-Striated -contraction occurs using same sliding filament mechanism.
-cardiac are diff b/c they are short, fat, branched + interconnected
-Cardiac muscle fibers have only 1-2 nuclei. More mitochondria.
Properties of Cardiac Muscle II
Desmosomes - hold cells together + prevent separation during contraction
Gap Junctions - Allow for AP to pass freely from cell to cell so whole heart contracts instead of a few cells
-all cells in heart are coupled electrically by gap junctions
Cardiac Action Potential
1% cardiac muscle = authorhymic -> start own depolarizations which leads to dp of rest of the Heart (pacemaker cells)
-Cardiac muscle = all or none effect
-abs refractory period of card. musc. longer - almost as long as contraction.
Cardiac Muscle Contraction
90%- contractile - resp. for pumping heart
10-20% Ca need for contraction enters extracellular space.
Depolarization -> Na channels opened
Slow Ca opened ->influx of Ca
K+ enters = repolarization * READ NOTES
Excitation + Electrical Events: Intrinsic Conduction System of Heart
- heart does not depend on nervous system to depolarize/contract. inbuilt mechanism = intrinsic cardiac conduction system. Pacemake cells→self excitory + initiate/distribute impulses.
Cardiac Conduction System
Sinoatrial Node→R atrium where superior vena cava enters.
Internodal Pathways→direct pathway from SA node to AV - no gap junctions.
AV Node→ fibrous septum btwn R atrium + R vent.
Purkinje Fibres→branch off AV bundle
Cardiac Conduction System II
STEP 1
Activation of an AP in the SA node first
Time = 0
Cardiac Conduction System II
STEP 2
Transmitted into the atrial myosites
-Reaches AV Node
Time = 50 sec
Cardiac Conduction System II
STEP 3
100-second delay @ AV Node. Atrial Contraction begins.
Time = 150 sec
Cardiac Conduction System II STEP 4
Impulse travels along the interventricular septum
within AV bundle. Bundle branches into Purkinje Fibres via moderater band to papillary muscles of R ventricle
time = 175 sec
Cardiac Conduction System II STEP 5
Impulse distributed by Purkinje fibres. relayed thruout ventricular myocardium. Atrial contraction completed. Vent. contraction begins
time = 225 seconds
Cardiac Conduction System III
No gap junctions between cardiomyocites of atria/ventricles. Av Bundle - only electrical connection btwn atria/ventricles. Branches into 2 paths -connects to purkinje fibres - rapid conduction b/c large fibres + large gap junctions
Defects = arrhymias
Electrocardiography
-diagnostic tests records electrical activity in heart by placing electrodes on body
P-wave-dp of atria, QRS complex-dp of ventricle+rp of atria at same time, T-wave-small rp of ventricle
Electrocardiography II
P-R Interval = time it takes for impulse to travel from SA>AV thru penetrating fibres down AV bundle Purkinje fibres
O-T Interval - time it takes for ventricle to contract + relax again
