Deck 48: Neurons, Synapses, and Signalling

Question 1

Refer to the following graph of an action potential to answer the question. The membrane potential is closest to the equilibrium potential for potassium at label ________.

A) A
B) B
C) C
D) D Disallow randomisation

Answer 1

D

Question 2

In a resting potential, an example of a cation that is more abundant as a solute in the cytosol of a neuron than it is in the interstitial fluid outside the neuron is ________.

A) Cl-
B) Ca⁺⁺
C) Na⁺
D) K⁺

Answer 2

D

Question 3

The concentrations of ions are very different inside and outside a nerve cell due to ________.

A) osmosis
B) diffusion
C) sodium-potassium pumps
D) symports and antiports

Answer 3

C

Question 4

The point of connection between two communicating neurons is called the ________.

A) axon hillock
B) dendrite
C) synapse
D) cell body

Question 5

The operation of the sodium-potassium pump moves ________.

A) sodium and potassium ions into the cell
B) sodium and potassium ions out of the cell
C) sodium ions into the cell and potassium ions out of the cell
D) sodium ions out of the cell and potassium ions into the cell

Question 6

The three stages of information processing in animals include ________.

A) chemical senses, mechanoreception, and vision
B) dendrites, a cell body, and an axon
C) a presynaptic cell, neurotransmitters, and a postsynaptic cell
D) sensory reception, an integrating centre, and effectors (motor neurons)

Question 7

The motor (somatic nervous) system can alter the activities of its targets, the skeletal muscle fibres, because ________.

A) it is electrically coupled by gap junctions to the muscles
B) its signals bind to receptor proteins on the muscles
C) its signals reach the muscles via the blood
D) it is connected to the internal neural network of the muscles

Question 8

Most of the neurons in the human central nervous system are ________.

A) sensory neurons
B) motor neurons
C) interneurons
D) peripheral neurons

Question 9

Refer to the following graph of an action potential to answer the question. The membrane's permeability to sodium ions is greatest at label ________.

A) A
B) B
C) C
D) D Disallow randomisation

Question 10

$$\begin{array} { | l | l | l | } \hline & \begin{array} { l } \bf{ Extracellular-concentration } \\( \bf { mM } )\end{array} & \begin{array} { l } \bf { Intracellular-concentration } \\( \bf { mM } )\end{array} \\\bf{ Inn }\\\hline \mathbf { Na } ^ { + } & 300 & 50 \\\hline \mathbf { K } ^ { + } & 40 & 350 \\\hline\end{array}$$

-Calculate the equilibrium potential for sodium. Assume a temperature of 37°C.

A) +48.2 mV
B) 0.0 mV
C) -58.4 mV
D) -80.0 mV

Question 11

Although the membrane of a "resting" neuron is highly permeable to potassium ions, its membrane potential does not exactly match the equilibrium potential for potassium because the neuronal membrane is also ________.

A) slightly permeable to sodium ions
B) fully permeable to calcium ions
C) impermeable to sodium ions
D) highly permeable to chloride ions

Question 12

A researcher uses the chemical inhibitor cyanide to reduce ATP production in a neuron. What would be one effect of preventing ATP production?

A) The sodium and potassium channels would all be closed.
B) The membrane would become more permeable to sodium.
C) Disruption to the normal "resting" distribution of potassium and sodium ions.
D) A physical breakdown of the plasma membrane would occur.

Question 13

The membrane potential in which there is no net movement of the ion across the membrane is called the ________.

A) graded potential
B) threshold potential
C) equilibrium potential
D) action potential

Question 14

In a simple synapse, neurotransmitter chemicals are released by ________.

A) the presynaptic membrane
B) axon hillocks
C) cell bodies
D) ducts on the smooth endoplasmic reticulum

Question 15

Two fundamental concepts about the ion channels of a "resting" neuron are that the channels ________.

A) are always open, but the concentration gradients of ions frequently change
B) are always closed, but ions move closer to the channels during excitation
C) are open or closed depending on their type, and are specific as to which ion can traverse them
D) open in response to stimuli, and then close simultaneously, in unison

Question 16

$$\begin{array} { | l | l | l | } \hline & \begin{array} { l } \bf{ Extracellular-concentration } \\( \bf { mM } )\end{array} & \begin{array} { l } \bf { Intracellular-concentration } \\( \bf { mM } )\end{array} \\\bf{ Inn }\\\hline \mathbf { Na } ^ { + } & 300 & 50 \\\hline \mathbf { K } ^ { + } & 40 & 350 \\\hline\end{array}$$

-Calculate the equilibrium potential for potassium. Assume a temperature of 37°C.

A) +48.2 mV
B) 0.0 mV
C) -58.4 mV
D) -80.0 mV

Question 17

Which of the following ions is most likely to cross the plasma membrane of a resting neuron?

A) K⁺
B) Na⁺
C) Ca2+
D) Cl-

Question 18

The Nernst equation specifies the equilibrium potential for a particular ion. This equilibrium potential is a function of ________.

A) hydrostatic pressure
B) ion concentration gradient
C) osmotic gradient
D) temperature (thermal) gradient

Question 19

In a simple synapse, neurotransmitter chemicals are received by ________.

A) the presynaptic membrane
B) dendrites
C) axon hillocks
D) cell bodies

Question 20

If you experimentally increase the concentration of Na⁺ outside a cell while maintaining other ion concentrations as they were, what would happen to the cell's membrane potential?

A) The membrane potential would become more negative.
B) The membrane potential would become more positive.
C) The membrane potential would be unaffected.
D) The answer depends on the thermodynamic potential.

Question 21

The "threshold" potential of a membrane is the ________.

A) lowest frequency of action potentials a neuron can produce
B) minimum hyperpolarisation needed to prevent the occurrence of action potentials
C) minimum depolarisation needed to operate the voltage-gated sodium and potassium channels
D) peak amount of depolarisation seen in an action potential

Question 22

Why do Na⁺ ions enter the cell when voltage-gated Na⁺ channels are opened in neurons?

A) because the Na⁺ concentration is much lower outside the cell than it is inside
B) because the Na⁺ ions are actively transported by the sodium-potassium pump into the cell
C) because the Na⁺ concentration is much higher outside the cell than it is inside, and the Na⁺ ions are attracted to the negatively charged interior
D) because the Na⁺ concentration is much higher outside the cell than it is inside, and the Na⁺ ions are actively transported by the sodium-potassium pump into the cell

Question 23

Which of the following statements about action potentials is correct?

A) Action potentials for a given neuron vary in magnitude.
B) Action potentials for a given neuron vary in duration.
C) Action potentials are propagated down the length of the axon.
D) Movement of ions during the action potential occurs mostly through the sodium pump.

Question 24

Opening all of the sodium channels on an otherwise typical neuron, with all other ion channels closed (which is an admittedly artificial setting), should move its membrane potential to ________.

A) -90 mV
B) 0 mV
C) equilibrium potential for sodium
D) The membrane potential would not change, only the ion concentrations would change.

Question 25

The fastest possible conduction velocity of action potentials is observed in ________.

A) thin, unmyelinated neurons
B) thin, myelinated neurons
C) thick, unmyelinated neurons
D) thick, myelinated neurons

Question 26

Refer to the following graph of an action potential to answer the question. The minimum graded depolarisation needed to operate the voltage-gated sodium and potassium channels is indicated by the label ________.

A) A
B) B
C) D
D) E Disallow randomisation

Question 27

Action potentials move along axons ________.

A) more slowly in axons of large than in small diameter
B) by activating the sodium-potassium "pump" at each point along the axonal membrane
C) more rapidly in myelinated than in unmyelinated axons
D) by reversing the concentration gradients for sodium and potassium ions

Question 28

After the depolarisation phase of an action potential, the resting potential is restored by ________.

A) the opening of voltage-gated potassium channels and the inactivation of sodium channels
B) a decrease in the membrane's permeability to potassium and chloride ions
C) a brief inhibition of the sodium-potassium pump
D) the opening of more voltage-gated sodium channels

Question 29

Why are action potentials usually conducted in one direction?

A) The nodes of Ranvier conduct potentials in one direction.
B) The brief refractory period prevents reopening of voltage-gated sodium channels.
C) The axon hillock has a higher membrane potential than the terminals of the axon.
D) Voltage-gated channels for both Na⁺ and K⁺ open in only one direction.

Question 30

The "undershoot" phase of hyperpolarisation is due to ________.

A) slow opening of voltage-gated sodium channels
B) sustained opening of voltage-gated potassium channels
C) rapid opening of voltage-gated calcium channels
D) slow restorative actions of the sodium-potassium ATPase

Question 31

A neurophysiologist is investigating nerve reflexes in two different animals: a crab and a fish. Action potentials are found to pass more rapidly along the fish's neurons. What is the most likely explanation?

A) The fish's axons are smaller in diameter; small axons transmit action potentials faster than large axons do.
B) Unlike the crab, the fish's axons are wrapped in myelin.
C) There are more ion channels in the axons of the crab compared with fish axons.
D) Unlike the crab, the fish's axons are wrapped in myelin, and the fish's axons are smaller in diameter; small axons transmit action potentials faster than large axons do.

Question 32

For a neuron with an initial membrane potential at -70 mV, an increase in the movement of potassium ions out of that neuron's cytoplasm would result in the ________.

A) depolarisation of the neuron
B) hyperpolarisation of the neuron
C) replacement of potassium ions with sodium ions
D) replacement of potassium ions with calcium ions

Question 33

If you experimentally increase the concentration of K⁺ inside a cell while maintaining other ion concentrations as they were, what would happen to the cell's membrane potential?

A) The membrane potential would become more negative.
B) The membrane potential would become less negative.
C) The membrane potential would remain the same.
D) The membrane potential would first become more negative and then less negative.

Question 34

Refer to the following graph of an action potential to answer the question. At label ________, the cell is not hyperpolarised; however, repolarisation is in progress, as the sodium channels are inactivated or becoming inactivated, and many potassium channels have opened.

A) B
B) C
C) D
D) E Disallow randomisation

Question 35

Pyrethroid insecticides prevent the voltage-gated sodium channels of insects from inactivating. Neurons that were exposed to pyrethroids would ________.

A) become hyperpolarised during an action potential
B) not repolarise during an action potential
C) not be able to open potassium channels
D) not release neurotransmitter molecules

Question 36

A graded hyperpolarisation of a membrane can be induced by ________.

A) increasing its membrane's permeability to Na⁺
B) decreasing its membrane's permeability to Cl-
C) increasing its membrane's permeability to Ca⁺⁺
D) increasing its membrane's permeability to K⁺

Question 37

Refer to the following graph of an action potential to answer the question. The neuronal membrane is at its resting potential at label ________.

A) A
B) B
C) D
D) E Disallow randomisation

Question 38

Conduction and refractory periods (states) are typical of ________.

A) action potentials
B) graded hyperpolarisations
C) excitatory postsynaptic potentials
D) threshold potentials

Question 39

Action potentials are normally carried in only one direction: from the axon hillock toward the axon terminals. If you experimentally depolarise the middle of the axon to threshold, using an electronic probe, then ________.

A) no action potential will be initiated
B) an action potential will be initiated and proceed only in the normal direction toward the axon terminal
C) an action potential will be initiated and proceed only back toward the axon hillock
D) two action potentials will be initiated, one going toward the axon terminal and one going back toward the hillock

Question 40

What would probably happen if a long neuron had one continuous myelin sheath down the length of the axon with no nodes of Ranvier?

A) The action potential would be propagated nearly instantaneously to the synapse.
B) There could be no action potential generated at the axon hillock.
C) The signal would fade because it is not renewed by the opening of more sodium channels.
D) Only potassium could move across the membrane, but not sodium.

Question 41

Tetrodotoxin blocks voltage-gated sodium channels, and ouabain blocks sodium-potassium pumps. If you added both tetrodotoxin and ouabain to a solution containing neural tissue, what responses would you expect?

A) immediate loss of resting potential
B) immediate loss of action potential with gradual shift of resting potential
C) slow decrease of resting potential and action potential amplitudes
D) No effect; the substances counteract each other.

Question 42

The activity of acetylcholine in a synapse is terminated by its ________.

A) diffusion across the presynaptic membrane
B) active transport across the postsynaptic membrane
C) diffusion across the postsynaptic membrane
D) degradation on the postsynaptic membrane

Question 43

In multiple sclerosis, the myelin sheaths around the axons of the brain and spinal cord are damaged and demyelination results. How does this disease manifest at the level of the action potential?
I) Action potentials move in the opposite direction on the axon.
II) Action potentials move more slowly along the axon.
III) No action potentials are transmitted.

A) only I
B) only II
C) only III
D) only II and III

Question 44

When two excitatory postsynaptic potentials (EPSPs) occur at a single synapse so rapidly in succession that the postsynaptic neuron's membrane potential has not returned to the resting potential before the second EPSP arrives, the EPSPs add together producing ________.

A) temporal summation
B) spatial summation
C) tetanus
D) the refractory state

Question 45

Which of the following will increase the speed of an action potential moving down an axon?
I) Action potentials move faster in wider axons.
II) Action potentials move faster in axons lacking potassium ion channels.
III) Action potentials move faster in myelinated axons.

A) only I and II
B) only II and III
C) only I and III
D) I, II, and III

Question 46

An inhibitory postsynaptic potential (IPSP) occurs in a membrane made more permeable to ________.

A) potassium ions
B) sodium ions
C) ATP
D) all neurotransmitter molecules

Question 47

The botulinum toxin, which causes botulism, reduces the synaptic release of ________.

A) acetylcholine
B) endorphin
C) nitric oxide
D) gamma-aminobutyric acid (GABA)

Question 48

The following steps refer to various stages in transmission at a chemical synapse.
1) Neurotransmitter binds with receptors associated with the postsynaptic membrane.
2) Calcium ions rush into neuron's cytoplasm.
3) An action potential depolarises the membrane of the presynaptic axon terminal.
4) The ligand-gated ion channels open.
5) The synaptic vesicles release neurotransmitter into the synaptic cleft.
Which sequence of events is correct?

A) 1 → 2 → 3 → 4 → 5
B) 2 → 3 → 5 → 4 → 1
C) 3 → 2 → 5 → 1 → 4
D) 4 → 3 → 1 → 2 → 5

Question 49

An example of ligand-gated ion channels is ________.

A) the spreading of action potentials in the heart
B) acetylcholine receptors at the neuromuscular junction
C) cAMP-dependent protein kinases
D) action potentials on the axon

Question 50

The amino acid that operates at most inhibitory synapses in the brain is ________.

A) acetylcholine
B) endorphin
C) nitric oxide
D) gamma-aminobutyric acid (GABA)

Question 51

The heart rate of a vertebrate will decrease in response to the arrival of ________.

A) acetylcholine
B) endorphin
C) nitric oxide
D) gamma-aminobutyric acid (GABA)

Question 52

Of those listed, which event occurs first following a depolarising stimulus applied to the presynaptic membrane of an axon terminal?

A) Voltage-gated calcium channels in the membrane open.
B) Synaptic vesicles fuse with the membrane.
C) The postsynaptic cell produces an action potential.
D) Ligand-gated channels open, allowing neurotransmitters to enter the synaptic cleft.

Question 53

Neurotransmitters categorised as inhibitory are expected to ________.

A) act independently of their receptor proteins
B) close potassium channels
C) open sodium channels
D) hyperpolarise the membrane

Question 54

How could you increase the magnitude of excitatory postsynaptic potentials (EPSPs) generated at a synapse?

A) Increase sodium-potassium pump activity.
B) Increase K⁺ permeability.
C) Increase Na⁺ permeability.
D) All of the listed responses are correct.

Question 55

Acetylcholine released into the junction between a motor neuron and a skeletal muscle binds to a sodium/potassium channel and opens it. This is an example of ________.

A) a voltage-gated channel
B) a ligand-gated channel
C) a second-messenger-gated channel
D) a chemical that inhibits action potentials

Question 56

Neurotransmitters are released from axon terminals via ________.

A) osmosis
B) active transport
C) diffusion
D) exocytosis

Question 57

Neurotransmitters can affect postsynaptic cells by ________.
I) initiating signal transduction pathways in the cells
II) causing molecular changes in the cells
III) altering ion channel proteins
IV) altering the permeability of the cells

A) I and III
B) II and IV
C) III and IV
D) I, II, III, and IV

Question 58

One-way synaptic transmission occurs because ________.

A) only dendrites can respond to electrical signals
B) the postsynaptic cell contains most of the synaptic vesicles.
C) receptors for neurotransmitters are mostly found on the postsynaptic membrane
D) more receptors for neurotransmitters are found on the presynaptic membrane

Question 59

A chemical that affects neuronal function but is not stored in presynaptic vesicles is ________.

A) acetylcholine
B) adrenaline
C) nitric oxide
D) gamma-aminobutyric acid (GABA)

Question 60

If excitatory postsynaptic potentials (EPSPs) are produced nearly simultaneously through two different synapses on the same postsynaptic neuron, the EPSPs can also add together creating ________.

A) a temporal summation
B) a spatial summation
C) a tetanus
D) the refractory state

Question 61

What happens when a resting neuron's membrane depolarises?

A) There is a net diffusion of Na⁺ out of the cell.
B) The equilibrium potential for K⁺ (EK) becomes more positive.
C) The neuron's membrane voltage becomes more positive.
D) The cell's inside is more negative than the outside.

Question 62

At the neuromuscular junction, the neurotransmitter acetylcholine (ACh) is degraded by acetylcholinesterase. If a neurophysiologist applies the naturally occurring acetylcholinesterase inhibitor, onchidal (produced by the mollusc Onchidella binneyi), to a synapse, what would you expect to happen?

A) paralysis of muscle tissue
B) convulsions due to constant muscle stimulation
C) decrease in the frequency of action potentials
D) no effect

Question 63

Why are action potentials usually conducted in one direction?

A) Ions can flow along the axon in only one direction.
B) The brief refractory period prevents reopening of voltage-gated Na⁺ channels.
C) The axon hillock has a higher membrane potential than the terminals of the axon.
D) Voltage-gated channels for both Na⁺ and K⁺ open in only one direction.

Question 64

Where are neurotransmitter receptors located?

A) the nuclear membrane
B) the nodes of Ranvier
C) the postsynaptic membrane
D) synaptic vesicle membranes

Question 65

What happens if twice as many inhibitory postsynaptic potentials (IPSPs) as excitatory postsynaptic potentials (EPSPs) arrive in close proximity at a postsynaptic neuron?

A) A stronger action potential results.
B) A weaker action potential results.
C) No action potential results.
D) Many action potentials result.

Question 66

Which of the following is the most direct result of depolarising the presynaptic membrane of an axon terminal?

A) Voltage-gated calcium channels in the membrane open.
B) Synaptic vesicles fuse with the membrane.
C) Ligand-gated channels open, allowing neurotransmitters to enter the synaptic cleft.
D) An EPSP or IPSP is generated in the postsynaptic cell.

Question 67

Suppose a particular neurotransmitter causes an IPSP in postsynaptic cell X and an EPSP in postsynaptic cell Y. A likely explanation is that

A) the threshold value in the postsynaptic membrane is different for cell X and cell Y.
B) the axon of cell X is myelinated, but that of cell Y is not.
C) only cell Y produces an enzyme that terminates the activity of the neurotransmitter.
D) cells X and Y express different receptor molecules for this particular neurotransmitter.

Question 68

A common feature of action potentials is that they

A) cause the membrane to hyperpolarise and then depolarise.
B) can undergo temporal and spatial summation.
C) are triggered by a depolarisation that reaches threshold.
D) move at the same speed along all axons.