During an anatomical class, Dr. Hales removes the heart of a frog and places it in a beaker of oxygenated Ringer's solution. He then instructs his health care trainees to observe how the muscles of the frog's heart continue to contract even without external stimulation. What property of the muscles of the heart is Dr. Hales asking his students to observe?
Autorhythmicity
Bradycardia
Tachycardia
Biorhythmicity

Autorhythmicity of the heart

Explanation:

It is the study of the characteristics features of the cardiac muscle cells with the ability to initiate action potential at certain level without connection to any external stimulus which the heart beats constantly and rhythmically. Cardiac muscle cells controls the rate of contraction of heartbeats.

Autorhythmicity

Explanation:

This is a unique future of  cardiac muscles of the heart.It is the ability of  these  muscles to generate and fire action potential spikes  at a fixed  rate without an external stimulus ;  the spread of these potential  to all the cells of the heart, with consequent  contraction heart  as a single unit , or rhythmically.

This process is mediated by nervous and endocrine  system, and  the action potential generated is conducted through the heart by the myocardial conduction cells.

Autorhythmicity is the due to lack of membrane potential in the myocardial conduction cells. This is because, the  sodium channels did not close up but  allow continuous influx of sodium ions, with the rise in the membrane potential from  -60mv to 40mv. Consequently,pre-potential depolarization sets in. This is followed by influx of Ca+ ions, though the voltage-gated Calcium channels; leading to generation of action potential and therefore spread to all parts of the heart,leading to autorhythmicity.