Cardiac Muscles, Heart as a Pump And Functions Of The Heart Valve

Question 1

What are the three major types of cardiac muscle fibers?

Answer 1

Atrial muscle, ventricular muscle, specialized excitatory and conductive muscle fibers

Question 2

The duration of the contraction of cardiac muscle is _____as compared to skeletal muscle?

Answer 2

Longer

Question 3

The specialized excitatory and conductive fibers contract feebly, instead they exhibit?

Answer 3

Automatic Rhythmical AP generation and propogation

Question 4

What is the duration of AP plateau in cardiac cells ?

Answer 4

O.2 sec or 200 Ms

Question 5

What are the two major causes of cardiac muscle AP plateau?

Answer 5

1) the AP is incurred by the opening of fast voltage gated sodium channels, which is succeeded by opening of slow calcium- Sodium channels which prolongs the AP.
2) AP plateau causes a five fold decrease in the membrane permeability of potassium ions, which reduces the outflow of positively charged potassium ions.

Question 6

What is the duration of slow calcium-Sodium channels opening during the AP plateau?

Answer 6

200-300 Ms

Question 7

What is the velocity of excitatory AP conduction through the atrial and ventricular muscle?

Answer 7

0.3 to 0.4 m/second

Question 8

What is the velocity of AP conduction through the His- purkinje system?

Answer 8

4 m/sec

Question 9

What is the duration of the refractory period of ventricles?

Answer 9

250 to 300 Ms ( which is same as the duration of cardiac AP plateau)!

Question 10

What is the duration of the atrial refractory period?

Answer 10

150 Ms.

Question 11

Explain the Excitation contraction coupling function of the calcium ions and T tubules in cardiac muscle?

Answer 11

When an AP reaches the cardiac muscles interior, it passes through the T tubules -> The T- tubule AP causes the longitudinal sarcoplasmic tubules to release calcium ions -> This calcium ions diffuse to the myofibrils and cause muscle contraction by actin-myosin sliding.
The large T tubules also release calcium ions to potentiate the cardiac muscle contraction by opening the voltage dependent calcium channels, which in turn activate the calcium release channels ( Ryanodine receptor channels) in the sarcoplasmic reticulum leading to actin and myosin cross bridge formation.

Question 12

How are calcium ions removed from the cardiac sarcoplasm after the AP plateau?

Answer 12

The calcium ions are transported back by the means of calcium ATPase pump into the sarcoplasmic reticulum and the T tubule- extracellular fluid space.

Question 13

How are sodium ions moved out of the cardiac sarcoplasm after the AP plateau?

Answer 13

By the means of sodium- potassium ATPase pump.

Question 14

The heart contracts in a _____ motion during systole?

Answer 14

Twisting motion

Question 15

The subepicardial fibers spirals in what direction during systolic ejection phase?

Answer 15

Leftward and clockwise direction

Question 16

The subendocardial fibers spirals in what direction during systolic ejection phase?

Answer 16

Rightward and anticlockwise direction

Question 17

What is the membrane potential of cardiac cells during Phase 0 of cardiac action potential?

Answer 17

It is characterized by fast sodium channel opening for sodium influx and the membrane potential reach +20 mV before the sodium channels close

Question 18

Explain Phase 01 of cardiac action potential

Answer 18

It is marked by initial repolarization due the closing of fast sodium channels and potassium exocytosis through the open potassium channels.

Question 19

Phase 2 of cardiac action potential: the plateau phase?

Answer 19

It is characterized by the plateau of action potential due to the opening of L type calcium channels and 5 fold decrease in membrane permeability of positively charged potassium ions

Question 20

Phase 03 or rapid repolarization phase of cardiac action potential?

Answer 20

This occurs due to the L-type calcium channels closure and opening of slow potassium channels.