Question

How is a cardiac impulse conducted in the heart?

Answer 1

Rhythmicity:

It is the property in which the beating of the heart takes place continuously.

It is one of the most significant properties of heart muscles.

1. The beating of the heart occurs due to systolic and diastolic pressure rhythmically in the heart muscles.
2. The beating of the heart depends on the junctional tissues of the heart.
3. Junctional tissues of the heart are tissues of the cardiac impulse responsible for the origin and conduction of cardiac impulses.
4. A cardiac impulse is a wave of electric potential generated by the stimulation of cardiac muscles by a specific stimulus.

Origin of cardiac impulse:

1. The source of cardiac impulse (electrical activity) is a network of specialized cardiac muscle fibers called autorhythmic fibers.
2. Autorhythmic fibers are self-excitable.
3. Autorhythmic fibers generate action potential that stimulates heart contractions.
4. Junctional tissue, ventricular muscle, and atrial muscle of the heart have different rates of stimulation of cardiac impulses.

Process of origin of cardiac impulse:

1. A cardiac impulse is an impulse produced in the muscle (myogenic impulse) which is at different rates at different levels.
2. Sino-atrial (SA) node of the heart is also known as the pacemaker of the heart.
3. SA node regulates rhythmical heartbeats according to the rate of origin of cardiac impulse per minute.
4. SA node originates cardiac impulse in resting condition 72 times per minute.
5. The Atrioventricular (AV) node regulates the heartbeats in absence of the Sino-atrial (SA) node at a slower rate, i.e, 50 times per minute.
6. Thus atrioventricular node is called a reserved pacemaker.
7. SA and AV nodes originated the rhythm of impulse is known as nodal rhythm.

Conduction of Cardiac impulse:

1. Conductivity is another important property of the heart muscle.
2. Conductivity is the spreading of cardiac impulses throughout the heart.
3. Heart muscle is excited and originates cardiac impulse which is conducted from the stimulated point to throughout the heart because heart muscle fibers are branched fibers.
4. Heart muscle fibers remain connected with each other.

Process of conduction of cardiac impulse:

1. (a) In a healthy heart, the Sinoatrial (SA) node (pacemaker) originates threshold impulse (myogenic impulse) rhythmically 70 to 80 times per minute.

(b) This impulse is conducted over both atria like concentric waves and reaches into the atrioventricular (AV) node.

(c) Through inter nodal fibers, the SA node also stimulates the AV node.

2. (a) The impulses take 0.08 seconds to travel from the SA node to the AV node.

(b) AV node is stimulated 72 times per minute in the presence of SA node.

3.

1. Cardiac impulse is transmitted along with the Bundle of His at a higher velocity from the AV node.
2. The impulse ultimately reaches the Purkinje fiber quickly passing through the right and left bundle branches which end in the ventricular muscle fiber of both sides.

(c) The action potential (impulse) from the Atrioventricular (AV) node to the ventricular muscle takes about 0.08 seconds.

$\mathrm{SA}\mathrm{node}\underset{\mathrm{inter}-\mathrm{nodal}\mathrm{fibres}}{\overset{\mathrm{atrial}\mathrm{muscles}}{\to }}\mathrm{AV}\mathrm{node}\underset{\mathrm{Purkinjey}\mathrm{fibres}}{\overset{\mathrm{bundle}\mathrm{of}\mathrm{His}}{\to }}\mathrm{ventricles}$

Pathway of conduction of cardiac impulse.