Biology Chapter 48

The minimum graded depolarization needed to operate the voltage-gated sodium and potassium channels is indicated by the label _____. A) A B) B C) D D) E

A) A

The cell is not hyperpolarized; however, repolarization is in progress, as the sodium channels are closing or closed, and many potassium channels have opened at label _____. A) B B) C C) D D) E

A) B

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-

A) K+

What happens if a neuron is stimulated enough midway in an axon to trigger an action potential? A) The nerve impulse would go both directions from the stimulus point, but only the axon end could transfer the message trough neurotransmitters to another neuron. B) Since neuron transmission is one-way, the nerve impulse would only be transmitted to the end of the axon and then through neurotransmitters to the next neuron. C) The nerve impulse could not be transmitted because it must be initiated at the dendrite end of a neuron. D) The nerve impulse would go both directions and the dendrite end would be stimulated to send a second message through this neuron.

A) The nerve impulse would go both directions from the stimulus point, but only the axon end could transfer the message trough neurotransmitters to another neuron.

Which of the following is a direct result of depolarizing 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.

A) Voltage-gated calcium channels in the membrane open.

The botulinum toxin, which causes botulism, reduces the synaptic release of _____. A) acetylcholine B) endorphin C) nitric oxide D) gamma-aminobutyric acid (GABA)

A) acetylcholine

The heart rate decreases in response to the arrival of _____. A) acetylcholine B) endorphin C) nitric oxide D) gamma-aminobutyric acid (GABA)

A) acetylcholine

Self-propagation and refractory periods (states) are typical of _____. A) action potentials B) graded hyperpolarizations C) excitatory postsynaptic potentials D) threshold potentials

A) action potentials

Ionotropic receptors found at synapses are operated via _____. A) ligand-gated ion channels B) electrical synapses C) inhibitory, but not excitatory, synapses D) excitatory, but not inhibitory, synapses

A) ligand-gated ion channels

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

A) potassium ions

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

A) slightly permeable to sodium ions

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

A) temporal summation

After the depolarization phase of an action potential, the resting potential is restored by _____. A) the opening of voltage-gated potassium channels and the closing 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

A) the opening of voltage-gated potassium channels and the closing of sodium channels

In a simple synapse, neurotransmitter chemicals are received by _____. A) the postsynaptic membrane B) the presynaptic membrane C) axon hillocks D) cell bodies

A) the postsynaptic membrane

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

A) the presynaptic membrane

The membrane's permeability to sodium ions is at its maximum at label _____. A) A B) B C) C D) D

B) B

The myelin sheath plays an important role in neuron structure and function. However, when the myelin sheath is missing or not fully intact, there are consequences. There are many conditions that cause demyelination of neurons, some are autoimmune disorders, such as multiple schlerosis, and others are hereditary. The symptoms of these conditions vary, but often include speech impairment and difficulty coordinating movement. Which of the following correctly connects the symptoms of demyelination with the process of nerve impulse transmission? A) Demyelination prevents the formation of an action potential in sensory neurons that transmit signals from the environment to the central nervous system. B) Demyelination slows nerve impulse transmission. C) Demyelination prevents the uptake of neurotransmitters needed to propagate a message to the next neuron. D) Demyelination targets the central nervous system.

B) Demyelination slows nerve impulse transmission.

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 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.

B) The brief refractory period prevents reopening of voltage-gated Na+ channels.

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.

B) The membrane potential would become less negative.

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 decrease. B) The membrane potential would increase. C) The membrane potential would be unaffected. D) The answer depends on the thermodynamic potential.

B) The membrane potential would increase.

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.

B) Unlike the crab, the fish's axons are wrapped in myelin.

Acetylcholine released into the junction between a motor neuron and a skeletal muscle binds to a sodium channel and opens it. This is an example of _____. A) a voltage-gated potassium channel B) a ligand-gated sodium channel C) a second-messenger-gated sodium channel D) a chemical that inhibits action potentials

B) a ligand-gated sodium channel

Excitatory postsynaptic potentials (EPSPs) produced nearly simultaneously by different synapses on the same postsynaptic neuron can also add together, creating _____. A) a temporal summation B) a spatial summation C) a tetanus D) the refractory state

B) a spatial summation

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

B) acetylcholine receptors at the neuromuscular junction

Motor neurons release the neurotransmitter acetylcholine (ACh) and acetylcholinesterase degrades ACh in the synapse. If a neurophysiologist applies onchidal (a naturally occurring acetylcholinesterase inhibitor 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

B) convulsions due to constant muscle stimulation

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) depolarization of the neuron B) hyperpolarization of the neuron C) replacement of potassium ions with sodium ions D) replacement of potassium ions with calcium ions

B) hyperpolarization of the neuron

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 loss of resting potential C) slow decrease of resting potential and action potential amplitudes D) No effect; the substances counteract each other.

B) immediate loss of action potential with gradual loss of resting potential

How could you increase the magnitude of inhibitory postsynaptic potentials (IPSPs) generated at a synapse? A) increase sodium-potassium pump activity B) increase K+ permeability C) increase the influx of calcium D) All of the listed responses are correct.

B) increase K+ permeability

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

B) ion concentration gradient

The motor (somatic nervous) system can alter the activities of its targets, the skeletal muscle fibers, 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

B) its signals bind to receptor proteins on the muscles

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

B) only II

A toxin that binds specifically to voltage-gated sodium channels in axons would be expected to _____. A) prevent the hyperpolarization phase of the action potential B) prevent the depolarization phase of the action potential C) prevent graded potentials D) increase the release of neurotransmitter molecules

B) prevent the depolarization phase of the action potential

The "undershoot" phase of after-hyperpolarization 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

B) sustained opening of voltage-gated potassium channels

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 depolarizes 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

C) 3 → 2 → 5 → 1 → 4

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.

C) Action potentials are propagated down the length of the axon.

The neuronal membrane is at its resting potential at label _____. A) A B) B C) D D) E

C) D

What happens if twice as many inhibitory postsynaptic potentials (IPSPs) as excitatory postsynaptic potentials (EPSPs) arrive at a postsynaptic neuron in close proximity? A) A stronger action potential results. B) A weaker action potential results. C) No action potential results.

C) No action potential results.

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.

C) The signal would fade because it is not renewed by the opening of more sodium channels.

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

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

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

C) equilibrium potential

Most of the neurons in the human brain are _____. A) sensory neurons B) motor neurons C) interneurons D) peripheral neurons

C) interneurons

The "threshold" potential of a membrane is the _____. A) lowest frequency of action potentials a neuron can produce B) minimum hyperpolarization needed to prevent the occurrence of action potentials C) minimum depolarization needed to operate the voltage-gated sodium and potassium channels D) peak amount of depolarization seen in an action potential

C) minimum depolarization needed to operate the voltage-gated sodium and potassium channels

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 non-myelinated axons D) by reversing the concentration gradients for sodium and potassium ions

C) more rapidly in myelinated than in non-myelinated axons

A chemical that affects neuronal function but is not stored in presynaptic vesicles is _____. A) acetylcholine B) epinephrine C) nitric oxide D) gamma-aminobutyric acid (GABA)

C) nitric oxide

Which of the following will increase the speed of an action potential moving down an axon? I) Action potentials move faster in larger diameter 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

C) only I and III

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) open and close depending on stimuli, and are specific as to which ion can traverse them D) open in response to stimuli, and then close simultaneously, in unison

C) open and close depending on stimuli, and are specific as to which ion can traverse them

Receptors for neurotransmitters are of primary functional importance in assuring one-way synaptic transmission because they are mostly found on the _____. A) axonal membrane B) axon hillock C) postsynaptic membrane D) presynaptic membrane

C) postsynaptic membrane

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

C) sodium-potassium pumps

The point of connection between two communicating neurons is called the _____. A) axon hillock B) dendrite C) synapse D) cell body

C) synapse

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) +30 mV D) +62 mV

D) +62 mV

Graph Question The membrane potential is closest to the equilibrium potential for potassium at label _____. A) A B) B C) C D) D

D) D

Neurotransmitters affect postsynaptic cells by _____. I) initiating signal transduction pathways in the cells II) causing molecular changes in the cells III) affecting 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

D) I, II, III, and IV

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+

D) K+

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

D) degradation on the postsynaptic membrane

Neurotransmitters are released from axon terminals via _____. A) osmosis B) active transport C) diffusion D) exocytosis

D) exocytosis

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)

D) gamma-aminobutyric acid (GABA)

Neurotransmitters categorized as inhibitory are expected to _____. A) act independently of their receptor proteins B) close potassium channels C) open sodium channels D) hyperpolarize the membrane

D) hyperpolarize the membrane

A simple nervous system _____. A) must include chemical senses, mechanoreception, and vision B) includes a minimum of twelve effector neurons C) has information flow in only one direction: away from an integrating center D) includes sensory information, an integrating center, and effectors

D) includes sensory information, an integrating center, and effectors

A graded hyperpolarization 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+

D) increasing its membrane's permeability to K+

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

D) sodium ions out of the cell and potassium ions into the cell

The fastest possible conduction velocity of action potentials is observed in _____. A) thin, non-myelinated neurons B) thin, myelinated neurons C) thick, non-myelinated neurons D) thick, myelinated neurons

D) thick, myelinated neurons

Action potentials are normally carried in only one direction: from the axon hillock toward the axon terminals. If you experimentally depolarize 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

D) two action potentials will be initiated, one going toward the axon terminal and one going back toward the hillock