exactly 28 - . Functional morphology and physiological characteristics of the conduction system of the heart. Automaticity. Cardiac Rhythm. Conduction abnormalities. Physiological characteristics of the working myocardium. Excitation and contraction. Refractory periods. Extrasystoles, flutter and fibrillation. Myocardial metabolism.

sections

• physiological characteristics of heart (working myocardium)

• structure of myocardium

• excitation and contraction

• main electro physiological properties of contractive myocardium are

• extrasystoles

• atrial flutter

• atrial fibrillation

• physiological characteristics of heart (working myocardium)

• The heart contains 4 chambers

• the upper atria receives the venous blood to the two lower ventricles that eject blood into the arteries.

• The right ventricle pumps deoxygenated blood to the lungs, to become oxygenated and the left oxygenated blood goes rest of the body.

• The right atria and ventricle are separated from the left V and A by a septum- prevents mixture of the oxygenated and deoxygenated blood.

• The right atrium receives blood from the SVC and IVC

• left receives from the left the pulmonary veins

• structure of myocardium

Made of three layers of cells

1. purkinje cells

2. cardiomyocytes

3. myocardial endocrine cells

-cells of myocardium have actin and myosin filaments (involuntary skeletal muscle)

-They receive contact by sliding filament mechanism. Cells electrically linked by gap junction which allows electrical impulses to spread across the whole mass

• excitation and contraction

• Cardiac muscle fibers contract via excitation-contraction coupling,

• using a mechanism called calcium-induced calcium release.

The stages of contraction are:

1. Electrical signal starts in the SA node (the heart’s pacemaker) and travels to the AV node, then spreads to heart muscle cells through gap junctions.

2. Action potential causes Na⁺ and Ca²⁺ to enter the heart muscle cells via T-tubules.

3. Calcium binds to troponin-C, which moves the troponin complex and exposes actin binding sites.

4. Myosin binds to actin and pulls it inward using energy from ATP, causing muscle contraction.

5. Calcium is removed by the sarcoplasmic reticulum, troponin blocks actin again, and the muscle relaxes.

   -…………………………………………………………………………………

   Metabolism- ATP needed for contraction and Ca2+

• refractory periods

Refractory periods:

• absolute refractory period

• relative refractory period

-……………………………………………………………………………………………

plateau it what is responsible for the long refractory period

• Absolute refractory period: The absolute refractory period is when no stimulus—no matter how strong—can trigger a new action potential. It lasts from the start of repolarization through rapid repolarization, covering all of systole and early diastole, during which the heart muscle can’t be re-excited.

• Relative refractory period, is the interval during which a second action potential can be generated but only at a higher stimulus intensity.

• …………………………………………………………………………………

  1. Fast Na+ channels open (Na+ influx, depolarization)

  2. Na+ channels close, K+ and slow Ca2+ channels open, the plateau phase elongating the refractory period

  3. Slow Ca2+ channels close hyperpolarization/repolarization occurs

  4. When resting potential is reached, K+ channels close

• extrasystoles

premature contractions of the heart which temporarily disturb cardiac rhythm – has lower amp of regular one and pause for next regular systole so next systole has higher amp

• atrial flutter

very rapid contraction of the atria with regular rhythm and rate 250 to 350 bpm

• atrial fibrillation

irregular very rapid ineffective contractions of section of atrial muscles caused by impulses with a rate of 300 to 600 per min

section

cells of heart

natural pacemaker

5 elements of heart

conduction system

automaticity

automatic and cardiac rhythm

cause of increased heart rate

cause of decrease in heart rate

cells of heart

made of cardiomyocytes- do not require such a stimulus as they have leaking Na+ and k+ ion channels that allow for the entry and exit of Na+ and K+ ions. This allows for constant AP generation.

natural pacemaker

• Sinoatrial node is the hearts natural pacemaker - pacemaker cellls

• it generates its own action potential

• causes the positive increase in voltage across the membrane.

5 elements of heart

1. SAN- in wall of the right atria—60-90 impulses

2. AVN-base of the right atrium- 40-60 impulses

3. Bundle of His- 30-40 impulses

4. Tawara fibres

5. Purkinje fibres- 20-40 impulses- spreads up to the ventricles

conduction system

• conduction system:The heart has a special system that sends electrical signals to make it beat

• It includes: SA node (sinus node), AV node, Bundle of His, and Purkinje fibers.

• Automaticity means some heart cells (like in the SA node) can start signals on their own — without brain signals.

automaticity

Automaticity means some heart cells (like in the SA node) can start signals on their own — without brain signals.

automatic and cardiac rhythm

• Sinoatrial node is the hearts natural pacemaker

• generates its own action potential

• causes the positive increase in voltage across the membrane. the pacemaker potential therefore controls the rate of the heart.

  • Normal cardiac rhythtm- 60-90bpm at rest

  • Tachycardia- increased HR >100 bpm

  • Bradycardia- decrease HR. <60bpm

cause of increased heart rate

• High temperature

• Sympathetic stimulation

• By hormones, T3/T4, circulation of catecholamines (adrenaline)

• Increased Ca2

cause of decrease in heart rate

• cardiac conduction disease- disruption of electrical impulses to the heart