Autorhythmic Cells and Stimulation

State the average intrinsic firing rate of the heart.

100 impulses per minute

Explain the mechanism of stimulation of autorhythmic cells of the heart.

At -60 mV, If channels open, allowing Na+ to enter the cell, at the same time K+ leaves the cell As depolarization approaches threshold, some Ca++ channels open, If channels close, and Ca++ begins to diffuse into the cell Due to Ca++ influx, cell rapidly reaches threshold. At threshold, many Ca++ channels open, and cell strongly depolarizes to peak depolarization. At peak depolarization, Ca++channels close, K+ channels open, and cell repolarizes to -60 mV.

How does each autorhythmic element's firing rate compare to the others, and what determines what the firing rate for all will be?

Firing rate is highest in the SA node; each successive element has a slower intrinsic firing rate

List the autorhythmic elements of the heart.

Sinoatrial node Internodal pathways Atrioventricular node Atrioventricular bundle Right and left bundle branches Purkinje fibers

Differentiate between the intrinsic firing rate of the autorhythmic cells, and the actual heart rate.

The intrinsic firing rate of autorhythmic cells sets the baseline rhythm, while autonomic influences and hormones modulate the actual heart rate.

State the function of the autorhythmic cells of the heart.

determine heart rate (the number of times per minute aparticular volume is moved into the pulmonary and systemic circuits)