Final Material Flashcards
What triggers cardiac myocytes to bring about ejection of blood?
AP sweeping across muscle membranes
What is autorythmicity?
Rhythmic beating of the heart as a result of self-propagated APs
Cells capable of autorhythmicity
SA node
AV node
Left/right branch of bundle of his
Purkinje fibers
T/F All autorhythmic cells have same rate of depolarization
FALSE! They have different rates, and all contain funny current and can act as pacemaker
Why is the SA node the pacemaker of the heart?
Exhibits fastest rate of automaticity
Diastolic depolarization is the fastest (gets to threshold quicker)
Generate AP quickly
Overdue suppression = directly suppresses automaticity of other autonomic cells
What happens if SA node is not functional?
AV is next group (aka latent pacemaker)
HR would be slower=escape beat….escape rhythm if continued
What is heart block?
Occurs in heart disease
AP is generated by SA node, can’t be transferred to ventricle
Atria beats at a different pace causing heart to beat out of rhythm
3 criteria needed for efficient cardiac function
Atrial excitation and contraction should be complete before ventricular contraction
Excitation of cardiac muscle fibers should be coordinated to ensure heart chambers contract as unit
Pairs of atria/ventricles should contract simultaneously (act as syncytium)
What is fibrillation?
Random uncoordinated excitation and contraction of cardiac cells
Ventricular fibrillation rapidly causes death due to inability of heart to pump blood into arteries
During the spread of cardiac excitation, what occurs during atrial excitation?
AP originating in SA node first spreads throughout both atria from cell to cell via gap junctions
During the spread of cardiac excitation, what occurs during interatrial pathway?
Extends from SA node within the right atrium to left atrium
Transmits impulses rapidly from SA node to left atrium and ensures both atria become depolarized to contract simultaneously
What is AV nodal delay? Why is it important?
AP is conducted slowly through AV node allowing for atria to be completely depolarized ant to contract, emptying contents into ventricle.
It allows for complete ventricular filling
