Lecture 2 Flashcards
Neuronal Activity, Membranes and Ion flow
What is depolarization?
-Decrease in |potential|
-Membrane becomes less negative (closer to 0)
-Usually the positive slop portion of a TimexMembrane potential graph
What is repolarization?
-Returning to resting potential after depolarization
-Usually the negative slope portion from the peak to the resting potential
What is hyperpolarization?
-Increase in |potential|
-Membrane becomes more negative, further from 0
-negative slope after resting potential
What are the 2 types of electrical signals?
Graded potentials and action potentials
Graded potentials can be _________ or _________ potentials.
synaptic or receptor
What are action potentials triggered by?
Graded potentials
What do the proteins int he lipid bilayer cell membrane serve as?
receptors, channels, and transporters
What type of molecules can easily diffuse through membranes? Examples?
Small hydrophobic molecules – O2, CO2, N2, benzene
What type of molecules can somewhat easily diffuse through membranes? Examples?
Smaller uncharged polar molecules – H2O, glycerol, and ethanol
What type of molecules can not pass through membranes via diffusion? What is required for them to pass through?
-Larger uncharged polar molecules (aa’s, glucose, nucleotides – H+, Na+ K+, Cl-, Ca2+)
-special membrane proteins
Def of ion movement
Movement through diffusion - random movement of molecules
What is ion movement driven by? Together they form?
Concentration/Chemical Gradient/Forces
Electrical Gradient/Forces
Electrochemical gradient
Ions move from ___ to ____ due to chemical forces
high to low
Ion movement needs proteins that create (hydrophobic/hydrophilic) or electrically (unfavorable/favorable) environment
hydrophillic – allows hydrophillic things to enter
favorable – will more likely happen
Channels – (passive/active)
Carriers – (passive/active)
Pumps – (passive/active)
Channels and carriers are passive.. Pumps are active
Channels open “holes” allowing ions to diffuse (up/down) their ___________ gradients.
down their electrochemical gradients
Carriers like Na+/glucose co transporter carry ions (up/down) their electrochemical gradient.
down – carriers are passive
Which one requires energy and drives ion movement against their electrochemical gradient? – channel, carrier, or pump?
pump – active
There is 5K+ and 3Cl- on both sides of the membrane. Is there an electrical gradient? Concentration gradient?
No concentration or electrical gradient - same concentration of types of ions on each side and same number of +/- charges on each side
What does the nernst equation calculate? When do you use it?
Equilibrium Potential of an Ion (Eion) // only when only one ion is permeable
What does Eion stand for? Ex: Ek+
Equilibrium potential – Equilibrium potential of K+
When intercellular and extracellular concentrations are equal, what is Eion (equilibrium potential)?
0
What is the equilibrium potential of K+? (Ek+)
-90mV
When a cell is permeable to only one ion, what is the resting membrane potential of the cell equal to?
The Equilibrium Potential of that Ion
What will
be the resting membrane potential be for a cell that is only permeable for Na+ (ENa+ = +50mV)? What about for K+ (EK+ = -90mV)
+50 / -90
RMP = Eion is ion is the only thing that’s permeable
If the cell is permeable to BOTH Na+
and K+, and it is equally permeable. What will be the
membrane potential across the membrane of this cell?
ENa+ = +50mV
K+ = -90mV
Exactly between -90 and +50 – equally permeable means same numebr of channels
If an ion has a positive charge (z = 1; K+)
a (-) equilibrium potential means that there are (more/less) ions inside
less
less k+ inside, (+) z == -Ek+
If an ion has a negative charge (z = -1; Cl-)
a (+) equilibrium potential means that there are (more/less) ions outside
less
less cl- outside, (-) z == +Ecl-
Overall, if you want to find the equilibrium potential of an ion, you should take into account of
does it have a (+/-) charge? Are there more concentration outside or inside?
What does a (-) equilibrium potential tell us about K+? - is there more/less K+ inside? Does K+ want to leave or enter the membrane?
More inside – leaves membrane
What does a (+) equilibrium potential tell us about Na+? - is there more/less Na+ inside? Does Na+ want to leave or enter the membrane?
Less inside – wants to enter the membrane
T/F Leak channels are constantly open.
T
In neurons, we have many more leak channels for Na+/K+/Cl-.
K+
What will be the approx. membrane potential of a
neuron that has many more leak channels for K+, than Na+ and for whom ENa+=+50mV; EK+=-90mV?
Closer to -90mV but more (+)
Each ion contributes to the resting potential in a manner somewhat
proportional to the ____________ of the cell to that ion
permeability(p)
What does the Goldman or GHK Equation calculate? When do you use it?
Resting potential (Vm)– when there are multiple ions that are permeable
What is the equilibrium potential of Cl-?
-70mV
GHK equation: For positively charged ions like Na+ and K+, is it:
[out]/[in] or
[in]/[out] ?
[out]/[in]
GHK equation: For negatively charged ions like Cl-, is it:
[out]/[in] or
[in]/[out] ?
[in]/[out]
What 2 things is resting membrane potential (Vm) determined by?
- selective permeabilities of ions
- electrochemical gradients of the ions
T/F -Resting potential is always nearest E for the most permeable ion (K+)
T
What is the typical resting potential for a neuron?
-70mV
Vrest = ?
Ek+ = ?
Ena+ = ?
Ecl- = ?
Vrest = -70mV
Ek+ = -90mV
Ena+ = +50mV
Ecl- = -70mV
What maintains the concentration gradients across the membrane?
Na+/K_ ATPase pump - it actively transports Na+ and K+ ions across the cell membrane
-Ions are pushed against their concentration gradients.
-3 Na+ leave = 2K+ enter — pump
is electrogenic
