What role do polarity and action potential play in sending out nervous signals?

A class of chemical called a neurotransmitter is important in the transmission of nerve impulses. Neurotransmitters are packaged by the cell into small, membrane-bound sacs called vesicles. Upon receiving a chemical signal, the vesicles move toward the cell membrane and fuse with it, releasing the enclosed neurotransmitters from the terminal end of the nerve cell.


Synaptic Vesicles

The neuron, a cell that composes the nervous system. For example a brain, an organ composed of thousands of neural fibers and glial cells that performs many important organismic functions. 
Neurons are specialised cells that have dendrites, axons and terminal buttons that sends and receives stimuli from the environment and transduces it into a meaningful information and understand the complexities which the brain now functions.