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Muscle/nerves (F&F) > Cardiac Muscle > Flashcards

Cardiac Muscle Flashcards

1
Q

Function of cardiac muscle

A
  • Generates waves of contraction responsible for squeezing the heart to pump blood throughout the body
  • Connected to the pulmonary circulation (lungs) and the systemic circulation (rest of body)
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2
Q

Chambers of the heart

A

4 chambers of the heart

  • Right Atrium and ventricle (lungs/deoxygenated blood)
  • Left atrium and ventricle (organs/oxygenated)
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3
Q

Fibers of cardiac muscle

A
  1. Contractile fibers
    - Striated, similar to skeletal fiber
  2. Conducting fibers (eg. Pacemakers)
    - Acts like a neuron to start electrical propagation
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4
Q

Contractile fibers

A
  • cardiomyocyte form complex junctions between extended processes
  • only 1-2 centrally located nuclei
  • intercalated discs in between cells; cell junctions= desmosomes (linking intermediate filaments) and fascia adherents (link actin bundles)
  • gap junctions longitudinally allowing for action potentials to pass in waves from cell to cell
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5
Q

How are electrical synapses passed between cells in cardiac muscle?

A

Action potentials pass in waves from one cell to the next cell through gap junctions

All cells contract as a single unit

Simultaneous contraction of all cardiac muscle fibers= functional syncytium

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6
Q

functional syncytium

A

Simultaneous contraction of all cardiac muscle fibers

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7
Q

Conducting fibers

A
  • few myofibrils (optimized for rapid contraction)
  • highly branched (allow for quick signal propagation)
  • specialized cells (node cells and bundle of His, Bundle branches, and Purkinje fibers)
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8
Q

Node cells of conducting fibers (conducting fibers)

A

SA and AV node cells

generate and relay electrical impulses. SA node cells are the primary pacemakers of the cell

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9
Q

Bundle of His, Bundle Branches, Purkinje fibers

A

Transmit impulses to the ventricular myocardium

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10
Q

ECG

A

Shows the action potential and contractile force
- AP lasts longer than skeletal muscle (has a plateau)
- AP lasts as long as the contractile force

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11
Q

Action potential in cardiomyocytes

A
  1. Phase 0: rapid depolarization
    - Triggered by the opening of voltage-gated sodium channels
    - Rapid influx of Na ions
  2. Phase 1: initial repolarization
    - Closure of Na channels and opening of K channels
    - Outward flow of K ions
  3. Phase 2: plateau phase
    - Sustained depolarization
    - Opening of slow L-type calcium channels, allowing Ca influx
  4. Phase 3: rapid repolarization
    - Closure of Ca channels
    - Rapid outflow of K ions
  5. Phase 4: resting membrane potential
    - Na/K pump and Na/Ca exchanger re-establish ion balance
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12
Q

L-type calcium channel regulation

A

Regulated by autonomic nervous system (sympathetic and parasympathetic)

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13
Q

L-type calcium channel (activation and deactivation)

A

Sympathetic: epinephrine binds to BAR (beta-adrenergic receptor). Binding activated adenylyl cyclase, which increases cAMP. cAMP activates PKA that phosphorylates/opens L-type Ca channel

Parasympathetic: acetylcholine binds to muscarinic cholinergic receptor. Binding inactivates adenylyl cyclase, decreasing cAMP

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14
Q

Sarcoplasmic reticulum and T-tubules in cardiac muscle compared with skeletal muscle

A
  1. Larger T-tubules and less developed SR, forming dyads rather than triads
  2. DHPR does not mechanically affect RyR opening in cardiac muscle
  3. The rise in intracellular Ca comes from extracellular space through DHPR from the t-tubules
    Then more Ca is released by Ca induced Ca release mechanism through the RyRs

Crossbridge cycling is the same as skeletal muscle

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15
Q

Contrast between skeletal and cardiac muscle Action potential

A
  • AP has a plateau phase and a long refractory period, which overlaps the time scale of force generation
  • The prolonged refractory period until the end of contraction means no summation occurs in cardiac muscle
  • The whole period of refractory period overlaps with the muscle contraction so no other muscle contraction can occur until finished
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16
Q

Length-Tension relationship of cardiac muscle

A
  • Has a shorter range of length over which its tension is near optimum (2.2 micrometer)

Cardiac myocyte has a narrower and steeper curve
- Increasing cardiac myocyte length from 75-90% increases tension from 0-70% of the maximum
- Tension that develops during contraction increases with increased length (Frank Starling Relationship)

17
Q

Frank Starling relationship

A

When you change the length of cardiac muscle, it will produce more force. So when you have more blood volume, the cardiac muscle will be further stretched so would need to produce more force to pump around the body

18
Q

Force-velocity Relationship terms

A

Preload: volume of blood in the ventricle prior to contraction

So increased preload results in stretching of cardiac muscle which increases force

Inotrophy: contractility refers to how powerful the heart can contract

Therefore Force of contractions increase with increased Ca concentrations

19
Q

Energy sources of cardiac muscle

A
  1. Oxidative phosphorylation of FFA – generates ~60% of all ATPs
  2. Oxidation of glucose and other carbs ~30%
  3. Lactate, ketone bodies and amino acids can also be used through oxidative pathway

**ATP-creatine system- not a primary energy source

20
Q

Biomarkers for heart attacks

A
  • Creatine kinase-MB (isoforms in heart muscle)
  • Now clinicians mainly use troponin
21
Q

Oxygen demand for cardiac muscle

A
  • Almost entirely aerobic, depends heavily on continuous oxygen supply
  • Relies on myoglobin to store and release oxygen within cells
  • Limited capacity to use glycolysis
22
Q

Fatigue in cardiac muscle

A
  • High resistance to fatigue due to constant demand for ATP and rich blood supply
  • No lactate being used
23
Q

Mitochondrial density in cardiac muscle

A

Mitochondria make up 25-30% of cell volume

24
Q

Cardiac muscle innervation

A
  • Acetylcholine binds to muscarinic cholinergic receptor (M)
  • Epinephrine/norepinephrine bind to beta-adrenergic receptor
25
Q

Cardiac muscle innervation

A

Autonomic system

  1. Sympathetic
    - Norepinepherine NT
    - Increases heart rate and contractibility
    - Beta-adrenergic receptor activates cAMP second-messenger
  2. Parasympathetic
    - Acetylcholine NT
    - Decreases heart rate
    - Muscarinic receptors
26
Q

Cardiac muscle adaptaion

A
  1. Hypertopy- increase in the size of individual muscle fiber, possible in all muscle fibers
  2. Hyperplasia- increase in the number of muscle fibers, not possible for the heart. If myocardial fibers die, they are replaced by fibrous non-contractile scar tissue and heart is never able to fully recover and pump as well as it did before

Muscle/nerves (F&F) (9 decks)

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