Week 1 Part 1 Flashcards
Where does the excitation of the heart normally originate?
Sino-atrial node
Where is the SA node located?
Upper right atrium
What happens to the ions during the slow depolarisation of the membrane potential (pacemaker) to threshold?
Decrease in K+ efflux
Na+ and K+ influx
Transient Ca++ influx
The rising phase of action potential depolarisation in pacemaker cells is caused by what?
Calcium influx
The falling phase of action potential in pacemaker cells is caused by what?
Potassium efflux
How does cardiac excitation spread across the heart?
SA node AV node Bundle of His Left and right branches Purkinje fibres
What type of cell:cell junctions allow excitation to spread through the heart?
Gap junctions
In the ventricular muscle action potential, what is the steep rise in membrane potential (phase 0) caused by?
Fast Na influx
In ventricular muscle action potential, what is the small decline in membrane potential after the steep incline due to?
Closure of the Na channels and transient K efflux
What is the horizontal part of the ventricular muscle action potential graph due to (phase 2)?
Calcium influx
What is the fall in action potential of the ventricular muscle action potential graph due to?
Closure of Ca++ channels and K+ efflux
What is the resting membrane potential of ventricular muscle?
-90mV
Stimulation of which nervous system increases the heart rate?
Sympathetic
Stimulation of which nervous system decreases the heart rate?
Parasympathetic
What is considered a normal resting heart rate?
60-100bpm
What is the neurotransmitter for parasympathetic stimulation of the heart?
What muscarinic receptors does it act on?
Acetyl choline
M2 receptors
What drug can be used in extreme bradycardia to speed up the heart rate?
Atropine
What does vagal stimulation of the heart do to the electrical impluses running through the heart?
Increases AV nodal delay
What is the neurotransmitter for sympathetic stimulation of the heart and what adrenoceptors does it act on?
Noradrenaline
Beta-1 adrenoceptors
True/False
Cardiac muscle is striated
TRUE
Muscle fibres are made up of many…
Myofibrils
Myofibrils are made up of 2 components. What are they?
Myocyin
Actin
What ion is essential for muscle contraction?
Extracellular calcium
What does actin bind to in order to allow contraction?
Troponin
Where is calcium released from in the cell to allow contraction of muscle fibres?
Sacroplasmic reticulum
What is a refractory period?
A period following an action potential in which it is not possible to produce another action potential
What is stroke volume?
The volume of blood ejected by each ventricle per heart beat
What is an intrinsic mechanism?
Mechanism from within the heart
What is an extrinsic mechanism?
Nervous/hormonal control
What is the Frank-Starling Mechanism or Law of the Heart?
The more the ventricle is filled with blood during diastole, the greater the volume of ejected blood will be during the resulting systolic contraction
What increases the affinity of troponin for Ca++?
Stretch
What is afterload?
The resistance into which the heart is pumping
What type of nerves supply the ventricular muscle?
Sympathetic
What is a positive inotropic effect?
Increase in the force of contraction
What is a positive chronotropic effect?
Increase in the heart rate
What does sympathetic stimulation do to the Frank-Starling curve?
Shifts it to the left
What does the heart failure do to the Frank Starling curve?
Shifts the curve to the right
What does vagal stimulation of the heart do to:
A: The heart rate
B: The force of contraction
Slows rate
No influence on force of contraction
Where are adrenaline and noradrenaline hormonesreleased from?
Adrenal medulla
What makes up cardiac output?
SV x HR
What is cardiac output?
Volume of blood pumped by each ventricle per minute
What events occur during the cardiac cycle?
Passive filling
Atrial contraction
Isovolumetric ventricular contraction
Ventricular ejection
Isovolumetric ventricular relaxation
What does the P wave signal in an ECG?
Atrial depolarisation
When do the atria contract on an ECG?
Between the P-wave and the QRS
When does ventricular contraction occur on an ECG?
After the QRS
What is an isovolumetric contraction?
When the tension rises around a closed volume (just before diastole)
What does the T wave on an ECG represent?
Ventricular repolarisation
What causes the dicrotic notch on the aortic pressure curve?
Second heart sound, aortic/pulmonary valves closing
On the jugular venous pulse graph, what do the following letters represent?
A
C
V
A - atrial contraction
C - bulging of tricuspid valve into atrium during ventricular contraction
V - is rise of atrial pressure during atrial filling: release as AV valves open
