Lecture 22. Synaptic Transmission Flashcards
What is a synapse?
Junction where information is passed from one neuron to another (or to eg muscle)
What are the two types of synapses?
Electrical and Chemical
What are the features of electrical synapses?
No delay
Can be two-way
Little plasticity
What are the features of chemical synapses?
Delay (at least 0.5 ms)
One-way
Plastic (history dependent)
What are chemical synapses?
Chemical released from presynaptic neuron to modulate postsynaptic neuron (or muscle)
How is neurotransmitter packed into vesicles?
A non-peptide neurotransmitter is synthesised in the nerve terminal and transported into a vesicle
What are the 4 steps of neurotransmitter release?
- Docking/priming
- Ca²⁺ entry
- vesicle fusion (exocytosis)
- Recycling of vesicles (endocytosis)
How does docking of the vesicles onto the membrane occur?
A combination of SNAP and SNARE proteins anchor vesicles to the presynaptic membrane
Docked vesicles are ready to release their contents
How does Ca²⁺ enter into the nerve terminals?
The action potential:
1) Depolarises nerve terminal via voltage-gated Na⁺ channels
2) Opens voltage-gated Ca²⁺ channels
3) Ca²⁺ moves into the nerve terminal down its electrochemical gradient into the neuron
How does Ca²⁺ entry lead to the fusion of docked vesicles and release of neurotransmitter?
Ca²⁺ binds to one of the SNARE proteins (synaptotagmin, is the Ca²⁺ sensor )
What are important features of Ca²⁺ dependent neurotransmitter release?
Neurotransmitter release requires binding of multiple Ca²⁺ ions (between 3 to 5)
Neurotransmitter release occurs very quickly after Ca²⁺ entry
Blocking Ca²⁺ entry blocks synaptic transmission (cadmium and toxins from spiders/snails)
Knockout of synaptotagmins: lose fast synchronous neurotransmitter release
What do different receptors produce?
Different speeds of signalling
What does acetylcholine act upon?
Nerves onto muscle (contraction)
Nerves onto heart (slows heart)
Neuron to neuron (brain)
How is acetylcholine synthesised?
Reaction between acetly-CoA and choline in CHAT (choline acetyltransferase)
What packages acetylcholine into vesicles?
Vesicular acetylcholine transporter (VAChT)
