(3) A comparison of the nervous system and the endocrine hormone system

(also on homeostasis page too)

Hormones effectively act as 'chemical messages' to trigger particular biochemical reactions and their effects are slower than nervous system.

The effect of hormones is more general around the body, but tend to affect particular cells in particular organs, and relatively long-lasting effect compared to eg the fast but short-term nervous impulses and responses of a reflex arc.

Generally speaking, if your body's response to a situation is relatively long lasting (e.g. minutes or hours) its probably a function of the hormone system.

Some hormones like endocrine-4.htm, can act quite quickly - see notes further down.

Nerves: Compared to the hormone system of response and control in the body, the nervous system, using nerve signals which are electrical in nature (not chemical).

The nervous system of neurones acts very fast e.g. a short burst of a nerve impulse for a short time, acting from one precise area to another in the body.

Generally speaking, if your body's response is fast, its probably a nervous reaction.

There are situations when information needs to be passed to your effectors quickly!

Examples of when nerve signal information has to be passed to effectors quickly include nerve signals from your retina, pain receptors, taste buds warning of danger etc. must be processed in microseconds, NOT minutes! too late!

Hormones act too slowly to be of use in most dangerous 'split second' decision making situations.

Hormone levels and negative feedback

Your body can control the level of hormones in the blood using a negative feedback system.

If the body detects that a level of a substance X is above or below the normal level it triggers a response to bring the level of substance X back to normal again.

A good example is the way thyroxine regulates metabolism.

(see thyroxine notes and graph below)

Endocrine hormone system	Receptor detects changes in the environment	Chemical messenger - hormone molecule signal Slower, but acts for much longer - carried in blood to all organs, but only affects target organ	Coordination centre A gland e.g. pancreas Receives signal and processes information	Chemical messenger - hormone molecule signal Slower, but acts for much longer - carried in blood to all organs, but only affects target organ	Effector A gland that secretes a hormone to restore an optimum level or trigger some other chemical response
Nervous system	Receptor detects changes in the environment	Electrical signal - nerve impulse Rapid and short duration - carried in nerve fibres to specific locations like muscles	Coordination centre Brain or spinal chord Receives signal and processes information	Electrical signal - nerve impulse Rapid and short duration - carried in nerve fibres to specific locations like muscles	Effector Muscles that respond to the signal

Reminder: Homeostasis the function of self-regulating processes by which biological systems (organisms) tend to maintain physical and chemical stability while adjusting to conditions that are optimal for survival i.e. counteracting unfavourable conditions. These process can involve hormones secreted from the glands of the endocrine system.

See also examples of homeostasis

Homeostasis - introduction to how it functions (negative feedback systems explained)

Homeostasis - control of blood sugar level - insulin and diabetes  gcse biology revision notes

Homeostasis - osmoregulation, ADH, water control, urea and ion concentrations and kidney function

Homeostasis - thermoregulation, control of temperature  gcse biology revision notes

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Summary of learning objectives and key words or phrases

Be able to compare and understand the differences between the nervous system and the endocrine hormone systems - including descriptions of what hormone molecules and nerve cell impulses do.

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