NEU Quiz 2 Flashcards
What components make up the neuronal cell membrane? What is the general role of this membrane?
Made of Lipid bilayer, proteins, some carbs
Plays dynamic role in cellular activity - The Gatekeeper
Separates intracellular fluid (ICF) from extracellular fluid (ECF)
Phospholipid Bilayer
Membrane Transport
Cell membranes selectively permeable
Some molecules pass through easily - lipid bilayer permeable to nonpolar + uncharged = hydrophobic substances like Lipids, O2,CO2
Some molecules need help to pass - bilayer impermeable to polar + ionic = hydrophilic substances
Passive transport
diffusion (high concentration to low concentration) which is no cellular energy (ATP) required and substance moves with concentration gradient
Diffusion
molecules move with their concentration gradient there is difference in concentration between two areas and continues until equilibrium is reached, rate depends on size of the concentration gradient and molecular weight of moving particle - 10:1 is larger concentration gradient than 2:1
Simple Diffusion
hydrophobic (nonpolar) substances like O2,CO2, Fat soluble vitamins, gasses and molecules directly through the phospholipid bilayer that just flow on through
Facilitated Diffusion
Diffusion through channel proteins which are specific – usually only 1 type molecule transported with certain hydrophilic/polar(not lipid soluble) molecules e.g., IONS, glucose, amino acids but requires an open door
Active transport
ATPases (AKA Pumps) with energy (ATP) required and moves against concentration gradient
Membrane Transport - Two types
Primary Active transport and Vesicular transport; both require ATP (Active=ATP) to move solutes across plasma membrane because: Solute too large for channels - vesicular, Solute not lipid soluble - vesicular, Solute might move against concentration gradient– primary active
Primary Active Transport
Requires solute pumps = “ATPases” and moves solutes against concentration/electrical gradient – from low to high concentration which requires ATP, Ions, small hydrophilic molecules moved (amino acids, monosaccharides, Na+, K+, Ca2+, Cl- etc.)
Vesicular Transport
another type of active transport also called exocytosis. Vesicles bud off golgi with material that needs to leave the cell and moves to cell membrane and fuses with it using ATP for movement, expels contents to outside ECF = EXOCYTOSIS, and makes neurons → neurotransmitters
Draw a cartoon cell (large circle) and fill in the intracellular and extracellular concentrations of each ion (K+, Na+, Cl-, Ca2+).
Sodium Potassium Pump
Ion: K, Na, Ca, Cl
Inside Cell (Intracellular ICF): 150, 10, 1, 5
Outside Cell (Extracellular ECF): 5, 145, 5, 100
Flow high to low concentration: out, in, in, in
Typical State: -90mv, +60mv,
3 sodium out and 2 potassium in
What types of transporters/channels are most important in the establishment of the resting membrane potential? Do most channels only allow one type of ion through?
Resting K channel also called leak channels are always open the ions can freely move through them at rest, the door is always open
Voltage gated channel they have lining the pore of the channel have charged amino acids such that when membrane reaches certain voltage cause a conformational change which causes them to open - voltage gated sodium and voltage gated potassium channel
ATPases or Pumps requires ATP to operate
Presence of transporters:
- Sets up electrochemical gradient (Resting Membrane Potential)
- Allows for neuron firing (Action Potential)
- Returns neuron to resting point (Resting Membrane Potential)
What is the resting membrane potential of a typical neuron?
Resting membrane at (RMP) = -70 mv → Established by LEAK channels (mostly K+, little Na+, very little Cl-) Maintained by Na/K ATPase
At resting potential concentration of ions is kept constant through Na+/K+ pumps. When the threshold is reached, the Na+ gated channels are opened.
A lot of K+ diffuses out through leak channels; a little Na+ leaks
- Cell more negative inside, more positive out
- Membrane is barrier, separating + from -
- Establishes resting membrane potential
Why is it valuable to have a resting membrane potential?
basis for neural signaling
When trying to calculate the equilibrium potential or resting membrane potential for a cell, explain the two different equations you might use and when you would use them. Highlight what properties of the ion(s) are important for these equations.
Nernst Equilibrium Potential - Calculates equilibrium potential for single ion crossing membrane
Goldman-Hodgkin Katz Equation - Calculates equilibrium potential when more than 1 ion crosses the membrane
The movement of which ion is more important for the establishment of the resting membrane potential?
Potassium ions are important for RMP because of its active transport, which increases its concentration inside the cell. However, the potassium-selective ion channels are always open, producing an accumulation of negative charge inside the cell
Why does this ion contribute more to the RMP than other ions? What value of this ion is the resting membrane potential closer to than other ions?
potassium (K+ ). Recall that resting membrane potential is due to a small buildup of negative ions on the inside of the plasma membrane in the cytosol and an equal accumulation of positive ions on the extracellular side of the plasma membrane.
Explain in several sentences how sodium and potassium move across the membrane at rest, including the direction they flow with their concentration gradient. Explain how they move through leak channels, which ion has more of these leak channels, and mention what helps to maintain the RMP once its been established.
Potassium and sodium are transported across the cell membrane using protein channels and protein pumps. Protein channels are a form of passive transport. Like a tunnel, they allow the passage of materials from an area of high concentration to an area of low concentration without using energy.
Think through how the resting membrane potential would change if the extracellular concentrations of potassium or sodium increased due to disease or dysfunction. For each ion, would the cell become hyperpolarized (more —) or depolarized (more +). Higher extracellular concentration of K+: and Higher extracellular concentration of Na+:
Increasing K+ extracellular concentration: we are creating a greater concentration gradient for potassium to move out of the neuron.
- This would result in an increased potassium efflux, causing the inside of the neuron to become more negative than usual.
- Resulting: the resting membrane potential would become MORE NEGATIVE→HYPERPOLARIZATION.
This hyperpolarization→too much of it→ more difficult for the neuron to reach the threshold required to generate an AP.
Increasing the extracellular concentration of sodium: creates a greater concentration gradient for sodium to move into the neuron
- This leads to an increase influx of sodium ions→causing the inside of the cell to be LESS NEGATIVE (MORE POSITIVE)–>DEPOLARIZED
This depolarization→the resting membrane potential becomes LESS NEGATIVE→easier for the neuron to reach the threshold & generate an AP!!!
Concentration gradient
high to low
normal the usual
Electrochemical gradient
the electrical and diffusional forces are competing, they jointly form this gradient
Which items are structural components of the cell that affect ion movement across the membrane?
Ion channels
Phospholipid bilayer
What is the membrane potential?
The difference in charge between the inside and the outside of the neuron
A cell is at rest at -70 mV, and sodium channels open. In which direction does sodium flow? How does this ion flow affect the membrane potential?
Into the cell; Makes membrane potential more positive
A cell is at rest at -70 mV, and potassium channels open.
In which direction does potassium flow and how does this affect the membrane potential
Out of the cell; Makes membrane potential more negative
Potassium is concentrated —— the cell
inside
everything else is out
The activity of the sodium-potassium pump can be evaluated by measuring how much sodium leaves the cell. If a cell was treated with a drug that prevented the synthesis of ATP, how would efflux of sodium change compared to baseline?
Sodium efflux would decrease
In a typical neuron, at rest, which ion channel has the most open non-gated (leak) channels?
Potassium
What structure is responsible for establishing and maintaining the presence of electrochemical gradients?
Sodium-potassium pump
If the concentration of ion X in the intracellular
space is 50 mM, and in the extracellular space is 15 mM, ion X will flow ______ the cell through their leak channels.
out
The following is an example of facilitated passive transport
- Vesicular release of a neurotransmitter
- Sodium/potassium pump moving ions against gradient
- Cation specific channel allowing sodium into the cell
- Oxygen movement across membrane
Vesicular release of a neurotransmitter (Active)
Sodium/potassium pump moves ions against gradient (Active)
Cation specific channel allowing sodium into the cell
Oxygen movement across membrane (Passive Simple) - hydrophobic/non-polar
Why does the Sodium-Potassium Pump require ATP to work?
It is pumping things against their concentration gradient
For our previous example using ion X, it had an
intracellular [50 mM] and extracellular [15 mM].
* If ion Y has an intracellular [150 mM] and an
extracellular [50 mM], is the drive for Y to leave the cell (created by its concentration gradient) greater or less than ion X?
X: 50:15 (divide 50/15 to get 3.33)
Y: 150:50 (divide 150/50 to get 3)
Therefore, X is greater than Y so the drive for Y is less to leave
Why is potassium the greatest contributor to the resting membrane potential of a neuron?
It has the greatest permeability across the membrane
