Chapter 3 pt 2 Flashcards
Exam 1
What is happening at resting membrane potential?
- 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)
What happens when the membrane potential reaches threshold?
- 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
What is going on when the voltage-gated Na+ channels inactivate?
- 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
Voltage-gated K+ channels activate
- 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
What is up w the leaky K+ channels throughout the action potential process?
- 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
What is active propagation?
- 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
What is passive propagation?
- Not dependent on voltage changes
- Is fast but it weakens so it could disappear
Saltatory Conduction
- 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
Neurotransmitter release
- 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
What is exocytosis?
When NT is released into synaptic cleft after Ca2+ causes the vesicle to fuse with the presynaptic membrane
Tetrodotoxin and Saxitoxin
- TTX- puffer fish
- STX/PTX- paralytic shell fish toxin
- block voltage-gated Na+ channels
Batrachotoxin
- BTX- frog
- Forces Na+ channels to open
Agitoxin and Betabungarotoxin
- A- Scorpion
- B-Snake
- Block voltage-gated K+ channels
Multiple Sclerosis
- 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