Properties Of Cardiac Muscle Flashcards
Why is plateau phase so critical to cardiac muscle function?
It is to prevent additional impulses from spreading prematurely through the heart and it allows sufficient time for muscle to contract and pump blood effectively
How does delay of the impulse at the AV node contribute to cardiac function?
It gives sufficient time for atrial muscle to contract & pump blood into ventricles before the impulse conducted into the lower chamber
How do gap junction and intercalated discs aid in contraction of the heart?
Gap junction within intercalated discs allows ions like calcium, potassium and sodium to flow between adjacent cell, transmitting impulse and action potential from one cell to another cell and ensuring synchronised contraction.
Conduction speed in cardiac tissue. High to low
A. AV node B. SA node C. Purkinje fibre D. Atrial pathway E. Bundle of his F. Ventricular muscle
SA node, atrial pathway, AV node, bundle of his, purkinje fibres, ventricular muscles
Which part of ECG corresponds to ventricular repolarization?
A. P wave B. QRS duration C. T wave D. U wave E. PR interval
C
- P wave & QRS duration are produced by atrial depolarisation and ventricular depolarisation respectively.
- U wave : by ventricular myocytes with long AP, purkinje fiber repolarization, electrolyte imbalance
- PR interval: btwn atrial & ventricular depolarisation
Which of the following normally has a slowly depolarising “prepotential”
A. SA node B. Atrial muscle cells C. Bundle of his D. Purkinje fibres E. Ventricular muscle cell
A
- Cells in SA & AV node have pacemaker potential that associated with slowly depolarising prepotential.
- B,C,D,E maintain stable depolarisation that is quickly polarised following activation of voltage gated Na+ channel
In second degree heart block
A. Ventricular rate is lower than the atrial rate
B. Ventricular ECG complexes are distorted
C. There is a high incidence of ventricular tachycardia
D. Stroke volume is decreased
E. Cardiac output is increase
A
- second degree heart block - atrial beats are blocked before reaching the ventricles. Constant PR interval
Currents caused by opening of which following channels contribute to the repolarization phase of the AP of ventricular muscle fibres?
A. Na+ channel B. Cl- channel C. Ca2+ channel D. K+ channel E. HCO3- channel
D
In complete heart block
A. Fainting may occur because the atria are unable to pump blood into the ventricles
B. Ventricular fibrillation is common
C. Atrial rate is lower than the ventricular rate
D. Fainting may occur because of prolonged periods during which the ventricles fail to contract
D
Explain AP of cardiac ms phase by phase
Phase 0,1,2,3,4
AP of cardiac ms is longer than skeletal ms. Why?
- due to prolong calcium ion influx via long lasting calcium Channel
- decrease permeability of K ion ( does not occur skeletal ms)
Non contractile pace maker
A. Atrial myocytes B. Ventricular myocytes C. Bundle of his D. Right bundle branch E. Purkinje fibers
A. Atrial myocytes, B ventricular myocytes, E. purkinje fibers
2 characteristics of SA node?
Initiate heart beats
Controls heart rate
AP potential of Pacemaker cells
SA node transmit AP > spreading it throughout contractile myocyte of atrium > myocyte are connected by gap junction which located within intercalated discs send ions from cell to cell producing electrical activity AP > impulse reach AV node > impulse slows down in AV node allowing sufficient time for atrium to fully contract and pump blood into ventricle > impulse now spread to contractile myocytes of ventricular.
Characteristics of AP in cardiac muscle
A. Fast impulse
B. Auto rhythmicity
C. Unstable membrane ( does not have defined phases)
D. Ability to cause conformational changes on troponin C
E. No rapid depol phase
B, C, E
