L6- The Action Potential Flashcards
What are the main electrical steps in the AP?
- The voltage is at a resting state
- Stimulus causes voltage to become more positive until it reaches threshold.
- Depolarization-> positive
- Repolarization-> back to negative
- Refractory period, then back to start
How long are APs in
a. cardiac muscle?
b. Neurone?
c. skeletal muscle?
a. 200ms
b. 2ms
c. 5ms
What is the structure of the sodium channel?
4 x 6 transmembrane domains = the alpha subunit
The 4th one is charge-sensitive.
Extracellular dip between 5th and 6th subunit
What is the Na+ channel related to?
K+ and Ca2+ channel
What’s the difference in K+ channel from the sodium and calcium?
The four subunits are separate proteins. Similar structure though.
What happens when Na channels open?
They open rapidly but inactivate after about 1ms
What happens when K channels open?
K channel open more slowly (than Na channels) but do not inactivate, simply close.
Which channels open and close in the AP?
Sodium channels open at first. Na floods in
This opens more sodium channels (voltage sensitive)
Sodium channels close (inactivate) and potassium channels open.
Re polarizes. K channels close
What is the threshold value for an AP?
about -55 mV
What happens when the 1st Na channels open?
This lets sodium in which dpolarises the membrane (makes it more positive).
This opens more sodium channels (positive feedback)
What is the absolute refractory period?
Cannot produce another AP>
Absolutely not
What is the relative refractory period?
The cell is less excitable. Would take very large stimulus to cause an AP.
What is the refractory period caused by?
Inactivation of Na current and activation of K current. Mostly due to inactivation of Na.
Before an AP, what is the proportion of conc. of ions inside and out the cell?
OUTSIDE INSIDE (mM)
Na 150 15 x10 outside
K 5 100 /20 outside
Ca 2 0.0002 x 10,000 outside
Cl 150 13 x 12ish outside
This hardly changes during an AP. Only needs a few ions to move surprisingly.
