There are two main co-ordination systems which interact and work together:
- The nervous system. Communication and co-ordination is by rapid, localised, short-lived electrical impulses. Nerve cells transmit impulses along their length and secrete neurotransmitters to stimulate their target cells. The target cells could be other nerve cells or a muscle cell at a neuromuscular junction.
- The hormonal system. Communication and co-ordination is by chemicals transmitted in the blood. The response is slower, more widespread and longer-lasting. Chemicals called hormones are transmitted in the blood. They bind to receptors on the cell surface membrane of target cells. These bring about a response. An example is the hormone insulin which binds to its target cells to lower the blood sugar concentration.