Reflexes and Hormones

Synapses and Reflexes
1. Neurones transmit information very quickly to and from the brain and your brain quickly decides how to respond to a stimulas
2. Synapses connect neurones
  1. The connection between two neurones is called a synapse
    1. The nerve signal is transferred by chemicals which diffuse (move) across a gap
      1. These chemicals then set off a new electrical signal in the next neurone
3. Reflexes help prevent injury
  1. Reflexes are automatic responses to certain stimuli - reducing the chance of being injured
  2. The passage of information in a reflex (from receptor to effector) is called a reflex arc
The reflex arc
1. 1. The neurones in reflex arcs go through the spinal cord or through an unconscious part of the brain
  1. 2. When a stimulus e.g bee sting is detected by receptors, impulses are sent along a sensory neurone to the CNS
    1. 3. When the impulses reach a synapse between the sensory neurone and a relay neurone they trigger chemicals to be released. These chemicals cause impulses to be sent along the relay neurone
      1. 4. When the impulses reach a synapse between the relay neurone and a motor neurone, the same thing happens. Chemicals are released and cause impulses to be sent along the motor neurone
        5. The impulses then travel along the motor neurone to the effector e.g. muscle
        6. The muscle then contracts and moves your hand away from the bee
        7. Because you dont have to think about the response (which takes time) its quicker than normal responces
2. Stimulus, receptor, neurones, effector, response
  1. Stimulas..Receptor..Sensory neurone..Relay neurone..Motor neurone..Effector..Response
Hormones
1. Hormones are chemical messengers travel in the blood to activate target cells
  1. Hormones are chemicals released directly into the blood
    1. They are carried in the blood plasma to other parts of the body but only affect particular cells (target cells) in particular places. Hormones control things in organs and cells that need constant adjustment
      1. Hormones are produced in (and secreted by) various glands
        Hormones tend to have long lasting effects
        The pituitary gland
        Produces many important hormones including FSH and LH which are involved in the menstrual cycle
        Ovaries
        Females only produce oestrogen which is involved in the menstrual cycle
2. Hormones and nerves carry messages in different ways
  1. Hormones and nerves do similar jobs - they both carry information and instructions about the body but there are many differences
  2. Nerves
    1. very fast message
    2. Act for a very short time
    3. Act on a precise area
  3. Hormones
    1. Slower message
    2. Act for a long time
    3. Act in a more general way
  4. If the response is really quick its probably nervous
  5. If the response lasts for a long time its probably hormonal

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Reflexes and Hormones

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