Lecture 11 3/4/14 Flashcards
SA Node
at the junction between the Superior Vena Cava and Right Atrium;
It is still cardiac muscle tissue but with a lot less of the actin and myosin in it. So the SA Node is more conductive in nature than contractile. Still a functional synctium.
We don’t need to send nerve fibers to every single muscle fiber, we have the gap junctions. So basically it is comprised of specialized nerve cells.
It initiates each cardiac cycle. SA Node is controlled by the Vagus Nerve. Vagus Nerve slows the heart rate down. It’s parasympathetic.
Speed can be altered by what nervous system? And what can slow it down?
by the autonomic nervous system. Norepinephrine and Epinephrine, and Thyroid, but thyroid deficiency can slow it down.
How does blood get to the AV Node?
Via the Internodal Pathways
AV Node
(Atrioventricular Node) is located at the junction of the Atria and Ventricles. More to the right side than the left.
Heart Contraction Process
When the heart contracts, the Atria contracts from the top and pushes blood down into the ventricles. And when the ventricles contract, they contract from the bottom and push upward, so that means the electrical wave goes from the top down, and then the ventricles contract from the bottom upward to push the blood up and out.
How does blood go from the AV Node to the Interventricular Septum?
Through the structure called the AV Bundle or Bundle of His
Bundle of His
branches off as bundle branches, left and right bundle branches.
Travels down to between the two ventricles, within the septum. From the left and right branches, we go to the terminal branches called the Purkinje Fibers - terminal walls in the walls of the ventricles.
Purkinje Fibers
End fibers
Terminal Walls in the walls of the ventricles
Order of Heart Muscle Contractions
1) Atria fires (contracts) first from the top down.
2) Then functionally, the Apex, contracts from the bottom towards the top.
3) Then walls of the ventricles contract upwards and out from the apex.
EKG or Electrocardiogram
It measures electrical wave moving through the heart muscle tissue, it doesn’t directly measure heart muscle contraction.
Records the electrical changes that accompany the cardiac conduction cycle.
Electrodes are placed on various places on the chest wall and extremities to monitor the electrical depolarization.
PQRST Sequence
P Wave -> QRS Complex -> T Wave
P Wave
Represents Atrial Depolarization
Relatively small
QRS Complex
Represents Ventricular depolarization.
Relatively larger.
Happens a half second later after the P Wave
T Wave
Represents ventricular re-polarization.
Larger muscle mass.
Happens a fraction of a second later after the QRS Complex.
Always larger than the P Wave. Should not be equal in size to the P Wave.
Atrial Repolarization is hidden by what complex?
QRS Complex
