The release of to muscle cell receptors triggers muscle contractions. ach serotonin dopamine adrenaline

The given blank can be filled with acetylcholine.  

Acetylcholine refers to a chemical messenger, that is, a neurotransmitter, discharged by the nerve cells in various segments of the peripheral nervous system. It monitors the contraction of all the voluntary muscles, like skeletal muscles. It also influences the contraction of the cardiac and smooth muscle.  

yes it is   dangerous

explanation:

because that foot is discusting and could get you sick

i got you i did it ya know what it is just needing to fill this in for a quick task!