Chapter 48

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.

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.

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.

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

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.

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.

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.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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)

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

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

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)

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.

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.

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.

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

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.

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 through 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.

C.elegans is a model organism and was the first eukaryotic organism to have its genome sequenced. The free-living nematode is often used in laboratories investigating reproduction, particularly egg-laying. There are 16 muscles, 2 types of neurons, and multiple receptors involved in the process of laying eggs in C.elegans, and there are mutations in all of those structures for the study of the process. One particular mutation that prevents the laying of eggs by the worm is rescued by the neurotransmitter, serotonin. That rescue suggests that this mutation is most likely in which of the following? A) a post-synaptic neuron involved in egg-laying B) a pre-synaptic neuron involved in egg-laying C) a receptor for serotonin on cells needed for egg-laying D) one of the muscles needed for egg-laying