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Muscles > Cardiac muscle > Flashcards

Cardiac muscle Flashcards

1
Q

What is contraction like in the heart

A

Constant

-muscle activation is near-synchronous in ventricles

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2
Q

how can the function of the heart be increased

A

Inotropy

Chronotropy

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3
Q

What is inotropy

A

Increased force of contraction (increase in stroke volume)

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4
Q

What is chronotropy

A

Increasing frequency of contraction (increase in heart rate

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5
Q

What is an infarct

-cause?

A

Zone of ischemic, dead/dying tissues

-Acute obstruction of coronary artery

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6
Q

Why is there a loss of staining in an infarct

A

Loss of staining due tp leakage in intracellular enzymes

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7
Q

How is cardiac muscle adapted for constant activation and maximum efficiency

A

As a result of constant activity, myosin isoforms are far more homologous than skeletal muscle

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8
Q

How are cardiac muscles adapted for synchronous electrical activity

A

Branched fibers are joined with intercalated discs with desmosomes
-allow strong adherence and low resistance gap junctions allow propogation of the myocardial action potential through the heart

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9
Q

What does cardiac muscle activation only deal in

A

Synchronous, single twitches

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10
Q

How does an action potential go into the myocyte

A

Propagated along the sarcolemma, and into the T-tubules

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11
Q

What contractions are there in cardiac muscle

A

twitch

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12
Q

What does the refractory period in a cardiac action potential avoid

A

Tetanus

Maintains twitch contraction

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13
Q

What is needed for a cardiac contraction

A

Extracellular Ca2+ (doesn’t happen in skeletal)

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14
Q

What is the plateau in the action potential a result of

A

Influx of Ca2+ ions from the extracellular space to the cytosol

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15
Q

What allows Ca2+ to enter

A

Opening of L-type Ca2+ channels which open more slowly than the Na+ channels responsible for for the first phase of the action potential

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16
Q

What does the opening of the L-type Ca2+ channels do

A

Delay depolarization of the sarcolemma

17
Q

Summary of events of what happens when an action potential travels down t tubules

A

1) action potential can travel down T tubules or along sarcolemma
2) A.P causes opening of L-type channels and some Ca2+ enters
3) Ca2+ makes a calcium ion cloud
4) Ca2+ enters Ryan-dine receptors and the binding causes Ca2+ stored in junctional sarcoplasmic reticulum to be released
5) Ca2+ goes to actin and myosin for contraction

6) Ca2+ then resequestered by SR via Ca2+ ATPase pumps
- also expelled from cell by Na+-Ca2+ exchange

18
Q

How is the cardiac muscle calcium handling apparatus different from skeletal muscle

A

Cardiac- Thick T tubules, limited SR, Diads

Skeletal- Thin t-tubules, extensive SR, Triads

19
Q

How to increase the sensitivity of the myocyte to Ca2+

A

Increase the diastolic length of the cardiac myocyte

20
Q

How does caffeine affect the heart

A

Positive inotrope

-acts on Ca2+ release channels of SR (increases release)

21
Q

What is an example of an L-type Ca2+ blocker

A

Verapamil

22
Q

What do negative inotropes do and their benefits

A

Benefivial in angina (chest pain) as reduced contraction reduces energy demand, reduces ischemia, and therefore chest pain. They block L-type Ca2+ channels

23
Q

What does Digitalis do

A

Enhances Ca2+ release, and increases contractility.

- tHis improves heart function and relieves symptoms of congestive heart failure

24
Q

What does cardiac muscle need ATP for

A

To detach and re-energise the myosin head

25
Q

How does cardiac muscle make ATP

A
  • Oxidation of fat
  • Oxidation of glucose
  • From other sources (e.g. glycolysis, lactate, ketones)
26
Q

What are the two populations of cardiac muscle mitochondria

A
  • Interfibrillar mitochondria

- Subsarcolemmal mitochondria

27
Q

What is the contraction of the ventricles like in cardiac muscle

A

Synchronous

28
Q

What is contraction via

A

a series of SIMULTANEOUS twitches

29
Q

What does the intracellular calcium do

A

regulates contraction

30
Q

what calcium concentrations do drugs affect

A

intracellular

Muscles (8 decks)

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