Neurophysiology Questions
1. In the timeline of an action potential, which event below happens LAST?
- A. Sodium (Na+) channels close, and potassium (K+) begins leaving the cell
- B. The neuron reaches threshold
- C. The neuron becomes hyperpolarized
- D. Sodium (Na+) channels open, and sodium rushes into the cell
Show Answer
Correct answer: C
After sodium (Na+) has rushed into the cell in the rising phase of the action potential, the sodium channels close and potassium (K+) begins to leave the cell. This brings the neuron back to its resting membrane potential. The potassium channels, however, close gradually and allow enough positively-charged potassium to leave the neuron that the cell becomes briefly hyperpolarized. This creates a "relative refractory period," when it's less likely for the neuron to fire another action potential.
2. The axons of most neurons in the nervous system are wrapped in an insulating material called myelin. On myelinated axons, the myelin sheath is interrupted by a number of small unmyelinated gaps. What are the unmyelinated gaps called?
- A. internodes
- B. sodium-potassium pumps
- C. nodes of Ranvier
- D. inter-myelin channels
Show Answer
Correct answer: C
The unmyelinated gaps in a myelin sheath are called nodes of Ranvier, named after their discoverer: Louis-Antoine Ranvier. The nodes of Ranvier are rich in sodium channels, which open in response to an action potential traveling down an axon, allowing positive sodium ions to rush in and "recharge" the action potential as it moves along the axon.
3. The sodium-potassium pump is a protein pump found in the cell membrane of neurons (and other cells). Its main function is to transport _____ ions out of the cell and _____ ions into the cell.
- A. potassium, chloride
- B. sodium, potassium
- C. sodium, chloride
- D. potassium, sodium
Show Answer
Correct answer: B
The sodium-potassium pump uses the energy of ATP to move 3 sodium ions out of the cell and 2 potassium ions into the cell with each cycle of the pump. The actions of the pump help to ensure that sodium ions are more concentrated outside the cell and potassium ions are more concentrated inside the cell, which helps create the conditions that enable action potentials to occur.
4. The resting membrane potential of a typical neuron is closest to:
- A. +40 mV
- B. 0 mV
- C. -70 mV
- D. -90 mV
Show Answer
Correct answer: C
The resting membrane potential of a typical neuron is about -70 millivolts (mV), meaning the inside of the neuron is negatively charged relative to the outside. The negative resting potential is essential for the neuron’s ability to generate action potentials when stimulated.
5. The membrane potential of a neuron changes from -70 mV to -60 mV. This type of change is referred to as:
- A. depolarization
- B. hyperpolarization
- C. repolarization
- D. unpolarization
Show Answer
Correct answer: A
When the membrane potential becomes less negative (e.g., goes from –70 mV to –60 mV), this is called depolarization. Depolarization increases the likelihood a neuron will fire an action potential.
6. When a neuron is at rest (i.e., not in the process of firing an action potential), where is the concentration of sodium ions highest?
- A. inside the cell
- B. outside the cell
- C. in the nucleus of the cell
- D. sodium ions are evenly distributed on both sides of the cell membrane
Show Answer
Correct answer: B
At rest, a neuron maintains its resting membrane potential by keeping more sodium ions (Na⁺) outside the cell and more potassium ions (K⁺) inside. Thus, sodium concentration is much higher outside the neuron when it’s at rest.
7. Repolarization during a neuron's action potential is primarily caused by which ion movement?
- A. Potassium (K⁺) moving out of the cell through voltage-gated channels
- B. Sodium (Na⁺) moving into the cell through voltage-gated channels
- C. Chloride (Cl⁻) moving out of the cell through ligand-gated channels
- D. Calcium (Ca²⁺) moving into the cell through voltage-gated channels
Show Answer
Correct answer: A
The opening of voltage-gated K⁺ channels leads to K⁺ flowing out of the cell, driving the membrane potential back toward resting membrane potential.
8. What makes the nodes of Ranvier important to the propagation of action potentials?
- A. They store and release neurotransmitters
- B. They prevent the action potential from traveling backward along the axon
- C. They insulate the axon to increase conduction velocity
- D. They are densely populated with voltage-gated sodium channels
Show Answer
Correct answer: D
Nodes of Ranvier contain high concentrations of voltage-gated sodium channels, which allow action potentials to be regenerated at each node. This enables saltatory conduction, where the signal “jumps” from node to node, greatly increasing conduction speed along myelinated axons.
9. Which of the following best describes the meaning of the term long-term depression (LTD) in neuroscience?
- A. A long-lasting decrease in serotonin levels
- B. A long-lasting decrease in synaptic strength
- C. The inability of neurons to fire action potentials after prolonged stimulation
- D. A progressive loss of neurons in the hippocampus with aging
Show Answer
Correct answer: B
LTD is a process by which synaptic connections between neurons become weaker. It is the opposing process to long-term potentiation. Although the functions of LTD are not completely understood, it’s thought to be important to memory formation, perhaps by resetting previous synaptic changes to allow for new memories to be formed via long-term potentiation.
10. Where in a neuron are neurotransmitters typically stored before being released into the synaptic cleft?
- A. axon hillock
- B. dendrites
- C. axon terminals
- D. nucleus
Show Answer
Correct answer: C
Neurotransmitters are stored in small membrane-bound sacs called synaptic vesicles, which cluster in the presynaptic axon terminal. When an action potential arrives, calcium influx triggers vesicle fusion with the presynaptic membrane, releasing neurotransmitters into the synaptic cleft.
11. The most well-characterized mechanism underlying long-term depression (LTD) involves the removal of which receptors from the neuronal cell membrane?
- A. NMDA receptors
- B. GABA_A receptors
- C. AMPA receptors
- D. Dopamine D1 receptors
Show Answer
Correct answer: C
During long-term depression (LTD), AMPA receptors are removed from the postsynaptic membrane, which reduces the strength of synaptic transmission. This trafficking is a key cellular mechanism for weakening specific synapses and is central to synaptic plasticity and learning processes.
12. When a neuron is depolarized to threshold, which event below is primarily responsible for the rapid depolarization of the action potential?
- A. Voltage-gated sodium channels open
- B. Voltage-gated potassium channels open
- C. Sodium-potassium pump activity increases
- D. Chloride channels open
Show Answer
Correct answer: A
Once threshold is reached, voltage-gated sodium channels rapidly open, allowing Na⁺ ions to rush into the neuron. This inward sodium current drives the depolarization phase of the action potential.
13. Which of the following accurately describes the function of the sodium-potassium (Na⁺/K⁺) pump?
- A. It allows Na and K ions to passively diffuse along their concentration gradients
- B. It uses ATP to move 3 Na ions out and 2 K ions into the cell per cycle
- C. It uses ATP to move 3 Na ions in and 2 K ions out of the cell per cycle
- D. It creates an equal distribution of Na and K ions across the cell membrane
Show Answer
Correct answer: B
The main function of the Na⁺/K⁺ pump is to transport sodium ions out of the cell and potassium ions into the cell. It uses ATP to accomplish this, and each cycle of the pump causes 3 sodium ions to move out of the cell and 2 potassium ions to move into the cell.
14. When an action potential reaches the synaptic boutons, it triggers the influx of which ion that is essential for neurotransmitter release?
- A. Potassium
- B. Chloride
- C. Magnesium
- D. Calcium
Show Answer
Correct answer: D
When an action potential reaches the axon terminal, it depolarizes the membrane and opens voltage-gated calcium channels. The resulting calcium influx helps mobilize synaptic vesicles, preparing them for neurotransmitter release.
15. After a large turkey meal, you begin to feel very drowsy. Which physiological mechanism below is most directly responsible for that post-meal sleepiness?
- A. increased brain uptake of tryptophan from the turkey
- B. activation of the sympathetic nervous system during digestion
- C. increased parasympathetic activity promoting "rest and digest" functions
- D. elevated GABA release triggered by high fat foods
Show Answer
Correct answer: C
Parasympathetic activation ramps up after a large meal to support digestion, increasing gut blood flow and promoting relaxation (and potentially drowsiness). While dietary tryptophan can contribute slightly to post-meal tiredness, turkey isn’t unusually high in tryptophan compared to other meats, and the drowsiness people feel after a turkey dinner is far more related to the overall size and carbohydrate load of the meal than to turkey itself.
16. This positively-charged ion flows out of the neuron during the falling phase of an action potential, promoting repolarization of the cell:
- A. sodium
- B. magnesium
- C. potassium
- D. calcium
Show Answer
Correct answer: C
Potassium (K⁺) ions flow out of the neuron during the falling (repolarization) phase of the action potential. This outward movement of positive charge helps restore the membrane potential toward its resting state after depolarization.
17. What is the term for the membrane potential at which depolarization opens voltage-gated sodium channels and triggers an action potential?
- A. threshold
- B. resting membrane potential
- C. refractory phase
- D. depolarization point
Show Answer
Correct answer: A
When neurotransmitters interacting with receptors causes repeated depolarization of the neuron, eventually the neuron reaches what is known as its threshold membrane potential. When threshold is reached, a large number of sodium channels open, allowing positively charged sodium ions into the cell and triggering an action potential.
18. The absolute refractory period of an action potential is primarily caused by which of the following?
- A. voltage-gated sodium channels becoming inactivated
- B. decreased sodium concentration outside the neuron
- C. breakdown of neurotransmitters in the synaptic cleft
- D. failure of ligand-gated ion channels to open
Show Answer
Correct answer: A
For a brief period after the initiation of an action potential, voltage-gated sodium channels become unresponsive and can't be activated. We call this period the absolute refractory period because a neuron will not be able to fire another action potential during this phase.
19. The inability of a neuron to generate another action potential during the absolute refractory period is primarily due to:
- A. closure of voltage-gated potassium channels
- B. reduced neurotransmitter release at the synapse
- C. temporary failure of the sodium–potassium pump
- D. inactivation of voltage-gated sodium channels
Show Answer
Correct answer: D
For a brief period after the initiation of the action potential, voltage-gated sodium channels become unresponsive and can’t be activated. We call this period the absolute refractory period, because a neuron will not be able to fire another action potential during this phase.
20. The sodium-potassium pump is a protein pump whose main function is to transport sodium ions out of the cell and potassium ions into the cell. Each cycle of the pump moves ____ sodium ions out of the cell and ____ potassium ions into the cell.
- A. 1, 3
- B. 2, 3
- C. 3, 2
- D. 3, 1
Show Answer
Correct answer: C
Each cycle of the pump moves 3 sodium ions out of the cell and 2 potassium ions into the cell. The actions of the pump help to ensure that sodium ions are more concentrated outside the cell and potassium ions are more concentrated inside the cell.
21. Which of the following supplies the energy needed for the sodium-potassium pump to function?
- A. sodium moving down its concentration gradient
- B. breakdown of ATP
- C. changes in membrane potential
- D. osmosis of water across the cell membrane
Show Answer
Correct answer: B
The sodium-potassium pump is a large membrane-associated enzyme that uses the energy of adenosine triphosphate, or ATP, to transport sodium and potassium ions across the cell membrane.
22. In NMDA receptor-dependent long-term potentiation (LTP), activation of NMDA receptors leads to an increase in the number of which type of receptor at the postsynaptic membrane?
- A. GABA-A receptors
- B. NMDA receptors
- C. AMPA receptors
- D. dopamine receptors
Show Answer
Correct answer: C
In NMDA receptor-dependent LTP, calcium influx through activated NMDA receptors initiates signaling cascades that promote the insertion of AMPA receptors into the postsynaptic membrane, enhancing synaptic strength.
23. At a neuron’s resting membrane potential, where are potassium ions more concentrated: inside or outside the cell?
- A. inside
- B. outside
Show Answer
Correct answer: A
When a neuron is at rest, potassium ions and organic anions are more concentrated inside the cell, while sodium and chloride ions are more concentrated outside the cell.
24. Which family of proteins is primarily responsible for getting synaptic vesicles ready to fuse with the presynaptic membrane during neurotransmitter release?
- A. SNARE proteins
- B. neurofilaments
- C. voltage-gated potassium channels
- D. kinesin motor proteins
Show Answer
Correct answer: A
SNARE proteins (including synaptobrevin/VAMP, syntaxin, and SNAP-25) form a complex that docks and primes synaptic vesicles and then drives membrane fusion during neurotransmitter release.
25. Which of the following best describes the primary mechanism by which GABA-B receptor activation inhibits neuronal activity?
- A. opening of ligand-gated chloride channels
- B. increased sodium influx through voltage-gated channels
- C. direct phosphorylation of ionotropic glutamate receptors
- D. activation of G proteins that open potassium channels
Show Answer
Correct answer: D
GABA-B receptors are metabotropic (or G protein-coupled) receptors; when activated they frequently cause the opening of potassium channels. These channels allow positively charged potassium ions to flow out of the neuron, making the neuron hyperpolarized and less likely to fire an action potential.
26. Which part of a neuron integrates incoming signals to determine whether an action potential will be initiated?
- A. dendrites
- B. axon
- C. synaptic boutons
- D. axon hillock
Show Answer
Correct answer: D
When information is received at the dendrites, it causes changes in the electrical properties of the cell, and the axon hillock is a region where those changes are integrated to determine if the incoming signals are strong enough for the neuron to initiate its own action potential.
27. Which of the following ion movements would help depolarize a neuron’s membrane to threshold?
- A. potassium leaving the neuron
- B. sodium entering the neuron
- C. chloride entering the neuron
- D. calcium leaving the neuron
Show Answer
Correct answer: B
Sodium entering the neuron brings positive charge into the cell, making the membrane potential less negative and moving it closer to threshold.
28. In the best-known mechanism of long-term potentiation (LTP), removal of which ion from the NMDA receptor channel initiates the process that ultimately leads to insertion of additional AMPA receptors into the postsynaptic membrane?
- A. sodium
- B. magnesium
- C. calcium
- D. potassium
Show Answer
Correct answer: B
NMDA receptors are not activated by low levels of glutamate release because the ion channel of an NMDA receptor is blocked by a magnesium ion. If frequent action potentials cause greater stimulation of AMPA receptors, however, this will cause the postsynaptic neuron to depolarize, which eventually causes the voltage-dependent magnesium blockage of the NMDA receptor to be removed.
29. After an action potential, the membrane potential temporarily becomes more negative than the resting membrane potential. Which term below best describes this phenomenon?
- A. depolarization
- B. hyperpolarization
- C. repolarization
- D. antipolarization
Show Answer
Correct answer: B
After the falling phase of the action potential, the neuron returns to resting membrane potential but actually to overshoots it, and the cell becomes more negative than resting membrane potential. This is referred to as hyperpolarization. During this phase, known as the refractory period, it is very difficult to cause the neuron to fire again.
30. The rapid conduction of an action potential along a myelinated axon by "jumping" from one node of Ranvier to the next is known as:
- A. graded conduction
- B. continuous conduction
- C. saltatory conduction
- D. synaptic conduction
Show Answer
Correct answer: C
Saltatory conduction is the propagation of an action potential along a myelinated axon by effectively "jumping" from one node of Ranvier to the next. This process greatly increases the speed of nerve impulse transmission compared to conduction along unmyelinated axons.
