Lecture 6 Flashcards
Functional phases of the AP?
- Rest membrane potential
- Graded depolarization phase
- Rapid depolarization phase
- Repolarization phase
- After hyperpolarization phase
Stages of the AP?
- Positive charge flows into cell and causes
slight depolarization - Threshold is reached. Voltage-gated Na+
channels begin to open fully, leading to
more positive charge entering cell and
further depolarization. - Rapid depolarization as the Na+
conductance increases dramatically and
the membrane potential approaches the
equilibrium potential for Na+ - Peak AP. Na+ channels are fully open and
Na+ conductance has peaked - Na+ channels begin to inactivate and Na+
conductance drops at the same time as
the K+ conductance starts to develop - Refractory period. Since K+ channels are
open and Na+ channels are in their inactive state, Vm gets close to EK, below the resting membrane potential. Due to closed inactivation gates Na+ channels are blocked, no further APs can be conducted. - The channels reset to their normal resting
conditions, resting membrane potential is
restored. All Na+ channels are now out of
their inactive state and can be reactivated
to form another full action potential.
Explain rectified and non-rectified channels?
non-rectified is ions can move in either direction
rectified is when the movement of ions is in one direction
What is channel gating?
opening and closing of a channel
this can be regulated by: voltage ligands calcium phosphatase/kinase activity cAMP oxygen carbon dioxide
What comprises the total conductance?
total conductance is equal to the number of channels x unit conductance x open probability
What is probability when referring to a channel?
Probability is the time a channel spends in an open state.
What are the two gates that are part of the Na channel?
The activation gate (m) which is extracellular
The inactivation gate (h) which is intracellular
What voltage opens the Na channel?
The Na channels will open around 50 mV and the channel will deactivate soon after a slight delay at the peak of the AP
The Na channel during the AP phases?
- resting stage
Activation gate is closed and inactivation gate is open
no flux of Na - Depolarization phase
the activation gate is open and the inactivation gate is open
the channel is open, full Na flux - Repolarization phase
activation gate is open, but inactivation gate is closed
No flux of Na
channel cannot be activated at this time (ARP) - Reset to resting state
activation gate closes while the inactivation gate opens
Once reset the ARP is over
Explain the refractory periods?
Absolutely refractory period- This is when no AP can be activated
relative refractory period- An AP can be activated, however it is more difficult due to hyperpolarization
Explain delayed rectifier K channels?
They are voltage and time dependent
highly expressed in neurons
Explain inward rectifying K+ channels?
Voltage dependent but not time dependent
One way flow
have a strong preference for inward flow
Expressed in the heart and vasculature
How does calcium levels impact sodium?
Hypocalcemia- threshold is lower, closer to RMP
This leads to increased excitability
this can lead tetany
hypercalcemia- threshold is further from RMP
Decreased electrical excitability
This could lead to weakness, but uncommon
Explain long slow depolarization?
This tends to keep inactivation gates closed
reduce electrical excitability
clinically relevant with changes in K plasma
could lead to weakness and paralysis
What is the normal range of the potassium?
3.5 to 5.0 mmol/L
