neuronal communication 2 *5

• what is meant by the term 'nerve impulse' ?

  moving area of charge
• nerve impulses always travel in one direction which is

  away from a receptor and towards an effector
• what concentration ions outside the axon are higher than inside the axon ?

  sodium ions
• what concentration of ions are higher inside the axon than outside the axon ?

  potassium ions
• why can sodium and potassium ions only cross the axon membrane through channel proteins and not by simple diffusion?


  they are polar, hydrophillic ,charged and are insoluble in lipids
• the sodium-potassium pump is an example of ...

  active transport
• characteristics of the sodium-potassium pump

  it uses energy from hydrolysis of ATP, it is a carrier protein, it is a co-transporter
• what does the sodium-potassium pump do ?

  moves sodium ions out of the axon and potassium ions into the axon
• how many sodium and potassium ions are moved by the sodium-potassium pump ?

  the sodium-potassium pump moves three sodium ions out of the axon in exchange for two potassium ions into the axon
• what is the purpose of a sodium-potassium pump ?

  maintain a more positive charge outside the axon and a less positive charge inside the axon
• what is resting potential of a neurone ?

  not exposed to a stimulus and a less positive charged is maintained inside the axon
• why is resting potential important for neurones ?

  as axons of neurones can only respond to a nerve impulse if the inside of the axon is less positive than the outside
• how is a resting potential established and maintained in a neurone ?

  has a sodium-potassium ion pump. at RP inside of the axon is less positively charged than the outside. 3 sodium ions out of the axon for every 2​ potassium ions in, carrier proteins in the membrane that pump sodium ions out of the axon
• what does a voltage gated ion channel open in response to ?

  in response to the positive charge of a nerve impulse. opens when the inside of the axon becomes more positively charged
• define the term action potential ?


  state of a neurone in which the inside of its axon reaches its maximum positive charge
• how is an action potential triggered ?

  triggered by the positive charge of a nerve impulse arriving at the axon, leading to the voltage gated sodium channels opening, meaning more sodium ions enter the axon
• define the term hyperpolarisation

  state of a neurone in which the inside of an axon reaches its minimum positive charge
• what transport protein is responsible for establishing a resting potential ?

  sodium-potassium pump and potassium channel
• what transport protein is responsible for establishing an action potential ?

  voltage-gated sodium channel
• what transport protein is responsible for establishing hyperpolarisation ?

  voltage-gated potassium channel
• explain how a neurone re-establishes resting potential after an action potential

  resting potential is restored when the axon inside is less positive than the outside. this happens when the VG sodium channels close, so less NA+ diffuse into axon. the VG potassium channels open so K+ ions diffuse out allowing axon inside to become more negative. it is now hyperpolarised to become normal again NA+ diffuse into the axon through NA+ channels, sodium potassium pump 3NA+ out for 2K+ in
• how does the axon membrane become depolarised ?

  nerve impulse arrives at the axon, membrane potential difference changes to positive, influx of NA+ into the axon and VG sodium channels open
• how does the axon membrane become repolarised ?

  efflux of K+ out of the axon, VG sodium channels close, membrane potential difference changes from positive to negative. VG potassium channels open
• what is the PD value of a neuron experiencing an action potential ?

  +40 mV
• what is the typical potential difference value of a neuron at resting potential ?

  -70mV
• what is the typical potential difference value of the threshold value of a neuron ?

  -55 mV
• what is the typical potential difference value of a neuron experiencing hyper-polarization?

  -75mV
• when is energy from the hydrolysis of ATP required ?

  when there is active transport of NA+ and K+ by the sodium-potassium pump
• which event starts depolarisation ?

  Opening of voltage-gated sodium channels.
• which event begins the process that changes the potential difference of the axon membrane from positive to negative ?

  voltage-gated potassium channels open
• during action potential, the potential difference....

  on the inside of the membrane changes form negative to positive and the outside of the membrane changes from positive to negative