DR. ZAHOOR ALI SHAIKH CARDIOVASCULAR SYSTEM LECTURE - IV

EXCITABILITY RHYTHMICITY CONDUCTIVITY CONTRACTILITY PROPERTIES OF CARDIAC MUSCLE

CONDUCTIVITY

CONDUCTION TISSUE OF THE HEART Action Potential that originates in SA node spread to both Atria through intercalated disc and gap junction From atria it can not pass to ventricle due to fibrous Skelton of heart which separates atria and ventricles Therefore specialized conducting tissue is required (it is composed of modified Myocardial cells)‏

SA Node AV Node Bundle of His Or AV Bundle Rt & Lt Bundle Branches Purkinje fiber CONDUCTION TISSUE OF THE HEART

CONDUCTION OF IMPULSE Conduction of impulse In Atria – 1 Meter/ sec AV Node slow conduction – 0.03 to 0.05 Meter / sec There is delay of 0.1 sec in AV node Purkinje fiber - 4 to 5 Meter / sec

Conductive System Of Heart

Q: Name the conductive tissue of the Heart? SA Node Internodal fibers AV Node Bundle of His Or AV Bundle Rt & Lt Bundle Branches Purkinje fiber

Q: Which conductive tissue has the fast conduction rate? Q: Which conductive tissue has slow conduction rate? Fast conduction ---- Purkinje fibers 4 m/s Slow conduction ---- AV node m/s Note: There is AV node delay of 0.1 second

WHAT YOU SHOULD KNOW FROM THIS LECTURE? 1.S – A Node Pace maker of the heart. 2.A – V Node - slowest conduction velocity. Delay of 0.1 sec. What is the importance of this delay? 3.Fastest conduction – purkinje fibers : meters / second. –What is the cause of fast conduction in purkinje fiber? 4.S-A node is supplied by right vagus nerve 5.A-V node is supplied by left vagus.

1.Effect of sympathetic & parasympathetic on conduction velocity. 2.Remember normal rhythmic rate of; S – A node is 70 – 80 / min. A – V node is 40 – 60 / min. Purkinje fiber is 15 – 40 / min.

Contd….. Applied: 1.If S – A node is not working as pace maker? 2.If conduction time increased due to the abnormality ( heart Blocks). 3.If no sympathetic or parasympathetic effect on S – A node, what will be the heart rate ( transplanted heart). 4.What is ectopic pace maker?

DR. ZAHOOR ALI SHAIKH CARDIOVASCULAR SYSTEM LECTURE - V

18 1.EXCITABILITY 2.RHYTHMICITY 3.CONDUCTIVITY PROPERTIES OF CARDIAC MUSCLE 1.CONTRACTILITY

19 CONTRACTILITY

20 We will study the contractility of cardiac muscle but before that let’s see the contractility of skeletal muscle.

22 Steps in Cardiac muscle contraction

23 Source of ca++ for cardiac muscle contraction

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26 Effect of Sympathetic & Parasympathetic ANS on Contractility (you should know effect on Heart rate & Conduction also)‏

27 FACTORS AFFECTING CONTRACTILITY Positive ionotropic effect. Sympathetic stimulation Adrenaline & Noradrenaline Calcium ion Caffine Drugs eg. Digitalis (Digoxin) Negative ionotropic effect Parasympathetic stimulation Acetyl choline Potassium ion Hypoxia (Decrease oxygen)‏ Acidosis Bacterial toxin Drugs eg. Calcium channel blockers, β- Blockers

28 Frank – Starling’s Law Within physiological limits, if there is increase in initial length of cardiac muscle fiber ( due to increase venous return) there will be increased strength of contraction. Reason: Because Actin & Myosin filaments are brought to more optimal degree of sliding therefore increase force of contraction Note: starling’s law affects cardiac contractility but details you will learn with Cardiac out put.

29 WHAT YOU SHOULD KNOW FROM THIS LECTURE? 1.Characteristics of cardiac muscle. 2.Comparison between cardiac & skeletal muscle. 3.Effect of sympathetic & parasympathetic stimulation on cardiac contractility. 4.Positive & negative ionotropic factors. 5.Frank – Starling’s law of heart – effect on contractility.