Cardiac Muscle and Electrical Activity Flashcards
What is the heart?
Muscular pump which creates pressure head to push blood through blood vessels
What is the approximate weight of the heart?
250g-350g
What is the cardiac cycle?
The rhythmic contraction and relaxation of the heart that generates heart pumping action
Which parts of the heart act as a unit?
Both atria
Both ventricles
What increases the pressure of the heart?
Contraction of the muscle
What drives blood to move through the body?
Pressure difference droves blood flow (pressure gradient)
Which kind of contraction comes first: atrial or ventricular?
atrial
What are adjacent myocardial cells linked by?
Intercalated discs containing gap junctions
What are gap-junctions?
Fluid filled channels that allow the rapid spread of action potentials from cell to cell
What name is given to cardiac muscle in regard to its simultaneous contraction?
Syncytium
What structure triggers the contraction of myocardial cells?
Autorhythmic or pacemaker cells
What kind of cells are pacemaker cells?
Specialised noncontractile myocardial cells
What special property do autorhythmic cells possess?
Their membranes may spontaneously depolarise and generate action potentials
Where are the autorhythmic cells concentrated?
Sinoatrial node
Where is the sinoatrial node located?
The right atrium near the opening of the superior vena cava
What is the path of depolarisations in myocardial cells?
Atrial myocardial cells
Pause in fibrous layer
Ventricular myocardial cells
Atrial syncytium and ventriucalr syncytium
What is the path of depolarisations in myocardial cells?
Atrial myocardial cells
Pause in fibrous layer
Ventricular myocardial cells
Atrial syncytium and ventricular syncytium
How do spontaneous action potentials generated by autorhythmic cells in the SA spread to atrial contractile myocytes and then the ventricles?
Cardiac conduction system
What is the velocity of impulses spread through atrial fibres?
1m/sec
What conducts the impulse from the right atrium into the left atrium?
Specialised fibres called Bachmann’s bundle
How are impulses spread following atrial conduction?
Atrioventricular node
Where is the AV node located?
Base of the right atrium near the interatrial septum
What is the conduction velocity of the AV node?
0.05m/sec
What does the slow in atrial and ventricular conduction velocity ensure?
A delay between their contraction
What does the delay between atrial and ventricular conduction permit?
Optimal ventricular filling during atrial conduction
What is the conduction path of the atrioventricular node?
Bundle of His, bundle branches, Purkinje fibres
What is the conduction velocity in Purkinje fibres?
1-4m/sec
What generates each heart beat?
Spontaneous depolarisation of the SA node
Why can’t the AV node set its own rate of excitation in spite of possessing pacemaker cells?
The action potentials from the SA node travel faster to the AV node than it generating its own action potentials
When can the AV node become the predominant pacemaker cell in the heart?
If the SA node is destroyed
Where would pacemaker cells generate action potentials in the case that both the AV node and SA node were destroyed?
Purkinje fibres
What are the two types of action potentials in individual cells in cardiac tissue?
Fast response and slow response
Where is fast response generated?
Atrial and ventricular myocytes
Where is slow response generated?
Autorhythmic cells in sinoatrial and atrioventricular nodes
What are the phases of action potentials in cardiac muscle?
Upstroke
Early repolarisation
Plateau
Repolarisation
FInal repolarisation
What are the phases of action potentials in cardiac muscle?
Upstroke
Early repolarisation
Plateau
Repolarisation
Final repolarisation
When can a relative refractory period occur?
During repolarisation - Phase 3
What is the major difference between cardiac and skeletal muscle’s action potentials?
Cardiac action potentials can last up to 300 msec while skeletal action potentials typically last for only 25 msec
What phase of action potentials define cardiac muscle?
Phase 2 of cardiac action potentials - plateau
What does arrival of AP at a contractile myocardial cell do?
Open voltage gated Na+ channels
What channels open at the arrival of APs?
Voltage-gated Na+ channels rapidly
Voltage-gated Ca++ channels slowly