6.2 How The Heart Beats Flashcards
The heart is made of cardiac muscle which is different from other kinds of muscle because it is…
Myogenic
Myogenic means that it does not…
Need to be stimulated by a nerve impulse to contract
A group of cells in the wall of the right atrium are called…
Sinoatrial node (SAN)
SAN start off the electrical activity that produces and is sometimes called…
The cardiac cycle and the pacemaker
Electrical impulses pass from the SAN through the walls of both atria causing them to contract, causes…
Atrial systole
There is a ring of fibrous tissue between the atria and the ventricles that prevents electrical impulses pass to the…
There is a short time delay here, allowing the…
Atrioventricular node (AVN)
Atria to empty completely
The electrical impulses pass very quickly down some special fibres called the…
Bundle of His, this carries them to the bottom of the septum
From the bottom of the septum, electrical impulses pass along the…
Purkyne fibres in the walls of the ventricles - causes ventricular systole, in which the ventricles contract from the bottom up
There is a short time day in which no electrical impulses pass through the cardiac muscle. This allows the…
Cardiac muscle to relax (diastole)
It also allows the atria to fill with blood before the next cardiac cycle
Aortic pressure rises when ventricles contract as blood is forced not the aorta. It then gradually falls (but never below 12kPa) because of…
The elasticity of its wall which creates a recoil action - the recoil produces a temporary rise in pressure at the start of the relaxation phase
Atrial pressure is always relatively low because the thin walls of the atrium cannot create much force.
It is highest when they are contracting, but drops when the left atrioventricular valve closes and its walls relax. The atria then fill with blood which leads to a…
Gradual build up of pressure until a slight drop when the left atrioventricular valve opens and some blood moves into the ventricle
Ventricular pressure is low at first, but gradually increases as the ventricles fill with blood as the atria contract, the left atrioventricular valves close and pressure rises dramatically as the thick muscular walls of the ventricle contract. As pressure rises above that of the aorta blood is forced…
Into the aorta past the semilunar valves. Pressure falls as the ventricles empty and the walls relax.
Ventricular volume rises as the atria contract and the ventricles fill with blood, and then drops suddenly as blood is forced out into the aorta when the…
Semilunar valve opens. Volume increases again as the ventricles fill with blood.
Sometimes a person’s SAN does not sen out electrical impulses quickly enough or there might be a blockage in the conducive tissue in a person’s heart, for these people an…
Artificial pacemaker may help
Artificial pacemakers are…
Electronic devices that are surgically implanted and use electrical impulses to regulate the beating of the heart.
