The Nervous System
- Stimulus- a change in the environment detected by receptors in the sense organs that bring about a response from a muscle or gland.
- Receptors- groups of cells which are sensitive to a stimulus.
- Sensory Neurones- nerve cells that carry signals as electrical impulses from the receptors in the sense organs to the central nervous system.
- Motor Neurones- Nerve cells that carry signals to a nervous impluse, whereas glands secrete hormones.
- Central Nervous System- all information from the sense organs is sent here, and reflexes and actions are co-ordinated.
- Synapses- connection between 2 neurones. Nerve signals are transferred by chemicals which diffuse (move) across the gap.
- Reflexes- automatic responses to a certain stimuli- reduces chances of injury- e.g. (pupils get smaller when a bright light is shone in your eye)
- Reflex arc- the passage of a nervous impulse from a stimulus to the nervous system and back again eliciting a response.
Reflex Arc & Sense Organs
- R- Receptor
- S- Sensory Neurone
- R- Relay Neurone
- M- Motor Neurone
- E- Effector
- R- Response
5 Sense Organs:
- 1. Eyes- Light Receptors
- 2. Ears- Sound & "Balance" Receptors
- 3. Nose- Smell Receptors
- 4. Tongue- Taste Receptors
- 5. Skin- Sensitive to Touch, Pressure and Temperature Change
Nervous System and Actions
CNS consists of:
- Spinal Cord
- They are under conscious control
- They have to be learned e.g. talking or writing
- Produce rapid involuntary responses
- Protect us from harm
- E.g. pupil's response to light
Some axons have a fatty sheath around them. This insulates the axon and makes the impulse travel along faster.
2 Points about Nerve Impulses:
- They are electrical signals
- They pass very quickly along the axon of the neurone
3 Points on Multiple Sclerosis:
- Fatty sheath breaks down
- Impulses slow down or may even stop
- People with this disease gradually lose the use of their muscles because the messages never reach them.
Examples of Nervous System Co-ordination- Blinking, Breathing and Swallowing.
Hormones are chemical messengers which travel in the blood to activate target cells.
- The Pituitary Gland- Produces many important hormones including LH, FSH and ADH
- Ovaries (females only)- Produce Oestrogen (controls the menstrual cycle and promotes all female secondary sexual charecteristics during puberty, e.g. extra body hair and widening of hips)
- Pancreas- Produces insulin for the control of blood sugar
- Testes (males only)- Produce Testosterone (promotes all male secondary sexual charecteristics at puberty, e.g. extra hair in places and changes in body proportions)
Hormones control various organs and cells in the body, though they tend to control things that aren't immediately life-threatening. For example, they take care of all things to do with sexual development, pregnancy, birth, breast-feeding, blood sugar levels, water content etc.
Hormones and Nerves
Hormones and Nerves do similar jobs but there are differences:
- Very fast message
- Act for a very short time
- Act on a very precise area
- Slower message
- Act for a long time
- Act in a more general way
The Menstrual Cycle has 4 stages:
- Day 1- the bleeding starts (uterus lining breaks down for about 4 days)
- Day 4-14- the lining of the womb builds up again into a thick spongy layer full of blood vessels, ready to recieve a fertillised egg.
- Day 14- An egg is developed and then released from the ovary
- The wall is then maintained for about 14 days, until day 28. If no fertillised egg has landed on the uterus wall by day 28, the spongy lining starts to break down again and the whole cycle starts again.
Hormones control the different stages:
There are 3 main horones involved- FSH, LH and Oestrogen.
- Produced by the pituitary gland
- Causes an egg to mature in one of the ovaries
- Stimulates the ovaries to produce oestrogen
- Produced in the ovaries
- Causes Pituitary to produce LH
- Inhibits the further release of FSH
- Produced by the pituitary gland
- Stimulates the release of an egg at around the middle of the menstrual cycle.
Hormones can be used to reduce fertility:
- the pill is over 99% effective of preventing pregnancy
- It reduces the risk of getting some types cancer
- It isn't 100% effective- there's still a very slight chance of getting pregnant
- It can cause side effects like headaches, nausea, irregular menstrual bleeding, and fluid retention.
- It doesn't protect against sexually transmitted diseases (STD's)
Controlling Fertility Cont.
Hormones can be used to increase fertility.
- It helps a lot of women to get pregnant, when previously they couldn't.
- It doesn't always work ( some women may have to do it many times- which could be expensive)
- Too many eggs could be stimulated, resulting in unexpected multiple pregnancies (twins, triplets, etc.)
IVF- helps couples have children
- Involves collecting eggs from the woman's ovaries and fertilising them in a lab using a man's sperm. These are then grown into embryo's, which are transferred to the woman's uterus.
- Hormones are given before egg collection to stimulate egg production (so more than one egg can be collected)
- Oestrogen and Progesterone are often given to make implantation of the embryo into the uterus more likely to succed.
But the use of hormones in IVF can cause problems for some women...
- Some women have avery strong reaction to the hormones- including abdominal pain, vomiting and dehydration.
- There have been some reports of an increased risk of cancer due to the hormonal treatment.
Homeostasis is all the functions of your body which try to maintain a "constant internal environment."
Body levels that need to be controlled:
- Ion content- regulated by the kidneys. Ions are lost in sweat and kidneys will remove excess from the blood, this is then got rid of in urine.
- Water content- lost through sweat (skin), breath (lungs), kidneys (urine), and also in the faeces.
- Sugar content- normal metabolism of cells and vigorous exercise remove glucose from the blood. Your body produces a hormone called insulin, which add or removes glucose from the blood to maintain the right level.
- Temperature- brain acts as personal thermostat. Its sensitive to the blood temperature in the blood, and it recieves messages from the skin that provide information about skin temperature.
Diabetes (type 1) is where your pancreas doesn't produce enough insulin.
Blood glucose level rises- Pancreas senses blood glucose level- Pancreas decreases secretion of insulin and increases secretion of glucagon- liver releases glucagon into the blood. Then it starts again.
Blood sugar level drops- Pancreas senses blood glucose level- Pancreas increases secretion of insulin and decreases secretion of glucagon- liver takes up extra glucose from the blood.
- Insulin lowers the blood sugar
- Glucagon raises the blood sugar
- Oestrogen is most likely to be found in oral contraceptives
- FSH is most likely to be used in fertility treatments.
Diet and Exercise
There are 7 types of food groups:
- Carbohydrates- Release Energy
- Fats- Keep you warm (insulate)
- Proteins- Growth, Repair Cells.
- Fibre- Digestion
- Vitamins and Minerals- Bones, Skin and Blood (keeps it healthy)
- Water- Our bodies cannot survive without water.
A healthy diet contains all the different nutrients in the correct amounts, and provides the right amount of energy for each individual. An unbalanced diet can lead to a person becoming malnourished. They may be too thin or too fat as a result, and they may suffer from deficiency diseases. Deficiency Diseases are caused by lack of specific nutrients, e.g. Lack of Vitamin C= Scurvy. A deficiency disease can cause problems with the skin, joints and gums.
Respiration is the chemical reaction that allows cells to release energy from food. The metabolic rate is the speed at which such chemical reactions take place in the body. It varies because of several factors, including:
- gender - male or female ( males tend to have a higher M.R.)
- the proportion of muscle to fat in the body
- the amount of exercise and other physical activity
- genetic traits
The metabolic rate increases as we exercise and stays high for a while afterwards.
- In developed countries the problem is too much food. Obesity is becoming a very serious problem, in the UK 1 in 5 adults are obese. Hormonal problems can lead to obesity, though the usual cause is a bad diet.
- Health Problems that can arise as a result of obesity include: arthritis, diabetes, high blood pressure and heart disease. It is also a risk factor for some kinds of cancer.
- In developing countries the problem is often to little. People suffer from lack of food. This can be a lack of one or more specific types of food (malnutrition), or not enough food of any sort (starvation). Young children and elderly tend to be the worst sufferers.
- The effects of malnutrition vary depending on what foods are missing from the diet. But problems commonly include slow growth (children), fatigue, poor resistance to infection and irregular periods in women.
Cholesterol and Salt
Cholestrol is a fatty substance that's essential for good health. It is found in every cell of the body.
A high cholesterol is a risk factor for heart disease as it cloggs the blood vessels. This reduces the blood flow to the heart, which can lead to angina (chest pain) or a heart attack (if the vessel is blocked completely)
The liver is realy important in controlling the amount of cholesterol. It makes new cholesterol and it removes it from the blood so that it can be eliminated from the body. The amount the liver makes depends on your diet.
- Cholesterol is carried around your body by HDL's and LDL's.
- LDL's bad cholesterol carry cholesterol from the liver to the body cells.
- HDL's good cholesterol carry excess cholesterol from body cells to the liver.
Cholesterol and Salt cont.
- Saturated Fats- (with no C=C double bonds) raise cholesterol in the blood by increasing the amount the liver makes and decreasing the amounts the liver gets rid of- so they should be eaten in moderation.
- Polyunsatured Fats- (with exactly one C=C double bond) tend to lower blood cholesterol by increasing it's removal from the body and improve LDL/HDL balance.
- Monounsaturated Fats- (with exactly one C=C double bond) were long considered to be neutral as far as health is concerned. But recent evidence suggests that they may also help to lower blood cholesterol and improve LDL/HDL balance. People who have a diet high in monounsaturates tend to have lower levels of heart disease.
Salt- too much increases the risk of heart disease as it causes high blood pressure (hypertension.) On labels salt is usually listed as Sodium.
Drugs, Alcohol and Tobacco
- Drugs alter what goes on in your body, they change your body chemistry.
- Tobacco smoke contains carbon monoxide which irreversibly combines with haemoglobin and causes the blood to carry less oxygen. In pregnant women this can deprive the foetus of oxygen and cause the baby to be born underweight.
- Tobbaco smoke also contains carcogens- chemicals that lead to cancer. Lung cancer is way more common among smokers than non-smokers. It is estimated 90% of lung cancers are asscoiated with smoking.
- Smoking also causes disease of the heart and blood vessels, and damages the lungs causing emphysema and bronchitis.
- Tar in cigarretes damage cilia.
- Drinking alcohol reduces the activity of the nervous system, it leads to impaired judgement, poor balance & coordiantion, lack of self-control, unconsciousness and more. Alcohol excess also causes dehydration, which can damage brain cells, causing a noticable drop in brain function. It also damages the liver, leading to liver disease. Alcohol also has its social costs; it causes way more than half murders, stabbings and domestic assaults. Alcohol misuse is also a factor in loads of divorces and cases of child abuse.
- Illegal drugs are often divided into 2 main classes- soft and hard. Hard drugs being heroin and cocaine (as they are seriously addictive and more harmful)
- The link between cannabis and hard drugs isn't clear, but three opinions are common: cannabis is a stepping stone ( create a desire to try harder drugs), cannabis is a gateway drug (brings people into contact with drug dealers), Its all down to the genetics (certain people are more likely to take drugs)