Nervous transmission

• What is a resting potential

  The potential difference across membrane when the neurone is at rest
• What is the resting potential in a neurone (including the number)

  Outside the membrane is more positively charged than inside the neurone so the membrane is polarised -70mV
• why can’t the ions just diffuse into the axon

  The membrane is a phospholipid bilayer
• How is the resting potential created and maintained

  By potassium ion channel, sodium ion channels and sodium potassium pump
• What does the sodium potassium pump do

  It uses ATP to pump 3 sodium ions out of the cell and two potassium ions into the cell
• Why is the resting potential negative

  Because 2 potassium ions are pumped in and 3 sodium ions are pumped out so more positive charge is leaving than entering
• At rest what is the membrane permeable to

  Potassium ions
• What is depolarisation

  A change in potential from negative to positive
• What is an action potential 


  a rapid change in potential difference across a membrane when a neurone is firing an impulse
• Describe each stage depolarisation

  1. The neurone is at resting potential the membrane is polarised
  2. Then a impulse is received, this triggers some voltage gated sodium ion channels to open, sodium enters down the electrochemical gradient and membrane begins to depolarise this is the generator potential
  3. If depolarisation reaches the the value -50mV, it activates voltage gated sodium ion channels in the first section of the axon to open. this change in charge (depolarisation) causes more sodium ion channels to open (positive feedback) causing an action potential

  
• Describe depolarisation

  4.The cell depolarises and reaches +40mV causing voltage gated potassium ion channels to open

  5. potassium ions diffuse out of the cell decreasing the potential difference eventually causing hyper polarisation so the voltage gated potassium ion channels close

  6. the sodium potassium pump works to return the cell to the resting potential

  
• What is a nerve impulse

  An action potential that is propagated along the axon from one end to the other end of the neurone
• how is an action potential passed along the axon

  The sodium ions inside the axon are attracted to the negative charge ahead
• How is an action potential propagated (4steps)

  1. Stimulus creates influx Of sodium ions so charge become positive and membrane is now depolarised
  2. more sodium ion channels are caused to open. Behind these the sodium ion voltage gated channels begin to shut and potassium ions channels open.
  3. the axon membrane behind the action potential returned to its original charged state
• What is refractory period

  There is a short period of time after an action potential where the axon cannot be excited again
• What is saltatory conduction 


  The axon potential jumps from one node of Ranvier to another rather than passing along the whole axon
• Why is saltatory conduction good


  It is much faster than waves along the whole length of the axon membrane
• What other two factors affect the speed of action potential

  axon diameter- bigger the axon the faster it travels

  temperature- The higher the temp the faster the impulse occurs (up to 40°c)
• What is the all or noting principle

  Action potentials are initiated when the membrane depolarisation reaches the threshold potential and almost all the voltage-gated sodium ion channels open so action potential always depolarises the axon to the same voltage.
• What happens if the threshold is not met

  There Is no action potential triggered