CTR - 7 - AP Flashcards
What is depolarisation?
A decrease in potential difference between the inside and outside of the cell. (inside less negative than RMP)
What is hyperpolarisation?
An increase in potential difference between the inside and outside of the cell. (inside more negative than RMP)
What is repolarisation?
Return to RMP from either direction
What is overshoot
When the inside of the cell becomes positive due to reversal of membrane potential polarity
What is this? A decrease in potential difference between the inside and outside of the cell.
Depolarisation
What is this? An increase in potential difference between the inside and outside of the cell.
Hyperpolarisation
What is this? Return to RMP from either direction
Repolarisation
What is this? When the inside of the cell becomes positive due to reversal of membrane potential polarity
Overshoot
What cells are excitable cells?
Muscle and nerve cells
What are excitable cells?
Allow an action potential to propagate along it
What are the two ways a change in membrane potential can be achieved?
1 - altered membrane ion permeability
2 - anything that alters ion concentrations on either side
What are the two types of potentials?
Graded potentials (sub threshold potentials)
Action potentials
How is a GP/AP generated (in broad terms)?
Increase in Na+ permeability –> sodium moves into cell –> if this reaches the threshold potential –> depolarise the cell
A _________ stimuli causes _________ potentials.
subthreshold stimuli –> sub threshold/graded potentials
suprathreshold stimuli –> APs
What is the threshold which must be reached?
-50 mV
The strength of a GP is proportional to the ________.
strength of the stimulus
The_________ is proportional to the stimulus strength.
GP strength
What happens to GP strength? Why?
Loses strength moving through the cell
Due to leakage of charge across membrane
What happens to GP strength in dendrites?
As there are NO voltage gated channels –> current leaks –> decreases GP strength
Do dendrites have voltage gated channels? Consequence of this?
NO! Current leaks –> decreases GP strength
The GP must _____________ at the trigger zone!
be above threshold (-50 mV)
What is another name for the trigger zone?
Axon hillock
What does a suprathreshold GP do at the trigger zone?
Triggers an AP
What does a subthreshold GP do at the trigger zone?
Does not trigger an AP
Do subthrehsold stimuli result in APs?
No (subhreshold stimulus –> sub threshold GP –> no AP)
Do suprathrehsold stimuli result in APs?
Yes (supra threshold stimulus –> suprathreshold GP –> AP)
What happens to the strength of a supra threshold GP in the ______?
Dendrite.
It decreases, but not enough to fall below threshold (-50mV) –> AP!
What happens to the strength of a subthreshold GP in the ______?
Dendrite.
It decreases, below threshold (-50mV) –> no AP!
The movement of K+ out of a cell results in
hyperpolarisation
The movement of Na+ into a cell results in
depolarisation
Chemically-Gated channels are also known as ______.
receptor-mediated
Voltage-gated channels are also known as _________.
Electrically stimulated
Duration of AP
4 milliseconds
What are the three states of the sodium channel? What happens to the gates?
Resting - activation gate closed
Activated - activation gate open
Inactivated - inactivation gate closed
What is the function of the absolute refractory period? Why does it exist?
Gates on Na+ channel have not reset
Assures one way propagation - so that the AP reaches the effector organ
Refractory periods limit ____________.
the rate of propagation
How do APs code behaviour
frequency
How does increased stimulus frequency affect APs?
Increased frequency (not size!)
What is the structural difference between the axon and dendrite
Axon has voltage gated sodium channels
Dendrite does not
What factors affect the rate of propagation?
Diameter of axon
- smaller diameter (greater resistance –> slower speed)
- larger diameter (less resistance –> higher speed)
Degree of myelination
- presence of myelin sheath (acts as an insulator –> prevents charge from leaking from axon)
What is the difference between continuous conduction and saltatory conduction. How much faster is one of these?
Continous = non-myelinated axons
- channels are immediately adjacent
- to ensure voltage does not decay - must regenerated AP at every voltage gated ion channels - SLOW
Saltatory conduction = myelinated axons (acts as insulator)
-channels separated by myelin sheaths (channels in nodes of ranvier)
-APs only generated in nodes of ranvier (decreased number of regeneration points)
FAST
What are the two types of conduction?
Saltatory (fast) and continuous (slow)
What is multiple sclerosis caused by? What cells does it affect?
Demyelination of nerves in CNS (not PNS) due to auto-immune disease
Affects oligodendrocytes
What are some symptoms of MS?
muscle, weakness, fatigue, difficulty walking, loss of vision
How is MS treated?
Anti-inflammatory drugs (prevent immune cells destroying myelin)
How do local anaesthetics works?
Blocking voltage gated Na+ channels (no Na+ entry) –> no AP.
