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These cells are called motor neurones and carry info from the CNS to the rest of your body.
The info is carried in impulses and these go to the effector organs, say a hand, and they then respond.
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Effector organs are muscles or glands. Muscles react to impulses by contracting, your glands, by secreting chemicals.
Receptor -> Sensory Neurone -> CNS -> Motor Neurone -> Effector
Your eyes respond to light.
Sensory neurones carry impulses to the CNS.
The info is processed and impulses are sent to the motor neurones to produce an action.
b. Reflex Actions:
- Actions that happen in response to something so fast that you don’t think about it.
- Automatic responses that are there to help protect yourself.
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When you touch something that your body does not like, like a hot or sharp object, you pull your hand back before you really feel it. This is a reflex.
i. Uses:
To avoid dander or harm, this is possible because they happen to FAST.
There are also many other uses besides defensive reactions, like breathing and food digestion.
It could be fatal if we had to always remember to breathe and then you forgot!
ii. How reflexes work:
Three types of neurone are involved in the process:
- Sensory neurones
- Motor neurones, and
- Relay neurones, (which connect the other two, often found in CNS and spinal cord).
An electrical impulse goes from:
Sensory receptor -> sensory neurone -> CNS -> relay neurone -> motor neurone
This is known as the reflex arc.
The idea of the reflex arc makes it so that it bypasses areas of conscious, so we never think about it!
iii. How Synapses Work:
Nerves do not join up together; they are separated by gaps called synapses.
As the impulse reaches the synapse, chemicals are released and end up at the other side at receptor sites. This then trigger an electrical impulse at the other neurone.
iv. The reflex arc in detail:
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A hot object is touched, which triggers stimulation of skin.
Object -> Skin
- Impulse travels along a sensory neurone to the CNS (here it’s the spinal cord)
Sensory -> CNS
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The impulse reaches a synapse with a relay neurone.
Sensory -> _synapse_ -> relay
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The chemical released crosses the gap; this triggers another impulse along a relay neurone.
Relay ->...
- It then reaches the gap from relay to motor neurone, another chemical is released.
Relay -> Motor
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This crosses the gap and triggers an impulse to travel along the motor neurone.
Motor ->...
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When it reaches the effector organ, the organ is stimulated in response.
Motor -> Effector
Stimulus -> Receptor -> Co-ordinator -> Effector -> Response
c. The menstrual cycle:
- Control of activities of a woman’s individual cells.
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The menstrual cycle is controlled by hormones produces in a woman’s brain.
- The levels of hormones changes, as does her attitude and the way her body works.
i. What is the menstrual cycle?
Preparation of the female body for an egg to be housed.
- This generally lasts for a month, 28 days, but can vary.
14 days into maturing of the egg, it is released from an ovary (ovulation).
The lining of the womb stays thick for a few days after.
If the egg is fertilised by sperm, pregnancy takes place, if not the lining and dead egg are shed.
This is the woman’s period.
ii. How the menstrual cycle works:
All these changes are brought around by hormones, produces in the pituitary gland and in the ovaries.
Every month hormones start eggs maturing. These hormones also make the woman produce oestrogen, the female sex hormone.
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FSH: secreted by the pituitary gland, makes eggs mature, stimulates ovaries to produce oestrogen.
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Oestrogen: Stimulates lining of womb t build up. Stimulates pituitary gland to make LH, another hormone.
- LH: Stimulates release of mature egg, in the middle of menstrual cycle.
iii. Fertility drugs:
Used when couples have a baby with IVF (in vitro fertilization). They use this method when one of the couple’s fallopian tubes is damaged.
Eggs removed from ovary, fertilised with sperm outside the body. The small developing embryos are then placed back inside the mother.
The woman is given fertility drugs to try to help, because the success rate of IVF is not high.
iv. Advantages and disadvantages of fertility control:
d. Controlling conditions
Internal conditions, also known as internal environment, change as your body gets ill etc. When this is happening, the body doesn’t function properly.
The thing keeping all the bodily functions stable is called homeostasis, and involves you nervous system, hormone systems and many organs.
ii. Controlling water and ions:
You gain water by eating and drinking.
You lose water by breathing out and salt as well by sweating.
Water and salt is also lost in urine, made in your kidneys.
Your kidneys control the amount of salt and water you lose depending on the conditions.
The kidneys are controlled by hormones and nerves.
iii. Controlling temperature:
The body needs to be kept at 37°, if not; the slightest change can cause your enzymes to stop working, shutting your body down.
You control this by sweating to cool down, and shivering to warm up. The nervous system is very important for responding to temperature change.
iv. Controlling blood sugar:
When digesting, sugar passes into the blood.
Without control, blood sugar levels would go up and down just after and a while after a meal.
This would cause chaos, so hormones in your pancreas keep your blood sugar levels constant.
