Cardiac muscle Flashcards
What are the three types of cardiac muscle?
Excitatory cells
Conducive muscle fibers
Myocardium
What are the properties of the cardiac muscle?
Striations
Actin and myosin filaments in the myofibrils
Dark bands called intercalated discs - forming gap junctions
Cell membrane that separates cardiac muscle cells
Syncytium (multinucleated)
Define syncytium
An arrangement of multinucleated muscle fibres in which the fibers fuse to form an interconnected mass of fibers
Name the sycytiums in the heart (heart divisions)
The heart is divided into atrial syncytium which is composed of atrial walls, and a ventricular scyncytium composed of ventricular walls
What separates the atria from the ventricles?
A fibrous tissue, and it does not allow for transmission of action potentials
What initiates action potentials in the heart?
Pacemaker (sinoatrial node)
What conducts Action potentials to the ventricles?
Atrioventricular bundle
What is the AV bundle composed of?
Conducive fibers
What is the myocardium resting potential?
-85 mV
What value is the membrane potential during depolarisation
+20 mV
Name the phases of cardiac action potential and give the term of what is happening at that phase.
Phase 0 – Depolarization
Phase 1 – Repolarization to plateau
Phase 2 – Plateau
Phase 3 – Repolarization
Phase 4 – Resting membrane potential
Explain what happens in each phase
Phase 0 - Rapid depolarization occurs when the cells reach threshold and fast sodium ion channels open.
Phase 1 - This phase is caused by closure of fast sodium ion channels, initiate repolarization and efflux of potassium ions through open potassium channels.
Phase 2 - The opening of voltage-gated, slow L-type calcium ion channels and potassium ion channels close.
Phase 3 - Voltage-gated slow L-type calcium ion channels close and opening potassium ion channels cause rapid repolarization.
Phase 4 - The resting membrane potential of these cells is restored, increase efflux of potassium ion.
Define cardiac cycle
A sequence of events the occur during one complete heartbeat.
It is spontaneously initiated by the SA node by the generation of action potentials
Differentiate between systole and diastole
Systole – contraction of cardiac muscle
Diastole – relaxation of cardiac muscle
How to calculate duration of cardiac cycle?
Duration=60sec/HR
What happens to the duration of each cardiac cycle when the HR decreases?
the duration of each cardiac cycle will increase
Describe the phases of a cardiac cycle
Phase I: Period of Filling
Phase II: Period of Isovolumic Contraction
Phase III: Period of Ejection
Phase IV: Period of Isovolumic Relaxation
What happens during late diastole?
Both sets of chambers are relaxed and ventricles fill passively
What happens during Atrial systole?
Atrial contraction forces a small amount of additional blood into ventricle
What happens during isovolumetric contraction?
The first phase of ventricular contraction pushes AV valves closed but does not create enough pressure to open semilunar valves.
What happens during ventricular ejection?
As ventricular pressure rises and exceeds pressure in the arteries, the semilunar valves open and blood is ejected.
Describe Isometric ventricular relaxation
As ventricles relax, pressure in the ventricles falls, blood flows beck into cusps of semilunar valves and snaps them closed.
What is the term for Maximum blood volume in ventricles
End diastolic volume
What is the minimum blood volume in ventricles?
End-systolic volume
