Nerves and Hormones

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  • Nerves and Hormones
    • The Nervous System
      • Stimuli: change in the everyday environment which is detected using senses.
      • Sense receptor detects stimulus: eyes-light, ears-sound/keep balance/change position, tongue-chemicals in food, nose-chemicals in air, skin-tough/pressure/pain/temperature.
      • The nervous system consists of the brain, spinal cord, spinal nerves and receptors.
      • The central nervous system consists of the spinal cord and brain. PNS (peripheral) sense organ to CNS.
      • It allows organisms to react to their surroundings and co-ordinate their behaviour.
      • Information from receptors passes along nerve cells/neurones to the brain which co-ordinates the response
      • Sensory receptor detects stimulus, the energy turns into an electrical impulse and is passed through the sensory neurone, the impulse is sent to the CNS
      • The brain reads the message and sends an impulse through the motor neurone, the nerve endings are usually muscle or gland (effector)
      • Synapse: gap between nerves which sends an electrical impulse along the axon. Releases chemical messagers (neuro transmitters) which diffuse across synpase then becomes an eletricial impulse when being passed through neurones
    • Reflexes
      • Reflexes are fast, automatic and protective responses.
      • They are involuntary (don't need to think about responses)
      • Receptor detects stimulus (change in environment), sensory neurone sends signal to relay neurone (by-pass brain), motor neurone sends signal to effector to produce a response. Relay neurone found in spinal cord.
      • Reflexes: blinking-prevent damage in eye, eyes watering- wash out dirt in eye, coughing-remove food stuck in wind pipe, sneezing- get rid of dust in nose, move hand from painful stimuli- prevent damage to hand.
      • The nerves involved in reflex actions form a reflex arc. This is made up of different types of neurone each one separated by a tiny gap called a synapse.
      • This stimulus could be a pin. It is detected by the sense receptor in the skin which causes impulses to pass along the sensory neurone to the relay neurone to the motor neurone which transmits impulses to effector to carry out response e.g. muscle contracts.
    • How Hormones Control Your Body
      • Hormones are chemical messengers used in the body by the endocrine system.
      • They co-ordinate our organs and bring about changes.
      • Hormones are produced by glands and are transported in the blood.
      • Hormones travel slower than nerve impulses but have a longer lasting effect (growth)
      • Hormones react quickly - brain/kidneys regulate water content
      • Water content: lost water from skin in sweat, lungs by breathing out, kidneys in urine. Gain water from drinks/food containing water, respiration of digested food.
      • Blood sugar levels: sugar delivered to cells for constant supply of energy, products from digestions (sugar) passes in bloodstream, pancreas detects levels, insulin regulates levels.
      • Ion content: blood and watery fluid between cells contain ions e.g. hydrogen ions, helped nerves work/body fluids at correct pH, kidney control levels, unwanted ions in urine.
      • Temperature: enzymes/proteins make fast chemical reactions at 37 degrees Celsius. High temperature= no chemical reactions, make heat through respiration, lose heat through sweat/breathing, blood vessel near skin surface.
      • Homoeostasis: How the body maintains constant internal environment
      • Lower concentration of sodium in Summer, due to high mean rate of water loss in Summer
      • Blood composition- less water, thick, less sodium ions. Kidneys: less water to excrete, less sodium ions.
    • How Hormones Control The Menstrual Cycle
      • Female reproductive system: fallopian tube/oviduct, ovary gland, uterus, cervix, vagina, uterus lining, egg/ovum.
      • Menstrual cycle every 28 days, ovulation in day 14 (egg released from ovary). Day 1-3 maturing egg, day 26-28 menstruation
      • A fertilised egg will bury itself (implant) in the uterus lining. The egg needs a plentiful supply of nutrients and oxygen to develop.
      • An important part of puberty for girls is the beginning of their monthly cycle (menstrual cycle). This involves the preparation of the uterus lining to be able to receive a fertilised egg.
      • If the egg isn't fertilised, there is menstrual bleeding (period), lining of the uterus breaks down and the cycle starts again. Menstruation is caused by sex hormones
      • FSH (follicle stimulating hormone) eggs mature/stimulate ovary for oestrogen-pituitary gland. Oestrogen stimulates pituitary gland to make LH, prevents FSH, repairs uterus lining- ovaries.
      • Progesterone maintains the uterus lining, works with oestrogen to prevent FSH- Ovaries
      • Contraceptive pills contain oestrogen and progesterone to prevent pregnancy by preventing production of FSH in pituitary gland and development of eggs.
      • Contraceptive pill: large scale trial, uneducated women, unethical to test on uneducated women, no placebo, people not told it was an experiment, high doses.
      • Temperature increases, LH high,hormones at peak, LH ovulation, chance of fertilization.
    • Using Hormones to Control Fertility (IVF)
      • Fertility drugs are used to help women who cannot produces eggs every month.
      • There are many types of fertility drugs but they all work by tricking the body into producing more eggs.
      • Some fertility drugs contain FSH (mature egg/ovulation).
      • Hormones are given to stimulate the ovaries to make lots of eggs to mature at the same time (FSH/LH). Eggs are removed from the ovaries through suction/surgery, sperm is collected from the male
      • Eggs and perm are combined in a dish to allow fertilization. 2-4 fertilized eggs are inserted into the uterus.
      • IVF vs Adoption: IVF couple have their own child, adoption is cheaper, 6% success rate for IVF
      • Financial: £4,000 for IVF, illegal to sell eggs, only suitable for couples 23-39, middles class (expensive).
      • Older mothers: children see mothers die, cannot see growth of children but women have the experience of being a mother
      • Rights: single mothers have rights (if they have a good income), need to check health for IVF
      • Embryos: used in medical research, find cause of diseases, embryos die by being flushed away, exposed to air, could result to twins with lower IQ
    • Controlling Plant Growth
      • Plants are sensitive to: light, moisture and gravity.
      • Plants produce hormones to co-ordinate and control growth. They are sensitive to their environment and can make adjustments to survive.
      • They produce a hormone known as auxin. Tropism is a plant's response to a stimulus.
      • Photo-tropism: stimlus is light. PP - Stem tip grows towards light to make food. NP - Root tip grows away from light
      • Geotropism: stimulus is gravity. PG - Root tip grows towards gravity for moisture . NG - Stem tip grows away from gravity.
      • Chemotropism: stimlus is a chemical. PC - fertilizing. NC - not fertilizing.
      • Thigmotropism: stimulus is touch. PT - grows towards touch. NT - grow away from touch.
      • Hydrotropism: stimulus is water. PH - roots grow towards moisture. NH - grow away from moisture
      • Phototropism: auxins move to shaded part of shoot causing bend. Auxins at the roots prevent growth, found on underside of roots, roots bend towards gravity.


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