Cardiac muscle Flashcards
(30 cards)
What is contraction like in the heart
Constant
-muscle activation is near-synchronous in ventricles
how can the function of the heart be increased
Inotropy
Chronotropy
What is inotropy
Increased force of contraction (increase in stroke volume)
What is chronotropy
Increasing frequency of contraction (increase in heart rate
What is an infarct
-cause?
Zone of ischemic, dead/dying tissues
-Acute obstruction of coronary artery
Why is there a loss of staining in an infarct
Loss of staining due tp leakage in intracellular enzymes
How is cardiac muscle adapted for constant activation and maximum efficiency
As a result of constant activity, myosin isoforms are far more homologous than skeletal muscle
How are cardiac muscles adapted for synchronous electrical activity
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
What does cardiac muscle activation only deal in
Synchronous, single twitches
How does an action potential go into the myocyte
Propagated along the sarcolemma, and into the T-tubules
What contractions are there in cardiac muscle
twitch
What does the refractory period in a cardiac action potential avoid
Tetanus
Maintains twitch contraction
What is needed for a cardiac contraction
Extracellular Ca2+ (doesn’t happen in skeletal)
What is the plateau in the action potential a result of
Influx of Ca2+ ions from the extracellular space to the cytosol
What allows Ca2+ to enter
Opening of L-type Ca2+ channels which open more slowly than the Na+ channels responsible for for the first phase of the action potential
What does the opening of the L-type Ca2+ channels do
Delay depolarization of the sarcolemma
Summary of events of what happens when an action potential travels down t tubules
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
How is the cardiac muscle calcium handling apparatus different from skeletal muscle
Cardiac- Thick T tubules, limited SR, Diads
Skeletal- Thin t-tubules, extensive SR, Triads
How to increase the sensitivity of the myocyte to Ca2+
Increase the diastolic length of the cardiac myocyte
How does caffeine affect the heart
Positive inotrope
-acts on Ca2+ release channels of SR (increases release)
What is an example of an L-type Ca2+ blocker
Verapamil
What do negative inotropes do and their benefits
Benefivial in angina (chest pain) as reduced contraction reduces energy demand, reduces ischemia, and therefore chest pain. They block L-type Ca2+ channels
What does Digitalis do
Enhances Ca2+ release, and increases contractility.
- tHis improves heart function and relieves symptoms of congestive heart failure
What does cardiac muscle need ATP for
To detach and re-energise the myosin head
