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Hypotheses: A theory that explains an observation
Stimulus: A change in your environment which you may react to.
Receptors: Groups of cells which are sensitive to a stimulus. They change stimulus
energy to electrical impulses
Sensory Neurones: Nerve cells that carry signals as electrical impulses from receptors
in sense organs to CNS.
Motor Neurones: Nerve cells that carry signals to the effectors muscles or glands.
Effectors: Muscles & glands. Muscles contract in response to a nervous impulse,
whereas glands secret hormones.
Reflexes: Automatic responses to certain stimuli
Hormones: Chemical messengers that travel in the blood to activate target cells.
Homeostasis: Maintaining a constant internal environment
Cholesterol: A fatty substance that's essential for good health
Pathogens: An infectious agent that causes disease in it self
Antibodies: Special proteins which are used to identify foreign objects e.g. bacteria
Antitoxin: An antibody with ability to neutralise a specific toxin
Antigen: A substance that can stimulate production of antibodies & combine
specifically with them.
Immunisation: A way of preventing a person from getting a disease
Vaccination: Giving someone a vaccine, substance that makes an immune
system react.…read more

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Sense organs detect stimuli
· Sense organs contain different receptors
· Stimulus can be light, sound, touch, pressure, pain,
chemical or change in position or temperature
· SENSE ORGAN = Eye, ear etc
· RECEPTORS = Light, sound etc
1. Eyes Light receptors
2. Ears Sound and balance receptors
3. Nose Smell receptors
4. Tongue Taste receptors
5. Skin Touch, pressure and temperature
change…read more

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The Central Nervous System Coordinates a Response
1. Central Nervous System (CNS) is where
all information from sense organs is sent
and where reflexes and actions are
CNS consists of the brain and spinal cord.
2. Neurons transmit the information as
electrical impulses quickly to and from
the CNS.
3. Instructions from CNS are sent to the
effectors (muscles and glands), which
respond accordingly.…read more

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Reflexes help prevent injury
When a receptor is stimulated, it sends a signal to the central nervous system,
where the brain co-ordinates the response. But sometimes a very quick response is
needed, one that does not need the involvement of the brain. This is a reflex action.
This is what happens:
1. Receptor detects a stimulus- change in
2. Sensory neurone sends signal to relay neurone
3. Motor neurone sends signal to effector
4. Effector produces response
Sensory Relay Motor
Stimulus Receptor Effector Response
Neurone Neurone Neurone…read more

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Synapses connect neurons
This is what happens:
1. The connection between two neurons are
called a synapse.
2. The nerve signal is transferred by chemicals
which diffuse across the gap.
3. These chemicals then set off a new electrical
signal in the next neurone.…read more

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