Lecture 02

• What is the resting membrane potential?

  The voltage across a neuron's membrane at rest
• What do chemical and electrical gradients influence in neurons?

  They influence the movement of ions
• What does the Nernst equation calculate?

  The equilibrium potential for an ion
• What is voltage in terms of electrical potential energy?

  Electrical potential energy between two points
• What does Ohm's Law state?

  V = IR
• What is the SI unit of current?

  Ampere or amps (I)
• What does resistance refer to in neurophysiology?

  Hindrance to the movement of ions
• What is the duration of a nerve action potential?

  About 1 millisecond
• How are nerve action potentials elicited?

  In an all-or-nothing fashion
• How do neurons code the intensity of information?

  By the frequency of action potentials
• What happens to the action potential size when stimulus intensity increases?

  The frequency of action potentials increases
• What is the typical resting potential (Vm) in most neurons?

  –60 to –70 mV

  
• How does the resting potential differ in smooth muscle cells?

  Vm is –50 to –60 mV
• What is the resting potential of skeletal muscle cells?

  Vm is –95 mV
• What is the resting potential of astrocytes?

  Vm is –80 to –90 mV
• What is the resting potential of epithelial cells?

  Vm is –50 mV
• What is the resting potential of erythrocytes?

  Vm is –12 mV
• What causes the resting potential in neurons?

  Unequal distribution of ions across the membrane
• What are the factors that the resting potential depends on?

  Chemical and electrical properties of ion flow
• What role do ion channels play in resting potential?

  They allow ions to flow across membranes
• What is the effect of chemical forces on ions moving through channels?

  They create a concentration gradient
• What do electrical forces do to ions in channels?

  They attract or repel charged ions
• What is the equilibrium potential for an ion?

  The point where driving forces are balanced
• What is the equilibrium potential for K+?

  Ek = -90 mV

  
• What is the equilibrium potential for Na+?

  ENa = +61 mV

  
• Why does resting potential not equal Ek?

  The membrane is more permeable to K+
• What are the properties of action potentials?

  • Short duration (about 1 millisecond)
  • Elicited in an all-or-nothing fashion
  • Intensity coded by frequency of action potentials
• What are the two forces acting on ions across membranes?

  • Diffusion (high to low concentration)
  • Electrical (toward opposite charge)
• What is the summary of potentials in neurons?

  • Result from ions moving across membranes
  • Each ion reaches equilibrium between two forces
  • K+ creates negative potentials; Na+ creates positive potentials
• What are the objectives related to ion flow and resting potentials?

  • Understand chemical and electrical forces on ions
  • Equilibrium of ion flow is a balance of forces
  • Resting potentials are a state of equilibrium
• What is the Nernst equation used for?

  To calculate equilibrium potential for an ion
• How is the Nernst equation abbreviated at 37°C?

  For monovalent ions
• What does the Nernst equation require to calculate Eion?

  Concentration of ion inside and outside the cell
• How is the equilibrium potential for K+ calculated?

  Using the Nernst equation with concentrations
• What is the significance of measuring inside compared to outside the cell?

  It determines the equilibrium potential
• What happens when both driving forces on an ion are equal?

  The ion's movement is balanced
• What is the relationship between concentration gradient and electrical potential?

  Steeper gradients require larger electrical potentials
• What is the role of leak channels in neurons?

  They allow ions to flow freely
• What is the effect of the Na+/K+ pump on resting potential?

  It maintains ion concentration gradients
• How do ions flow through channels?

  Down their concentration gradient