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The Nervous System
1. enables us to respond to external changes
2. control conditions inside our bodies
3. enables humans to react to their surroundings
  1. and coordinate their behaviour
  2. does this by having cells calledRECEPTORS that detect STIMULI
    1. STIMULI = change in environment
    2. RECEPTORS and STIMULI they can detect:
      1. receptors in the eyes that are sensitive to light
      2. receptors in the ears that are sensitive to sound
      3. receptors in the ears that are sensitive to the changes in position
        enable us to keep our balance
      4. receptors on the tongue and in the nose that are sensitive to chemicals
        enable us to taste and smell
      5. receptors in the skin that are sensitive to touch, pressure, pain and temperature change
    3. information from receptors passes along cells (NEURONES) in the nerves in the BRAIN.
      1. the BRAIN then coordinates a response
4. Synapses
  1. At the junction (synapse) between relay neurones and a sensory or motor neurone..
    1. the impulses are transmitted across the gaps by a chemical
Hormones used as forms of contraception and fertility treatments
Plants produce hormones and respond to external stimuli
1. plant hormones control plant growth and react to changing conditions
  1. these responses are caused by unequal distributions of hormones
    1. causing opposite sides of the roots or shoots to grow at different rates
    2. GEOTROPISM
      1. plants have been shown to respond to gravity with their roots growing downwards and shoots upwards
    3. PHOTOTROPISM
      1. plant shoots also grow towards the light
    4. plant roots grow towards moisture
2. Plant hormones can be used:
  1. as weedkillers
  2. as rooting hormones to enable cuttings to grow roots
Homeostasis
1. = keeping internal conditions consistant
2. to keep us alive, internal conditions have to be constantly monitored and controlled
  1. these include:
    1. water content of the body
      1. - water leaves the body via the lungs when we breathe out
      2. - via the skin when we sweat
      3. - in urine
    2. ion content of the body
      1. ions are lost via the skin when we sweat
      2. excess ions are lost via the kidneys in urine
    3. temperature
      1. to maintain the temperature at which enzymes work best
    4. blood sugar levels
      1. to provide the cells with a constant supply of energy
Hormones
1. = chemical messengers produced by glands and released into the blood
2. hormones travel to all parts of the body, but only affect certain targets
3. examples of glands and their associated hormones:
  1. The Pancreas
    1. produces insulin, which regulates blood sugar levels
  2. The Testes
    1. produce male sex hormones
  3. The Ovaries
    1. produce female sex hormones... which control menstruation
      1. The Menstrual Cycle
        hormones are secreted by the pituitary gland and the ovaries regulate the monthly release of an egg from the ovaries
        they also regulate the changes in the thickness of the lining of her womb
        hormones that promote egg release:
        FOLLICLE STIMULATING HORMONE (FSH)
        secreted by the pituitary gland
        causes eggs to mature in the ovaries and stimulates the ovaries to produce hormones including oestrogen
        LUTEINISING HORMONE (LH)
        stimulates the release of eggs from the ovary
        OESTROGEN
        secreted by the ovaries and inhabits the further production of FSH
  4. The Pituitary Gland (the master gland)
    1. produces hormones that control many other glands
4. Using hormones to reduce fertility
  1. as the menstrual cycle is controlled by hormones, it can be disrupted by artificially changing the levels using a CONTRACEPTIVE 'PILL'
    1. contraceptive pills may contain:
      1. PROGESTERONE
      2. a combination of OESTROGEN and PROGESTERONE
      3. these hormones inhibit FSH production so no eggs mature
      4. first birth control pills contained large amounts of OESTROGEN which caused women to have many side effects
        modern pills have much lower levels or are PROGESTERONE ONLY (POP) with fewer side effects
5. Using hormones to increase fertility
  1. infertility is caused by women having low hormonal levels of FSH
    1. can be treated by giving fertility treatments
      1. IVF - In vitro fertilisation
        FSH and LH are given to stimulate the production of several eggs
        the eggs are collected from the mother and fertilised by the sperm from the father
        the fertilised eggs develop into embryos
        when they are big enough, one or two embryos are inserted into the womb where they grow into babies

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Nerves and Hormones - B1

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