Nervous & Hormonal Control (Edexcel IGCSE Biology)

• There are two different control systems in humans that work together to help us respond to stimuli. These are:
  • The nervous system
  • The hormonal system (also known as the endocrine system)
• Changes in our external environment or in the internal environment of our bodies act as stimuli
• The nervous and hormonal systems coordinate a suitable response to these stimuli
• This allows us to make sense of our surroundings, to respond to the changes that occur in our surroundings and coordinate and regulate body functions

The nervous system

• Information is sent through the nervous system as electrical impulses – these are electrical signals that pass along nerve cells known as neurones
• These impulses travel along neurones at very high speeds (up to 100 metres per second)
• This allows rapid responses to stimuli (e.g. the withdrawal reflex that causes you to move your hand away extremely quickly when it touches a flame)
• The nervous system coordinates the activities of sensory receptors (e.g. those in the eye), decision-making centres in the central nervous system, and effectors such as muscles and glands
• The nervous system is used to control functions that need instant (or very rapid) responses

The human nervous system

The endocrine system

• Information is sent through the endocrine (hormonal) system as chemical substances known as hormones
• Hormones are carried by the blood and can therefore circulate around the whole body
• Hormones transmit information from one part of the organism to another and bring about a change (they provide a signal that triggers a response)
• They alter the activity of one or more specific target organs
• Hormones are used to control functions that do not need instant responses
• Hormones are produced by endocrine glands
• The endocrine glands that produce hormones in animals are known collectively as the endocrine system
  • A gland is a group of cells that produces and releases one or more substances (a process known as secretion)

A comparison of the nervous and endocrine systems table