The nervous system enables humans to
React to their surroundings and coordinate their behaviour
Stimulus
Change in environment
Receptors detect
Stimuli
Receptors in the eyes are sensitive to
Light
Receptors in the ears are sensitive to
Sounds and changes in position, enable us to keep our balance
Receptors on the tongue are sensitive to
Chemicals which enable us to taste
Receptors in the nose are sensitive to
Chemicals which enable us to smell
Receptors in the skin are sensitive to
Touch, pressure, pain and temperature changes
Light receptor cells have a
Nucleus, cytoplasm and cell membrane
A stimulus can be
Light, sound, touch, pressure, pain, chemical or a change in position or temperature
The central nervous system consists of
The brain and the spinal cord
Neurones transmit information as
Electrical Impulses
Sensory neurones
Nerve cells that carry signals as electrical impulses from the receptors to the central nervous system
Relay neurones
Nerve cells that carry signals from sensory neurones to motor neurones
Motor neurones
Nerve cells that carry signals from the central nervous system to the effector muscles or glands
Effectors - muscles
Contract in response to a nervous impulse
Effectors - glands
Secrete hormones as a response to a nervous impulse
Reflex actions are
Automatic and rapid
First stage of a simple reflex action
A receptor detects a stimuli. Impulses are sent from the receptor along a sensory neurone to the central nervous system
Second stage of a simple reflex action
At a synapse between a sensory neurone and a relay neurone in the central nervous system, a chemical is released that causes an impulse to be sent along a relay neurone
Third stage of a simple reflex action
A chemical is then released at the synapse between a relay neurone and motor neurone in the central nervous system, causing impulses to be sent along a motor neurone to the effector that brings about the response
Fourth stage of a simple reflex action
The effector (either a muscle or a gland) responds by contracting or by secreting chemical substances
Synapse
The connection between two neurones. The nerve signal is transferred by chemicals which diffuse across the gap
What is the name of the passage of information in a reflex (receptor to effector)?
The reflex arc
What conditions in your body need to be controlled?
Ion content, sugar content, water content and temperature
What is ion content regulated by?
The kidneys
How is ion content regulated?
It is removed via the skin when we sweat and through the kidneys in the urine
How is water content regulated?
Leaves the body via the lungs when we breathe out, via the sweat and via the kidneys in the urine
Why is temperature controlled?
To maintain the temperature at which enzymes work best
What controls body temperature?
The brain
Why are blood sugar levels controlled?
To provide the cells with a constant supply of energy
What hormone controls blood sugar levels?
Insulin
Where are hormones produced and secreted?
In the glands
How do hormones travel?
In the bloodstream
What are hormones?
Chemical messengers which travel in the blood to activate target cells
Which hormones does the pituitary gland produce?
FSH and LH, involved in the menstrual cycle
Which hormone does the ovary produce?
Oestrogen, involved in the menstrual cycle
How do hormones act compared to nerves?
Slower action but for a longer time. They also act in a more general way
What chemical substance controls many processes in the body?
Hormones
What is an example of a function in the body that hormones regulate?
The menstrual cycle
What does the hormone FSH do?
It causes eggs to mature in the ovaries. It also stimulates the ovaries to produce oestrogen
What does the hormone LH do?
It stimulates the release of an egg from the ovary
What does the hormone oestrogen do?
Inhibits further production of FSH
What is the first stage of the menstrual cycle?
When the bleeding starts. This is due to the uterus lining breaking down for about four days
What is the second stage of the menstrual cycle?
The lining of the uterus builds up again, from day 4 to 14, into a thick spongy layer full of blood vessels ready to receive a fertilised egg
What is the third stage of the menstrual cycle?
An egg is released from the ovary at day 14
What is the fourth stage of the menstrual cycle?
The wall is maintained for about 14 days, until day 28. if no fertilised egg has landed on the uterus wall by day 28, the spongy lining begins to break down again and the whole cycle starts again
Which hormones can be used in the reducing of fertility?
Oestrogen and progesterone
Why is oestrogen in oral contraceptives?
It inhibits the production of FSH
Why is progesterone used in oral contraceptives?
It stimulates the production of a thick cervical mucus which prevents any sperm getting through and reaching the egg
What did the first pill contain?
High levels of oestrogen
Why was the level of oestrogen in the pill reduced?
Women experienced side effects
Why are progesterone only pills being used more?
They have fewer side effects
What hormone can be injected into women to stimulate egg release?
FSH and LH
What does IVF involve?
Collecting eggs from the women’s ovaries and fertilising them in a lab with the man’s sperm. These are then grown into embryos. Once the embryos are tiny balls of cells , one or two of them are transferred into the women’s uterus to improve the chance of preganancy
What hormones are given in IVF before egg collection?
FSH and LH to stimulate egg production
What are plants sensitive to?
Light, Moisture and Gravity
What do shoots grow towards?
Light
What do shoots grow against?
The force of gravity
What do roots grow towards?
Moisture
What direction do roots grow in?
The force of gravity
What hormone do plants release to control growth?
Auxin
What is the name given to the growth of a plant in response to light?
Phototropism
What is the name given to the growth of a plant in response to gravity?
Gravitropism / Geotropism
Where is auxin produced?
At the tips
What happens when there is extra auxin?
Growth is stimulated in the shoots but inhibited in the roots
When a shoot is exposed to light, more auxin accumulates on…
The side that’s in the shade than the side in the light
When a root is growing sideways, the auxin will build up on…
The lower side of the root
Auxin in shoots causes the cells to…
Grow faster (elongate more) on the shaded side so the shoot bends towards the light
The responses of plant roots and shoots is the result of…
The unequal distribution of hormones, causing unequal growth rate
When a shoot is growing sideways, gravity causes more auxin to build up on…
The lower side of the root, causing the lower side cells to grow faster and bend the shoot upwards
Auxin in roots causes the cells to…
Stop growing. This means the cells on the top grow faster and the roots bend downwards
When a root is exposed to moisture, more auxin accumulates on…
The side with more moisture
What can plant hormones be used for in agriculture and horticulture?
Weedkillers and rooting hormones
