Cardiac cycle Flashcards
What is the function of an EEG
the function of an EEG is to measure electrical frequency of the heart.
What are artificial cardiac pacemakers
artificial pacemakers regulate the heart rate
Describe the Sinoatrial node and atrioventricular node
-SA node is a group of cells located in the wall of the right atrium
-it has the ability to spontaneously produce action potential that travels through the heart via the electrical conductor system
- sets the rhythm of the heart and is known as the hearts natural pacemaker
- the rate of action potential production is influenced by the nerves that supply it.
-The AV node is part of the electrical conduction system of the heart. It electrically connects the right atrium and right ventricle, this can delay impulses so the atria has time to eject the blood towards the ventricles before ventricular contraction
Explain what happens in the resting membrane
-an action potential occurs
-3 Na+ ions move out of the electrically positive membrane
-2 K- ions move in the membrane
-the membrane now becomes intracellularly negative and has the resting potential of -70mV
Explain the SA pacemaker potentials
[-there is a resting negative voltage (-70)
- the Sodium-potassium pump, uses ATP to transport the sodium ions out of the celll and two potassium ions in
- As the cell depolarises, it reaches a threshold for voltage gated Ca2+ channels which leads to Ca2+ influx (rapid depolarisation)
- Ca2+ channels switch off at max depolarisation.
Explain atrial and ventricular muscle action potentials
phase 0- rapid depolarisation::
-receives depolarisation stimulus from SA node causing the voltage gated Na+ channels to open. (Na+ influx)
- voltage gated Ca2+ channels start to open very slowly
Phase 1- early repolarisation:
-Na+ channels close cells beginning to repolarise
Phase 2- plateau phase:
-Voltage gated Ca2+ channels open-, Ca2+ influx halts the repolarisation. Voltage gated K+ channels start to open slowly.
Phase 3- rapid repolarisation:
-Ca2+ channels close and K+ channe;s open fully so K+ influx
Phase 4- resting phase:
-Stable- Na+/K+ pump- 3 Na+ out and 2K- in
Explain the 4 stages of electrical conduction through the heart
1) Electrical activity generated in the SAN node, spreads out via gap junctions into the atria
2) At the AV node conduction is delayed to allow correct filling of ventricles
3) Conduction occurs rapidly through bundle of His into ventricles
4) Conduction through Purkinje fibres spreads quickly throughout the ventricles
Explain what happens at the P wave of an ECG
P wave- atrial depolarisation and contraction:
-the atria contracts first and then ventricles contract
Explain what happens at the PR segment
PV segment- AV nodal delay:
-to allow atria to pump blood
Explain what happens at the ST segment
ST segment- ventricles contracting and emptying:
-to get rid of excess blood
Explain what happens at the QRS complex
QRS complex- ventricular depolarisation contraction (atria repolarising simultaneously)
Explain what the T wave is
T wave- ventricular repolarisation (becomes more negative)
Explain the TV interval
TV interval- ventricles are filling and relaxing (this is the final stage)
Explain the general principles of the cardiac cycle
-electrical activity is generated at SA node and conducted throughout the heart.
-electrical activity is converted to myocardial contraction which creates pressure changes within chambers
-Blood flows from an area of high pressure to an area of low pressure via the pressure gradient
-valves open and close depending on pressure changes in chambers
-events on the right and left sides of the heart are the same but pressures lower on the right (due to thinner walls)
