Bio372

• Neuronal communication process

  1. Receives input

  2. Integrates input

  3. Propagates input

  4. Sends output
• Previous Module

  1. Introduction to the different cell types in the nervous system (CNS and PNA), neuronal structure and diversity

  2. Gross Nervous System Anatomy (CNS and PNS)

  3. Nervous System Development- gastrulation, neurulation, segmentation, cell specification, cortical lamination

  4. Development of neuronal circuits- axon guidance

  5. Methods for examining the nervous system- genetically modified animals, histology, microscopy
• Exam 1 Average: 77%
• Neurons communicate through synapses, the activity of the synapse is controlled by changes in neuronal membrane voltage
• Lecture 5

  1. Ions and ion flow

  2. The physical principles of neuronal communication
• The physical properties of neurons (and the ionic composition of the cellular environment) create neuronal membrane voltage that changes to produce neuronal communication at the synapse
• Most neuronal communication is through the release of neurotransmitters
• V = I/G

  • V: voltage
  • I: current
  • G: conductance (G = 1/R)
• This release is controlled by the electrical properties of the neuron
• V = IR

  • V: voltage
  • I: current
  • R: Resistance
• Water is the universal solvent
• Water

  • Water is polar with a positive charge on the hydrogen pole (side) and a negative charge on the oxygen pole (side)
  • Positively charged is cation, negatively charged is anion
• The phospholipid bilayer is a barrier to ion diffusion
• Electrical conductance and resistance

  • Electrical conductance (G) is the ease of movement for a charged particle
  • Electrical resistance (R) is the difficulty of movement for a charged particle
• Specialized membrane proteins (ion channels) conduct ions across the otherwise impermeable plasma membrane to produce current that alters membrane voltage
• Protein amino acid sequence generates proteins that pass through the membrane to form pores that pass ions into and out of neurons
• Protein structure and function derives from its constituent amino acid composition
• Protein structure and function

  Derives from its constituent amino acid composition
• Ion channels alter neuronal voltage


  By changing the permeability of charged ions across the membrane
• Polar amino acids

  • Serine (Ser)
  • threonine (Thr)
  • cysteine (Cys)
  • asparagine (Asn)
  • glutamine (Gln)
  • tyrosine (Tyr)
• Nonpolar amino acids

  • glycine (Gly)
  • alanine (Ala)
  • valine (Val)
  • leucine (Leu)
  • isoleucine (Ile)
  • proline (Pro)
  • phenylalanine (Phe)
  • methionine (Met)
  • tryptophan (Trp)
• Neuronal signaling


  To move ions across the membrane
• If diffusion was the only force, ion movement would stop when concentrations were balanced
• The ion channel is comprised of multiple protein subunits that open and close
• Channel proteins

  • Polar R groups and nonpolar R groups
  • Ion selectivity and gating
• Ion pumps


  • Formed by membrane-spanning proteins
  • Use energy from ATP breakdown
• Electrochemical Gradient


  Distribution of ions controlled by the charge difference and difference in concentration of molecules (ions)
• Electricity


  Produced by the movement of electrons or by the movement of positively charged ions
• The resting membrane potential is the basal electrical potential of a non-active neuron, typically around ~-65mV
• Ohm's Law


  Fixed relationship between current (I), conductance (G), and voltage (V)
• The movement of ions across the neuronal membrane underlies neuronal communication
• The electrical potential across the membrane influences ion movement, either promoting or opposing diffusion of ions via the influence of the electrochemical gradient
• The distribution of ions across the membrane: K+ more concentrated on the inside, Na+ and Ca2+ more concentrated outside
• Distribution of ions across the membrane

  • K+ more concentrated on inside
  • Na+ and Ca2+ more concentrated outside
• Membrane potential

  Electrical potential (V) across the membrane influencing ion movement, either promoting or opposing diffusion of ions via the influence of the electrochemical gradient
• Equilibrium potential for each ion

  Membrane potential where the net flow through any open channels is 0, chemical and electrical forces are in balance
• Nernst equation

  • Calculates the exact value of the equilibrium potential for each ion in mV
  • Takes into consideration: Charge of the ion, Temperature, Ratio of the external and internal ion concentrations
• Equilibrium potential (Eion)


  1. No net movement of ions when separated by an (impermeable) phospholipid membrane

  2. Equilibrium reached with K+ channels in the phospholipid bilayer

  3. Electrical potential difference that exactly balances ionic concentration gradient
• The distribution of ions on either side of the lipid bilayer gives rise to the membrane potential
• The number of ions that must move across the membrane to set up a membrane potential is a tiny fraction of those present