4.1.2 Nerves

4.1.2 Nerves

All receptor cells are transducers, in which one form of energy, the stimulus energy, is converted into another form, electrical energy.
1. Receptors in mammals are adapted to respond to different aspects of the environment such as: • light intensity and wavelength • sound • touch and pressure • temperature • chemicals
2. sensory neurons transmit nerve impulses from a receptor to the central nervous system (brain or spinal cord)
Structure of a motor neuron
1. Large nucleus, large quantities of rough er and golgi bodies, short dentrites that carry nerve impulses towards the cell body
Structure of a sensory neuron
1. Long dendrite, short axon, transmit impulses from a receptor to the CNS
When not conducting a nerve impulse, there is a p.d across the plasma membrane, such that the inside has a -70mV charge compared with the outside
1. Na+-K+ pumps in the plasma membrane actively transport K+ ions into the cell and Na+ ions out
  1. 3 Na+ ions actively transported out for every 2 K+ ions actively transported in. The axon contains organic anions tro which the membrane is impermeable
    1. This and a slight loss of K+ ions through the permeable membane, accounts for the resting potential
      1. The membrane is effectively impermeable to Na+ ions
2. Resting potential
Action potential
1. generated by a stimulus that excites the neurone causing sodium ion channels to open allowing Na+ to diffuse in making the inside less negative

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