In order for living organisms to find food, avoid danger, find a mate, basically everything they need to do to live, they've got to be able to respond to what's around them and anything any changes in their environment. Now any changes that occur in the environment we call in biology stimuli okay so or stimulus is the singular so organisms need to be able to detect the stimuli and then respond to them and then they will be able to hopefully stay alive and ideally reproduce. Now organisms have evolved all different amazing different types of receptors to be able to detect these stimuli.
In humans obviously we've got things like the eyes and the ears and all our senses and that helps us to detect different stimuli and then we can coordinate the suitable response to them and like I said that should keep us alive longer. Now not only do organisms need to be able to respond to changes in their external environment but they also need to be able to respond to changes in their internal environment what's going on inside their bodies as well cells must be kept in the right conditions for all the metabolic reactions and enzymes to work properly so keeping in your internal environment constant is what we call homeostasis is a really important word in biology maintaining a constant internal environment I'm talking about things like water carbon dioxide glucose pH salt temperature you've got to keep all these these things as constant as possible in order to survive. Now in order to work out what's going on externally and what's going on internally, you've got to be able to detect stimuli, therefore you've got to have special receptors, and you've also got to have other types of cells which we call effectors, things that cause effects, things that then can carry out the response that you need.
So you touch something hot, but actually you need to be able to do something then to move your hand away, so you need some kind of effect. Now, effectors tend to be muscle cells because quite often it's movement involved, or it might be a gland because then that gland can secrete the stuff it needs to then cause that effect in the body. Now, there are two systems in humans that connect the receptors to the effectors, and these are what we call the nervous system and the endocrine system.
And it's great because they work together depending on what the stimulus is. The organism can decide which system to use. Each system has different pros and cons. depending on what that stimulus is the body can then decide to use either the nervous system or the endocrine system or maybe even a combination of both so how are they different well the nervous system is all to do with rapid communication via electrical impulses that get fired along neurons special cells called neurons in endocrine system we're talking about much slower response and it happens via hormones that travel in the blood so a completely different communication system the nervous system it happens instantly straight away the endocrine system the effects may take a long time before they happen in the nervous system the response is very short-lived doesn't last very long it's usually bang and then it's done response the endocrine system though can last for a long time you might want it to last for weeks or even longer the impulse in nervous system only usually acts on a very small area a couple of cells when again hormones can have huge widespread effects on whole organs or whole parts of the body or hundreds and hundreds of different different cells.
So two completely different systems but they kind of complement each other and the body can decide which one to use in which scenario.