ABSTRACT
The hormone or endocrine system provides, generally, a slower means of control over the functions of the body than the nervous system. Like neurotransmitters hormones are specialized chemicals that change the activity of cells by attaching to receptors on the cells. The peptides and proteins exhibit a wide variety of sizes and shapes of molecule and include insulin. The amino acids include the thyroid hormones such as thyroxine, and epinephrine which is derived from tyrosine. Hormones mostly travel in the bloodstream where they come into contact with all cells. However, they only have an effect once they reach their own target cells. These cells have specially adapted receptors that accept the hormone in the same 'lock and key' fashion that we saw for neurotransmitters. Direct integration between endocrine activity and activity of the nervous system is achieved by a group of chemicals called neurohormones. These are released by the endocrine system but have their targets in the nervous system.
