Module 3: Lecture 3 Flashcards
What is the threshold potential?
its the potential that comes after graded potentials that allows for an action potenial to occur
What is included in an action potential?
- everything that occurs after the threshold potential has been reached
- big explosive depolarization phase followed by a repolarization phase back down to rest
At the peak of an action potential, at the end of the depolairizaiton what is the resting membrane at in mV?
+30
How long does an action potential last?
a millisecond
What is an action potential?
the rapid change in potential from threshold to peak and the back to the resting potential
What is a voltage gated channel?
- gated channel that responds and open when the threshold potential is reached
- when opened it will allow ions to travel down their electrochemical gradient
Which gated channels are responsible for action potentials?
voltage channels
which voltage channels respond faster, sodium or potassium?
sodium
What are the components of the Sodiums voltage-gated channel?
- activation gate (gate)
- inactivation gate (ball in chain)
*Both are triggered by the threshold potential but the inactivation gate moves at a slower rate allowing some ions to pass through before closing
What is the mV of the threshold potential?
-50 to -55 mV range
What are the 4 steps in the positive- feedback cycle with sodium gated ion channels?
- Triggering event, Na+ gated channels either mechanically or chemically
- Depolarization which decreased membranes potential
- Causes the membrane to reach the threshold potential and open some voltage-gated Na+ channels, allowing more sodium into the cell
- Influx of Na+
True or False
The membrane after all the Na+ voltage-gated channels are open is now 600 times more permeable to Na+ than K+?
True
What causes the Na+ to stop and not reach its equilibrium potential of +65?
the inactive gates from the sodium voltage-gated channels
When does the inactived ball and chain gate open again?
when the resting membrane is re-achieved at -70mV
- until the cell repolarizes
Does the potassium votage-gate open fast or slow when the threshold potential is reached?
slow
What repolarizes the cell at peak action potential?
the potassium voltage-gated channels
- as potassium leaves the cell the inside of the cell becomes more negative
When does the potassium gates fully open?
at the peak of the action potential
True or False
The K+ permeability is increased to about 300 times at peak action potential?
true
Which two gradients are acting together to push potassium out of the cell when the cell hits +30?
- chemical gradient
- electrochemical gradient
Why is there a hyper polarization period after an action potential?
due to the slow closing of the K+ channels
What is the typical rule when thinking about how to find a threshold?
it is about 15 mV less negative than the resting potential
What is a sub-threshold potential?
weak depolarization due to gated channels that do not reach the threshold
How do we differentiate the magnitude of the stimulus for action potentials? (Light touch and stabbing should have different results)
- the frequency
