What are some sources of nitrogen

The main source of nitrogen include: atmospheric precipitation, geological sources, agricultural land, livestock and poultry operations and urban waste. Agricultural emissions show a strong increase due to the application of fertilizer to agricultural soils, grazing of animals and spreading of animal manure.

after receiving a stimus, the sensory receptors send(s) signals to the appropriate area of the body.  

the must be sensory neurons.  

hope its .