Neurone excitability Flashcards
When Vm is negative is the inside of the cell more positive or negative than the outside?
Inside of the cell is more negative
What does Nernst equation calculate?
How much a given ion contributes to a resting potential
Describe the net flow of an ion when Vm = Vnerst for that ion?
No netflow
Which ion will pull Vm to its own Vnerst
a) the most ionic
b) the most permeable
c) largest ion
d) smallest ion
e) the least permeable
b
Which ions is Vm closest to?
a) Cl
b) K
c) Na
Cl and K
Why is Vm close to Pk?
Lots of K+ leaky channels
Why does Vm not equal Ek exactly?
Some leakage of Na+ and Cl-
Why is Goldman-Hodgkin_Katz constant more accurate that Nernst?
Takes into account all ions and permeabilities
What causes a neural signal?
Large changes in ratios of permeabilities for different ions through gated channels
Does active or passive propagation cause propagation without decrement?
Active
Why can axons with a larger diameter propagate further/
Less resistance
What is a graded response?
Bigger stimuli = bigger response
What is a summate response?
Multiple stimuli = summed response
What is overshoot?
When the membrane potential is above 0mV
What gates do Na+ voltage gated channels have?
Internal h gate (inactivation)
External m gate (activation)
What gates do K+ voltage gates channels have?
n gate
What is the state of the gates in resting conditions?
Most Na+ h gates open but all m gates closed - so the Na+ channels are closed
K+ n gates closed
Neither contribute to Vm
In terms of voltage gated ion channel gates what happens during depolarisation?
Na+ m gates open, Na+ moves into the cell
Depolarisation occurs and this causes more m gates to open = positive feedback.
Na+ is very permeable and Vm moves towards ENa
Why does Vm never reach ENa during depolarisation?
h gates begin to slowly close, so Vm is just below ENa
What is the stage called when h gates are closing?
Absolute refractory period
What happens to gates during depolarisation?
n gates slowly open
What is the purpose of undershoot?
K+ is higher out of the cell that it is at rest, undershoot allows K+ channels to close and membrane potential to settle
What is the purpose of refractory period?
Limits firing frequency
During relative refractory period when can an AP occur?
Suprathreshold stimuli
What will an AP during relative refractory period look like?
Reduced amplitude as fewer NA+ channels are open
Why does an AP always propagate forward?
Refractory period - ahead of the AP Na+ channels are ready to be opened
Behind they are in the inactive state
What type of propagation occurs between the nodes of Ranvier?
Passive propagation
