Electrical Activation Of The Heart Flashcards
What is the resting potential and how is it produced?
Relative negative charge on the inside of the cell.
The Na/K pump pumps out 3Na+ and 2K+ into the cell.
There are leak channels where K+ can move out.
This produces a relative negative charge on the inside of the cell known as the resting potential.
It is usually -90mV
What is the Nernst equation used for?
Used to calculate the cell or membrane potential of an electrochemical cell at any given temperature, pressure and substrate concentration. It defines the relationship between concentrations of ions either side of the membrane.
What is a syncytium?
A single cell containing several nuclei firmed by the fusion of cells or by the division of nuclei.
Job of the intercalated discs in cardiac myocytes?
They contain gap junctions and desmosomes.
Gap junctions - allow ions to directly spread from one myocyte to the next allowing a.p to rapidly move and hence the heart to have simultaneous contractions.
Desmosomes - hold adjacent myocytes together.
What in an action potential?
Change to the resting potential that happens during an impulse.
- Generation of a resting potential - including Ca2+ out of the cell via active transport.
- Voltage gated Na channels open due to incoming action potential.
Na+ move down an electrochemical gradient into the cell - known as depolarisation - K+ channels open, Na+ channels shut. The K+ channels are open for longer and hence there’s a dip - depolarisation
- Slow Ca2+ channels open - Ca2+ move into the cell, but transient K+ outward channels remain open and so there is not net change.
- Delayed rectifier K+ channels open and the Ca2+ channels close — depolarisation
- Resting potential is generated again.
How does cardiac contraction differ to that of skeletal cells?
The contraction lasts longer - - up to 15 times. This is because of the slow calcium channels prolonging the action potential.
The contractions are also involuntary.
How does the action potential spread?
The action potential spreads over the cell membrane the depolarisation affects adjacent cells to cause them to to depolarise. The ions can travel via the gap junctions.
What is the job of the sinus node?
Determines the rate the heart beats at.
It has a resting potential of -60mv
How does it work????
What is the confusion velocity of the atrial and ventricular muscle and then the Purkinje fibres?
0.3– 0.5 m/s - ventricular muscle
4m/s
What is the job of the AV node?
Transmits cardiac impulses between the atria and ventricle.
It delays the impulse allowing atria to empty blood into ventricles fully.
This is because it has fewer gap junctions.
After the SAN— AV where does the impulse next travel to?
It travels to the the Bundle of His via the Purkinje fibres. Here there is rapid conduction to allow coordinated ventricular contraction. This is produced via large fibres and high permeability gap junctions.
What is the refractory period?
Period immediately following stimulation during which a nerve or muscle is unresponsive to further stimulation.
It usually lasts 0.25s
Prevents excessive contraction
And allows the heart to adequately fill before next contraction
What is the total refractory period made up of?
Made up of the Absolute refractory period and then the relative refractory period.
During the relative refractory period only some Na+ channels are activated and hence only a strong stimuli will cause an action potential
How does sympathetic stimulation affect heart rate?
Increased sympathetic stimulation increases heart rate increases force of contraction and hence increases cardiac output.
Decreased sympathetic stimulation
Decreases heart rate and force of contraction and hence decreases cardiac output.
Adrenaline is an example of something that controls this
How does parasympathetic stimulation affect cardiac contraction?
Increased parasympathetic stimulation:
Decreased heart rate and force of contraction.
Decrease stimulation = increased heart rate.
Acetyl choline = controls this
