Microsoft word - biology_nervous.doc
GCSE Revision Notes
Biology Revision Notes – Nervous Systems And Homeostasis
1. The nervous system consists of the brain and the spinal cord (the central nervous system or
CNS), as well as all the nerves in the body. 2. Nerve cell are very long and thin, allowing nerve impulses to travel in one direction only:
Sensory nerve cells – carry impulses from the sense organs to the CNS.
Motor nerve cells – carry impulses from the CNS to muscles and glands.
3. Reflex actions happen without thinking. Voluntary actions are those that you think about.
4. The following words are to do with the nervous system:
Stimulus – a change in the environment.
Receptor – the sense organ that detects the change.
Effector – the organ that responds (usually a muscle).
Response – the reaction that takes place.
5. The reflex arc is as follows:
Stimulus à receptor à sensory neurone à relay neurone à motor neurone à effector à response. 6. A synapse is the chemical connection between two neurones.
7. The eye functions in the following ways:
• Light is focused on the retina with the lens, upside down (corrected by the brain).
• In bright light, circular muscles in the iris contract to make the pupil smaller.
• In dim light, radial muscles in the iris contract to make the pupil bigger.
• To see a distant object, the ciliary muscles relax and the suspensory ligaments tighten to
stretch the lens – making it thin to give a good focus on the retina. • To see a near object, the ciliary muscles contract and the suspensory ligaments slacken to make the lens fatter, and focus the image on the retina. • Accommodation is the process of altering the lens to focus.
• The sclerotic layer is the tough white layer of the eye.
• The cornea is a clear window in the sclerotic layer.
8. Homeostasis is the maintenance of a constant internal environment.
9. The skin controls the temperature:
If it’s too hot – sweating occurs, the hairs are lowered, and vasodilation occurs.
If it’s too cold – shivering occurs, the hairs are raised, vasoconstriction occurs, and there is
10. Excretion is the removal of waste products produced by the body (e.g. CO2 in the lungs).
11. In the kidneys:
• There is a good blood supply, to filter out urea, salts and water. • This travels through the cortex (outside of the kidney), the medulla, and then the pelvis.
• This urine travels through the ureter to the bladder.
• The sphincter muscle relaxes when the bladder is full, to open up the urethra.
12. Ultrafiltration and the nephron:
GCSE Revision Notes
Too little water à Blood à Brain à ADH (anti-diuretic hormone) à Blood à Kidneys.
14. The hormonal control of blood sugar: Blood glucose is too high à Pancreas à Insulin à Liver à Changes glucose to glycogen.
Blood glucose is too low à Pancreas à Glucagon à Liver à Changes glycogen to glucose.
15. The female menstrual cycle has the following stages:
• Stage 1 à The uterus lining breaks down (days 1 to 4).
à FSH (follicle stimulating hormone) is released by the pituitary gland.
• Stage 2 à The follicle develops (days 4 to 14).
à Oestrogen is made by the ovaries to build up the uterus lining and inhibit FSH
production. Oestrogen causes the pituitary gland to make LH (luteinising hormone).
• Stage 3 à LH causes the egg to be released on day 14.
à The corpus luteum develops, to produce progesterone.
• Stage 4 à The progesterone maintains the uterus lining.
à If the egg doesn’t fertilise, the corpus luteum breaks down and the progesterone production is stopped. à Progesterone and oestrogen are at their lowest level on day 28, therefore the cycle starts again. 16. FSH can be taken to stimulate egg production in fertility treatment.
17. Oestrogen can be taken as ‘the pill’ to stop egg production (it inhibits FSH).
18. A tropism is the way a plant responds to a stimulus. The response is slow growth movements.
19. Growth towards a stimulus is positive, and growth away from one is negative:
Phototropism – the stimulus is light. The shoots are positive and the roots are negative.
Geotropism – the stimulus is gravity. The shoots are negative and the roots are positive.
Hydrotropism – the stimulus is water. The roots are positive.
20. Auxin is the plant hormone:
• It makes cells grow in the shoots, and inhibits growth in the roots. • It is produced only in the shoot and root tips. • It moves away from a light source, and towards gravity. 21. The following are types of drugs:
Sedatives – slow you down and make you sleepy, e.g. tranquillisers and alcohol.
Analgesics – are painkillers, e.g. aspirin, paracetamol, morphine and cocaine.
Hallucinogenic drugs – distort the mind’s ability to interpret the surroundings.
22. Alcohol has the following effects:
• It interferes with the messenger molecules in the synapses – slowing down messages. • Heavy drinking damages the liver, as it is the liver that removes alcohol from the body. • It takes one hour to remove one unit of alcohol from the body (1 unit = ½ pint beer etc.) 23. Protein synthesis takes place in the following stages:
• The DNA unwinds and is copied to messenger RNA (mRNA).
• The mRNA moves into the cytoplasm.
Transfer RNA (tRNA) attaches onto each codon (group of three bases).
• This codes for specific amino acids – peptide bonds form to create a protein chain.


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