Flashcards in Lecture 22: The Action Potential Deck (14)
(1) How does the action potential start?
- With a stimulus causing a local depolarisation
- Small number of Na+ channels open
- Membrane potential depolarises toward the threshold potential (-59mV)
- This triggers another event (opening of all Na+ channels)
(2) What happens when all Na+ channels open?
- Further depolarisation occurs
- There's so much sodium in the cell, that now there is a positive value of +30mV
- After this all sodium channels close and another event occurs (K+ channels open)
(3) What happens when the K+ channels open?
- The membrane repolarises as it becomes more negative inside (hyperpolarisation)
- At high negativity the K+ channels close and potassium pumps restore the RMP (recharge the battery)
To summarise action potential generation:
- Timing is everything
- Order of channel events (opening/closing)
- There are different types of ion channels (stimulus-gated and voltage-gated)
Go over different types of potentials and polarisation
- table ^O^
Conduction of the action potential down axons relies on.....this generates......
- The speed of the depolarising electrical signal
- An electric field
When the action potential moves along the axon it instantly activates....
- The next set of voltage gated Na+ channels
What two parts make up the refractory period?
- Absolute --> no response
- Relative --> large stimulus required
What does the refractory period limit?
- The number of action potentials at a given time
Sodium channels can be in three different states...this prevents....
- Open (at most 0.5ms)
- Inactive Open (open but there is a 'plug' which prevents sodium from further entering the cell)
- Backward movement
If you are a small invertebrate what is the difference in conduction speed?
- Slower due to unmyelination
What is something that humans have to speed up conduction of action potentials?
- Myelinated axons!!!!
- This improves velocity
How do myelinated axons improve conduction speed?
- Electrical field around node of ranvier is able to extend to next node of ranvier, travels instantly
- This means that the action potential is able to leap between the nodes of ranvier