Why does the nervous system use impulses?
So you can react quickly to your surroundings and coordinate what you do.
What is a stimulus?
A change in the environment.
What detects a stimuli?
Receptors Eg: light receptors in your eyes.
The nervous system cycle:
Receptor -> sensory neuron -> coordinator CNS -> motor neuron -> effector.
How does the nervous system work?
A sensory receptor detects a stimulus The information sent as an electrical impulse passes along special cells called neurons. The impulse travels along the neuron until it reaches the CNS The CNS coordinates the information and sends impulses along motor neurons to the effector organs The effector organ is either a muscle or a gland Muscles respond by contracting Glands secrete chemical substances (hormones)
What are fast and automatic responses to stimuli called?
Why are reflex actions important?
Reflex actions help to run everyday bodily functions and to help avoid danger.
What three neurons are involved in reflex actions?
Sensory neurons Motor neurons Relay neurons
What are relay neurons?
Relay neurons connect a a sensory neuron to a motor neuron. They are in the CNS.
What is important in a reflex arc?
The key point is that the impulse from a reflex arc bypasses the conscious areas of the brain. This enables the reflex action to remain as short as possible.
What are synapses?
Junctions between the neurons. The electrical impulses travelling along the neurons have to cross the synapse.
What happens at a synapse?
When an impulse arrives at the junction between two neurons, chemicals are released which cross the synapse and arrive at the receptor site on the next neuron. The chemicals attach to the neuron's surface to set up a new electrical impulse.
What are hormones?
Hormones are chemical substances that coordinate many processes within the body.
What happens after 14 days in a woman's menstrual cycle?
Ovulation, the egg starts maturing and it's released from the ovary.
How does the menstrual cycle work?
Follicle stimulating hormone or FSH is secreted by the pituitary gland and it makes eggs mature in the ovaries. FSH also stimulates the ovaries to produce oestrogen. Oestrogen is made and secreted by the ovaries and oestrogen stimulates the lining of the womb to build up for pregnancy. Oestrogen also inhibits FSH production. Oestrogen also stimulates the release of a mature egg. Lutenising hormone or LH releases the egg at peak.
How do oral contraceptives prevent pregnancy?
Oral contraceptives contain female hormones (particularly oestrogen). As oestrogen inhibits FSH production, no eggs are able to mature so women can't get pregnant. The pill has to be taken regularly so the artificial hormone levels don't drop.
Why were oral contraceptives criticised?
Initially, the large amounts of oestrogen caused serious side effects such as high blood pressure and headaches. Now much lower doses are taken.
Why do some people want fertility treatments?
Many families want fertility treatments due to family complications. For example, a woman might have a damaged fallopian tube or a man might have a low sperm count.
Describe the process of IVF
1. Fertility drugs are used to make lots of eggs mature at the same time for collection. 2. The eggs are collected and placed in a special solution in a Petri dish. 3. A sample of semen is collected and the sperm and eggs are mixed in the Petri dish. 4. The eggs are checked to make sure they are developing. 5. When the fertilised eggs have formed tiny balls of cells, they are placed back in the uterus of the mother for further development. The hormones used are FSH and LH.
Advantages and disadvantages of fertility treatments:
Advantages: •Less poverty due to fewer children being born and fewer mouths to feed. •The pill has helped to control population growths on some countries such as China. Disadvantages: •Can cause health problems •Health risks to the mother •Expensive •Ethical issues, some say preventing conception is denying life •The mature eggs can be stored but what if the mother dies?
The balancing act inside the body where everything is kept constant.
Controlling water and ions
If too much water moves into your cells, they can be damaged or destroyed. Water is taken in as you eat and drink and it's lost as you breathe out. Salt is lost in your sweat alongside water. The same occurs with urine. The kidneys control the balance of mineral ions in your body.
It's vital your temperature is kept at 37 degrees Celsius as enzymes work best here. The body controls temperature in several ways: you sweat to cool down and shiver to warm up.
Controlling blood sugar
The concentration of glucose on your blood is kept constant by the hormones made on the pancreas. This ensures that your body cells are provided with a constant supply of energy that they need.
What are plants sensitive to?
Light, moisture and gravity.
What are plant responses brought about by?
Plant hormones (auxin).
Sensitivity and plants
Plant roots are sensitive to gravity and water. The roots grow towards moisture and in the direction of gravity. Plant shoots are sensitive to light and gravity. They grow towards light and against the force of gravity.
Response of a plant to light
Response of a plant to gravity
Auxin in phototropism
In a young plant, auxin will gather on the shaded side. The cells on that side respond to the hormone by growing more so the shoot bends towards the light. Once light falls equally along the plant, the levels of auxin will balance.
Auxin in gravitropism
High levels of auxin makes shoot cells grow more but they inhibit the growth of root cells. Shoots grow more on the side with the most auxin but roots grow more on the side with the least auxin.
What can plant growth hormones be used as?
Weed killers and as rooting hormones on cuttings.
Plant hormones are very useful as weed killers but their use can damage the environment. Eg: Agent Orange in Vietnam still causes limb deformities in developing foetuses.