Rate and Rhythym

What is another term for parasympathetic stimulation?

Vagal stimulation

What receptors is vagal stimulation acting on?

Muscarinic cholinergic receptors on the target tissue

What is the effect of parasympathetic stimulation on the sinoatrial node?

Activating the sinoatrial increases potassium permeability, which will move the membrane potential closer to the Nernst potential and make it more negative. By association, it will hyperbolize the membrane. This depresses the currents in the calcium channels and funny channels, which will lower the sodium and calcium permeability and slows spontaneous depolarization, leading to a decrease in heart rate.

What effect does parasympathetic stimulation have on the AV node?

It has similar beginning effects as the sinoatrial node, it increases potassium permeability, so it makes the membrane potential more negative, leading to a decrease in excitability. This will lead to conduction velocity or impulse transmission slowing/stopping. This achieves the goal of increasing AV nodal delay or inducing third degree AV block

If there is an increase in parasympathetic tone, what happens to the P-R interval?

P-R interval is the time between atrial depolarization and ventricular depolarization therefore, if there is an increase the parasympathetic tone, the AV nodal delay will increase and the P-R interval will increase by association.

What are the primary effects of increased parasympathetic (vagal) tone?

1) Slowing heart rate 2) Slows AV conduction velocity (AV nodal delay)

What receptors are involved in sympathetic stimulation?

B-1 receptors on the cardiac myocyte

What is the effect of sympathetic stimulation on the S-A node?

Sympathetic stimulation will increase sodium and calcium conductance, which will move the membrane closer to membrane potential and excite the cell, leading to an increase in spontaneous depolarization, increasing overall heartrate.

What is the effect of sympathetic stimulation on the A-V node?

Sodium and calcium conductance will increase (similar to SA node), which will increase conduction velocity, resulting in a decrease in AV nodal delay

What is the sympathetic effect on atrial and ventricular contractile cells?

Calcium channels in the plasma membrane will be phosphorylated, leading to an increase in calcium permeability of the cell membrane. It also phosphorylates phospholambam, which in turn stimulated the SR calcium pump, increasing calcium uptake into the sarcoplasmic reticulum. This will lead to an overall enhancement on calcium release, activating calcium load and increasing strength of contractility during systole. Additionally, during diastole, phorylation of troponin I via cAMP, the calcium sensitivity of the troponin complex will decrease, which will lead to the rate of relaxation increasing during diastole.

Sinus rhythm

“Normal” rhythm: the cardiac depolarization begins at the SA node, follows normal depolarization path, upright P wave in lead II, P leads to QRS, narrow upright QRS in lead II

What is sinus arrhythmia?

Sinus beat that has an irregular R-R interval, positive P wave in lead II, related to changes in vagal and sympathetic tone during respiration, occurs in animals that have a relatively high vagal tone

1st degree AV block

Slow AV conduction, long P-R interval

2nd degree AV block

Some impulses are not conducted through the AV node, P is not followed by a QRS

3rd degree AV block

No impulses are conducted, P and QRS both occur but are not related in time. 

Fibrillation

An arrhythmia characterized by rapid. continuous, uncoordinated excitation of myocardium, may be atrial or ventricular

What is the Premature Ventricular Complex?

The QRS complex occurs early, and the impulse does not originate in the SA node. It arises from the septum ore ventricular free wall; ventricular depolarization is wide and bizarre because it cannot utilize the specialized conduction system effectively. Decides it will be a pacemaker and depolarize first.

What is the Premature Supraventricular Complex

The QRS complex occurs early but does not occur in the SA node. It originates at or above the AV bundle, the depolarization wave traverses the specialized conduction system in the ventricle in normal fashion. The QRS has a normal shape.