ELM 3.2 Flashcards
Voltage gated channels are all what?
Cation selective
In response to a stimulus above the threshold potential, the size of a neuronal action potential:
is independent of the stimulus size. Action potentials are “all or nothing events”. Information is transmitted via the frequency of action potentials rather than their magnitude
The duration of a typical cardiac action potential is approximately
200 ms
What name is given to the mechanism by which potassium ions pass through the channel of voltage gated potassium channels?
knock on - The knock on mechanism idea is actually quite old (it dates back to a 1955 paper by Hodgkin and Keynes). However, we now know that it involves desolvated ions passing through the channel in single file. The effect is like hitting a ball into another ball on a snooker or pool table.
Sodium channel + potassium channel - positive or negative feedback loops?
Na - positive
K - negative
What is the relative refractory period?
The cell is less excitable, and so a larger stimulus is needed - this period is due to inactivation of Na current and activation of K current
on a graph of membrane potential, at which point is the permeability to sodium ions the greatest?
the peak - the membrane potential peaks because the majority of the voltage gated sodium channels are open. The permeability to sodium then decreases due to channel inactivation
What are the two refractory periods?
There are two refractory periods. The absolute refractory period is during the initial phase of an action potential firing (first 1 ms). Because an action potential is an “all or nothing” event, another action potential cannot be initiated during this period. When the membrane gets into the “undershoot” phase, however, it is possible to fire another action potential, but only if the stimulus is larger than normal. This is due to the fact that some of the sodium channels are still inactivated, and some of the voltage gated potassium channels are still open
