Unit 6

• Objectives


  • Define the principles of bio-electricity
  • Define a graded potential and define the different types
  • Describe the resting membrane potential and how to calculate it
  • Define an action potential and its different phases
• Electrical occurrence at the cell's plasma membrane


  Due to ionic distribution
• Ions in ICF


  • K+, phosphate and proteins
• Ions in ECF


  • Na+, Cl- ions
• Like charges repel each other, while opposite charges attract each other
• Electrical potential


  Potential for two separate charges to do work
• Electrical potential units


  Volts (V), millivolts (mV) (biological systems)
• Current (I)


  Movement of electrical charge
• Resistance (R)


  Hindrance to electrical charge movement
• Ohm's law


  I = V/R
• Electrical forces role on ion movement
• Different membrane potential terminology

  • Potential (potential difference)
  • Membrane potential
  • Equilibrium potential
  • Resting (membrane) potential
  • Graded potential
  • Action potential
  • Synaptic potential
  • Receptor potential
  • Pacemaker potential
  • Threshold potential
• Objectives


  • Define the principles of bio-electricity
  • Define a graded potential and define the different types
  • Describe the resting membrane potential and how to calculate it
  • Define an action potential and its different phases
• Resting membrane potential (RMP)


  Potential difference across the plasma membrane
• Electrical occurrence at the cell's plasma membrane


  Due to ionic distribution
• Ions in ICF


  • K+, phosphate and proteins
• Ion distribution across plasma membrane

  • Sodium: 145 mmol/L extracellular, 15 mmol/L intracellular
  • Chloride: 100 mmol/L extracellular, 7 mmol/L intracellular
  • Potassium: 5 mmol/L extracellular, 150 mmol/L intracellular
• Ions in ECF


  • Na+, Cl- ions
• Like charges repel each other, while opposite charges attract each other
• Factors affecting membrane potential

  Concentration gradient of specific ion, Membrane permeability to different ions
• Electrical potential


  Potential for two separate charges to do work
• Electrical potential units


  Volts (V), millivolts (mV) (biological systems)
• Nernst equation


  Calculation of the equilibrium potential for any ion
• Current (I)


  Movement of electrical charge
• Resistance (R)


  Hindrance to electrical charge movement
• Calculating equilibrium potential


  Using the Nernst equation: E_ion = (61/Z) * log(C_out/C_in)
• Ohm's law


  I = V/R
• Electrical forces role on ion movement
• Different membrane potential terminology

  • Potential (potential difference)
  • Membrane potential
  • Equilibrium potential
  • Resting (membrane) potential
  • Graded potential
  • Action potential
  • Synaptic potential
  • Receptor potential
  • Pacemaker potential
  • Threshold potential
• Goldman-Hodgkin-Katz (GHK) equation


  Calculation of the membrane potential, affected by more than one ion channel
• Resting membrane potential (RMP)


  Potential difference across the plasma membrane
• Na+/K+-ATPase pump


  Pump maintains concentration gradients, helps establish the membrane potential, electrogenic pump: moves charges across the membrane
• Ion distribution across plasma membrane

  • Sodium: 145 mmol/L extracellular, 15 mmol/L intracellular
  • Chloride: 100 mmol/L extracellular, 7 mmol/L intracellular
  • Potassium: 5 mmol/L extracellular, 150 mmol/L intracellular
• Factors affecting membrane potential

  Concentration gradient of specific ion, Membrane permeability to different ions
• Concentration gradient


  Established by pump, creating a negative charge, higher net movement of K+ than Na+ making membrane potential negative
• Nernst equation


  Calculation of the equilibrium potential for any ion
• At steady RMP


  Ion flow through channels & pumps balance each other
• Goldman-Hodgkin-Katz (GHK) equation


  Calculation of the membrane potential, affected by more than one ion channel
• Excitable membranes


  Contain channels (gated) that give cells ability to produce electrical signals
• Calculating equilibrium potential


  Use Nernst equation