NROB60H3 Chapter Notes - Chapter 3: Resting Potential, Extracellular Fluid, Electric Charge
11 Jun 2018
School
Department
Course
Professor
Chapter 3-The Neuronal Membrane at Rest
• Introduction
o Neuron conducts information over a distance by using electrical signals that move across axons
o Electrical charge in the cytosol of the axon is carried by electrically charged atoms (ions) instead
of free e-, thus the cytosol is far less conductive
o The axon is not well-insulated and there is salty extracellular fluid surrounding it that also
conducts electricity (the electrical charge will leak out)
o Action potential-nerve impulse that the axonal membrane conducts
o Potential is the separation of charge over a membrane; these sigals do’t diiish oer a
distance because they exist at a fixed size and duration
o The number of neurons and the frequency of action potentials hold the information/electrical
impulses
o Cells that can generate and conduct action potentials (nerve and muscle cells) have an excitable
membrane
o When no impulses are being made by the membrane then the neuron is said to be at rest
o resting membrane potential-the difference in electrical charge across the membrane (the inside
become positive relative to the outside)
• The Cast of Chemicals
o Membrane potential involves the salty fluids, the membrane and the proteins that are in the
membrane
➢ Cytosol and Extracellular fluid
o Water makes up both extracellular fluid (bathes the neuron) and the cytosol
o Electrically charged atoms-ions are dissolved in water (cause the potentials)
o Water
▪ The uneven distribution of electrical charge because of the net positive charge on
hydrogen and the net negative charge on oxygen
▪ Held together by polar covalent bonds, this electric polarity allows water to be a good
solvent for charged or polar molecules
o Ions
▪ Ions- atoms with a net electrical charge
▪ The ions are held together by the attraction to the opposite charge (ionic bond)
▪ Spheres of hydration- when clouds of water surround ions and insulate the ions from
the other ions
find more resources at oneclass.com
find more resources at oneclass.com
2
▪ The difference between the proton and electrons is the electrical charge
• Difference=1 is monovalent
• Difference=2 is divalent
• Ions with a net positive charge is cation
• Ion with net negative charge is anion
➢ The Phospholipid Membrane
o Substances with a net or an uneven electrical charge will dissolve in water because of the
polarity
o Some substances can be hydrophilic or hydrophobic
o Atos that are oded y opolar oalet ods do’t hae ay chemical interactions in
water because these ods do’t leae a et eletrial harge
o Building blocks of the cell membrane are phospholipids; they have long non polar chains of
carbon (tail) and they have a polar phosphate group (head)
o Phospholipid bilayer the hydrophilic heads face outwards and the hydrophobic tails face
inwards and it isolated the cytosol of the neuron from the extracellular fluid
➢ Protein
o Enzymes that catalyze reactions; cytoskeleton that gives neurons its shape; receptors that are
sensitive to neurotransmitters that are made by the protein molecule
o These proteins provide routes from ions to cross the neuronal membrane
o Protein Structure
▪ Proteins are made up by a combination of 20 amino acids
▪ The general structure of the protein includes the alpha carbon, hydrogen atom amino
group, carboxyl group and the R(esidue) group
▪ Proteins are synthesized by the ribosomes of the neuronal cell body; here the amino
acids are assembled into a chain by peptide bonds, a single chain of amino acids is also
called a polypeptides
▪ Primary structure is the chain of amino acids liked by peptide bonds
▪ This chain can coil up to make a secondary structure of alpha helix
▪ The r groups can interact with other groups and make a tertiary structure (3D) then the
polypeptide chain (subunits) can bond together to make a quaternary structure
o Channel Protein
▪ The surface of a protein may be heterogeneous because a non polar R group will
associate with a lipid and a polar R group wont associate with the lipid group
▪ The hydrophobic part of the protein will be in the middle of the lipid bilayer and the
hydrophilic ends will be exposed on either of the watery sides
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Ions with a net positive charge is cation. Ion equilibrium potential/ equilibrium potential- electrical potential difference that balances an ionic concentration gradient (eion: 1. Large changes in membrane potential are caused by minuscule changes in ionic concentrations: 2. The net difference in electrical charge occurs at the inside and outside surfaces of the membrane: 3. Ions are driven across the membrane at a rate proportional to the difference between the membrane potential and the equilibrium potential. Ionic driving force (vm-eion) difference between the real membrane potential and the equilibrium potential: 4. The distribution of ions across the membrane: k+ is more concentrated on the inside and na+/ca2+ is more concentrated on the outside. 4: calcium pump is an enzyme that transport ca2+ out of the cytosol across the cell membrane, the internal concentration of calcium decreases with calcium binding proteins and organelles (mitochondria and e. r) Ion pumps allow the existence of the resting membrane potential.
