Describe the characteristics of a slow response action potential, including its phases and the ion channels involved.

The text describes the characteristics of a slow response action potential, which is typically found in pacemaker cells like those in the sinoatrial node (SAN). Here's a summary and explanation: The slow response action potential has five phases, but it differs significantly from the fast response action potential (found in ventricular muscle, for example). Its key features are: It begins with a prepotential*, which is a slow depolarization leading up to the action potential. The upstroke (depolarization phase) is slow and reaches a lower peak voltage, typically only +1 to +10 mV. This slow upstroke is primarily caused by the influx of calcium ions (Ca²⁺) through slow L-type Ca²⁺ channels*. Unlike fast response action potentials, there is almost no plateau phase*. Phases 1, 2, and 3 merge into a single, more gradual descending repolarization phase. This repolarization is also due to an increase in potassium ion (K⁺) efflux*. In essence, slow response action potentials are characterized by their slower depolarization, lower peak, and lack of a distinct plateau, relying mainly on calcium influx for their upstroke.