Membrane potential and action potentials

• where do neurons recieve information from?

  dendrites and the integrate into the cell body
• what is an action potential?

  Information is transmitted along the axon in the form of electrochemical signals or nerve impulses
• how action potential generated?

  flow of Na and K ions through protein channels
• what is chemical force?

  Differences in concentration diffusion from a region of high conc to a region of low conc
• what is electrical force?

  interior of cell is negatively charged cations are retained and negative ions will be expelled
• What is the electrochemical driving force?

  Combination of electrical force and chemical forces acting on any particular ion
• what are the 2 categories of ion channels?

  gated, open
• what may a gated channel require?

  ligand, mechanical force or voltage stimulation to open
• are gated channels specific to ions?

  yes
• what drives movement through open channel?

  electrochemical driving force
• what are the 3 main ions?

  K+, Cl- and Na+
• which concentration of ions is greater inside the neuron?

  K+
• what concentration of ions is greater on the outside of neuron?

  Cl-, Na+
• which way does K+ flow?

  inside to outside
• why does k+ move?

  Moves by open (leaky) channels)
• What is the ultimate result of Na+/K+ ATPase pump?

  Is more positive outside the neuron
• what is resting membrane potential?

  70mV
• what drives movement when channels are open?

  chemical gradient of ions
• what stops equilibrium being reached?

  electrical forces
• What occurs when Na+ channels are open?

  chemical gradient drives ions movement into the cell

  Electrical force pulls positive ions into the cell

  So Na+ will enter the cell
• what is the equilibrium potential?

  The membrane potential require to exactly counteract the chemical forces acting to move one particular ion across the membrane
• what occurs when K+ channels are open?

  Chemical gradient drives movement out cell

  Electrical force pulls into the cell

  K+ moves out of the neuron
• why does K+ move out of the cell?

  the chemical force is greater than the electrical force
• how can the equilibrium potential be calculated?

  Using the Nernst equation
• At what voltage is there no net movement of Na+?

  +60mV
• At what voltage is there no net movement of K+ ions?

  -94mV
• what can incoming signals do?

  depolarise the cell membrane
• What occurs if the membrane potential reaches critical threshold?

  an action potential is triggered
• what is the threshold potential?

  -55mV
• what can incoming signals do?

  depolarise or hyperpolarise
• where are volatge-gated ion channels found?

  embedded in the plasma membrane
• when will voltage-gated ions channel open?

  when voltage in the cell reaches a certain value
• What is the Na+ conc at rest?

  greater outside the cell
• what are the stages of activation of action potential?

  initial stimulation, depolarisation, inactivation of Na+ channels, repolarisation, hyperpolarisation
• when is a Na+ inactivated?

  when the inside of the neuron is highly positive, the pore of the voltage-gated Na+ channels is plugged by the inactivation gate and flow of Na+ into neuron stops
• how is repolarisation occur?

  Voltage-gated K+ channe;s begin to open slowly out of the cell
• what causes hyperpolarisation?

  Increased potassium efflux
• what occurs in the refractory period?


  A neuron will not able to fire another action potential
• When will the neuron be able to fire an action potential?

  when Na+/K+ ATPase pump will restore the resting potential
• how many Na+ and K+ are moved by the Na+/K+ ATPase pump?

  3 Na+ out of cell, 2 K+ into cell