Cardiac Action Potential: Lecture 5

Question 1

Are cardiac muscle cells autorhythmic or non-autorithmic?

Answer 1

non-autorithmic

Question 2

What is relaying the pace of the heart?

Answer 2

SA node

Question 3

What do the cardiac cells do?

Answer 3

• they receive a signal
• then they initiate contraction that is going to happen in the cardiac muscle

Question 4

What is the primary purpose of cardiac muscle?

Answer 4

contraction

Question 5

What is the membrane potential range? (FULL RANGE IE GRAPH)

Answer 5

-90 to +30

Question 6

What value is the threshold potential for action potentials in a cardiac muscle cell?

Answer 6

-70

Question 7

What is the resting membrane potential in a cardiac muscle cell?

Answer 7

-90 mv

Question 8

Why is it -90?

Answer 8

because the resting membrane is very permeable to K+, K+ channels are open

Question 9

True or False
Resting cells have a high concentration of K+ inside the cell and a low concentration of Na+ inside the cell

Answer 9

True

Question 10

What regulates the resting cells ion (K+, Na+) concentrations?

Answer 10

Sodium-Potassium pump

Question 11

What happens when we have a “leaky K+” channel?

Answer 11

cell becomes more negative as we are losing positive ions

Question 12

What is the key ion that maintains the rest of the membrane potential in cardiac cells?

Answer 12

K+

Question 13

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)

Answer 13

sodium

Question 14

How does Na+ come into the cells?

Answer 14

via the gap junction

Question 15

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

Answer 15

True

Question 16

Na+ permeability describes what kind of feedback process?

Answer 16

positive feedback

Question 17

Once the sodium rises the membrane potential is enough to hit the threshold the membrane will do what?

Answer 17

depolarize

Question 18

What are the 3 phases in Cardiac Action Potentials?

Answer 18

1. Atrial/Ventricular action potentials
2. Membrane depolarization and plateau phase
3. Membrane repolarization

Question 19

At the membrane depolarization and plateau phase what is the ion’s permeability?

Answer 19

• decrease sodium permeability
• increased calcium permeability
• decreased potassium permeability

Question 20

How does Ca2+ start increasing in the cell?

Answer 20

via voltage-gated calcium channels
- detecting the voltage change in the membrane due to the previous influx of sodium

Question 21

What is the voltage-gated Ca2+ channel called that is open at the plateau phase?

Answer 21

L-type Ca2+ channel
- stays open for a LONG time

Question 22

Via the L-type Ca2+ channel, how fast does the Ca2+ move into the cell?

Answer 22

not fast, SLOW

Question 23

What is happening at membrane repolarization?

Answer 23

• Ca2+ channels close, decreasing Ca2+ permeability
• K+ rapidly leaves the cell

Question 24

What is responsible for the slow movement of the Ca2+? (THE DIP IN THE GRAPH, plateau phase)

Answer 24

There is a balance between the Ca2+ moving into the cell and the K+ ions moving outside of the cell

Question 25

To repolarize the cell, K+ will rapidly leave the cell until the cell gets back to what?

Answer 25

-90 mv, resting

Question 26

What is the time that it takes to start and end a cardiac action potential?

Answer 26

250

Question 27

In Atrial muscle cells, what is the time it takes for a full action potential to occur?

Answer 27

150

Question 28

What are the processes involved in Excitation-Contraction Coupling

Answer 28

1. Membrane depolarization - action potentials down T-tubules 2. Entry of Ca2+ into the cell -through L-type Ca2+ channels 3. Ca2+ binds to ryanodine-receptor and regulates the exit of Ca2+ 4. 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)

Question 29

What is the role of the sarcoplasmic reticulum?

Answer 29

store calcium

Question 30

True or False Cardiac muscle cell regulates Ca2+ entry into the cell

Answer 30

True

Question 31

What is the refractory perisod

Answer 31

cannot have another action potential occurring at this time

Question 32

How long is the refractory period?

Answer 32

250 ms

Question 33

How could we calculate the max heart rate given the refractory period being 250 ms?

Answer 33

- 4 possible action potentials that can happen in one second 4 x 60 = 240 beats per minute

Question 34

What is the primary purpose of the plateau phase of the cardiac action potential?

Answer 34

To cause Ca2+ induced-Ca2+ release - The primary purpose is to cause contraction

Question 35

What are all the steps involved in creating an action potential in cardiac cells?

Answer 35

1. Sodium influx from gap junction - membrane reached -70 threshold potential - K channels are closed 2. 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 3. K efflux and Ca influx ( i ) repolarizes cell ( ii ) allows for excitation-contraction coupling via calcium-induced calcium release 4. K efflux - all channels are closed - after muscle contraction K voltage channels open getting the cell back to the resting membrane 5. Leaky K channels open - everything else is closed

Question 36

What is responsible for the dip in the graph after the peak?

Answer 36

Increased K permeability as K transient tare open trying to repolarize the cell

Question 37

What is responsible for the plateau part of the graph?

Answer 37

- 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