Question 1

Which of the following support the hypothesis that Na⁺ transport is affected by saxitoxin?

Accepted Answer

Clam cells transformed with the mutated form of the Na⁺ transporter were more resistant to saxitoxin, which suggests that the transporter is affected by saxitoxin. Choice A is incorrect because it only shows that saxitoxin affects clam cells, not specifically the transporter. Choice C is incorrect because removing the transporter completely would result in the inability to transport any molecule, not just saxitoxin. Choice D is incorrect because it contradicts the statement in the question stem. Choice E is also incorrect because it does not address the interaction between saxitoxin and the transporter.

Question 2

Unmyelinated regions between adjacent myelin sheath cells are called synaptic clefts.

Accepted Answer

Unmyelinated regions between adjacent myelin sheath cells are actually called Nodes of Ranvier, not synaptic clefts. Synaptic clefts are the spaces between neurons where neurotransmitters are released and received.

Question 3

The dendrite,also called the nerve fiber is typically a single long extension of the cell body.

Accepted Answer

Dendrites are typically short, branched extensions of the cell body, while the axon is the single long extension.

Question 4

In Figure 25.21 the researchers measured a clam's ability to burrow as an indicator of paralysis due to inhibition of a Na⁺ transporter by saxitoxin.Which of the following would occur in sensitive clam cells that have been exposed to saxitoxin?

Accepted Answer

The answer of In Figure 25.21 the researchers measured a...

Question 5

The toxins responsible for most shellfish poisonings are water-soluble,heat and acid-stable,and ordinary cooking methods do not eliminate the toxins.Would you predict saxitoxin to affect myelinated and non-myelinated neurons equally?

Accepted Answer

Saxitoxin binds to voltage-gated sodium channels in the neuronal membrane, preventing the influx of sodium ions and thus blocking action potential propagation. Myelinated neurons have a thicker myelin sheath, which acts as an insulating layer and reduces the diffusion of saxitoxin into the neuronal membrane. Therefore, saxitoxin will have a greater effect on non-myelinated neurons, which have a thinner myelin sheath and are more exposed to the toxin.

Question 6

During an action potential sodium ions pour into the cell.

Accepted Answer

During an action potential, there is a rapid influx of sodium ions into the cell which depolarizes the membrane potential.

Question 7

Which of the following neurons would you predict to be sensitive to saxitoxin?

Accepted Answer

Saxitoxin is a potent neurotoxin that blocks voltage-gated sodium channels, which are present in all types of neurons, making all neurons sensitive to it.

Question 8

A typical neuron consists of a cell body,dendrites,and an axon.

Accepted Answer

A typical neuron consists of a cell body that contains the nucleus and other organelles, dendrites that receive signals from other neurons or sensory receptors, and an axon that carries the signal away from the cell body to other neurons or muscles.

Question 9

How would exposure to saxitoxin from algae cause changes in clams?

Accepted Answer

Exposure to saxitoxin from algae would not cause mutations in the clam's DNA or increase mutation rates, as saxitoxin is not a mutagen. Clams sensitive to saxitoxin may not necessarily migrate away from the algae bloom as they are filter feeders and may continue to consume the toxin. Clams may not have the ability to deliberately change their transporters to become resistant to saxitoxin. Therefore, the most likely scenario is that saxitoxin would select for existing mutations in the clam population, favoring individuals with mutations that confer resistance or tolerance to the toxin.

Question 10

Only motor neurons reside entirely within the central nervous system.

Accepted Answer

Motor neurons send signals from the central nervous system to muscle fibers located outside the central nervous system, so they do not reside entirely within the central nervous system.

Question 11

A nerve impulse does not spread backwards because of a refractory period in which the membrane reestablishes its resting potential and cannot generate another action potential.

Accepted Answer

The refractory period is a temporary state in which the membrane is unable to generate another action potential immediately after one has been generated. This ensures that the nerve impulse travels in one direction only, from the dendrite to the axon terminal, and prevents backwards propagation.

Question 12

Why would saxitoxin be water soluble?

Accepted Answer

Saxitoxin has amino and hydroxyl functional groups that can readily form hydrogen bonds with water molecules. This makes saxitoxin highly water-soluble.

Question 13

If a person has a stroke and their speech becomes impaired,which region of the brain was likely to be affected?

Accepted Answer

The frontal lobe is responsible for speech production and its impairment can lead to difficulty in speaking, known as aphasia. A stroke in this area can damage the neurons that control speech production, leading to speech impairment.

Question 14

Neurons that connect one neuron to another within the central nervous system are the interneurons.

Accepted Answer

Interneurons are a type of neuron that connects one neuron to another within the central nervous system.

Question 15

If a person with a brain tumor develops impaired vision,which region of the brain was likely to be affected?

Accepted Answer

The occipital lobe is responsible for processing visual information, therefore impaired vision suggests that this region has been affected.

Question 16

In figure 25.2,the evolution of nervous systems in vertebrates and invertebrates is shown.Given that humans who eat clams contaminated with saxitoxin develop paralysis,which of the following statements is most likely correct?

Accepted Answer

Saxitoxin affects Na⁺ transporters, suggesting that these transporters in clams and humans share a common evolutionary origin.

Question 17

A neural impulse usually begins at the nodes of Ranvier within the axon.

Accepted Answer

A neural impulse, or action potential, typically begins at the axon hillock, not the nodes of Ranvier. The nodes of Ranvier are involved in the propagation of the impulse along the axon.

Question 18

Some shellfish can store saxitoxin for several weeks after a harmful algal bloom passes,but others such as butterclams are known to store the toxin for up to two years.A human eating a mussel that ate algae would be which of the following?

Accepted Answer

The human would be a secondary consumer, as they are consuming a mussel which is a primary consumer (feeding on algae, a producer).

Question 19

In Figure 25.21,which of the following was the dependent variable?

Accepted Answer

The answer of In Figure 25.21,which of the following was...

Question 20

If a neuron is at rest the concentration of potassium ions is greatest outside the cell and the concentration of sodium ions is greatest inside the cell.

Accepted Answer

If a neuron is at rest, the concentration of potassium ions is greatest inside the cell, and the concentration of sodium ions is greatest outside the cell. This concentration gradient is maintained by the sodium-potassium pump, which actively transports sodium ions out of the cell and potassium ions into the cell.

Quiz 25: The Nervous System

Which of the following support the hypothesis that Na+ transport is affected by saxitoxin?