NEU Quiz 2

Question 1

What components make up the neuronal cell membrane? What is the general role of this membrane?

Answer 1

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

Question 2

Membrane Transport

Answer 2

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

Question 3

Passive transport

Answer 3

diffusion (high concentration to low concentration) which is no cellular energy (ATP) required and substance moves with concentration gradient

Question 4

Diffusion

Answer 4

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

Question 5

Simple Diffusion

Answer 5

hydrophobic (nonpolar) substances like O2,CO2, Fat soluble vitamins, gasses and molecules directly through the phospholipid bilayer that just flow on through

Question 6

Facilitated Diffusion

Answer 6

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

Question 7

Active transport

Answer 7

ATPases (AKA Pumps) with energy (ATP) required and moves against concentration gradient

Question 8

Membrane Transport - Two types

Answer 8

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

Question 9

Primary Active Transport

Answer 9

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.)

Question 10

Vesicular Transport

Answer 10

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

Question 11

Draw a cartoon cell (large circle) and fill in the intracellular and extracellular concentrations of each ion (K+, Na+, Cl-, Ca2+).

Sodium Potassium Pump

Answer 11

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

Question 12

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?

Answer 12

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)

Question 13

What is the resting membrane potential of a typical neuron?

Answer 13

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

Question 14

Why is it valuable to have a resting membrane potential?

Answer 14

basis for neural signaling

Question 15

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.

Answer 15

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

Question 16

The movement of which ion is more important for the establishment of the resting membrane potential?

Answer 16

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

Question 17

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?

Answer 17

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.

Question 18

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.

Answer 18

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.

Question 19

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+:

Answer 19

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!!!

Question 20

Concentration gradient

Answer 20

high to low
normal the usual

Question 21

Electrochemical gradient

Answer 21

the electrical and diffusional forces are competing, they jointly form this gradient

Question 22

Which items are structural components of the cell that affect ion movement across the membrane?

Answer 22

Ion channels
Phospholipid bilayer

Question 23

What is the membrane potential?

Answer 23

The difference in charge between the inside and the outside of the neuron

Question 24

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?

Answer 24

Into the cell; Makes membrane potential more positive

Question 25

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

Answer 25

Out of the cell; Makes membrane potential more negative

Question 26

Potassium is concentrated —— the cell

Answer 26

inside
everything else is out

Question 27

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?

Answer 27

Sodium efflux would decrease

Question 28

In a typical neuron, at rest, which ion channel has the most open non-gated (leak) channels?

Answer 28

Potassium

Question 29

What structure is responsible for establishing and maintaining the presence of electrochemical gradients?

Answer 29

Sodium-potassium pump

Question 30

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.

Answer 30

out

Question 31

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

Answer 31

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

Question 32

Why does the Sodium-Potassium Pump require ATP to work?

Answer 32

It is pumping things against their concentration gradient

Question 33

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?

Answer 33

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

Question 34

Why is potassium the greatest contributor to the resting membrane potential of a neuron?

Answer 34

It has the greatest permeability across the membrane