The Nervous System

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Sense Organs

A STIMULUS is a change in your environment, which you may need to react to.

For example, a grizzly bear looking hungrily at you

You have 5 different sense organs - eyes, ears, nose, tongue and skin.

These 5 sense organs all contain different RECEPTORS

Receptors = groups of cells- sensitive to a stimulus.

They change stimulus energy (eg light energy) into electrical impulses.

A stimulus can be light, sound, touch, pressure, pain, chemical or a change in position or temperature.


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Sense Organs And Their Receptors

1) Eyes - light receptors - sensitive to light

2) Ears - sound receptors - sensitive to sound

3) Nose - smell receptors - sensitive to chemical stimuli

4) Tongue - taste receptors - sensitive to bitter, salt, sweet, sour and savory things - chemical stimuli

5) Skin - sensitive to touch, pressure, pain and temperature change

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The Central Nervous System (CNS)

-The CNS is where all the information from the sense organs is sent, and where reflexes and actions afre coordinated.

-The CNS consists of the brain and the spinal cord only.

-Neurones (nerve cells) transmit the information (as electrical impulses) very quickly to and from the CNS.

-'Instructions' from the CNS are sent to the effectors (muscles and glands), which respond quickly accordingly.

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Sensory Neurones - carry signals as electrical impulses from the receptors in the sense organs to the CNS

Relay Neurones - carry signals from the sensory neurones to the motor neurone

Motor Neurones - carry signal from the CNS to the effector muscles or glands

Effectors - muscles and glands - they respond in different ways. Muscles contract in response to a nervous impulse, whereas glands secrete hormones

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Synapses and Reflexes

Synapses connect neurones

1) The conncetion between two neurones is called a synapse.

2) The nerve signal is transferred by chemicals which diffuse (move) across the gap.

3) These chemicals then set off a new electical signal in the next neurone.

Reflexes help prevent injury

1) Reflexes are automatic responses to certian stimuli.

2) For example -  bright light is shone in eyes, pupil automatically gets smaller, less light gets into the eye, stops it getting damaged.

3) Or if you get a shock, your body releases the hormone adrenaline automatically.

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The Reflex Arc

The Reflex Arc is the passage of information in a reflex (from receptor to effector)

1) Cheeky bee stings finger

2) Stimulates pain receptor

3) Impulses travel along the sensory neurone

4) Impulses are passed along a relay neurone, via a synapse

5) Impulses travel along a motor neurone, via a synapse

6) When impulse reaches muscle, it contracts

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