Reflex Action

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  • Reflex Action
    • Rapid involuntary (brain not involved) and protective (function) from the stimulus
      • e.g. withdrawal reflex, light reflex, stretch reflex, whisker reflex, triceps surae reflex, stepping reflex.
        • The reflex arc is related to nerve pathways and nerve impulses are passed to the brain/from the brain via ascending and descending tracts.
    • What is the difference between white and grey matter?
      • Grey matter contains the cell bodies/nuclei of the neurons whilst the white matter is mainly axons and made up of myelin.
    • With any reflex action there is also a pathway for impulses to be sent to the brain via ascending nerve fibers that originate in the synapse in the grey matter of the spinal cord.
      • The brain may stire this inforation or it may relate the information with sense data, say, he eyes.
        • As a result of recieving extra information, impulses may be sent form the brain to modify the rsponse.
          • Sometimes the response is over-ridden by the brain to modify the response.
            • Soetimes the response is over-ridden by the brain along inhibitory nerve fires.
    • Nerve nets in simple organsms
      • Simple organisms do not posses many recptors and effectors.
        • The sense reptors respond to a limited number of stimuli and the number of effectors is small.
          • An example of this is the hydra-coelenterates (jellyfish)
      • The hydra does not have a recognisable brain or true muscles.
        • It has a simple nervous system known as a nerve net.
          • Nerve nets connect sensory receptors and touch sensitive cells locatd in the body walls and tentacles.
            • The nerve nets consists of simple nerve cells with shirt extensions joined to each other and branching in a number of different directions
              • This means that the transmission of the nerve impulse is slow
      • Direction of impulse
        • Impulse can transmit in BOTH directions
      • Speed transmission = slow
      • Description = short and branched
      • Non - myelinated
    • Nerve nets in complex nervous system
      • Direction of impulse
        • Impulse is transmitted in ONE direction
      • Speed of trasmission
        • Fast
      • Description
        • Long and unbranched
      • Myelinated

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