B1.2 Nerves and hormones

The nervous system
1. Enables humans to react to their surroundings and coordinate their behaviour
2. Receptors
  1. Detect stimuli
    1. Changes in environment
  2. In the eyes
    1. Sensitive to light
      1. Have a nucleus, cytoplasm and a cell membrane like most animal cells
  3. In the ears
    1. Sensitive to sound and changes in position (enables us to keep our balance)
  4. In the nose and on the tongue
    1. Sensitive to chemicals which allow us to taste and smell
  5. In the skin
    1. Touch
    2. Pain
    3. Pressure
    4. Temperature changes
3. Simple reflex action
  1. Impulses from receptor pass along sensory neurone
    1. Reach a synapse between a sensory neurone and a relay neurone
      1. Chemical is released that diffuses through synapse and causes an impulse to be sent along a relay neurone
        Reaches a synapse between a relay and motor neurone, same process occurs again
        Impulse sent along motor neurone to the effector
        Response is brought about by the effector
        Effector is either a muscle or gland
        Muscle responds by contracting
        Gland responses by releasing a chemical substance
      2. Synapse is a junction
  2. Coordinated by brain
    1. Automatic and rapid
Control in the human body
1. Internal conditions which are controlled
  1. Water content
    1. Leaves through sweat, when we breathe out and through urine
  2. Ion content
    1. Lost via sweat and urine
  3. Temperature
    1. Enzymes work best at certain temperatures
  4. Blood sugar levels
    1. Provide cells with constant energy supply
2. Many processes coordinated by hormones
  1. Secreted by glands
    1. Transported through the bloodstream
      1. Regulate the functions of many organs and cells
        E.g. the menstrual cycle
        FSH
        Secreted by pituitary gland
        Causes eggs to mature in the ovaries
        Stimulates the production of oestrogen
        LH
        Secreted by pituitary galnd
        Stimulates egg release from the ovaries
        Oestrogen
        Secreted by the ovaries
        Inhibits production of FSH
        Hormones can be used in controlling fertility
        Oral contreceptives
        Contain oestrogen and progesterone
        They inhibit FSH production and therefore egg maturation
        They now contain less oestrogen and more progesterone
        Women suffered significant side effects from oestrogen pills
        Progesterone only pills lead to fewer side effects
        Fertility drugs
        FSH and LH can be given as fertility drugs
        Used in IVF
        IVF
        Given FSH and LH to stimulate maturation of several eggs
        Eggs are collected and fertilised by father's sperm
        Develop into embryos
        When they are tiny balls of cells, one or two are inserted into the mother's womb
Control in plants
1. Plants are sensitive to
  1. Light
  2. Moisture
  3. Gravity
2. Shoots
  1. Grow towards light
  2. Against the force of gravity
3. Roots
  1. Grow towards moisture
  2. In the direction of the force of gravity
4. Produce hormones to coordinate and control growth
  1. Auxin controls phototropism and gravitropism
  2. Responses of plant roots and shoots to light, gravity and moisture
    1. Due to unequal distribution of hormones, causing unequal growth rates
      1. Extra auxin
        Growth is stopped in the roots
        Growth is stimulated in the shoots
    2. Roots
      1. When growing sideways, auxin will accumulate on the lower side
      2. Auxin causes
        The cells to stop growing, meaning the cells at the tips grow faster and as a result bend downwards
      3. When exposed to moisture, more auxin accumulates on the side with more moisture
    3. Shoots
      1. When a shoot is exposed to light
        More auxin accumulates on the side that is in the shade
      2. Auxin causes
        The cells to grow faster (elongate more) on the shaded side, causing it to bend towards the lgiht
      3. When a shoot is growing sideways
        Gravity causes more auxin to accumulate on the lower side, causing it to grow faster and bend upwards
5. Plant hormones are used as weed killers and rooting hormones

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B1.2 Nerves and hormones

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