Every aspect of our lives is influenced or enabled by the transmission of messages between nerves. For instance, even the mundane matter of attraction involves thousands, or millions of messages sent between nerves that receive stimuli from the outside world and those that send messages that affect our behaviour. Every time we register a sensation and respond in some way (by breathing more heavily, blushing, trembling, cringing etc.), our behaviour is stimulated by actions of the nervous system. We are motivated into action by what we see, hear, touch, smell, taste and think. A woman’s smiling eyes might add to her attractiveness; a man’s odour might attract us; the colour of a suit might influence an employer’s decision whether or not to give the person a job; the tone of a person’s voice persuade, even though the information given is questionable.
Nerves do not actually touch, but are separated by gaps called synapses, usually located where an axon from one neuron meets the dendrites or cell body of another. Neurons communicate through electrical impulses that travel down the axon to the synaptic knob. There, the impulse triggers the release of a chemical called a neurotransmitter which carries the message across the synapse to receptors at the end of the receiving dendrite. Neurotransmitters can either excite or inhibit the transmission of an impulse. Each chemical transmission changes the electrical impulse in some way, either increasing or decreasing the likelihood that it will fire an impulse. Endorphins, for instance, are neurotransmitters that generally inhibit impulses, reducing sensations of pain or stress when the body is injured.
Other chemical agents that affect body behaviour are hormones, which are responsible for promoting growth, maintaining functions, and preparing the body to deal with stress, among other things. Some hormones stimulate parts of the body to develop in particular ways. For example, androgens are hormones that tend to promote masculine traits, whereas oestrogens are hormones that stimulate the development of feminine traits.