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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
Inotropic factors affect...
force of contraction
26
Positive inotropic effect leads to...
increase in force | - occurs by increasing Ca2+ or decreasing Na+ gradient
27
Decreasing Na+ gradient increases the force b/c...
increasing ICF Na+ = decreased activity of Na+/Ca2+ exchanger
28
Na+ gradient can be decreased by...
- increasing ICF Na+ | - decreasing ECF Na+
29
Cardiac glycosides:
inhibit Na+/K+ ATPase, which leads to increase of ICF Na+ | - eventually reduces activity of Na+/Ca2+ exchanger
30
What terminates contractions?
removal of Ca2+
31
How does Ca2+ get moved?
- Ca2+ ATPase on SR | - Na+/Ca2+ exchangers
32
Ca2+ ATPase on SR is stimulated by...
membrane protein phospholamban | - activity of protein gets altered by protein kinase
33
Na+/Ca2+ exchanger:
secondary active transporter that's powered by Na+/K+ ATPase | - pumps out 1 Ca2+ and 3 Na+ in
34
Differences between skeletal and cardiac muscles:
- 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
DHPR is the same as...
L-type LGC Ca2+ channels
36
Types of Ca2+ channels:
- LGC Ca2+ in sarcolemma and T-tubule | - Ca2+ channels in SR
37
LGC Ca2+ in sarcolemma and T-tubules are opened by...
depolarization or phosphorylation | - for phosphorylation, norepi binds to beta 1, which activates Gs mechanism (cAMP dependent PK)
38
Ca2+ channels in SR opens by...
- Ca2+ entry from plasma membrane | - releases Ca2+ from SR
39
Fast myocytes:
- rapidly depolarizes
40
Contractile cardiomyoctes:
- located in myocardium of both atria and ventricles of heart - generates contractile force that moves blood
41
Contractile cardiomyocytes have a stable RMP of...
- 90 mV | - Na+/K+ ATPase contributes up to 20 mV of RMP
42
Contractile cardiomyocytes have a higher conductance of ______ and very small conductance of _____
K+, Na+ | - K+ goes through leak, LGC, VGC
43
Phases of AP:
- 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
Phase 0 of AP occurs b/c...
AP makes membrane less negative
45
What occurs during Phase 0 of AP?
- fast VG Na+ opens at threshold - rapid upstroke - depolarization to 20 mV - slow VGC Ca2+ begins to open
46
Fast VG Na+ is double gated because...
has activation and inactivation gates
47
What occurs during phase 1 of AP?
transient outward movement of K+ through open channel
48
What occurs during phase 2 of AP?
- slow VGC Ca2+ are open (DHPR is predominant) - lasts 100-200 ms - still permeable to K+ remains, but at lower conductance
49
What occurs during phase 3 of AP?
- 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
What occurs during phase 4 of AP?
- cells at RMP - excess Na+ and Ca2+ eliminated - relaxation of muscle occurs during this period
51
AP duration:
- is long (300 ms) - almost same length as contraction - membrane is refractory for most of contraction, which prevents sustained contractions of myocardium
52
At increased heart rates, the length of both AP and contractions are...
reduced
53
Energy requirements for cardiac muscles:
- has a lot of mitochondria (30% volume of heart) - big dependence on aerobic respiration - little ability for anaerobic respiration
54
Cardiac muscles can readily switch...
food sources for respiration | - will use lactic acid from skeletal muscles
55
Electrical events in the heart:
- depolarizes and contracts without NS stimulus | - rhythm can be controlled by ANS
56
Coordinated heart beat is a function of...
- gap junctions | - intrinsic cardiac conduction system
57
Intrinsic cardiac conduction system:
- network of noncontractile cells | - initiate and distribute impulses, which leads to coordinated depolarization and contraction of heart
58
2 electrical classes of cardiac myocytes:
- slow myocytes | - fast myocytes
59
Slow myocytes:
- few specialized myocytes that can generate AP - found in SA/AV node - act as pacemaker - don't contribute to contraction
60
Fast myocytes:
- 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
Autorhythmic cells have unstable RMP b/c of...
opening of slow Na+, which continuously depolarizes
62
When there is an increase in Ca2+ influx in autorhythmic cells, then it leads to the....
rising phase of AP
63
T/F: cellular recruitment for contraction is possible
F, not possible
64
Stretch will increase the...
forces of contraction
65
Stretch:
- change in sensitivity to Ca2+ and actin/myosin interaction | - reduces space between thick and thin filament
66
When the space between thick and thin filament is reduced...
it allows more myosin to interact with actin
67
Frank-Starling Law:
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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