on the sodium ion channels.
Sodium ion channels open

15. Ca2+
Ca2+
Ca2+
Ca2+
Neurotransmitter (acetlycholine) is released into the synaptic cleft. Acetlycholine binds to the receptor site on the sodium ion channels.

16. Sodium Channels
The sodium channels on the postsynaptic membrane are normally closed.
When the neurotransmitter binds there is a conformational change opening the channel.
This allows sodium ions to flood in and causes depolarisation.
Na+
Neurotransmitter binds and opens the channel.

17. Depolarised Empty Synaptic Vesicles
Sodium ions diffuse into the postsynaptic neurone
Depolarised

18. Step 3 – Sodium Channels
Neurotransmitter (acetylcholine) is released into the synaptic cleft.
Acetylcholine binds to the receptor site on the sodium ion channels.
Sodium ion channels open
Sodium ions diffuse in (down steep concentration gradient)
Postsynaptic neurone depolarises

19. Step 4 – New Action Potential
Depolarisation inside the postsynaptic neurone must be above a threshold value
If the threshold is reached a new action potential is sent along the axon of the post synaptic neurone

20. Incoming
Action Potential
Neurotransmitter
New action Potential

21. Questions When do the calcium channels open and close?
Why are the calcium ions important?
What is the name of the neurotransmitter?
Explain how the neurotransmitter causes a new action potential to be generated.

22. The rest of the process Step 1 Calcium channels open
Step 2 Neurotransmitter release
Step 3 Sodium Channels
Step 4 New action potential
Step 5 Acetylcholinesterase
Step 6 Remaking acetylcholine

23. Step 5 Acetylcholinesterase
A hydrolytic enzyme
Breaks up acetylcholine (the neurotransmitter) into acetyl (ethanoic acid) and choline.

25. Acetylcholinesterase
Acetylcholinesterase is an enzyme that hydrolyses acetylcholine in to separate acetyl (ethanoic acid) and choline.
Sodium ion channels close.
The two bits diffuse back across the cleft into the presynaptic neurone.
This allows the neurotransmitter to be recycled.

26. Depolarised Acetylcholine binds and opens Sodium channels
Acetylcholinesterase breaks up acetylcholine. Sodium channels close

27. Why break down acetylcholine?
If the neurotransmitter is not broken down this could allow it to continuously generate new action potentials
Breaking down acetylcholine prevents this

28. Questions Name the hydrolytic enzyme and the products of the reaction.
Why must the neurotransmitter be broken down?
What happens to the remnants of the neurotransmitter?

29. Step 6 Remaking Acetylcholine
ATP released by mitochondria is used to recombine acetyl (ethanoic acid) and choline thus recycling the acetylcholine.
This is stored in synaptic vesicles for future use.
More acetylcholine can be made at the SER.
Sodium ion channels close in the absence of acetylcholine at their receptor sites.
The synapse is now ready to be used again.

30. The Whole Process

31. Incoming
Action Potential
Ca2+
Ca2+
Ca2+
Ca2+
Steps 1 + 2

32. Step 3

33. Step 4 + 5

34. Features of a synapse Unidirectionality
Synapses can only travel in one direction: from the presynaptic neurone to the postsynaptic neurone (like valves)

35. Features of a synapse Summation
Low frequency action potentials often produce insufficient amounts of neurotransmitter to trigger a new action potential in the postsynaptic neurone. They can, however, be made to do so in summation.

36. Q. What is Temporal Summation?
Spatial Summation
Q. What is Temporal Summation?

37. Features of a synapse Spatial summation
A number of different presynaptic neurones together release enough neurotransmitter to exceed the threshold value of the postsynaptic neurone. Together they therefore trigger a new action potential
Temporal summation
A single presynaptic neurone releases neurotransmitter many times over a short period. If the total amount exceeds the threshold value of the postsynaptic neurone, then a new action potential is triggered

38. Most All Synapses WAL: An overview of the synapse
What functions do synapses perform?
What is a synapse?
Plenary– 1) Fill in A3 mind-map
2) Refections: What did you learn?
What do you want to find out? How might you find this out? What skills did you use?