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1.1 ­ Responding to Change
Two types of messenger systems within the body :
1. Nervous System ­ Electrical Impulses via Neurons
2. Hormones- Chemical Signals, secreted by special
glands, transported via the blood…read more

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The Nervous System
· Any changes in the world around us (Stimuli)
are picked up by cells called receptors
· Receptors are usually found clustered in Sense
Organs (eyes, skin, nose)
· Once a sensory receptor detects a stimulus
the information is passed on as an electrical
impulse along the neuron
· Multiple neurons = nerve…read more

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CNS is made up of the brain and spinal cord
1. Stimuli detected by sense organs
2. Impulse travels along sensory neuron to CNS
3. Relay neuron transfer impulse from Sensory
neuron to motor neuron
4. Motor neurons carry impulse to effector
organs
5. Effector organs are muscles (contract) or
glands (secrete)…read more

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1.2 Reflex Actions
· Some responses are so fast that they happen
without time to think
· Automatic responses are known as reflexes
· Important to help avoid danger and harm because
they are so fast
· RELAY NEURONS ­ found in the CNS link sensory
and motor neurons
· Reflex arc ­ impulse bypasses the consious areas
of the brain. Time between stimulus and the
reflex action is as short as possible…read more

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