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The Nervous System
Sense organs contain receptors, groups of cells which are sensitive to and so can detect a
stimulus. The change stimulus energy e.g. light energy, into electrical impulses. Stimulus is a
change in your environment, which you may need to react to. A stimulus can be: light, sound,
touch, chemical, pressure, chemical, change in position or temperature.
Five Sense Organs The Central Nervous System
· Eyes: light receptors The CNS consists of the brain and spinal cord. It is
· Ears: sound receptors where all the information from the sense organs are
· Nose: smell receptors sent to and where reflexes and actions are
chemical stimuli coordinated.
· Tongue: taste receptors 1) Sensory Neurons are the nerve cells that carry
bitter, sweet, salt, sour, savory signals as electrical impulses from the receptors in
· Skin: sensitive to touch the sense organs to the CNS.
pressure, temperature change 2) Motor Neurons are the nerve cells that carry
signals to the effector.
3) Effectors are muscles and glands. Instructions are
sent to the effectors. Muscles contract in response to
a nervous impulse and glands secrete hormones.…read more

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Reflexes help prevent injury because sometimes waiting for your brain to make a decision is
just too slow. They are automatic responses to certain stimuli. The passage of information in
a reflex is called a reflex arc.
The Reflex Arc Synapses Connect Neurons
The neurons in a reflex arc go through the spinal · The connection between two
cord or an unconscious part of the brain. neurons is called a synapse.
1) A stimulus is detected by receptors, an · The nerve signal is transferred
impulse is sent along a sensory neuron to the by chemicals which diffuse
spinal cord. across the gap.
2) In the spinal cord the sensory neuron passes · These chemicals then set off a
on the message to a relay neuron. new electrical signal in the next
3) The relay neuron passes the impulse to a neuron.
motor neuron.
4) The impulse travels along the motor neuron
to the effector.
5) The effector produces a response and
because you don't have to think about it the
reaction is quicker.
SensoryNeuron RelayNeuron MotorNeuron…read more

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Hormones are chemical messengers which travel in the blood to activate target cells. They
are produced in various glands and normally have a relatively long lasting effect.
· The Pituitary Gland produces important Hormones & Nerves
hormones including LH, FSH and ADH which They do similar jobs but there
controls water content. are differences.
· The Pancreas produces insulin for the Nerves
control of blood sugar. · very fast message
· The Ovaries produce oestrogen which · act for a very short time
controls the menstrual cycle and promotes all · act on a very precise area
female secondary sexual characteristics Hormones
during puberty. · slower message
· The Testes produce testosterone which · act for a long time
promotes all male secondary sexual · act in a more general way
characteristics at puberty.…read more

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The Menstrual Cycle
Hormones & Nerves
The hormones control the
different stages.
FSH (Follicle Stimulating
· produced by the pituitary gland
· causes an egg to mature in one
of the ovaries
· stimulates the ovaries to
The Four Stages produce oestrogen
1) Day 1 is when the bleeding starts. The uterus Oestrogen
breaks down for about four days. · produced in the ovaries
2) Day 4 ­ Day 14 the lining of the womb builds up · causes pituitary to produce LH
again into a think layer of blood vessels ready to · stops the further release of
receive a fertilized egg. FSH
3) Day 14 an egg is developed and then released from LH (Luteinising Hormone)
the ovary. · produced by the pituitary gland
4) Day 14 ­ Day 28 the wall is maintained, if no · stimulates the release of an
fertilized egg has landed on the uterus wall by day egg at around the middle of the
28 the lining starts to break down again and the menstrual cycle
cycle repeats.…read more

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Missing a few topics - No carbon cycle, no pyramid of biomass

Good though :)


Muldip Bassi


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