Lecture 3 Flashcards
What neuron is associated with an afferent nerve?
Sensory neuron
What neuron is associated with an efferent nerve?
Motor neuron
What is membrane potential (Vm)?
difference in electrical charge across the membrane
What is membrane potential when neuron is at rest?
steady negative electrical potential (-65 mV)
What is electrical potential?
the force exerted on a charged particle (ion)
How is the resting membrane potential established and maintained?
Charge separation: neuronal membrane
Selective permeability: ion channel proteins
Concentration gradients: ion pumps
What’s the key ingredient and feature in the cytosol and extracellular fluid?
Water! It’s a polar solvent
What (besides water) is in the cytosol and extracellular fluid?
Ions
- cations: net positive charge
- anions: net negative charge
- hydrophilic!!
What’s the main features of the phospholipid bilayer?
-Hydrophobic lipids (tails)
- Hydrophilic phosphate groups (head)
How does the phospholipid bilayer act as a wall?
Ions hydrated in solution can’t pass through the hydrophobic core of the bilayer
What are proteins made from and where can they be found?
Made from amino acids
found in: enzymes, cytoskeletal elements, receptors, ion channels
What is the role of transmembrane proteins?
- control resting membrane potential and action potential
- control synaptic transmission
- control extracellular to intracellular signaling - control
What is the structure of proteins?
many amino acids linked via peptide bonds to form polypeptide chains
- r groups alternate sides
What are the 4 levels of protein structure?
1) Primary: polypeptide chain
2) Secondary: coiling into alpha helix and beta-sheets
3) Tertiary: 3D folding of the coils and beta-sheets
4) Quaternary: different polypeptides bonding together
What are channel proteins and their role?
Polar R groups exposed to the cytosol or extracellular fluid and nonpolar t groups in the membrane
- ion selectivity and gating
What are the 3 types of ion channels and what do they affect?
1) Voltage gated: contribute to action potential
2) Ligand Gated: contribute to alterations in post-synaptic potentials
3) Leak: alter resting membrane potential
What is the role of Ion pumps?
- critical for establishing cellular concentration gradients
- formed by membrane-spanning proteins
- use energy from ATP breakdown
What does the sodium-potassium pump work?
(321NoKiA)
3 Na+ out
2 K+ in
1 ATP used
- uses ~70% of the total amount of ATP in the brain
Define diffusion force.
force on an ion due to its concentration gradient
- doesn’t change significantly under physiological conditions
Define electrostatic force.
force on an ion produced by the membrane voltage
- amount and direction of the force is a function of the membrane voltage and the charge of the ion
Define equilibrium potential
voltage that exactly offsets the diffusional force of the ion
- calculated by the Nernst Equation
Define driving force.
sum of the diffusion and electrostatic forces
- membrane voltage minus ionic Eion)
- controls the rate of ion flux if the membrane is permeable to the ion
- ion flux alters membrane voltage
Define ion flux.
mechanism by which membrane potential is changed.
- controlled by driving force of an ion and permeability of the membrane to that ion
What is the law of permeability?
membrane potential is always driven toward the equilibrium potential of the ion to which the membrane is most permeable
