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Reflex actions
Responding to
change

Homeostasis

B1
...


Stimulus

Change in the
environment

Receptor

E
...
Eyes, skins, found in
sense organs

Sensory neuron
CNS

Brain and spinal cordcoordinates response

Motor neuron
Effector

Muscles (contract) or
glands (secrete)

Reflex actions
• Automatic responses important for survival
• Similar response to a normal conscious action but
involves a relay neuron in the spinal cord or
unconscious area of the brain
• It then travels to the conscious area so you know
about the reflex - after it has happened
Synapses
Junctions between nerves
Impulses cross the synapses
Chemicals released into the
gap between neurons
Chemicals attach to the
surface of the next neuron
and set up a new electrical
impulse

• Sensory receptor --> sensory
neuron --> CNS --> relay neuron
(spinal cord) --> motor neuron -->
effector
4

Hormones and fertility
• Glands secrete hormones which are then carried around in the blood
Menstrual cycle
Brought about by hormones made and released
by pituitary gland and ovaries
Hormones:
FSH
- causes eggs to mature
- Stimulates the ovary to produce oestrogen
Oestrogen
- Causes the lining of the uterus to develop
- Inhibits FSH production
- Stimulates the release of the mature egg
Others: progesterone and LH

28 days: womb lining thickens, Eggs
released from ovary after 14 days ovulation, If not fertilised, the womb
lining and egg come out as a period

Contraception
Inhibits production
of FSH so eggs
don't mature in the
ovaries

Fertility treatments
FSH used to stimulate eggs to mature
and trigger oestrogen production
IVF - eggs collected and fertilised in the
lab then implanted

Advantages - fewer children
(cost), women freedom
Disadvantages - expensive,
multiple births, embryo use

Homeostasis
Internal environment is maintained by homeostasis
Controlling water and ions
- Water moves in an out of body
cells
- taken in from food and drink
- lost from breathing out, sweat
and urine (salt lost here too)
- Kidneys control this

Controlling temperature
- Core temperature 37C, enzymes
work best
- Sweat to cool down, shiver to
warm up
- Below 35C hypothermia risk
- too high leads to heat stroke /
heat exhaustion enzymes and
cells don’t work properly

Controlling blood glucose
- Kept constant by hormones from pancreas

Hormones and plant growth
Plants are sensitive, they need to grow the right way

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