Lecture 5 - action potential Flashcards
What is action potential?
- electrical impulses send signals
- temporary shift in membrane (elec.) potential
- causes the release of NTs
What causes action potential?
- it starts when a NT binds to the receptor
What is the voltage change for action potential?
-70mV to +50mV
At what charge do Na+ channels open?
-50mV (negative 50)
What happens when Na+ channels open?
The cell gets really positive really fast
At what voltage do K+ channels open up?
+50mV
What is the axon hillock?
Where all the electrical energy in the cell ends up to determine if there will be an action potential propagating through (moving along) the axon
What happens when the action potential reaches the terminal?
- It causes the release of NTs from the terminals
- The NT does not enter the new cell, it just binds to the receptor
- Opens ion channel for the new neuron
- in the membrane of the terminal, there are Ca++ voltage-gated channels
- Action potential activates Ca++ channels
- when the Ca++ channels open, the terminal membrane and vesicle membrane blend together/fuse
- NT binds to receptor
The pufferfish contains tetradotoxin, this toxin blocks Na+ voltage-gated channels what will happen to the action potential? What will happen to the transmission in the neuron?
If the Na+ voltage-gated channels can’t open, action potential can’t occur. There will be no transmission in the neuron
Draw an action potential indicating what causes the changes in charge (eg Na+ goes in…)
- at -50mV, Na+ goes in, neuron shoots up (positive)
- at +50mV, K+ channels open, K+ goes out, cell becomes super negative
Draw an action potential indicating what causes the changes in charge (eg Na+ goes in…)
- at -50mV, Na+ goes in, neuron shoots up (positive)
–> Depolarizing phase - at +50mV, K+ channels open, K+ goes out, cell becomes super negative
–> Repolarizing phase - cell temporarily gets lower than -70mV
–> undershoot
Where in the neuron is action potential generated? Why this location?
- Action potential only happens at the nodes of ranvier
- It happens at the nodes because…
- that’s the only place on the axon where there
isn’t myelin - that’s the only place where there are voltage-
gated channels
- that’s the only place on the axon where there
The action potential starts in the axon hillock. Why does it start in the AH and not dendrites?
- Dendrites DO NOT have voltage-gated channels
- AH DOES have voltage-gated channels
What causes the release of NTs? What happens to the NTs after they’re released? What happens after that?
- at the membrane of the terminal, there are Ca++ channels
- they open up, which causes the membrane to blend/fuse
- the NT crosses the synapse and binds to the receptor of the post-synaptic neuron
- the NT causes ion channels to open on the post-synaptic neuron, which changes its charge
–> can make it generate its own action potential
–> can make the neuron inhibited
List 3 characteristics of a substance to be classified as a NT
- it must be created by and stored in a neuron
- it must be the only thing causing the reaction
–> If you experimentally put only the neurotransmitter on the receptor, the postsynaptic cell would respond the same way - it must be able to return to the original neuron
- it must be released when the neuron is excited