Deck 2: Signaling Within Neurons

Question 1

Which membrane proteins use the electrochemical gradient to move ions across the membrane? Choose all that apply.
(a) Symporters
(b) Pumps
(c) Antiporters
(d) Ion channels

Answer 1

(A),(C), AND (D).
All these types of transport use electrochemical gradients to move ions across the membrane. For symporters the electrochemical gradient of one ion is used to drive another ion in the same direction, up its electrochemical gradient. For antiporters, the electrochemical gradient of one ion is used to drive another ion in the opposite direction, up its electrochemical gradient.

Question 2

In transportation within neurons, which direction is retrograde? Which direction is anterograde?

Answer 2

Retrograde refers to movement toward the cell body. Anterograde refers to movement down an axon, away from the cell body.

Question 3

List in order of size: neurofilaments, microtubules, microfilaments.

Answer 3

Microfilaments < neurofilaments < microtubules

Question 4

Changes in ion conductance or ion concentration can alter the resting membrane potential of a cell. For each of the following, write in the letter indicating whether each condition would cause hyperpolarization (H), depolarization (D), or very little change (LC) in the resting membrane potential, and the reason for this change. $\begin{array}{lll}\text { Condition } & \begin{array}{l}\text { Membrane } \\\text { potential } \\\text { change }\end{array} & \text { Reason } \\\text { ncrease in }\left[\mathrm{K}^{+}\right]_{0} &\text{ ----------- } &\text{ ----------- } \\\text { increase in }\left[\mathrm{Na}^{+}\right]_{0} & \text{ ----------- }& \text{ ----------- }\\\text { increase in } \mathrm{K}^{+} \text {permeability } & \text{ ----------- } & \text{ ----------- }\\\text { increase in } \mathrm{Na}^{+} \text {permeability } & \text{ ----------- } & \text{ ----------- }\\\end{array}$

Question 5

What is the function of exocytosis? Choose all that are correct.
(a) To take proteins to the plasma membrane
(b) To take proteins away from the plasma membrane
(c) Potential degradation of proteins
(d) To secrete proteins from the cell

Question 6

Proteins that are destined for export from the cell or that are inserted into the lipid bilayer are synthesized in/on which organelle?
(a) Free ribosomes
(b) Endoplasmic reticulum
(c) Golgi apparatus
(d) Nucleus

Question 7

The brains of patients with Alzheimer's disease show degradation of microtubule function, in part from over-phosphorylation of the microtubule-associated protein, tau. What might happen to neurons when microtubule function is disrupted?

Question 8

Which membrane proteins require ATP to move ions across the membrane? Choose all that apply.
(a) Symporters
(b) Pumps
(c) Antiporters
(d) Ion channels

Question 9

What is the transcription unit?
(a) The part of the gene that serves as a template for RNA synthesis
(b) The part of RNA that serves as a template for protein synthesis
(c) The part of the gene that serves as a template for protein synthesis
(d) The unit of RNA that is made from a particular gene

Question 10

What helps maintain the ion concentration across the membrane of neurons?
(a) The driving force for any ion
(b) Na⁺/K⁺ ATPase
(c) Leak K⁺ channels
(d) Leak Na⁺ channels

Question 11

According to the Goldman-Hodgkin-Katz equation, if the membrane were more permeable to Na⁺ at rest, instead of K⁺, what would the approximate resting membrane potential be?
(a) -70 mV
(b) +50mV
(c) -79 mV
(d) +100mV

Question 12

Label depolarization, repolarization, and hyperpolarization in Figure Q2-14. Figure Q2-14

Question 13

What kinds of organelles have been localized to dendrites?
(a) Polyribosomes
(b) ER
(c) Golgi
(d) All of the above
(e) None of these are located in dendrites.

Question 14

What is the function of endocytosis? Choose all that are correct.
(a) To take proteins to the plasma membrane
(b) To take proteins away from the plasma membrane
(c) Potential degradation of proteins
(d) To secrete proteins from the cell

Question 15

Figure Q2-10 shows an interpretive drawing of a microtubule moving rightward on a glass slide to which a substance purified from squid axoplasm had been immobilized, in the presence of ATP. Figure Q2-10
A. What is the substance that was purified that allows movement of the microtubule?
B. What would happen if a non-hydrolyzable form of ATP was added to the solution?

Question 16

Which equation is used to determine the equilibrium potential of any ion?
(a) Ohm's law
(b) The driving force
(c) The Nernst potential
(d) The Goldman-Hodgkin-Katz equation

Question 17

The equilibrium potential for any ion is the point at which two forces/gradients balance each other. What are the two forces/gradients?

Question 18

What does 'local protein translation' mean in neurons?
(a) Proteins are synthesized only in the nucleus.
(b) Proteins are synthesized only in the cell body.
(c) Proteins can be synthesized in dendrites.
(d) Proteins can be synthesized by a neighboring neuron.

Question 19

Proteins that function in the cytoplasm and nucleus are synthesized in/on which organelle?
(a) Free ribosomes
(b) Endoplasmic reticulum
(c) Golgi apparatus
(d) Nucleus

Question 20

In the cochlea of the ear sounds waves are turned into electrical signals through special cells called hair cells. When a wave travels through the cochlea it moves the 'hairs' and opens ion channels that are permeable to K⁺ and Ca²⁺. These 'hairs' are in a fluid that has a very high K⁺ concentration compared to the inside of the cell.
A. When the ion channels open, in what direction do K⁺ ions flow and why?
B. Based on this relative concentration difference of K⁺, what do you predict the equilibrium potential for K⁺ will be: positive, negative or zero?

Question 21

In order to understand how currents move during an axon potential Hodgkin and Huxley used the voltage clamp technique. Why was this technique so important? Choose all that apply.
(a) It allowed the investigators to measure ions moving across single channels.
(b) It prevented the change in membrane potential associated with ions flowing across the membrane.
(c) It allowed them to calculate the conductance of the individual ions.
(d) It showed that currents vary with voltage and time.

Question 22

Why are action potentials usually generated at the axon hillock in vertebrate neurons?
(a) There is a high concentration of Na⁺ channels.
(b) There is a high concentration of K⁺ channels.
(c) This is the point at which most synaptic contacts are made.
(d) It is located at the beginning of the axon.

Question 23

In order to test the hypothesis that the rising phase of the action potential is caused by Na⁺ influx, researchers recorded the magnitude of the action potential when in a normal solution (like sea water) and then again after increasing the extracellular Na⁺ concentration. What do you predict will happen to the action potential with the increased extracellular Na⁺ concentration and why? Draw the action potential on Figure Q2-30. Figure Q2-30

Question 24

What is an RC circuit? Choose all that apply.
(a) A circuit with a resistor and capacitor
(b) An electronic representation of a biological membrane
(c) An electronic representation of voltage dependent ion channels
(d) A circuit with ions and voltage

Question 25

You are in a lab and conduct a patch clamp experiment (Figure Q2-39) in which you change the voltage across the membrane by +20 mV (top trace). You record the resulting single channel current (lower three traces). Based on these single channel currents, what do you think the whole-cell current would look like? Figure Q2-39

Question 26

What best describes current?
(a) Resistance
(b) Movement of charge
(c) Potential difference
(d) Storage of charge

Question 27

Why does the Na⁺ conductance decrease after a short time?
(a) The channels close.
(b) The cell reaches E_Na.
(c) The Na⁺ channels inactivate.
(d) The K⁺ channels start to open.

Question 28

Label Figure Q2-29 with the following terms: action potential threshold, action potential, subthreshold stimulus, suprathreshold stimulus. Figure Q2-29
B. In Figure Q2-29, stimulus 4 is of larger amplitude than stimulus 3. What happened to the action potential when a larger stimulus was provided and why?
C. In Figure Q2-29, what do you predict would happen if you increased the duration of stimulus 4?
How Do Electrical Signals Propagate from the Neuronal Cell Body to Its Axon Terminals?

Question 29

If myelin makes action conduction velocity faster, why are axons not completely covered with myelin? That is, what would happen to the electrical signal if the axon was completely covered in myelin and had no Nodes of Ranvier?

Question 30

Figure Q2-37 shows a whole-cell sodium current (bottom trace) elicited by stepping the membrane potential from -70 mV to 0 mV (top trace). The dashed line is 0 nA. Upon depolarizing the membrane, there is an inward current. This whole-cell current is a reflection of the cumulative activity of many individual ion channels. What is the probable state of an individual sodium channel at each point (A, B, and C)? Figure Q2-37

Question 31

Invertebrates and vertebrates have evolved different strategies to change the length/space constant (λ) of a neuron. For each strategy, say whether this increases or decreases the length constant and what property in the following equation it influences. A. Invertebrates increased the diameter of the axon.
B. Vertebrates use myelination of the axon.

Question 32

If there is a large voltage across a membrane and a low resistance, is the current going to be larger or small?
B. In order to have a large current, if there is a large resistance what should the voltage difference be?

Question 33

Why do action potentials usually travel unidirectionally down an axon?
(a) Delayed activation of K⁺ channels
(b) Inactivation of Na⁺ channels
(c) Myelin prevents travel in the opposite direction.
(d) Action potentials are all-or-none.

Question 34

For each labeled point (A-D) on the action potential shown in Figure Q2-34, state whether the conductance through voltage-dependent Na⁺ and K⁺ channels is low, high, or no conductance. Explain. [Note: For this answer, ignore conductance through leak channels.] Figure Q2-34

Question 35

What is the size of the primary structure of K⁺ channels compared to Na⁺ channels?
(a) It is twice the size.
(b) It is half the size.
(c) It is one quarter the size.
(d) It is four times the size.

Question 36

Figure Q2-38 shows the response of a single Na⁺ channel patch clamp recording. Which individual ion channel state best describes the current in A, B, and C? Figure Q2-38

Question 37

What is the function of the 'capacitor' in a neuron? Choose all that apply.
(a) Storage of charge across the membrane
(b) To allow the movement of ions across the membrane
(c) To provide the ability to integrate signals
(d) To provide a delay in changes in voltage across the membrane

Question 38

Using the voltage clamp technique, Hodgkin and Huxley found an early inward current and a later outer current (Figure Q2-32, recorded current). What would happen to the current if you would apply tetrodotoxin to the bath before changing the voltage across the membrane? Please select between currents A and B and explain your answer. Figure Q2-32

Question 39

What is the 'driving force'?
(a) The concentration gradient
(b) The conductance of an ion
(c) The equilibrium potential for an ion
(d) The difference between the membrane potential and equilibrium potential

Question 40

Reconstruct an action potential starting with the resting potential and ending with the voltage across the membrane coming back to rest after the action potential. Describe single channel behavior, whole cell current and/or conductance, and changes in voltage with respect to the equilibrium potential for each ion.?

Question 41

In Figure Q2-42, amino acids 6-46 were removed from the ShB channel through mutagenesis.
A. What happened to the single channel response?
B. When the ShB peptide (the first 20 amino acids of the ShB protein) was added to the ShBΔ6-46 protein, what happened to the single channel response and what does that tell you about the function of the first 20 amino acids?

Question 42

How do Na⁺ and K⁺ ion channel structures allow them to detect changes in voltage across the membrane?
Note: Questions 2-42 and 2-43 refer to the data in Figure Q2-42. These questions may be used independently or as a group.

Question 43

Figure Q2-42 shows a patch clamp recording from the Shaker channel (ShB). What is the presumed molecular mechanism for inactivation of the channel? Figure Q2-42
(a) Several positively charged amino acids in S4
(b) Several negatively charge amino acids in S4
(c) The N-terminal 'ball-and-chain'
(d) A block by Na⁺ ions

Question 44

The structure of the selectivity filter is known.
A. Why are the electronegative carbonyl groups important for K⁺ to move across the filter?
B. How do electrostatic forces of K⁺ ions help move K⁺ across the filter?