Chapter 3 pt 2

Question 1

What is happening at resting membrane potential?

Answer 1

• During the resting potential there is free-flowing “leaky” K+ channels and closed Na+ channels
• When a depolarizing stimulus comes along, the membrane potential becomes less negative and approaches the threshold potential (-40mV)

Question 2

What happens when the membrane potential reaches threshold?

Answer 2

• The voltage-gated Na+ channels open, triggered by the certain membrane voltage being reached (not by a chemical)
• the channels activate: Na+ ions rush into the cell
• the membrane potential moves towards the positive range

Question 3

What is going on when the voltage-gated Na+ channels inactivate?

Answer 3

• After a fixed period of time after the positive voltage is reached, the Na+ channels inactivate
• Relative refractory period: step 4… the neuron can fire an action potential but needs a stronger stimuli

inactivation= state in which channel is “closed”/ nonfunctioning and temporarily unable to open again

Question 4

Voltage-gated K+ channels activate

Answer 4

• As the inside of the cell becomes more +, voltage-gated K+ channels open.
• K+ moves out and the resting potential is restored. MORE flows out bc of delayed activating channels opening
• The membrane becomes more negative again

Question 5

What is up w the leaky K+ channels throughout the action potential process?

Answer 5

• The leaky K+ channels remain open throughout the whold process- what changes is the direction the K+ is flowing
• Movement is in both directions until the action potential peak occurs, at this point it is only allowed to go outside.
• Mostly driven by the concentration gradient

Question 6

What is active propagation?

Answer 6

• Active propagation of an action potential is slow (10m/s) but it does not weaken due to sodium-ion channels “recharging”
• Takes many small steps down the axon with some chance of failure at every step due to not enough Na+ ions… requires activation of valtage-gated sodium channels along the entire length of the axon

Question 7

What is passive propagation?

Answer 7

• Not dependent on voltage changes
• Is fast but it weakens so it could disappear

Question 8

Saltatory Conduction

Answer 8

• An action potential starts at the axon hillock, moving passively through the myelinated segment- quick but weakening
• When it reaches first NoR, it regains full charge through active means
• Then moves passively through next myelinated segment

takes about 7ms to move one meter

Question 9

Neurotransmitter release

Answer 9

• As a result of an action potential, Ca2+ channels in the axon terminal (bouton) will open, Ca2+ will enter the cell
• Ca2+ causes synaptic vesicles to fuse with the presynaptic membrane and release neurotransmitter into the synaptic cleft, a process known as exocytosis

Question 10

What is exocytosis?

Answer 10

When NT is released into synaptic cleft after Ca2+ causes the vesicle to fuse with the presynaptic membrane

Question 11

Tetrodotoxin and Saxitoxin

Answer 11

• TTX- puffer fish
• STX/PTX- paralytic shell fish toxin
• block voltage-gated Na+ channels

Question 12

Batrachotoxin

Answer 12

• BTX- frog
• Forces Na+ channels to open

Question 13

Agitoxin and Betabungarotoxin

Answer 13

• A- Scorpion
• B-Snake
• Block voltage-gated K+ channels

Question 14

Multiple Sclerosis

Answer 14

• person’s immune system makes antibodies that attack myelin, disrupting the conduction of action potentials
• symptoms vary widely, affecting sensory and/or motor systems depending on which axons are attacked
• risk is much higher to people exposed to the Epstein-barr virus