Tag Archives: Action potential


In saltatory conduction, an action potential a...

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Nerves Have Axons, Dendrites and Cell Bodies

  • Nerve cells are designed to respond to stimuli and transmit information over long distances
  • Nerve cell has 3 parts:
    • Cell body:
      • Has single nucleus
      • Has most of nerve cell metabolism, especially protein synthesis
      • Proteins made in cell body must be delivered to other parts of nerve
    • Axon:
      • Long cylinder, designed to transmit an electrical impulse
      • Can be several meters long in vertebrates (giraffe axons go from head to tip of spine)
      • Has axonal transport system for delivering proteins to ends of cell


Chemical Transmitters Carry the Signal Across Synapses & Neuromuscular Junctions

  • A contact between 2 nerves is called a synapse
  • At the synapse there is a break in electrical transmission (the action potential cannot cross)- instead chemicals are released that carry the signal to the next nerve
    • The release of chemical transmitters at nerve endings was first shown by Otto Loewi in the frog heart
  • A neuromuscular junction (NMJ) is a contact between a nerve and a muscle- it is like a synapse, the action potential stops and the signal is carried by a chemical


Muscles Are Organized Into Motor Units

  • When a single nerve enters a muscle it splits and makes neuromuscular junctions (NMJs) with several muscle cells
  • A nerve and the muscle cells it makes NMJs with is called a motor unit
  • When the nerve fires the whole motor unit is stimulated and the muscle cells contract together
  • Muscles with large motor units have coarse movements
  • Muscles with small motor units give fine, graded movements
  • This is a small motor unit with only 3 muscle fibersTwo Basic Types of Contraction Are Isotonic and Isometric