Synaptic Transmission Flashcards
What is an action potential?
A transient reversal in a membrane potential
How does an action potential occur? 5 steps
1) Action Potential Depolarises Axon terminal
2) Voltage-gated Ca2+ channels open, Ca2+ enters
3) Vesicle fuses with membrane
4) Release neurotransmitter by exocytosis which diffuses across synaptic cleft
5) Binds to receptors on postsynaptic neurone and activates it - known as postsynaptic response
Characteristics of local responses? 4 features
1) Not Propagated
2) Decay in intensity rapidly
3) No refractory period
4) Can summate
What are Excitatory Postsynaptic Potentials? EPSP
Raise the membrane potential so it is closer to the threshold which therefore increases the chance of an impulse occurring
Example of EPSP?
Acetylcholine binds at Nicotinic Receptors which creates a sodium channel which increases sodium potential in the neurone.
What are Inhibitory Postsynaptic Potentials? IPSP
Reduce the ability of the cell to fire an action potential by moving the membrane potential further away from the threshold.
Example of IPSP?
GABA binding to GABA receptors allows more Cl- ions to enter which hyperpolarise the cell causing the membrane potential to move further away from the threshold.
Where are Excitatory and Inhibitory synapses located on the neurone?
Excitatory - Mainly on Dendrites
Inhibitory - Cell Body
What is spatial summation?
2 EPSP’s on adjacent membranes adding together to reach the threshold and cause an action potential
What is temporal summation?
2 EPSP’s close in time can add together to cause an action potential
What is presynaptic inhibition?
Where an inhibitor binds to the presynaptic neurone and prevents the neurotransmitter from travelling across the synapse. Eg, inhibiting the calcium influx
