Lecture 22: The Action Potential Flashcards Preview

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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....

- Closed
- 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


How long can action potentials travel in 3ms?

- 150mm
- Dominoes vs Jenga

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