Question 1

Axon guidance allows neurons to connect to their appropriate targets. Growing neurons must find their targets, some of which are very nearby (such as in a developing embryo) and some of which are farther away. Outline the processes that allow neurons to know the "routes" to take over short and long distances.

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Question 2

Consider the process described in figure 4.22. in the text Create a figure that depicts how chemotactic signaling molecules and their receptors interact and change to allow axons to first grow toward the floor plate and then away from the floor plate in the developing spinal cord.

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Question 3

The ability to re-grow neurons and help them form appropriate connections would greatly benefit patients with spinal cord injuries. Predict what some of the obstacles might be in helping adult patients regain full function in the nervous system after damage to axons has occurred?

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Question 4

Which statement best characterizes the contrasts between axon guidance in the developing spinal cord and retina?

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Question 5

Predict what would happen if a gene necessary for the expression of ephrin was mutated so that it becomes non-functional.

Accepted Answer

Ephrin gradients are crucial for directing axonal growth along the rostral-caudal axis of the tectum. If ephrin expression is disrupted, the spatial cues that guide nasal axons to their proper locations would be absent, leading to abnormal growth patterns, including potential growth toward both the rostral and caudal tectum.

Question 6

Which is NOT true of dendrite development?

Accepted Answer

Dendrites typically spread out to receive signals from multiple neurons, unlike axons which may be more bundled or clumped.

Question 7

Which of the following needs to occur to begin the process of synapse formation?

Accepted Answer

All of the options listed are critical steps in the process of synapse formation. Agrin and neurexin help bridge the gap between pre- and post-synaptic cells, neurotransmitter receptors cluster at the post-synaptic membrane to receive signals, and structural proteins give the synapse its shape, facilitating efficient signal transmission.

Question 8

In your research lab you observe a number of brain sections under the microscope from various phases of development in a mouse embryo. You notice that in the later sections, fewer neurons are present. What might you conclude?

Accepted Answer

During normal development, the process of neuronal pruning occurs where excess neurons and synapses are eliminated to improve the efficiency of neuronal transmissions. This is a normal part of the developmental process, leading to a more refined and efficient nervous system.

Question 9

Relate the study of embryonic chickens to the discovery of trophic factors.

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Question 10

Analyze figure 4.30 In the text. Which of the following is true of this figure?

Accepted Answer

Without access to the specific figure (4.30) in the text, it's impossible to accurately determine the content and thus the correct answer. The response is based on the fact that without seeing the figure, none of the provided options can be confirmed as true.

Question 11

An example of a chemical compound that can stimulate neuronal growth is ________________________.

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Question 12

In the text, the author states: "It is a strange sort of economy: if demand for neurotrophic factor exceeds the supply, then the demand is trimmed. Thank goodness our own economies tend to adjust supply instead!". What does demand and supply refer to in neuronal development, and how does it relate to the presence of trophic factors?

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Question 13

The phrase "pruning" is used to describe the development of the nervous system. The author contrasts this with marble sculpture. What do these analogies represent?

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Question 14

You label the developing corticospinal neurons of a cat with a fluorescent compound that permits axon visualization. You see that in the spinal cord, fluorescence is found on only one side of the spinal cord. This finding suggests that the age of the animal is most likely

Accepted Answer

The presence of fluorescence on only one side of the spinal cord suggests that the corticospinal tract axons have already crossed the midline (decussated) and are descending on the contralateral side. This decussation occurs around the time of birth in cats, which is approximately 25 days of gestation. Therefore, the animal is most likely at least 25 days old.

Question 15

Based on findings regarding retinal activity waves in utero, which of the following would NOT be expected in a developing organism?

Accepted Answer

Retinal activity waves are spontaneous, indicating that neurons in the developing organism display activity even before they are engaged in specific tasks. This contradicts the idea that neurons remain largely inactive until needed for a specific function.

Question 16

Consider the retina, LGN, and visual cortex. Which of the following is a true statement?

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Question 17

The time during development when the nervous system is vulnerable to a specific environmental variable is known as the ________________________.

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Question 18

Why is it dangerous for a pregnant woman to take the drug Accutane? Propose a hypothesis that specifically addresses the role of retinoic acid as described in previous chapters.

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Question 19

Excessive alcohol exposure is harmful at all ages, but particularly during development. How is it that alcohol produces such deleterious effect at early ages?

Accepted Answer

Excessive alcohol exposure is indeed harmful at all ages, but it is particularly detrimental during developmental stages, such as during fetal development and adolescence, because the brain is undergoing critical periods of growth and maturation. The deleterious effects of alcohol during these early ages can be attributed to several factors:
a) It may impair neurogenesis: Neurogenesis is the process by which new neurons are formed in the brain. During development, especially in the fetal stage, neurogenesis is crucial for proper brain formation. Alcohol can disrupt this process, leading to a reduced number of neurons being created.
b) It may impair neuronal migration: Neuronal migration is the movement of neurons to their proper positions in the brain during development. This process is essential for the correct organization and connectivity of the brain. Alcohol can interfere with neuronal migration, resulting in neurons not reaching their intended destinations, which can cause structural and functional abnormalities.
c) It may lead to abnormally high rates of neuronal death: During normal development, there is a balance between the creation of new neurons and the programmed death of excess neurons, a process known as apoptosis. Alcohol can disrupt this balance, leading to excessive neuronal death, which can reduce the overall number of neurons and affect brain development.
d) All of the above: The effects of alcohol on the developing brain are multifaceted, and all the mechanisms mentioned above can contribute to its deleterious impact. The impairment of neurogenesis, disruption of neuronal migration, and increased rates of neuronal death can all occur simultaneously or in different combinations, leading to significant developmental issues that can have long-term consequences on cognitive function, behavior, and overall brain health.
Therefore, the correct answer is d) all of the above. Excessive alcohol exposure during development can have widespread and lasting effects on the brain due to its interference with critical developmental processes.

Question 20

Which areas of the brain tend to develop first?

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Quiz 4: Developing a Nervous System