Question 1

Synaptic vesicles discharge their contents by exocytosis at the
A)dendrite.
B)axon hillock.
C)nodes of Ranvier.
D)postsynaptic membrane.
E)presynaptic membranE.

Accepted Answer

Synaptic vesicles store and release neurotransmitters at the presynaptic membrane. Exocytosis of vesicles occurs at the presynaptic membrane in response to an action potential, leading to the release of neurotransmitters into the synaptic cleft. The dendrites, axon hillock, nodes of Ranvier, and postsynaptic membrane all play important roles in transmitting or receiving signals but are not directly involved in the exocytosis of synaptic vesicles.

Question 2

Complete the Nernst Equation by deciding what symbol belongs in the first blank. _________ = 60 mV log₁₀ ([X_{extracellular}/X_{intracellular}]). A)the equilibrium potential B)the membrane potential C)the action potential D)resting potential E)refractory potential

Accepted Answer

The Nernst Equation is commonly used to calculate the equilibrium potential of an ion, which is the membrane potential at which the net flow of that ion is zero. The equation takes into account the concentrations of the ion inside and outside the cell, and the charge of the ion. Choice A is the only option that specifically mentions the equilibrium potential in the context of the Nernst Equation.

Question 3

If you applied a toxin that blocked non-voltage-gated potassium channels (i.e. ,the potassium "leak channels")in a resting neuron,it would cause the membrane potential to be
A)less negative.
B)more negative.
C)No change would be observed.

Accepted Answer

Non-voltage-gated potassium channels known as the potassium "leak channels" play a crucial role in maintaining the resting membrane potential. These channels allow potassium ions to move freely out of the cell, and as a result, the inside of the cell becomes more negative. Blocking these channels will result in fewer potassium ions flowing out of the cell, reducing the distance between the inside and outside of the cell, and making the membrane potential less negative.

Question 4

After an action potential is triggered,the rapid increase in membrane potential can be attributed to
A)the direction reversal of the sodium/potassium pump.
B)the closing of sodium leak channels.
C)the opening of the activation gates of voltage-gated sodium channels.
D)the closing of potassium leak channels.
E)the opening of the voltage-gated potassium channels.

Accepted Answer

The rapid increase in membrane potential following an action potential is due to the opening of the activation gates of voltage-gated sodium channels, which allows an influx of sodium ions into the cell. This generates a positive feedback loop, causing even more activation gates to open and more sodium ions to enter, leading to depolarization of the membrane potential.

Question 5

It is accurate to say that neural transmission across nearly all mammalian synaptic clefts is the result of A)neural impulses involving the flow of K⁺ and Na⁺ across the cleft. B)neural impulses traveling across the gap as electrical currents. C)neural impulses causing the release of chemicals that diffuse across the cleft. D)neural impulses traveling across the cleft in both directions. E)the calcium within the axons and dendrites of nerves adjacent to a synapse acting as the neurotransmitter.

Accepted Answer

The majority of neural transmission is mediated through the release of chemical neurotransmitters that diffuse across the synaptic cleft and bind to receptors on the postsynaptic membrane, stimulating or inhibiting neural activity. Electrical currents and specific ion flows noted in choices A and B play a role in the process, but are not the primary mechanism for transmission. Choice D is incorrect, as impulses typically travel in one direction across the synaptic cleft. Choice E is also incorrect, as calcium ions are not neurotransmitters; they have a role in the release of neurotransmitters, but do not themselves participate in transmission across the cleft.

Question 6

Identify the point in time during an action potential when a positive feedback process is occurring in a neuron.
A)when the neuron is at rest
B)as the neuron is being depolarized and passes the threshold potential
C)after the peak depolarization of the action potential when it is rapidly repolarizing
D)during the undershoot phase when the neuron is slightly hyperpolarized relative to the resting potential
E)A positive feedback process is occurring at all the time points given.

Accepted Answer

A positive feedback process occurs during the depolarization phase, specifically after the threshold potential is reached. This positive feedback is due to the opening of voltage-gated sodium channels, leading to a rapid influx of sodium ions, which further depolarizes the membrane and triggers the opening of more sodium channels. This process continues until the peak of the action potential is reached.

Question 7

Propose a valid reason to explain why is it critical that the K⁺ channel activation gate responds slightly slower to depolarization than the Na⁺ channel activation gate. A)If both gates showed identical response times,movements of Na⁺ and K⁺ ions would cancel out each other's effects on membrane potential changes. B)If both gates showed identical response times,movements of Na⁺ and K⁺ ions would magnify each other's effects on membrane potential changes,creating dangerously large action potentials. C)It is not critical and there would be no change in action potential characteristics if this difference in response time did not exist. D)The conformational change in one gate is necessary to trigger the activation of the other.

Accepted Answer

The slower response of the potassium (K⁺) channel compared to the sodium (Na⁺) channel is crucial for the proper sequence of depolarization and repolarization during an action potential. If both channels opened simultaneously, the influx of Na+ ions and the efflux of K+ ions would occur at the same time, negating each other's effects on changing the membrane potential, which would disrupt the generation of action potentials.

Question 8

Predict the expected consequence(s)of applying a toxin that blocks voltage-gated Ca²⁺ channels in a neuron. A)No resting membrane potential would be observed (i.e. ,measures at 0 mV). B)A rapid increase in membrane potential at threshold voltage would not occur. C)Membrane potential would increase rapidly to peak with an action potential,but would not decrease immediately afterwards. D)The neuron would become hyperpolarizeD. E)Neuron conducts action potentials normally,but would not transmit these potentials across chemical synapses.

Accepted Answer

Blocking voltage-gated calcium channels would primarily affect the release of neurotransmitters at the synapse, which is essential for transmitting action potentials across chemical synapses. The other processes mentioned (resting membrane potential, rapid increase in membrane potential at threshold, and repolarization after an action potential) are mainly dependent on sodium and potassium channels, not calcium channels.

Question 9

When a neuron undergoes a change in membrane potential that is proportional to (i.e. ,varies depending on)the strength of the stimulus given to that neuron,this is referred to as a/an
A)equilibrium potential.
B)action potential.
C)resting potential.
D)reversal potential.
E)graded potential.

Accepted Answer

Graded potentials are changes in membrane potential that vary in strength based on the strength of the stimulus. This is in contrast to action potentials, which have a fixed threshold for initiation and always have the same magnitude. Equilibrium potential refers to the membrane potential at which there is no net movement of a particular ion across the membrane. Resting potential refers to the membrane potential of a neuron when it is not undergoing any synaptic inputs. Reversal potential refers to the membrane potential at which an ion will not flow across the membrane when the electrochemical gradients for that ion are equal and opposite.

Question 10

The synaptic cleft is most accurately described as
A)a deep furrow in a postsynaptic cell where signals are received.
B)specialized channels in the presynaptic membrane that allow the passage of ions.
C)the narrow extracellular space between the presynaptic and postsynaptic neurons at the synapse.
D)recesses in the postsynaptic neuron membrane where neurotransmitters binD.
E)the area of neuronal membrane between the dendrites and the axon hillock.

Accepted Answer

The synaptic cleft is the narrow extracellular space between the presynaptic and postsynaptic neurons at the synapse. It is the space where neurotransmitters are released by the presynaptic neuron and received by receptors on the postsynaptic neuron.

Question 11

The period following an action potential during which a neuron cannot be stimulated to generate another action potential is referred to as
A)the refractory period.
B)the threshold period.
C)the resting period.
D)the inactivation perioD.
E)the critical period.

Accepted Answer

The refractory period is the time after an action potential during which a neuron cannot be stimulated to generate another action potential. This is due to the inactivation of sodium channels and the restoration of the resting membrane potential. During the refractory period, the neuron is unable to respond to any stimulus, no matter how strong, until it has returned to its resting state.

Question 12

Increasing the flow of Na⁺ ions into a neuron at rest (-70 mV initially)would trigger A)hyperpolarization. B)depolarization. C)repolarization. D)active transport. E)None of the choices are correct.

Accepted Answer

Increasing the flow of Na+ and decreasing the flow of K+ into a neuron at rest will cause depolarization, bringing the neuron closer to the threshold for an action potential to occur.

Question 13

Identify the key feature of the action potential that ensures it will travel only one direction. A)the activation state of the voltage-gated Na⁺ channel B)the inactivation state of the voltage-gated Na⁺ channel C)the activation state of the voltage-gated K⁺ channel D)the inactivation state of the voltage-gated K⁺ channel E)the temporary cessation in activity of the Na⁺/K⁺ pump

Accepted Answer

The inactivation state of the voltage-gated Na⁺ channel ensures that the action potential travels only one direction. Once the channel has been activated and sodium ions have entered the cell, the channel becomes inactivated, preventing further sodium ions from entering the cell in the same location. This allows the action potential to move in one direction down the axon.

Question 14

The ion that increases its intracellular concentration in order to trigger the release of neurotransmitters is _____. A)Ca²⁺ B)Mg²⁺ C)HCO₃^- D)K⁺ E)Cl^-

Accepted Answer

The ion that increases its intracellular concentration to trigger the release of neurotransmitters is calcium (Ca2+). Option A represents Ca2+ with its proper charge and symbol, making it the correct answer. Option B is magnesium (Mg2+), which is not involved in neurotransmitter release. Option C is bicarbonate ion (HCO3-), which does not play a role in triggering neurotransmitter release. Option D is potassium (K+), which does not have a direct role in neurotransmitter release. Option E is chloride (Cl-), which can modulate neurotransmitter release but does not trigger it.

Question 15

The level of depolarization at which an action potential will be triggered is referred to as the
A)resting potential.
B)membrane potential.
C)cationic potential.
D)refractory potential.
E)threshold potential.

Accepted Answer

The level of depolarization at which an action potential will be triggered is referred to as the threshold potential.

Question 16

An excitatory neurotransmitter will produce an ______ that will ____ the postsynaptic neuron.
A)EPSP,depolarize
B)EPSP,hyperpolarize
C)IPSP,depolarize
D)IPSP,hyperpolarize
E)IPSP,not affect

Accepted Answer

An excitatory neurotransmitter, such as glutamate, will produce an EPSP (excitatory postsynaptic potential) which will depolarize the postsynaptic neuron and make it more likely to fire an action potential.

Question 17

Graded potentials are particularly important for conveying stimulus intensity in
A)sensory neurons.
B)motor neurons.
C)interneurons.
D)skeletal muscle cells.
E)Schwann cells.

Accepted Answer

Graded potentials are important in conveying stimulus intensity in sensory neurons, as they allow the neuron to respond to the strength of a stimulus and translate it into an electrical signal that can be transmitted to the central nervous system. In comparison, motor neurons primarily rely on action potentials to convey information to muscles, while interneurons act as connectors between different neurons and their graded potentials are not typically involved in transmitting information to other neurons. Skeletal muscle cells and Schwann cells do not generate electrical signals that would require graded potentials.

Question 18

Pufferfish (Fugu)are a delicacy in Japan,but must be cleaned very carefully as their liver contains tetrodotoxin which blocks voltage-gated Na⁺ channels.Imagine you are testing for the presence of this toxin using a neuron in a dish.You apply an electrical stimulus to the neuron that should produce an action potential.What will you observe if tetrodotoxin levels are high enough to block the neuron's voltage-gated Na⁺ channels? A)The neuron will exhibit a slow depolarization even before the stimulus is applied,followed by a normal action potential. B)The neuron will exhibit a slow hyperpolarization even before the stimulus is applied. C)The neuron will show a normal resting potential,but will not exhibit depolarization when the stimulus is applied. D)The neuron will exhibit rapid depolarization,but will not repolarize. E)The neuron will depolarize normally,but then become hyperpolarized such that the membrane potential is much lower than usual.

Accepted Answer

If tetrodotoxin levels are present, it will block voltage-gated Na+ channels, preventing the depolarization necessary for an action potential to occur. Therefore, the neuron will show a normal resting potential but will not exhibit depolarization when the stimulus is applied.

Question 19

Indicate the mechanism responsible for the rapid depolarization that occurs as the "upsweep" of membrane potential peaks during the action potential. A)closing of the voltage-gated Na⁺ channel activation gates B)closing of the voltage-gated Na⁺ channel inactivation gates C)opening of the voltage-gated K⁺ channel gates D)both opening of the K⁺ channel gates and closing of the Na⁺ channel inactivation gates E)both opening of the K⁺ channel gates and closing of the Na⁺ channel activation gates

Accepted Answer

The rapid depolarization during the action potential is due to the opening of voltage-gated potassium (K⁺) channels and the closing of voltage-gated sodium (Na⁺) channel inactivation gates. This allows for an efflux of potassium ions and prevents further influx of sodium ions, leading to repolarization of the cell membrane.

Question 20

Saltatory conduction is a term applied to the "jumping" movement of action potentials
A)across electrical synapses.
B)along the postsynaptic membrane from dendrite to axon hillock.
C)in two directions at the same time.
D)from one neuron to another.
E)along myelinated axons.

Accepted Answer

Saltatory conduction refers to the faster conduction of an action potential along myelinated axons. The action potential appears to jump from one node of Ranvier to the next rather than traveling continuously along the axon. This jumping results in faster conduction because the action potential is able to "skip" the sections of the axon that are covered in myelin and only depolarize the unmyelinated nodes of Ranvier.

Quiz 32: Neuroscience I: Structure, Function, and Evolution of Nervous Systems

Synaptic vesicles discharge their contents by exocytosis at the

Complete the Nernst Equation by deciding what symbol belongs in the first blank. _________ = 60 mV log₁₀ ([X_{extracellular}/X_{intracellular}]) .

If you applied a toxin that blocked non-voltage-gated potassium channels (i.e. ,the potassium "leak channels") in a resting neuron,it would cause the membrane potential to be

After an action potential is triggered,the rapid increase in membrane potential can be attributed to

It is accurate to say that neural transmission across nearly all mammalian synaptic clefts is the result of

Identify the point in time during an action potential when a positive feedback process is occurring in a neuron.

Propose a valid reason to explain why is it critical that the K⁺ channel activation gate responds slightly slower to depolarization than the Na⁺ channel activation gate.

Predict the expected consequence(s) of applying a toxin that blocks voltage-gated Ca²⁺ channels in a neuron.

When a neuron undergoes a change in membrane potential that is proportional to (i.e. ,varies depending on) the strength of the stimulus given to that neuron,this is referred to as a/an

The synaptic cleft is most accurately described as

The period following an action potential during which a neuron cannot be stimulated to generate another action potential is referred to as

Increasing the flow of Na⁺ ions into a neuron at rest (-70 mV initially) would trigger

Identify the key feature of the action potential that ensures it will travel only one direction.

The ion that increases its intracellular concentration in order to trigger the release of neurotransmitters is _____.

The level of depolarization at which an action potential will be triggered is referred to as the

An excitatory neurotransmitter will produce an __ that will the postsynaptic neuron.

Graded potentials are particularly important for conveying stimulus intensity in

Indicate the mechanism responsible for the rapid depolarization that occurs as the "upsweep" of membrane potential peaks during the action potential.

Saltatory conduction is a term applied to the "jumping" movement of action potentials