Lecture 11 : The Initiation and Regulation of the Heart Beat Flashcards
What does the Depolarisation period of the Cardiac Action Potential Cycle consist of?
Fast initial upstroke,due tot he rapid depolarisation as Na2+ inflow when voltage gated fast Na2+ channels open - causes contraction
What does the Plateau period of the Cardiac Action Potential cycle consist of?
Plateau phase of depolarisation (maintained depolarisation) due to the inward sustained Ca2+ current of movement, causing AP to last almost as long as the contraction of the cell
Because the muscle if refractory, both during and shortly after the passage of action potential- the long plateau phase ensures the unidirectional excitation of the myocardium. (means that a second contraction cannot be triggered and gives chance for heart to relax) Caused by the Ca2+ inflow when voltage-gated slow Ca2+ channels open and K+ outflow when some K+ channels are open
Ca2+ Inflow = K+ outflow
-much longer than nerves
-no ca2+ channel for nerve AP
-less likely to tetanus as long
How are ventricular myocytes arranged?
In sheets
Lots of CT between those sheets
Coronary vessels
What is the moment of the heart?
“Twisting and ringing motion”
Contracting and Turning
with wavering of pressure through coronary vessels
What is the inherent rhythmicity of the heart?
inherent rhythmicity based on SA node 90-100 beats per min
no nervous input, but will still receive hormonal input
What is the SA Node?
A specialised knot/bundle of cells in the heart which has an auto rhythmic function, generating a pattern of activation
the cells go through a cycle of generating AP with a known delay refractory period, and generate a known electrical activity which spread through the heart, causing coordinated contractile function (myocytes active in a pattern)
What doe the phrase “ wavefront of electrical activity mean”?
Not all parts of the heart are activated at once
The Myocytes of the heart are activated in a sequence, which spread through the heart and down the Purkinje fibres
What is the whole basis of the heart’s electrical activity?
To co-ordinate the mechanical activation and generate pressure
What happens when the electrical activity does occur perfectly?
There electrical activity may not go through the tissue (dead tissue)
May be a defect in Purkinje Fibres so it doesn’t transfer
Region is now not acting in a co-ordinate fashion
Generations of force or pressure is less/not as efficient
seen through EF or Echo
What does the Repolarisation Period of the Cardiac Action Potential consist of?
Occurs when Voltage gated Ca2+ channels Inactivate, causing repolarisation of myocardial cells
Closure of Ca2+ channels and K+ outflow when additional K+ channels open.
Resets back to Negative membrane potential.
What happens if you change the ionic composition in blood?
Sensitive to changes in circulating K+, Na+ and Ca2+ levels in the plasma, and it could affect the potential to Generate AP,
therefore you need to Maintain Osmolarity(# or quantity in the plasma) and Ionic Gradient
Relies on Stability of sodium in the plasma
Affects ECG
Can alter saltiness/osmolarity of the plasma if you drink a lot of water, or become very dehydrated, worst case could have large effects on euro physiology and cardiac action potentials
What does ECG stand for?
Electrocardiogram
What is the role of an ECG?
Measures the Electrical activity in the heart
ECG is the summation of tall cardiac Action Potential from different parts of the body, as they spread through the chest wall, at different positions and different times of the cardiac cycle
Electrical activity can be measured throughout the body
The biggest electrical acuity in the body that we can measure is about 1-1.5 mV spread throughout tissue, and this can be picked up in different regions of the body
Connected by different (12) Lead Placement of different parts of the body, about 4 electrodes, getting different “view” of the heart (relative position is different)
you can get different Patterns relative to where the chest pattern view has been taken
What is the feature of having water in our body?
Our body is mostly water
Water is a good conductor of electrical activity
this allows us to measure the spread of the measure of action potentials out over the heart and throughout the body
Comes out to the surface of the skin - where we can make the measurement of ECG
What is an installed pacemaker?
Leaves have been put down one of the veins, and cathode gets pretty close to the RA, and are able to pulse and Resynchronise the electrical activity
Lots are sensing and analysing the ECG, but when ECG is disturbed, the pacemaker will act (give the person an electric shock) and get the heart back into rhythm.
What happens if the AV node overtakes some of the roles of the Pacemaker?
The Inherent pacemaker like activity of the AV node isn’t as fast 50-40 bp
can replicate via having
What is the RMP of Cardiac Action potential?
- 90 mV