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CRRAB 1 Week 1 > Cardiac Muscle > Flashcards

Flashcards in Cardiac Muscle Deck (49)
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1
Q

What are the three ways cardiac muscle APs differ from skeletal muscle APs?

A

they’re self generating
they conduct directly from cell to cell
they have a long duration

2
Q

What are the three most important ions for cardiac APs?

A

sodium, calcium, potassium

3
Q

On what side of the membrane is sodium concentration higher? calcium? potassium?

A

sodium and calcium are higher in the interstitial fluid (so they want to move into the cell)

Potassium is high in th eintracellular fluid, so it wants to move out

4
Q

What structures in the membrane are responsible for the resting membrane potential and rapid changes?

A

ion channels

5
Q

What are the three possible states of ion channels?

A

open, closed, inactivated

6
Q

What is the resting membrane potential for cardiac cells? Closes to what ion equilibrium?

A

-90 mV - which is potassium’s equilibirum

7
Q

What are the two types of myocardial cells?

A

myocardial contractile cells

myocardial autorhythmic cells = pacemaker cells

8
Q

Contractile cell APs are similar to neurons exept for what important difference?

A

much longer AP due to extended Ca2+ entry

9
Q

How can pacemakers spontaneously generate APs?

A

their membrane potential is inherently unstable

10
Q

Which cells produce the “slow response” and which produce the “fast response”

A

pacemaker cells = slow response

contractile cells = fast response

11
Q

How many phases are there in a contractile cell AP?

A

5, but they’re numbered 0-4

12
Q

For contractile cells, what is the first step in firing an AP?

A

the Na channels open and the K+ channels close. THis means K+ can’t leave the cell and Na+ rushes in. This causes a rapid depolarization.

13
Q

For contractile cells, what happens at the peak - the overshoot?

A

the Na+ channels close and FAST K+ channels open. K+ is now wanting to enter the cell based on the electrochemical gradient - this is what makes the initial repolarization happen briefly.

It doesn’t last long though - the K+ channels close

14
Q

After the fast K+ channels close, what opens?

A

the slow inward Ca2+ channels open. Ca 2+ enters the cell very slowly, halting the repolarization and causing the characteristic plateau

15
Q

What causes the repolarization after the plateau?

A

the Ca2+ channels close and the delayed rectifier slow K+ channels open, allowing K+ to rush out of the cell causing the rapid repolarization

16
Q

What slows the rapid repolarization such that the resting membrane is reached and maintained?

A

the slow K+ channels close and the inward rectifier channels open when you reach the K+ resting membrane potential

17
Q

What current characterizes the pacemaker cells

A

the funny current

18
Q

what are the phases of the apcemaker cell AP/

A

three phases: 0, 3, and 4 to coincide with the contractile

19
Q

What makes the funny current funny?

A

both Na and K are going in and out

20
Q

What causes the potential to gradually rise?

A

a gradual influx of Na

21
Q

When the potential reaches a threshold, what happens?

A

you have a transient opening of the Ca2+ channels and you get an influx of Ca2+ to further depolarize

22
Q

How does the influx of Ca2+ essentially sustain itself?

A

It triggers long-lasting Ca2+ channels to open

23
Q

What causes the depolarization to stop and then result in repolarization?

A

opening of the K+ channels so K leaves the cell

24
Q

So what ion primarily mediates phase 0 in contractile cells/ in pacemaker cells?

A

Na in contractile

Ca in pacemaker

25
Q

What keeps the contractile cells from going into summation or tetanus?

A

they have a really long refractory period

26
Q

What are the structures that connect the ends of two adjacent cardiac contractile cells?

A

intercalated disks

27
Q

In the intercalated disks, what forms the firm mechanical attachments?

A

desmosomes with adherens proteins

28
Q

In the intercalated disks, what causes the electrical connection between the cells?

A

gap junctions with channels formed by connexin proteins

29
Q

What do the gap junctions allow for?

A

THey allow positive charged ions to flow away from the depolarized membrane of the first cell over to the hyperpolarized membrane of the adjacent cell.

This triggers a depolarization in the adjacent cell, leading to an AP

30
Q

How do we measure electrical events of the cardiac cycle/

A

electrocardiogram

31
Q

What is happening during the P wave?

A

atrial depolarization

32
Q

What does the PR interval represent?

A

the conduction time through the atria and the AV node

33
Q

What is the QRS complex?

A

ventricular depolarization

34
Q

What is the QT interval?

A

the duration of ventricular systole, or contraction

35
Q

What does the ST segment signify?

A

duration of the plateau phase in the contractile cells

36
Q

What does the T wave represent?

A

ventricular repolarization

37
Q

Why can’t you see repolarization on an EKG?

A

Because is occurs during ventricular depolarization, which has the enormous QRS segment

38
Q

THe parasympathetic fibers from the vagus nerve release what NT? To what effect?

A

ACh
It increases the permeability of the resting membrane to K+, leading to a hyperpolarization - this means you have a slower rate of spontaneous depolarization - a negative chronotropic effect; heart slows down

39
Q

What do sympathetic fibers release? to what effect?

A

NE

it increases the spotnaneous depolarization of the membrane - a positive chronotropic effect; the heart speeds up

40
Q

What is the ion that really drives the actual contraction?

A

Ca2+

41
Q

What happens when you have an action potential in a contractile cell?

A

you get an opening of a voltage-gated Ca2+ channel, which allows Ca2+ to enter the cell

42
Q

What does the Ca2+ do in the cell?

A

It binds to ryanodine receptors on the sarcoplasmic reticulum, which triggers more Ca2+ channels to open, allowing stored Ca2+ to flow out of the SR into the cell further increasing Ca2+ concentration

43
Q

What does this high Ca2+ concentration cause in the cell?

A

It binds to troponin and allows actin and myosin to interact, leading to a cotnraction

44
Q

Why does relaxation occur?

A

Because Ca2+ will be pumped back into the SR and out of the cell after about 200 ms

45
Q

What’s the difference between isometric and isotonic contraction?

A

isometric is when the length is fixed by having the ends of hte muscle held rigidly - means it can develop tension but not shorten

Isotonic is when the tension is fixed - an unrestrained muscle causes it to shorten without force development

46
Q

Active tension developed during isometric contraction depens on what?

A

the muscle length at which contraction occurs

too short - no contraction
too long - no contraction
appropriate length is the most myosin-actin interactions possible = contraction

47
Q

What is an inotrope? Example?

A

something that influences the amount of tension the muscle can develop, or the amount of shortening a muscle can achieve

NE is a positive inotrope because it increases isometric tension

48
Q

Mechanical response of the myocyte depends upon what?

A

preload, afterload, and contractility

49
Q

Cardiac myocyte length-tension relationshipsa re correlated with what?

A

changes in volume and pressure in the intact ventricle