nerve impulse transmission- myelinated neurone & nerve nets

• what is meant by a myelinated neurone


  this is when the axon is surround by Schwann cells that form a myelin sheath
• what are the properties of of a myelin sheath


  it is an electrical insulator
• how do electrical impulses transmit along a myelinated neurone


  they jump from one node of Ranvier to the next
• what property is given to the myelin by it being a lipid type substance


  it is impermeable to ions
• what does the myelin sheath being an electrical insulator mean about the transmission of neurones


  action potentials can only take place on the nodes of ranvier
• what is there an abundance of at the nodes of Ranvier


  ions channels and Na+/k+ pumps
• what are local currents caused by


  the diffusion of sodium ions
• what is meant by salutatory conduction


  this is when local currents causes by the diffusion of sodium ions are elongated and the speed of transmission is increased
• what is a nerve net


  series of interconnected nerve cells
• what is the simplest type of nervous system

  nerve net
• give examples of organisms with nerve nets


  hydra jellyfish and sea amoebas
• list the the features of nerve nets


  the sense receptors only respond to a limited number of stimuli and there is only a small number of effectors
• give an example of one organism that can regenerate neurones


  hydra
• in what direction do hydras send electrical impulses


  any direction
• what factors effect the speed of the conduction of an impulse


  temperature , diameter of axons and myelination
• how does a larger diameter mean a greater speed of conduction

  the greater its volume in relation to the area of the membrane,so more Na+ can move along the axon
• why does a higher temperature mean a greater speed of impulse conduction

  more kinetic energy in the ions