Week 2 Regional Anesthesia & LA's 1 of 4 Flashcards
Makes the cell membrane potential less negative due to movement of positively charged sodium ions into the cell is called:
Depolarization
Change after depolarization, that returns the membrane potential back to resting potential is known as:
Repolarization
Repolarization results from the movement of positively charged potassium ions out
of the cells
Is a property of excitable cells (nerve and muscle) that consists of a rapid depolarization, or upstroke, followed by repolarization of the membrane potential. this is:
action potential
Action potential have stereotypical
size and shape
Action potential are propagating and are
all or none
Is the membrane potential at which the action potential is inevitable is known as
threshold
At threshold potential, net inward current becomes larger than
net outward current
The resulting depolarization becomes self-sustaining and gives rise to
upstroke of AP
If net inward current is less than net outward current
no AP will occur (i.e. all or none response)
AP sequence
Initial segments of the axon
depolarizes
AP Sequence
When depolarization reaches threshold
- Na channels open
- Na rushes inward down concentration gradient (depolarization occurs)
- the inside of the cell momentarily becomes positively charged (with respect to the outside of the cell which is negative)
- Na channels Shut (inactivated state)
- K channels Open
- K rushes out of the cell causing electronegativity to be restored to resting level (repolarization / restoration of the membrane potential to resting level)
- when membrane repolarizes, Na channels return to original configuration (closed) and in the “activated state”
After the AP has passed, what restores the Na/K ionic balance again?
the Na/K pump
- after AP has passed, the Na/K pump extrudes the Na that has entered the cell and recaptures the K that has left the cell (reinstating balance of Na/K ionic balance)
The AP causes the segment of the nerve to:
depolarize to threshold
The AP is “self propagating” and does not stop until
it reaches the nerve terminal
The AP triggers the release of chemicals from
nerve terminal
Nerve AP lasts
1 ms (one thousandth of a second)
In the neuron, voltage-gated sodium channels are found principally in:
the AXON
The axon is where
voltage gated na-channels are located in neurons
At rest, the K-gates are open/closed?
closed
Activation of K channels starts what:
repolarization
How many k- gates are on the inside of membrane?
1 (one)
K channels will open when Na gates are
closed.
phase 1 AP
Na channels open
Na begins to enter cell
Phase 2 AP
K channels open
K begins to leave cell
Phase 3 AP
Na channels become refractory
no more Na enters cell
Phase 4 AP
K continues to leave cell
Causes membrane potential to return to resting level
Phase 5 AP
K channel closes
Na channels reset
Phase 6 AP
Extra K outside diffuses away
Cells contain high ___ concentrations
potassium
cells have membranes that are essentially permeable to K+ at
at rest
what is generated by diffusion of K+ ions and charge separation
Membrane Potential
membrane electrical potential difference
Membrane Potential is measure in
mV
Typically resting membrane potentials in neurons are
-70 to -90 mV
During the UPSTROKE of an AP:
-Na permeability increases due to
opening of Na channels
inward movement of Na
During the DOWNSTROKE of an AP:
Na permeability decreases due to
inactivation of Na channels
During the DOWNSTROKE of an AP:
K permeability increases due to
Opening of K channels
outward movement of K
After HYPERPOLARIZATION of membrane following an AP:
There is
increased K conductance
due to delayed closure of K channels
The measured potential difference across the cell membrane in mV is known as:
resting membrane potential
At rest, the nerve membrane is more permeable to ___ than to ____.
K+ > Na+
Na/K pump maintains
resting membrane potential
3Na OUT and 2K in
a property of excitable cells (nerve, muscles) that consist of a rapid depolarization followed by repolarization of membrane potential is:
Action Potential
Interior becomes less negative
rapid depolarization
Excitable cells are
nerves
muscles
Depolarization
Upstroke of the AP
-Inward Na movement
Lidocaine blocks these
voltage sensitive Na-channels
-and abolish AP
Repolarization
Downstroke of AP
-outward K movement
Hyperpolarizing the membrane potential is a result of
outward flow of K
A period during which another AP cannot be elicited no matter how large the stimulus is called:
Absolute refractory period
Absolute refractory Period is due to closure of
inactivation Na gates
A period during which an AP can be elicited only if a larger than usual stimulus is provided is called:
Relative refractory period
Purpose of refractory period
to protect the cell from over excitation
allow for a recovery period b/w the AP’s
Name 4 Properties of AP:
- constant size and shape
- Propagation
- All or none Law
- Threshold is the membrane potential at which the AP is inevitable
