Properties Of Cardiac Muscle

Properties Of Cardiac Muscle

Properties of cardiac muscle. (or) Name the specialized conducting tissues of heart.
Answer:

1. Excitability:

Definition:

• The ability of a tissue to give response to a stimulus is called excitability.

Features:

• Excitability is increased by the stimulation of sympathetic or catecholamine activity
• It is inhibited by stimulation of vagus nerve or acetylcholine secretion.

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2. Rhythmicity:

Definition:

• Rhythmicity is the ability of a tissue to produce its own impulses regularly.

Features:

• This property is present in all the tissues of the heart.
• The sinoartrial node (SA node) has the highest rhythmicity.
• If the SA node is destroyed, next AV node takes over the function.
• Stimulation of SA node accelerates heart rate.

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3. Conductivity:

• This property is highly developed in a specialized conductive system of myocardium.
• It comprises of
  1. AV node.
     • Present in the right posterior portion of intra-atrial septum.
  2. Bundle of his.
     • Arises from AV node.
  3. Right and left bundle branches.
     • They are branches of bundle of his.
  4. Purkinje fibers.
     • They arise from each branch of bundle of His.
     • Thus impulses is conducted and spread all over the ventricular myocardium through this conductive system.

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4. Contractibility:

Contractibility Definition:

• It is ability of the tissue to shorten in length after receiving a stimulus.

Properties of contractibility:

1. All or none law:

• According to it, when a stimulus is applied, whatever may be strength, the whole cardiac muscle responds to the maximum or it does not give response at all.

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2. Staircase phenomenon:

• The force of contraction increases gradually for the first few contractions and then it remains same.

3. Refractory period:

• It is the period in which the muscle does not show any response to a stimulus.
• It is of two types:
  • Absolute refractory period.
  • Relative refractory period.