Lecture 2, Chapter 4&7 Flashcards
What is diffusion?
Random movement of molecules from high energy state to lower total energy
Find some reading on membrane potentials is highly recommended!
!
What are the driving forces acting on solutes that determine net diffusion?
- Chemical (concentration gradient high to low)
- Electrical (charge attraction) opposite ions attract. Only important for charge particles like ions (K+, Na+, Cl-)
Ions can move in or out regardless of the chemical or electrical gradients but must think of ______ diffusion
Net
Does glucose have a charge?
No not charge but polar just like water, so glucose is only affected by chemical gradients
Charged molecules are affected by what type of gradients?
Both chemical and electrical gradients
* electrochemical gradient
Can a electrical gradient overpower a strong chemical gradient?
Yes
Separation of charge across a cell membrane. Difference between outside and inside the cell
Membrane potential. Produces a voltage measured in millivolts
A difference in voltage between two points?
Potential difference = E
Difference in voltage across the plasma membrane, always given in terms of voltage inside the cell relative to voltage outside the cell.
Membrane potential***
Difference in voltage across the plasma membrane when I saw is at rest, not receiving or sending signals
Resting Vm
A relatively small change in membrane potential produce by some type of stimulus that triggers the opening or closing of ion channels, strength is relative to strength of stimulus
-dif. Levles
Graded potential
Graded potentials produced in the post synaptic cell in response to neurotransmitters binding to receptors
Synaptic potential
Graded potentials produced in response to a stimulus acting on a sensory receptor.
(Hands, touch receptors, sensory neuron)
Receptor potential
A large, rapid change in membrane potential produced by depolarization of an excitable cells plasma membrane to the threshold.
(Pain- three for small pain, 50 for intense pain, how many and how often…)
Action potential
The membrane potential that counters the chemical force acting to move an ion across the membrane, thereby putting the ion at equilibrium
Equilibrium potential
The millivolts at which an action potential is initiated.
Threshold potential***
Potential that will generate an action potential
Threshold potential?
A cell is in equilibrium and has equal concentrations of sodium and potassium and chloride between inside and outside in what case?
Only when the cell is dead
The cell membrane is completely impermeable to sodium potassium and chloride but the membrane contains….
Na+,K+ pumps (uses ATP to pump)
2 K+ in and 3 Na+ out**
What is the primary active transport on the cell membrane?
What charge does it create on the inside and outside of the cell?
Sodium potassium pump
This will cause more negative inside the cell and positive on the outside of the cell
What if a typical cell is only permeable to potassium (K+)?
The electrical and chemical gradient will eventually reach equilibrium
Hypothetical membrane potential where the chemical an electrical gradients for the ions are equel opposite
Equilibrium potential
What is the Nernst equation?
E(ion) = (61mV/z) log [I]o/[I]i
E= equilibrium potential of ion I
Z= valence of ion I
[I]o=ECF Concentration of ion I
[I]i=ICF concentration of ion I 
If the particular ion equals that calculated concentration then it is in equilibrium
What can change the resting membrane potential?
Changes in ionic concentrations
-
- Na+/K+ pump
-  relative permeability of membrane to different ions (determined by presence of ion channels - Leak channels in this case.
Need to know the Goldman-Hodgkinz-Katz (GHK) equation!!!
This equation takes into account of shared permeability
Kind of like a weighted average
At rest, a cell (neuron or skeletal muscle) is about 20 times more permeable to ____ than ____.
K+, Na+
Changes in membrane permeability are mediated by…
Ion channels
What are the different types of ion channels?
- Leak channel
- ligand gated channels
- voltage-gated channels
This channel is always open and has no gates
Leak Channels
This channel needs to be unlocked, signaling molecules. Regulated by some compound like a neurotransmitter or hormone; usually rasies Vm to threshold.
(response may be small or big)
Ligand gated channels
These channels are regulated by changes in voltage (membrane potential)
Voltage-gated channels
Triggered when the Vm (membrane potential) reaches threshold potential
The action potential**^
Where are leak channels, ligand-gated channels, and voltage-gated channels found? 
Leak- everywhere
Ligand- gated- are only on dendrites and soma
Voltage-gated channles- only on axon (underline action potential)
Action potential is all-or-none changes in Vm triggered at _________.
There are three phases (depolarization, repolarization, hyperpolarization)
Axon hillock (base of axon)
What are the three phases of action potential?
- depolarization phase (due to increased Na+ perm, 100x more perm)
- repolarization phase (due to increased K+ perm)
- hyperpolarization phase (due to increased K+ perm) 
What kind of channels underline action potential?
Voltage-gated
V-gated Na+ channel
- 2 gates
1. Activation gate
2. Inactivation gate
V-gated Na+ channel…
At rest: activation gate ________; inactivation gate is _______.
Threshold: activation gate _______; ____ goes in.
Brief time later: inactivation gate ______; _____ Na+ stops 
Closed, open
Opens, Na+
Closes, inward
- Gates do not return to at rest configuration untill Vm drops below threshold
In activation is (slow or quick)?
And inactivation is?
Does Na+ go up or down dor each? 
Inactivation is creaky and slow, Na+ goes down
Activation gate is quick and sodium goes up
This channel only has one gate and it is closed at rest and activated by threshold Vm, Time course much like the sodium in activation gate (slow), must go below threshold too close.
K+ Channel
V-gated K+ channels has how many gates?
At rest it is…
One
Closed
Is Na+ or K+ voltage-gated channel slower?
K+ is slower than Na+ activation gate
How does the puffer fish toxin call People?
It binds voltage-gated sodium channels
How does potassium chloride effectively euthanize animals?
Voltage can’t drop past threshold. The action potential becomes a one and done
Explain the conduction of action potentials down axons
Na+ entry during action potential spreads to adjacent region of the cell causing it to depolarize to threshold and generate an action potential
This repeats down Axon until reaches axon terminal
