Myelination as a Factor

• Some neurones are what?


  myelated
• what does it mean if neurones are myelinated?

  they have a myelin sheath
• what is the myelin sheath?


  An electrical insulator
• what is the myelin sheath made of in the PERIPHERAL NERVOUS SYSTEM?

  Made of a type of cell called a Schwann cell
• What are found between Schwann cells?


  the nodes of Ranvier

  Sodium ion channels are concentrated at the nodes
• What are the nodes of Ranvier?

  Tiny patches of bare membrane found between the Schwann cells
• Where does depolarisation happen in a MYELINATED NEURONE?

  Depolarisation ONLY happens at the nodes of Ranvier - where sodium ions can get through the membrane
• What does the neurone's cytoplasm conduct?

  Enough electrical charge to depolarise the next node, so the impulse 'jumps' from node to node . =SALTATORY CONDUCTION - really fast
• How does the impulse travel in a non-myelinated neurone?

  As a wave along the whole length of the axon membrane (so depolarisation occurs along the whole length of the membrane)

  • SLOWER than saltatory conduction
• What are dendrites?

  Extensions of the cell body that connect with other neurones