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.
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
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.
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
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.
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