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My notes > Cardiac Muscle and Intrinsic Conduction > Flashcards

Cardiac Muscle and Intrinsic Conduction Flashcards

1
Q

How does cardiac muscle contract

A

the sliding filament mechanism - sarcomeres

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2
Q

Cardiac myocytes

A

shorter and fatter than skeletal muscle cells - also more branched and interconnected

push and pull on the cardiac skeleton

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3
Q

How many cardiac myocyte are centrally located nuclei

A

1 or 2

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4
Q

Large mitochondria accounts for how much cardiac myocyte nuclei

A

25%-35%

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5
Q

Intercalated Discs

A

the plasma membranes of adjacent cardiac myocytes interlock at junctions

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6
Q

Desmosomes

A

prevent separation during contraction

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7
Q

Gap junctions

A

allow ions to pass from cell to cell - transmitting current across the entire heart

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8
Q

Sarcomere

A

Thick (Myosin)
Thin (Actin)

Unlike skeletal muscles, cardiac muscle cell sarcomeres vary greatly in diameter and branch extensively

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9
Q

Calcium delivery

A

fewer, wider t tubules - 1 per sarcomere - regulate calcium concentration

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10
Q

Similarities between skeletal and cardiac

A

both muscle types are contractile tissues - contractions are preceded by depolarization in the form of action potentials

transmission of an action potential across the t tubules tiriggers the release of calcium from the sarcoplasmic reticulum

calcium binds to toponin, moves tropomyosin, allows cross bridge cycling to begin

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11
Q

Differences between skeletal and cardiac muscle (Self Excitability)

A

some cardiac muscle cells are self-excitable - these are specific, noncontractile cells called pacemaker

self- generated depolarization travel throughout the heart via gap junctions

no neural input is needed for cardiac myocytes

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12
Q

Automaticity/Autorhythmicity

A

the ability to spontaneously depolarize

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13
Q

Differences between skeletal and cardiac muscle (Functional Syncytium)

A

cardiac muscle cells are tied together to form a functional syncytium

either all cardiac myocytes contract together, or the heart doesn’t contract

skeletal muscles contract via motor unit recruitment

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14
Q

Differences between skeletal and cardiac muscle (Release of calcium)

A

in skeletal muscle, depolarization causes release of calcium from the sarcoplasmic reticulum

in cardiac muscle, depolarization opens special slow-flow calcium channels in the cell membrane - the combination of extracellular calcium and calcium from the SR allows contraction

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15
Q

Differences between skeletal and cardiac muscle (Tetany)

A

in skeletal muscle, the refractory period is shorter than contraction allowing for summation

in cardiac muscle, the refractory period is longer than contraction preventing tetany

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16
Q

Absolute refractory period

A

the period during an AP when an additional AP cannot be generated

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17
Q

Differences between skeletal and cardiac muscle (Aerobic Respiration)

A

cardiac myocytes are dense in mitochondria reflecting a great dependence on oxygen

cardiac muscles is more adaptable to using different nutrient sources as fuel

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18
Q

Intrinsic Conduction System

A

noncontractile cells specialized to initiate and distribute impulses throughout the heart

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19
Q

Cardiac Pacemaker Cells

A

the 1% of cardiac myocytes that are autorhythmic - able to depolarize spontaneously - and set the pace of the heart

found in the sinoatria and atrioventricular nodes

20
Q

Initiation of an Action Potential (Pacemaker Potential)

A

K+ channels are closed, slow Na+ channels are open, the cell’s interior becomes more positive (-60mV to -40mV)

21
Q

Initiation of an Action Potential (Depolarization)

A

Calcium channels open (around -40mV), calcium influxes leading to an AP

22
Q

Initiation of an Action Potential (Repolarization)

A

K+ channels open, K+ effluxes, cell’s interior becomes more negative

23
Q

What is the order that cardiac pacemaker cells pass impulses across the heart

A

Sinoatrial (SA) Node
Atrioventricular (AV) Node
Atrioventricular Bundle
Right and Left Bundle Branches
Purkinje Fibers

24
Q

The Sinoatrial (SA) Node

A

“The pacemaker”

Crescent shaped, located in the right atrial wall - just below the entrance of the SVC

generates impulse 75 times/minute and sets the pace for the heart (“Sinus Rhythm”)

25
Q

The Atrioventricular (AV) Node

A

from the SA Node, the impulse travels down the intranodal pathway to the AV Node

located in the inferior portion of the interatrial septum - just above the tricuspid valve

at the AV Node, the impulse is delayed .1s allowing the atria to complete their contraction

the AV Node has smaller diameter fibers and fewer gap junctions than the other places on the intrinsic conduction pathway

26
Q

The Atrioventricular (AV) Bundle

A

starts in the superior part of the interventricular septum

the AV Bundle is the only electrical connection between the atria and the ventricles

the cardiac skeleton is nonconducting

27
Q

Right and Left Bundle Branches

A

AV Bundles splits into 2 pathways - the Right and Left Bundle Branches

these bundles branches course along the interventricular septum towards the heart’s apex

28
Q

Purkinje Fibers

A

long strands of barrel-shaped cells with few myofibrils

these fibers complete the pathway through the interventricual septum, penetrate the heart’s apex, and turn superiorly into the ventricular walls

provide the impulse for the bulk of ventricular depolarization

there is a more elaborate network of pukinje fibers on the left side of the heart

29
Q

Ejection of Blood

A

ventricular contraction almost immediately follows ventricular depolarization

the heart contracts with a “wringing” motion starting at the apex

the wave of the contraction moves toward the atria

blood is “ejected” superiorly in the great vessels

30
Q

What would happen without input from the SA Node

A

the AV Node would depolarize about 50 times/minute

31
Q

What would happen without the input of the AV Node

A

the pacemakers of the AV Bundle of the Purkinje Fibers would depolarize about 30 times/minute

32
Q

When do slow pacemakers dominate

A

when the fast pacemakers stop working

33
Q

Arrythmia

A

an irregular heart rhythm resulting from a defect in the intrinsic conduction system

34
Q

Fibrillation

A

rapid or irregular contractions of the heart

control of the heart by the SA Node is disrupted

fibrillating ventricle are not useful pumps

35
Q

Defibrillation

A

electricity shocking the heart to depolarize the entire myocardium - ideally, the SA Node begins to function normally, and sinus rhythm is restored

36
Q

Implanatable Cardioverter Defibrillators (ICDs)

A

devices that continually monitor heart rhythms; they will slow tachycardia and emit an electrical shock in the event of fibrillation

37
Q

Ectopic Pacemaker

A

an abnormal pacemaker

if the AV Node takes over, the heart rate will be slower (40-60 bpm), still adequate for tissue perfusion/circulation

38
Q

Premature Ventricular Contraction (PVC) (extrasystole)

A

small regions of the heart become hyper excitable and the heart prematurely contracts

after PVC, the heart has a slightly longer time to fill, and the next normal contraction feels like a “thud”

typically, an occasional PVC is harmless

39
Q

Damages to what structures will prevent impulses from reaching the ventricles (Heart Block)

A

AV Node > AV Bundle > R/L Bundle Branches

40
Q

Total Heart Block

A

no impulses get though, the ventricles beat at their own intrinsic rate - too slow for adequate tissue perfusion

41
Q

Partial Heart Block

A

only some impulses get through

42
Q

Artificial Pacemakers

A

medical devices to recouple the atria and ventricles - pacemakers can be reprogrammed to change with changing energy demands and interrogated to with symptoms appear

43
Q

What can sympathetic branch do?

A

Accelerate heart rate and increases contractility

44
Q

What can parasympathetic branch do?

A

decelerate heart rate

45
Q

Where are cardiac centers located

A

Medulla Oblongata

46
Q

Cardioacceleratory Center

A

sends impulses through the sympathetic trunk - stimulates the SA Node, AV Node, myocardium, and the coronary arteries to increase heart rate and contractility

47
Q

Cardioinhibitory Center

A

sends impulses through the vagus nerve to decrease heart rate

My notes (11 decks)

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