Chapter 3 Flashcards
(93 cards)
1
Q
What is membrane potential?
A
Membrane potential is the difference in electrical charges across the membrane
2
Q
What is the membrane potential at rest?
A
At rest, the neuron has a steady negative electrical potential
3
Q
What is electrical potential?
A
Electrical potential is the force exerted on a charged particle (ion)
4
Q
Our typical neuron has a resting membrane potential of about…
A
-65 mV
5
Q
The neuronal membrane separates…
A
Charge
6
Q
How is the resting membrane potential established and maintained?
A
- Charge separation (neuronal membrane)
- Selective permeability (ion channel proteins)
- Concentration gradients (ion pumps: Na+/K+ ATPase)
7
Q
Why is water important in the membrane?
A
Water’s the key ingredient in extracellular & intracellular fluid
- Water IS A POLAR SOLVENT
8
Q
What are ions?
A
Ions are atoms or molecules with a net electrical charge
- Hydrophilic
9
Q
What charge do cations have?
A
Net positive charge
10
Q
What charge do anions have?
A
Net negative charge
11
Q
What does the phospholipid bilayer consist of?
A
Lipids and phosphate groups
12
Q
Lipids are hydro___
A
Hydrophobic
13
Q
Phosphate groups are hydro___
A
Hydrophilic
14
Q
Why can’t ions pass the lipid bilayer?
A
Ions in solution are hydrated and therefore cannot pass across the hydrophobic core of the cell membrane lipid bilayer
15
Q
What are proteins?
A
Proteins are molecules assembled from amino acids (ex: enzymes, cytoskeletal elements, receptors, ion channels)
16
Q
What are transmembrane proteins?
A
Transmembrane proteins are special proteins that span the phospholipid bilayer
17
Q
What are the functions of transmembrane proteins?
A
- Control resting membrane potential and action potentials
- Control synaptic transmission
- Control extracellular to intracellular signaling
18
Q
Proteins are structured via…
A
Amino acids
19
Q
What do amino acids consist of?
A
Amino acids are made of a alpha carbon and an R group
- Linked together via peptide bonds to form polypeptides
20
Q
What 4 layers do proteins consist of?
A
- Primary
- Secondary
- Tertiary
- Quaternary
21
Q
What does the primary protein layer consist of?
A
Sequence of amino acids in polypeptide
22
Q
What does the secondary protein structure consist of?
A
Coiling of polypeptide into alpha helix
23
Q
What does the tertiary protein structure consist of?
A
3-dimensional folding of the polypeptide
24
Q
What does the quaternary protein structure consist of?
A
Different polypeptides bonding together
25
What are channel proteins?
Polar R groups (exposed to cytosol or extracellular fluid) and non-polar R groups (imbedded in the membrane)
26
What are channel proteins responsible for?
Ion selectivity and gating
27
What are the different types of ion channels?
Voltage gated, Ligand gated, "Leak"
28
What is the purpose of voltage gated ion channel?
Contribute to action potential
29
What is the purpose of ligand gated ion channel?
Contribute to alterations in post-synaptic potentials (PSP)
30
What is the purpose of "leak" ion channel?
Alter resting membrane potential (RMP)
31
What are the functions of ion pumps?
- Critical for establishing cellular concentration gradients
- Formed by membrane-spanning proteins
- Use energy from ATP breakdown
ex: sodium-potassium pumps, calcium pumps
32
What is the sodium-potassium pump?
- An enzyme that breaks down ATP when Na is present
- Pumps 3 Na+ ions out, 2 K+ ions in
- Uses ~70% of the total amount of ATP in the brain
33
What is the concentration of Na+ in extracellular fluid?
150 mM
34
What is the concentration of K+ in extracellular fluid?
5 mM
35
What is the concentration of Na+ in cytosol?
15 mM
36
What is the concentration of K+ in cytosol?
100 mM
37
What is diffusion force?
The force on an ion due to its concentration gradient (ex: the ratio of extracellular to intracellular concentration of an ion)
38
What is electrostatic force?
The force on an ion produced by the membrane voltage
- the amount and direction of the force is a function of the membrane voltage and the charge ion
39
What is equilibrium ptential?
A voltage (electrostatic force) that exactly offsets the diffusional force of the ion
- It is the point where diffusion and electrostatic forces counteract each other
- Calculated by the Nernst Equation
40
What is driving force?
The sum of the diffusion and electrostatic forces
- The force that controls the rate of ion flux IF the membrane is permeable to the ion (the ion flux then alters the Vm)
- Calculated by Vm-Eion (membrane voltage minus ionic equilibrium potential)
41
What is ion flux?
The mechanism by which membrane potential is changed
- Controlled by the driving force of an ion and the permeability f the membrane to that ion
42
What is the Law of Permeability?
The membrane potential is always driven toward the equilibrium potential of the ion to which the membrane is most permeable
43
How do ions move throughout a membrane?
Ions diffuse throughout a membrane
- Dissolved ions distribute evenly
- Ions flow down the concentration gradient when channels are permeable to specific ions and the concentration gradient exists across the membrane
44
How does electrical potential correlate with ion movement?
Electrical potential (voltage) influences ion movement
45
Electrical current (I) is directly proportional to.... and inversely proportional to....
Electrical potential (V), resistance (R)
46
Ohm's Law
I= V/R
V= IR
I: current (amperes)
V: voltage across the conductor (volts)
R: resistance of the conductor (ohms)
47
How does electrical current move across a membrane?
Electrical current flows across a membrane
48
What does it mean to be in "equilibrium potential"?
- No net movement of ions when separated by a phospholipid membrane
- Equilibrium reached with K+ channels in the phospholipid bilayer
- Electrical potential different that exactly balances ionic concentration gradient
49
What is the voltage that will exactly counteract the ion's diffusional force (concentration gradient)?
Equilibrium potential (electrostatic force)
50
What is membrane potential (Vm)?
The voltage across the neuronal membrane at any moment
51
How do changes in membrane potential occur?
Large changes in membrane potential occur even with small changes in ionic concentrations
52
Electrical charges are ___ at the inside and outside membrane surfaces
Balanced
53
Rate of movement of ions across membrane (should it become permeable to that ion) is determined by...
Driving force
54
If concentration difference is know, equilibrium potential can be calculated using....
Nernst Equation
55
Potassium equilibrium potential is ___ relative to outside
Negative; -Vm
56
Sodium equilibrium potential is ___ relative to outside
Positive; +Vm
57
Increasing the concentration gradient or temp will ____ the absolute value of equilibrium potential
Increase
58
An ion with twice the charge will have ____ the equilibrium potential
Half
59
The Nernst Equation
Eion= 2.303 RT/zF log [ion]out//[ion]in
Eion= equilibrium potential
R= gas constant
T= absolute temperature
F= Faraday's constant
z= charge of the ion (valence)
60
K+ is more concentrated on ____
Inside
61
Na+ and Ca2+ is more concentrated ____
Outside
62
What is the concentration of K+ outside and inside the membrane?
Outside: 5; Inside: 100
63
What is the ratio Out:In of membrane concentration for K+?
1:20
64
What is Eion for K+?
-80 mV
65
What is the concentration of Na+ outside and inside the membrane?
Outside: 150; Inside: 15
66
What is the ratio Out:In of membrane concentration for Na+?
10:1
67
What is Eion for Na+?
62 mV
68
What is the concentration of Ca2+ outside and inside the membrane?
Outside: 2; Inside: 0.0002
69
What is the ratio Out:In of membrane concentration for Ca2+?
10,000:1
70
What is Eion for Ca2+?
123 mV
71
What is the concentration of Cl- outside and inside the membrane?
Outside: 150; Inside: 13
72
What is the ratio Out:In of membrane concentration for Cl-?
11.5:1
73
What is Eion for Cl-?
-65 mV
74
The membrane potential is always driven ____ the equilibrium potential to which the membrane is most ____
Toward; permeable
75
What is the Nernst Equation for K+?
61.54mV x log [ion]out/[ion]in
76
What is the Nernst Equation for Na+?
61.54mV x log [ion]out/[ion]in
77
What is the Nernst Equation for Cl-?
-61.54mV x log [ion]ut/[ion]in
78
What is he Nernst Equation for Ca2+?
30.77mV x log [ion]out/[ion]in
79
The membrane potential is the ___ as an equilibrium potential for an ion if the membrane is ____
Same; permeable ONLY to that ion
80
What does resting cell mean?
Resting cell means there is no special synaptic event or action potential
81
In the resting cell, no ion is _____
Strictly impermeable across the membrane
82
What is the order of permeability?
K+ >> Cl- >>> Na+
83
Is the K+ leak channel a ligand gated or voltage gated?
The K+ leak channel is neither ligand gated or voltage gated
84
The default state of K+ leak channel is ____
Open
85
Where does the K+ leak channel exist?
The K+ leak channel exists in all zones of the neuronal membrane (dendrites, soma, axon)
86
The K+ leak channel results in ___ resting permeability to K+?
High
87
Why is there a large outward diffusional force on K+?
There is a large diffusional force on K+ due to its concentration gradient?
88
What is a key determinant of resting membrane potential?
Selective permeability of potassium channels
89
Mutations of specific K+ channels lead to ___
Inherited neurological disorders
90
Why is it important to regulate external K+ concentration?
- Resting membrane potential is close to Ek because it is mostly permeably to K+
- Membrane potential sensitive to extracellular K+
- Increased extracellular K+ depolarizes membrane
91
What mechanisms regulate the external potassium concentration?
Blood-brain barrier and potassium spatial buffering by astrocytes
92
Membrane permeability determines...
Membrane potential
93
What is the purpose of the Goldman equation?
It takes into account permeability of membrane to different ions
