Nernst equation

• what was used to pioneer investigation of action potentials?

  giant squid
• What is the resting membrane potential of most neurons?

  -74mV
• how are the concentration gradients of K+ and Na+ ions maintained at rest?

  Action of the Na+/K+ ATPase pump
• what is the charge difference per cycle of Na+/K+ ATPase pump?

  1
• which forces dictate ion movement?

  Na+ = both electrical and chemical driving force

  K+ = if the membrane potential is more positive than the equilibrium potential, the chemical force is larger and force is in the direction of chemical driving force.
• how to record to correct significant figures?

  take the fewest significant figures for answer
• What is the Ek+ and Ena+?


  intracellular
• what is the Ek+ and Ena+?


  Intracellular

  • Na= 50.2
  • K+ = 396.4
  • Cl- = 42.6

  Extracelluar

  • Na= 421.5
  • K+= 36.4
  • Cl-= 393.8

  Na

  =61/1 log10(421.5/50.2)= 56.4mV

  K

  = 61/1 log10(36.4/396.4)= -63.3mV

  Cl

  =61/-1 log10(393.8/42.6)=-58.9mV
• who calculated the -70mv?


  Goldman, Hodgkin, Katz
• what does the GHZ equation use?


  the relative membrane permeabilities
• why is the resting neuronal plasma membrane more permeable to k+ than to Na+?


  due to leaky channel of potassium
• Calculate resting membrane potential

  permeability

  • Na= 1
  • K = 10
  • Cl = 5

  inside

  • Na= 50.2
  • K= 396.4
  • Cl= 42.6

  outside

  • Na= 421.5
  • K= 36.4
  • Cl= 393.8

  = 61 X log10(10 X 36.4/396.4) + (1 X 421.5/50.2) + (5 X 42.6/393.8) = -47.4mV
• what occurs without Cl?

  permeability

  • Na= 1
  • K = 10

  inside

  • Na= 50.2
  • K= 396.4

  outside

  • Na= 421.5
  • K= 36.4

  =61 log10(10 X 36.4/396.4) (1 X421.5/50.2) = -43.2mV
• An action potential will travel at 1.23 m/sec in an unmyelinated neuron compared to 194.9m/sec in an amyelinated neuron.

  How many more milliseconds would it take for a nerve impulse to travel 1.12 metres in an individual with MS compared to someone with fully myelinated neurons?

  MS= 1.12/1.23 =0.911 s or 911ms

  normal= 1.12/ 194.9= 5.75 X10^-3 s or 5.75 ms

  difference = 905ms