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Lecture

NROC69H3 Lecture Notes - Cytoskeleton, Alpha And Beta Carbon, Electric Current


Department
Neuroscience
Course Code
NROC69H3
Professor
d

Page:
of 11
NROB60 Study Package: Week 5
Homira Osman
Week 5: Lecture
June 3, 2008
Lecture Topics
Lecture V
Readings: The Resting Neuronal Membrane (Pages 52-61)
Lecture Summaries [L5]
- The Cast of Chemicals
o At rest, the cytosol along the inside surface of the membrane has a negative electrical
charge compared to the outside
Referred to as the Resting Membrane Potential
When a cell with excitable membrane is not generating impulses, it is
said to be at rest
In the resting neuron, the cytosol along the inside surface of the
membrane has a negative electrical charge compared to the outside
This difference in electrical charge across the membrane is called the
resting membrane potential
o Also called resting potential
o Action Potential is the brief reversal of this condition where for one instant, the inside
surface becomes positively charged compared to the outside
The axonal membrane has properties that enable it to conduct a special type of
signal the nerve impulse, or action potential - that overcomes these biological
constraints
Action potentials do not diminish over distance
They are signals of fixed size and duration
Information is encoded in the frequency of action potentials of individual neurons,
as well as in the distribution and number of neurons firing action potentials in a
given nerve
Cells adaptable of generating and conducting action potentials, which include
both nerve and muscle cells, are said to have excitable membrane
The action in action potentials occurs at the cell membrane
o How does this occur?
o Understand the Three Main Players
Salty Fluids on either side of the membrane
The Membrane itself
The Proteins that span the membrane
- Cytosol & Extracellular Fluid
- Water
o Polar Covalently bonds
o Effective solvent for other charged or polar molecules
- Ions
o Net electrical charge
o Dissolve in water because the charged portions of the water molecule have a stronger
attraction for the ions than they have for each other
o A sphere of water molecules surrounds each ion (spheres of hydration)
o Insulate the ions from each other
o Monovalent vs divalent
o Cations (net +’ve charge)
o Anions (net -’ve charge)
NROB60 Study Package: Week 5
Homira Osman
- Why Are Ions Important?
- Ions are the major charge carriers involved
in the conduction of electricity in biological
systems (including neurons)
- The ions of particular importance for
cellular neurophysiology are:
o The monovalent cation Na+
(sodium)
o The monovalent cation K+
(potassium)
o The divalent cation Ca2+ (calcium)
o The monovalent anion Cl-
(chloride)
- The Resting Membrane Potential
Difference (Membrane Potential)
- Electrical gradient between extracellular
fluid and intracellular fluid due mostly to
Potassium
- Phospholipid Bilayer: A Barrier
- Phospholipid bilayer is not permeable to ions
- Each ion has a different chemical concentration within the cell than outside
- Each ion has an electrical charge
- The Phospholipid Membrane
QUESTION: How are electrical signals generated?
ANSWER: Through ION MOVEMENT ACROSS THE CELL MEMBRANE
HOW? Through a change in either the potassium concentration gradient or by changing the ion
permeabilities
QUESTION: How can a change in ion permeability occur?
ANSWER: Insert protein channel into the membrane that is specific to a particular ion
Open a channel that is specific to a particular ion
NROB60 Study Package: Week 5
Homira Osman
Close a channel that is specific to a particular ion