The Nervous System
- The Nevous System allows you to react to things going on around you
- Sense organs detect stimuli which is a change in the environment, which you may need to react to. A stimulus can be light, sound, touch, pressure, pain, chemical or a change in position or temperature.
- Five different sense organs: Eyes, ears, nose, tongue and skin.
- Each sense organ contains different receptors, which are groups of cells which are sensitive to a stimulus
- Eyes (light) Ears (Sound and Balance) Nose (Smell sensitive to chemical) Tongue (Taste chemical) Skin (Touch, Pressure and Temperature Change)
Sensory Neurones - The nerve cells which carry signals as electrical impulses from the receptors in the sense organs to the central nervous system.
Motor Neurones - The nerve cells that carry signals to the effector muscles or glands
Effectors - Muscles and glands are known as effectors. They respond in different ways: Muscles contract in response to a nervous impulse, whereas glands secrete hormones.
- Reflexes are automatic responses to certain stimuli and they can reduce the chances of being injured.
- For example if someone shines a bright light in your eye, your pupils automatically get smaller to prevent your eye from being damaged.
- The route taken by the information in a reflex is called a reflex arc.
- 1. Hot pan of boiling water touches arm
- 2. The pain receptors in the skin are stimulated
- 3. Message of pain travels along a sensory neurone to the CNS.
- 4. Message is passed along a relay neurone in the CNS.
- 5. The relay neurone relays the message to the motor neurone.
- 5. Message travels back along a motor neurone to the effector
- 6. Message reaches the muscles and it contracts to move the arm away from the pan of hot water to prevent injury. If it were a shock the effector would be a gland, which would respond by secreting adrenaline.
- Neurones transmit information as electrical impulses around the body.
- Neurones have branched endings so they can connect with lots of other neurones. They are also long, which speeds up the impulse as the smaller the number of connections the quicker the impulse can be recieved.
- The connection between two neurones is called a synapse.
- The nerve signal is transferred by chemicals which diffuse across the gap between the neurones.
- These chemicals then set off a new electrical signal in the new neurone.
The Menstrual Cycle
The menstrual cycle has four stages:
- Stage 1: The uterus lining breaks down for about four days. (Bleeding starts)
- Stage 2: The lining of the uterus builds up again, from day 4 to day 14, into a thick spongy layer full of blood vessels, ready to recieve a fertilised egg.
- Stage 3: An egg is developed and then released from the ovary at day 14.
- Stage 4: The wall is then maintained for about 14 days, until day 28. If no fertilised egg has landed on the uterus wall by day 28, the spongy lining starts to break down and the cycle begins again.
Hormones Controlling the Menstrual Cycle
The menstrual cycle is controlled by 4 hormones:
- Follice Stimulating Hormone (FSH)- Causes an egg to develop in one of the ovaries and also stimulates the ovary to produce oestrogen. PITUITARY GLAND.
- Luteinising Hormone (LH)- Stimulates the release of an egg at day 14. PITUITARY GLAND.
- Oestrogen- Causes the lining of the uterus to thicken and grow and stimulates the production of LH and inhibits the production of FSH. OVARIES.
- Progesterone- Maintains the lining of the uterus. When the level of progesterone falls, the lining breaks down. OVARIES.
Controlling Fertility-Contraceptive Pill
- The contraceptive pill harnesses the hormone oestrogen to prevent the release of an egg.
- Oestrogen usually stimulates the production of an egg, however if taken every day to keep the level permanently high, it inhibits the production of FSH, and eventually egg development stops
- ADVANTAGES: The pill is over 99% effective at preventing pregnancy. It also reduces the risk of some cancers.
- DISADVANTAGES: It can have side effects like headaches, nausea irregular periods and fluid retention. It doesn't protect against STI's.
- Some women have levels of FSH that are too low to allow their eggs to mature, which means that no eggs are released and a woman cannot get pregnant.
- These women can take FSH to stimulate egg production in their ovaries
- ADVANTAGES: It helps a lot of women who were unable to get pregnant, get pregnant.
- DISADVANTAGES: It is not 100% successful. Too many eggs could be stimulated resulting in multiple pregnancies (twins, triplets etc.)
Controlling Fertility- IVF
- IVF involves collecting eggs from the woman's ovaries and fertilising them in a lab using the man's sperm. They develop into embryos and are then transferred to the woman's uterus.
- Hormones are given before egg collection to stimulate egg production in order for several eggs to be taken.
- Oestrogen and progersterone are often given to make implantation most likely to succeed.
- Some women can have a strong recation to the hormones which can include abdominal pains, vomiting and dehydration.
- There has been some reports of an increased risk of cancer due to the hormonal treatment
Controlling Body Temperature
- 37 degrees is the temperature our body attempts to maintain. This is because this is the temperature that the enzymes in the body work best at.
When you're too hot:
- Hairs lie flat
- Lots of sweat is produced, when it evaporates it transfers heat from you to the environment
- Blood vessels close to the skin widen (vasodilation) This allows more blood to flow near the surface of the skin, so it can therefore radiate more heat into the surroundings.
- You can take off layers of clothing
When you're too cold:
- Hairs stand on end to trap an insulating layer of air which helps keep you warm.
- Very little sweat is produced.
- Vasoconstriction allows less heat to be transferred from the blood to surroundings.
- You shiver, and the movement generates heat in the muscles.