What does the P Wave indicate on an EKG?
The depolarization of the atria from -90 to 0mv and therefore contraction of the atria
What does the QRS wave indicate on the EKG?
The depolarization of the ventricle and therefore contraction of the ventricles
What does the T Wave indicate on the EKG?
The repolarization of the ventricles from 0 to -90 and therefore the ventricles are relaxed.
What happens during the Depolarization phase of cardiac muscle?
*threshold is reached and Voltage Gated Sodium Channels open which rapidly depolarizes the membrane to +20mv (therefore, it's a positive inside the cell)
*sodium channels close
What happens in the plateau phase?
*calcium channels open and inflow of calcium is balances by inflow of potassium
*this maintains membrane potential at 0mv for 0.2 seconds
What happens in the Repolarization
Potassium channels open and there is a rapid repolarization of the membrane
What does the plateau phase mean?
That after a cardiac cell contracts it cannot contract again for 0.2 seconds
What is the maximum rate of conrtraction of the heart?
One beat every 0.2 or 0.3 seconds or ~200 beats per minute
How does blood flow through the hear from L ventricle and back to the L ventricle?
L ventricle to Aorta and its branches, to the body, back to the Vena Cava, and then R Atria, and R Ventricle, to the Pulmonary arteries, to the lungs, then the Pulmonary Veins and back to the L ventricle
What is special about Nodal Cells in the heart?
They have autorhythmicity, they contract on their own (with no neurological input)
How does excitation spread throughout the heart?
*AV node authorhythmically excites, then signal send through atria and Atria contract to AV Bundle
*AV bundle brings the signal across the AV septum to the R and L Bundle Branches bringing excitiation to the apex
*Perkinje fibres excite the ventricles so they contract
Re. blood pressure Systolic Pressure is defined as?
*the pressure in the large arteries of the heart during contraction ~120mmhg
Diastolic pressure is defined as?
*the pressure in the large arteries when the ventricles are relaxed
Explain how blood pressure works
Cuff collapses brachial artery and blood pressure is the sound of the artery opening and closing