THE NERVOUS AND THE ENDOCRINE SYSTEM.
Humans need both the Nervous and the Endocrine systems basically because they do different things in different ways. They both have a co-ordination role and send instructions to other parts of the body. The nervous system does this by way of neurotransmitters,( chemical messengers), which are able to get messages through at very high speeds, and the endocrine system by way of hormones,( also chemical messengers), which are released from glands and travel slowly as they can only move at the speed of the blood flow into which they have been released. In those areas where there is most co-operation of the two systems, there is a third entity referred to as the Neuroendocrine system. The nervous system is a communication network for the body and it receives and passes on messages to the endocrine system in order that specific areas may make or increase production of specific hormones which are then sent to the target area in order to begin or inhibit a process taking place at that site, i.e. a target cell. The specific hormone has a unique ‘entry code’ that enables it to affect the target cell. The nervous system works by the brain receiving signals from the sensory neurons and then messages are sent back again via the connecting neurons in order to target the area required. Things happen fast and the reactions are communicated over short distances with a short lived response. The endocrine system gets messages from the brain and then releases hormones from the relevant gland into the blood stream. Distances are longer and the transmission can take minutes or days, the response also being longer lived: the one exception to the latter being the hormones Adrenaline and Noradrenaline. The best example of the speed available to the nervous system is evidenced by the Reflex Arc, Figure 1 below. Figure 1. The Reflex Arc....
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