Cardiac Action Potential: Lecture 5 Flashcards
Are cardiac muscle cells autorhythmic or non-autorithmic?
non-autorithmic
What is relaying the pace of the heart?
SA node
What do the cardiac cells do?
- they receive a signal
- then they initiate contraction that is going to happen in the cardiac muscle
What is the primary purpose of cardiac muscle?
contraction
What is the membrane potential range? (FULL RANGE IE GRAPH)
-90 to +30
What value is the threshold potential for action potentials in a cardiac muscle cell?
-70
What is the resting membrane potential in a cardiac muscle cell?
-90 mv
Why is it -90?
because the resting membrane is very permeable to K+, K+ channels are open
True or False
Resting cells have a high concentration of K+ inside the cell and a low concentration of Na+ inside the cell
True
What regulates the resting cells ion (K+, Na+) concentrations?
Sodium-Potassium pump
What happens when we have a “leaky K+” channel?
cell becomes more negative as we are losing positive ions
What is the key ion that maintains the rest of the membrane potential in cardiac cells?
K+
In resting membrane cells, which ion begins to initiate a rise of the resting membrane potential? (Going from -90 and getting to a less negative number)
sodium
How does Na+ come into the cells?
via the gap junction
True or False
Sodium influx into the cell is going to increase the permeability of the sodium channels which will in turn bring in more sodium, raising the membrane potential
True
Na+ permeability describes what kind of feedback process?
positive feedback
Once the sodium rises the membrane potential is enough to hit the threshold the membrane will do what?
depolarize
What are the 3 phases in Cardiac Action Potentials?
- Atrial/Ventricular action potentials
- Membrane depolarization and plateau phase
- Membrane repolarization
At the membrane depolarization and plateau phase what is the ion’s permeability?
- decrease sodium permeability
- increased calcium permeability
- decreased potassium permeability
How does Ca2+ start increasing in the cell?
via voltage-gated calcium channels
- detecting the voltage change in the membrane due to the previous influx of sodium
What is the voltage-gated Ca2+ channel called that is open at the plateau phase?
L-type Ca2+ channel
- stays open for a LONG time
Via the L-type Ca2+ channel, how fast does the Ca2+ move into the cell?
not fast, SLOW
What is happening at membrane repolarization?
- Ca2+ channels close, decreasing Ca2+ permeability
- K+ rapidly leaves the cell
What is responsible for the slow movement of the Ca2+? (THE DIP IN THE GRAPH, plateau phase)
There is a balance between the Ca2+ moving into the cell and the K+ ions moving outside of the cell
To repolarize the cell, K+ will rapidly leave the cell until the cell gets back to what?
-90 mv, resting
What is the time that it takes to start and end a cardiac action potential?
250
In Atrial muscle cells, what is the time it takes for a full action potential to occur?
150
What are the processes involved in Excitation-Contraction Coupling
- Membrane depolarization
- action potentials down T-tubules - Entry of Ca2+ into the cell
-through L-type Ca2+ channels - Ca2+ binds to ryanodine-receptor and regulates the exit of Ca2+
- Increase Ca2+ being stored in the sarcoplasmic reticulum
- gets released into the cytosol (via calcium-induced calcium release
- Ca2+ will initiate contraction with the actin and myosin
- Ca2+ is pumped back into the sarcoplasmic reticulum (via SERCA)
What is the role of the sarcoplasmic reticulum?
store calcium
True or False
Cardiac muscle cell regulates Ca2+ entry into the cell
True
What is the refractory perisod
cannot have another action potential occurring at this time
How long is the refractory period?
250 ms
How could we calculate the max heart rate given the refractory period being 250 ms?
- 4 possible action potentials that can happen in one second
4 x 60 = 240 beats per minute
What is the primary purpose of the plateau phase of the cardiac action potential?
To cause Ca2+ induced-Ca2+ release
- The primary purpose is to cause contraction
What are all the steps involved in creating an action potential in cardiac cells?
- Sodium influx from gap junction
- membrane reached -70 threshold potential
- K channels are closed - Sodium influx from voltage-gated channels
- membrane reached +30 then closes
- positive charges travel down the membrane doing two things:
( i ) activates K transient channels
( ii ) activates Ca L-type channels - K efflux and Ca influx
( i ) repolarizes cell
( ii ) allows for excitation-contraction coupling via calcium-induced calcium release - K efflux
- all channels are closed
- after muscle contraction K voltage channels open getting the cell back to the resting membrane - Leaky K channels open
- everything else is closed
What is responsible for the dip in the graph after the peak?
Increased K permeability as K transient tare open trying to repolarize the cell
What is responsible for the plateau part of the graph?
- K leaky and transient channels are open but trying to close
- Ca L type is open
meaning K leaving the cell in counteracting Ca entering the cell
