1. what causes the autorhythmicity or action potentials of the nodal cells? a. a decrease in chloride permeability b. a gradual calcium efflux or movement out of the cell c. a gradual depolarization of the cell membrane until threshold is reached d. a gradual repolarization of the cell membrane until threshold is reached

The correct answer will be option-C

Explanation:

The rhythm of the heartbeat is controlled by the pacemaker of the heart called the sino-atrial node.

The SA node generates action potentials which trigger the contraction and relaxation of the atrium and ventricles. The membrane potential generation initiates by the depolarization of the cell membrane when the L type of Ca⁺² ions opens up and calcium ions enter the cell.

This depolarizes the cell until the potential threshold is reached which lies between the -40 and -30 mV.

Thus, Option-C is the correct answer.

european union policies. the eu's long-term objective is to achieve levels of air quality that do not result in unacceptable impacts on, and risks to, human health and the environment. eu policies aim to reduce exposure to air pollution by reducing emissions and setting limits and target values for air quality.

the main environmental problems in western europe were: energy production/acid rain, nuclear power/waste, air pollution/climate, heavy metals, pesticides, water pollution, solid waste, and unforeseen accidents. many environmental problems are common to most european countries.