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Physiology > Cardiac Muscle > Flashcards

Cardiac Muscle Flashcards

1
Q

Myocytes are…

A

cardiac contractile cells

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2
Q

Cardiac muscle is more similar to _____ muscle b/c…

A

skeletal

  • striated
  • single central nucleus
  • rich in mitochondria
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3
Q

Cardiac muscle:

A
  • shorter than skeletal muscle
  • branched
  • joined at intercalated discs
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4
Q

At intercalated discs, there are…

A
  • desmosomes: prevent cells from separating during contraction
  • gap junctions: form electrical connections
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5
Q

Gap junctions here are similar to…

A

single unit of smooth muscle

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6
Q

Gap junctions :

A
  • allow ions to pass from cell to cell

- facilitate conduction of cardiac impulse from one cell to next

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7
Q

Intercalated discs allow cells to function as…

A

a syncytium: single coordinated unit

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8
Q

T/F: atrial and ventricular syncitia are connected to intercalated discs

A

F

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9
Q

Desmosomes utilize…

A

mechanical contraction

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10
Q

Gap junctions utilize…

A

electrical contraction

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11
Q

Sarcolemma has…

A
  • fast Na+

- slow Ca2+ channels: open slowly and remain open longer

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12
Q

The onset of AP leads to…

A

a decrease in K+ permeability

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13
Q

Decreased efflux of K+ will lead to…

A

prolonged AP

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14
Q

T-tubules:

A
  • larger than skeletal muscles
  • branches internally
  • fewer connections between T-tubule and SR compared to skeletal muscles
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15
Q

SR:

A
  • smaller than skeletal muscles
  • less Ca2+ for contraction from SER (rest come from ECF)
  • few terminal cisternae
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16
Q

Increase in ECF [Ca2+] leads to…

A

increase of contractile strength

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17
Q

Contraction:

A
  • similar to skeletal muscle
  • shorten via sliding filament model
  • direct length-force relationship
  • refractory period is longer than skeletal muscles
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18
Q

Prolonged relative refractory period prevents…

A

premature heartbeats

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19
Q

For excitation contraction coupling, AP originates…

A

spontaneously in pacemaker cells

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20
Q

Steps of excitation contraction coupling:

A
  1. depolarization opens few VGC fast Na+ in sarcolemma and spreads to contractile cells via gap junctions
  2. Ca2+ entry opens RYR in SER
  3. Ca2+ binds to troponin
  4. tropomyosin shifts and actin binding sites exposed
  5. filaments slide
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21
Q

T/F: enough extracellular Ca2+ leads to contraction

A

F, intracellular Ca2+

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22
Q

Contraction is classified as…

A

graded

- directly proportionate to ICF [Ca2+]

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23
Q

Preload:

A

force that stretches out muscle before contraction

  • creates resting tension
  • increases blood returning to heart
  • increases efficiency of heart
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24
Q

Stretching of myocardium will…

A

increase the load, which will in turn increase the affinity of troponin C for Ca2+

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25
Q

Inotropic factors affect…

A

force of contraction

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26
Q

Positive inotropic effect leads to…

A

increase in force

- occurs by increasing Ca2+ or decreasing Na+ gradient

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27
Q

Decreasing Na+ gradient increases the force b/c…

A

increasing ICF Na+ = decreased activity of Na+/Ca2+ exchanger

28
Q

Na+ gradient can be decreased by…

A
  • increasing ICF Na+

- decreasing ECF Na+

29
Q

Cardiac glycosides:

A

inhibit Na+/K+ ATPase, which leads to increase of ICF Na+

- eventually reduces activity of Na+/Ca2+ exchanger

30
Q

What terminates contractions?

A

removal of Ca2+

31
Q

How does Ca2+ get moved?

A
  • Ca2+ ATPase on SR

- Na+/Ca2+ exchangers

32
Q

Ca2+ ATPase on SR is stimulated by…

A

membrane protein phospholamban

- activity of protein gets altered by protein kinase

33
Q

Na+/Ca2+ exchanger:

A

secondary active transporter that’s powered by Na+/K+ ATPase

- pumps out 1 Ca2+ and 3 Na+ in

34
Q

Differences between skeletal and cardiac muscles:

A
  • depolarizing wave also opens Ca2+ channels in sarcolemma
  • Ca2+ surge prolongs depolarization phase
  • AP and contractile phase is a lot longer, which allows blood ejection from the heart
35
Q

DHPR is the same as…

A

L-type LGC Ca2+ channels

36
Q

Types of Ca2+ channels:

A
  • LGC Ca2+ in sarcolemma and T-tubule

- Ca2+ channels in SR

37
Q

LGC Ca2+ in sarcolemma and T-tubules are opened by…

A

depolarization or phosphorylation

- for phosphorylation, norepi binds to beta 1, which activates Gs mechanism (cAMP dependent PK)

38
Q

Ca2+ channels in SR opens by…

A
  • Ca2+ entry from plasma membrane

- releases Ca2+ from SR

39
Q

Fast myocytes:

A
  • rapidly depolarizes
40
Q

Contractile cardiomyoctes:

A
  • located in myocardium of both atria and ventricles of heart
  • generates contractile force that moves blood
41
Q

Contractile cardiomyocytes have a stable RMP of…

A
  • 90 mV

- Na+/K+ ATPase contributes up to 20 mV of RMP

42
Q

Contractile cardiomyocytes have a higher conductance of ______ and very small conductance of _____

A

K+, Na+

- K+ goes through leak, LGC, VGC

43
Q

Phases of AP:

A
  • phase 0: depolarization
  • phase 1: brief early repolarization phase
  • phase 2: plateau phase
  • phase 3: repolarization develops slower than depolarization
  • phase 4: resting state
44
Q

Phase 0 of AP occurs b/c…

A

AP makes membrane less negative

45
Q

What occurs during Phase 0 of AP?

A
  • fast VG Na+ opens at threshold
  • rapid upstroke
  • depolarization to 20 mV
  • slow VGC Ca2+ begins to open
46
Q

Fast VG Na+ is double gated because…

A

has activation and inactivation gates

47
Q

What occurs during phase 1 of AP?

A

transient outward movement of K+ through open channel

48
Q

What occurs during phase 2 of AP?

A
  • slow VGC Ca2+ are open (DHPR is predominant)
  • lasts 100-200 ms
  • still permeable to K+ remains, but at lower conductance
49
Q

What occurs during phase 3 of AP?

A
  • high K+ permeability due to slow VGC K+
  • L-type Ca2+ channels (DHPR) close
  • Na+ inactivation gates remain closed until midway through this phase
50
Q

What occurs during phase 4 of AP?

A
  • cells at RMP
  • excess Na+ and Ca2+ eliminated
  • relaxation of muscle occurs during this period
51
Q

AP duration:

A
  • is long (300 ms)
  • almost same length as contraction
  • membrane is refractory for most of contraction, which prevents sustained contractions of myocardium
52
Q

At increased heart rates, the length of both AP and contractions are…

A

reduced

53
Q

Energy requirements for cardiac muscles:

A
  • has a lot of mitochondria (30% volume of heart)
  • big dependence on aerobic respiration
  • little ability for anaerobic respiration
54
Q

Cardiac muscles can readily switch…

A

food sources for respiration

- will use lactic acid from skeletal muscles

55
Q

Electrical events in the heart:

A
  • depolarizes and contracts without NS stimulus

- rhythm can be controlled by ANS

56
Q

Coordinated heart beat is a function of…

A
  • gap junctions

- intrinsic cardiac conduction system

57
Q

Intrinsic cardiac conduction system:

A
  • network of noncontractile cells

- initiate and distribute impulses, which leads to coordinated depolarization and contraction of heart

58
Q

2 electrical classes of cardiac myocytes:

A
  • slow myocytes

- fast myocytes

59
Q

Slow myocytes:

A
  • few specialized myocytes that can generate AP
  • found in SA/AV node
  • act as pacemaker
  • don’t contribute to contraction
60
Q

Fast myocytes:

A
  • majority of myocardium
  • contractile atrial, ventricular myocytes, and Purkinje cells
  • move the blood
  • single AP produces single twitch contraction
  • can’t summate AP in cardiac muscle
61
Q

Autorhythmic cells have unstable RMP b/c of…

A

opening of slow Na+, which continuously depolarizes

62
Q

When there is an increase in Ca2+ influx in autorhythmic cells, then it leads to the….

A

rising phase of AP

63
Q

T/F: cellular recruitment for contraction is possible

A

F, not possible

64
Q

Stretch will increase the…

A

forces of contraction

65
Q

Stretch:

A
  • change in sensitivity to Ca2+ and actin/myosin interaction

- reduces space between thick and thin filament

66
Q

When the space between thick and thin filament is reduced…

A

it allows more myosin to interact with actin

67
Q

Frank-Starling Law:

A

ability of heart to increase force of contraction when stretched

  • occurs when blood flows back
  • helps heart pump back what it receives
  • increases passive tension

Physiology (33 decks)

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