The Nervous System

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  • The Nervous System
    • Nerve Cells
      • Bundles of neurones form nerves and these nerves form the nervous system: The central nervous system consists of the brain and spinal chord. The peripheral nervous system consists of nerves connecting the sense organs with the CNS.
      • Nerves consist of different types of neurone which send impulses in particular directions:
        • Sensory Neurones send impulses from receptors in the sense organs to the CNS
        • Motor Neurones send impulses from the CNS to muscles and glands
      • A neurone is a nerve cell that consists of a cell body with thin fibres stretching out from it. These fibres carry electrical impulses.
    • Receptors
      • Receptors in the sensory neurone fibres detect stimuli and convert them into electrical impulses; these are sent along neurones to muscles and glands.
      • Different types of receptor detect different types of stimuli: Photoreceptors detect light; thermoreceptors detect body temperature changes.
      • Some types of receptor can be found all over the body. ie. the thermorecep-tors are found across the skin.
      • Other types of receptor are concentrated in sense organs.       ie. The photoreceptors form a layer of cells in the eye called the retina.
      • Sensitivity to touch depends on the force bearing down on that area and the number of touch receptors in that area.
    • Dendrons and Axons
      • Sensory and Motor Neurones have similarities and differences
        • They both have a cell body and fine branches called dendrites
        • The fibre that carries the impulses from the cell body to the dendrites is called the axon. Motor Neurones have very long axons, whereas sensory neurones have short axons.
        • The fibre that carries impulses to the cell body is called the dendron.

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