1. Autorhythmic cells and the funny current

Why do cardiac muscles not need an outside action potential to begin each cycle?

They do not have a stable resting membrane potential, instead they just slowly drift to threshold after each depolarization

What happens at relatively negative voltages after repolarization?

The funny-current channels open and produce and inward current by sodium, creating the pacemaker potentail

Does the pacemaker reach threshold on its own? What happens after threshold?

Yes, voltage-gated calcium channels then produce the action-potential upstroke in the autorhythmic cell

What is the last step of the cycle?

Potassium efflux repolarizes the cell. The funny current becomes active again, and the cycle repeats.

Where did the funny current get its name?

It is unusual and is activated by hyper polarization (from the K) rather then depolarization

SA-node cells normal rhythm is _.

70 bpm

AV-node cells normal rhythm is _.

50 bpm

Purkinje fibers rhythm is _.

25-40 bpm if higher pacemakers fail