Biology GCSE Part 1A

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  • Created by: Katy Head
  • Created on: 14-05-11 13:02

CO-ORDINATION AND CONTROL - responding to change

Hormones secreted by special glands are  chemicals that help and control and co-ordinate processes in your body

The nervous system uses electrical impulses to enable you to react to your surroundings and co-ordinate what you do

Cells called receptors detect stimuli (changes in the environment)

Impulses from receptors pass along sensory neurones to the brain

Impulses are sent from the brain to the effector organs along motor neurones

Impulses travel between 1 and 120 metres per second

Hormones are chemical substances

Special glands make and  secrete  hormones

Glands making hormones :-  pituitary (FSH and Oestrogen), Thyroid, Adrenal (adrenaline) Pancreas, Ovaries (Oestrogen and LH), Testes

Hormones are carried to where they are needed in the blood stream

The nervous system - the body is very sensitive to changes around us - these changes known as stimuli are picked up by cells in the body called receptors

stimuli to receptor to sensory neurone to CNS to motor neurone to effector organs

effector organs are muscles which contract or glands which secrete chemical substances.


This is summed up in this picture

Nerves                                                                    Hormones

Impulses                                                                 Chemicals

Carried by nerve cells                                            Carried in the blood stream

Very fast                                                                 Not so fast

Short term effects                                                   Long term effects

Co-ordinates reactions to surroundings                  Internal body processes

Hormone  reaction can target a number of different organs at the same time

Nerve fibres only travel to one effector organ. Of course, the brain can stimulate a number of effector organs at the same time


Some responses happen so fast that they happen before you can think. These automatic reactions are known as reflexes

Reflexes  - help avoid danger, take care of basic bodily functions such as breathing or moving food through the gut

Reflex actions involve three types of neurones

  • Sensory neurones
  • Motor neurones
  • Relay neurones  - these connect sensory neurones to motor neurones and are found in the CNS

The receiving of stimuli through to the impulse being delivered to an effector organ is known as the reflex arc.

There are junctions between neurones.  These are called synapses.

To pass an electrical impulse across the synapse the first neurone creates a chemical which is sent across the synapse and received in receptor cells of the next neurone and used to create the electrical impulse in this neurone

Stimulus to Sensory Receptor to Sensory Neurone across Synapse to Relay Neurone across Synapse to Motor Neurone  to Effector Organ.


  • Some response to stimuli are automatic and rapid and are called reflex actions
  • Reflex actions run everyday bodily functions and help people avoid danger.  


Hormones control the menstrual cycle

These hormones are in the brain and the ovaries

Average length 28 days - womb thickens to support developing baby - egg starts maturing in ovary - if egg is not fertilised lining of womb and egg ares shed in monthly period

All these changes are hormones…



thanks helped a lot

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