An accelerated heartbeat is to a slowed heartbeat as the nervous system is to the nervous system.

symphathetic, parasymphatetic

Explanation:

The accelerated heartbeat has a opposite action as compared to the slowed heartbeat likewise the symphathetic nervous system has a opposite action that of parasymphatetic system.

The symphathetic nervous system helps the body to perform intense physical activity like in case of fight or flight response. The parasympathetic nervous system relaxes the body and inhibits its functions that require energy.

atomic = no of protons.

mass number-atomic number = neutron number

when it gains or loses electrons