1 / 30

Learning Objectives

Learning Objectives. What is a synapse? Explain the role of calcium ions Explain the role of the neurotransmitter Explain the role of Acetylcholinesterase. The Basic Idea. Synapses are gaps between neurones Information is sent between neurones by chemical transmission

winona
Download Presentation

Learning Objectives

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Learning Objectives • What is a synapse? • Explain the role of calcium ions • Explain the role of the neurotransmitter • Explain the role of Acetylcholinesterase

  2. The Basic Idea • Synapses are gaps between neurones • Information is sent between neurones by chemical transmission • Neurotransmitters pass across the synaptic cleft • A new action potential will be triggered in the post synaptic neurone

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

  4. Incoming Action Potential Neurotransmitter New action Potential

  5. 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

  6. Incoming Action Potential Ca2+ Ca2+ Ca2+ Ca2+

  7. 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

  8. Incoming Action Potential Ca2+ Ca2+ Ca2+ Ca2+

  9. 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

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

  11. Sodium Channels Na+ • 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. Neurotransmitter binds and opens the channel.

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

  13. 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

  14. 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

  15. Incoming Action Potential Neurotransmitter New action Potential

  16. 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.

  17. 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

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

  19. 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.

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

  21. 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

  22. 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?

  23. 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.

  24. The Whole Process

  25. Incoming Action Potential Ca2+ Ca2+ Ca2+ Ca2+

More Related