- What is the histological difference between a cardiac muscle fibre from that of cardiac conducting system fibre?
Fewer striations with indistinct boundary
- Atria and ventricles are separated by a fibrous ring of tissue. How is the impulse transmitted from the atria to the ventricle?
Through the bundle of His
- In adults, the SA node is supplied mainly by right vagus and the AV node by the left vagus. What is the reason for this difference in innervations?
SA node develops from right side of embryo while the AV node from the left side.
- What is the increase in the rate of heart contractions called?
Positive chronotropic effect
- What makes the cardiac muscle to discharge spontaneously?
Property of autorhythmicity
- Name the ion that is responsible for the plateau phase of cardiac muscle fibre action potential.
Calcium (slow opening of Ca² channels)
- What is the alternate name of pacemaker potential?
Prepotential
- What are the two types of Ca++ channels present in the cardiac muscle?
T (transient) and L (long-lasting) calcium ion channels
- Which Ca++ channel opening completes the prepotential?
T-channels
- Which Ca++ channel opening produces an impulse in a cardiac muscle?
L-channels
- During prepotential there is local release of Ca++ from sarcoplasmic reticulum, what is it called?
Calcium ion sparks
- Name the major ion that is responsible for the development of action potential in SA and AV nodes
Calcium ion
- If the SA node or AV node fails to generate an impulse, the rest of the conducting system has the ability to generate prepotentials. What are these pacemaker called?
Latent pacemakers- Will the atrial / ventricular muscle fibres be able to generate prepotentials when the conducting system fails?
They do not generate prepotentials
- When cholinergic vagal fibres to the SA node are stimulated, why does the membrane become hyperpolarized with a decrease in the slope of prepotential?
Ach release increases the K+ conductance of the SA node.
(Physiology; UMS 2008)
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