1.3 Regulation of the heartbeat and cardiac cycle Flashcards
What is the difference between cardiac muscle and other muscles?
cardiac muscle contracts spontaneously. It is myogenic.
What are the principle features of cardiac muscle?
Intercalated discs, central nuclei with perrinuclear space, branched fibres, good blood supply.
Where is the pacemaker region?
Sinoatrial node (SAN)
What other areas of the heart can produce spontaneous contractions?
Atrial Foci (60-80bpm)
Junctional Foci (40-60bpm)
Ventricular Foci (20-40bpm)
Why is the SAN the pacemaker of the heart and not the other regions?
It overrides the other areas because otherwise oxygen wouldn’t get around the body at the correct rate and cells couldn’t function properly.
What is arrhythmias?
Where the conduction pathways of the heart are out of sync.
What is the purkinje system?
It is a system of chains of special myocardial cells that ensure correct direction of flow and ARE NOT NERVES. Connective tissue that action potential travels down.
How does the wiring of the heart ensure that it pumps most efficiently?
SAN - AVN - apex - Budle of His - Purkinje fibres
Ensures venticles contract from bottom up optimum blood removed
What is the simple order the impulse travels through the tissue?
SAN–>Atrial Muscle–>AVN–>Purkinje System–>Ventricular Muscle
What happens at each phase of the cardiac muscle action potential graph?
Phase 0: Rapid depolarisation (fast Na+ channels open)
Phase 1: ‘Notch’ (fast Na+ channels close)
Phase 2: Plateau (Ca2+ enters, K+ permeability low)
Phase 3: Repolarisation (K+ channels open, Ca2+ channels close)
Phase 4: Resting membrane potential
What makes cardiac muscle contract?
Action potential reaches transverse-tubules, Ca2+ influx via voltage-gated channels, (Ca2+ influx from ecm causes Ca2+ influx from sarcoplasmic reticulum), Ca2+ binds troponin C = CONTRACTION
What causes cardiac muscle to relax?
Ca2+ removal by Na+/Ca2+ transporter (3:1) or pumped out via ATP
Pumped into sarcoplasmic reticulum or intercellular space
Why can’t cardiac muscle be tetanized and why is this advantagous?
Peak tension occurs at the end of repolarisation and relaxtion quickly follows so you can’t get repeat contractions between the action potential and the peak contraction so no cramp. Cramp in your heart would kill you.
Why can skeletal muscle be tetanized?
Because the action potential is so short that there is time for more action potentials to be propergated between it and peak tension in the muscle.
What is systole and diastole?
Systole= contraction (chamber emptying)
Diastole= relaxing (chambers filling)
What does an electrocardiogram tell you?
Anatomical orientation of the heart
Relative sizes of the heart chambers
Heart rate/rhythm
Origin of excitation
Spread of impulse
Secay of excitation.
Which nerves initiates the SAN and AVN?
Vagus nerve (parasympathetic)
Adrengergic fibres (sympathetic)
What do the parasympathetic and the sympathetic nerves do to the heart beat?
Sympathetic (noradrenaline) increase heart beat
Parasympathetic (acetylcholine) decreases heart beat
What are the 7 stages of the cardiac cycle?
Atrial systole
Isovolumetric contraction
Rapid ejection
Reduced ejection
Isovolumetric relaxtion
Rapid ventricular filling
Diastasis
Explain each step of the ECG
P wave: atrial depolaristaion
QRS complex: depolarisation of the ventricles
T wave: repolarisation of the ventricles
PR interval: AV contraction time
ST segment: isoelectric period - both ventricles completely depolarised
QT interval: time for both ventricular depolarisation and repolarisation (estimated duration of ventricular action potential)
