Lecture 5- Action potential propagation

Question 1

Propagation of Action potentials

Answer 1

DURING REPOLARIZATION:
- The action potential spreads down the length of the axon, much like a WAVE
- During the action potentials, Na+ channels are INACTIVE
- Due to this, the action potential cannot
propagate back in this direction.

DURING DEPOLARIZATION:
The sodium channels here are CLOSED but can be opened.

Due to this, the surge of Na+ that spreads through the axon in this direction causes another action potential to occur.

This process repeats

Question 2

Passive diffusion of currents

Answer 2

charges diffuse passively down an axon, but there is an exponential decay or charge from the point of insertion

Question 2

Axonal conduction

saltatory conduction

Answer 2

There are voltage-gated Na+ and K+ channels but only at the nodes of Ranvier.

therefore the action potential is regenerated at each node

Saltatory conduction
- the action potential goes fast, slow, fast, slow as it jumps down the axon and goes slow at the Nodes of Ranvier

Question 3

What does myelin do and where are the voltage gated channels

Answer 3

myelin moves the action potential down the axon faster as it goes down like a wave.

There are Na+ and K+ voltage-gated channels ONLY at the nodes of Ranvier

Therefore the action potentials are regenerated at the nodes of Ranvier

Question 4

what is a synapse

Answer 4

meeting point between two neurons

Question 5

anatomy of a synapse

Answer 5

1. Neurotransmitters are stored in vesicles
2. as an action potential races down the axon it invades the presynaptic terminal

3.. depolarization of the presynaptic terminal causes opening of Ca2+ channels

4. Ca2+ comes in and causes Vesicles to fuse with presynaptic membrane
5. Transmitter inside the vesicle is released into synaptic cleft via exocytosis
6. transmitter binds to receptors in postsynaptic membrane and opens or closes the channels

6.5. Neuro transmitters diffuse across post synaptic membrane

7. Postsynaptic current causes excitatory or inhibitory postsynaptic potential to occur which changes the excitability of the postsynaptic cell, and perhaps the formation of another action potential in the next neuron, or inhibit it and stop the next action potential
8. Removal of neurotransmitters by glial cells or enzymes
9. Vesicles are recycled or budding process

Question 6

contact points of postsynaptic neuron

Answer 6

Small cellular projections called dendritic spines

contact points of post-synaptic neurons connects to a pre-synaptic neuron

Question 7

what happens when Ca2+ stimulates cell

Answer 7

synaptic vesicles fuse and release neurotransmitters into the cleft

omega formations and vesicle fusion

Question 8

what does the SNARE complex do

Answer 8

activated by entry of Ca2+ in the presynaptic terminal

in the membrane of the synaptic terminal

docking and fusion of synaptic vesicles and release of contents and neurotransmitters into the cleft.