Both the nervous and the hormonal (exocrine and endocrine) systems in mammals are systems that transfer information around the body. The major differences are the signals that are transmitted, the speed at which the signals are transmitted, and how the transmission occurs.

In the hormonal system the only actions that occur are responses to stimuli. A certain organ will release a certain chemical when exposed to a certain stimulus. In the nervous system however there may be much complex interaction between the stimulus and the act associated with it.

The nervous system uses its own tissue to transmit signal around the body at high speed. In almost all cases these signals are either going towards or from the brain. The central nervous system includes the brain and the spinal cord, as opposed to the peripheral nervous system that includes all other nerves, both cranial and spinal (words that describe their origins). The nervous system is therefore one that is spread throughout the body.

To contrast with this the endocrine and exocrine systems are located in specific organs, or glands. These release chemicals into the bloodstream, or into ducts within in which they are dispersed around the body, or to where they are needed. The glands are in many different locations, but the hormonal (especially the endocrine) system in is no way physically interconnected. It must act in response to stimuli that have not been created by the system.

For example, the islets of langerhans in the pancreas form part of the endocrine system. Blood glucose level is sensed, and depending on the situation with respects to the ideal either insulin or glucagon is released to counteract the abnormality. Signals in the nervous system must be caused initially by some other stimulus, e.g. pressure, which triggers a response in the pacinian corpuscles in that area. This will initiate an action potential, and thus a transmission of signal.

In the nervous system there will be a very clear path that the signal will follow, and this will be done at a great speed. Transmission in the nervous system appears, to the human eye to be nearly instant. The hormonal system is different from this. It may take minutes, to an hour or more for the effects to become significant. The effects of hormones are less likely to be immediately visible compared to those of the nervous system. The nervous system may make someone move their arm, but it is their hormonal system that controls their growth and development. The transmission of signals along mylienated axons is quick and direct, but the release of adrenaline can only take an effect once the hormone has circulated to the tissues where it takes effect.

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