Question

Which of the following is true to describe Wallerian Degeneration? a. If a nerve fiber is crushed, the part proximal to the injury (i.e. the part of the axon that is connected from the neuron's nucleus) will degenerate b. Target tissues of the nerve (typically an innervated muscle) never atrophies c. Wallerian degeneration is named after Augustus Volney Waller who first described it in 1850 , in the Zebra fish d. None of the above

Short answer

Answer: Augustus Volney Waller first described Wallerian Degeneration in 1850, in the Zebra fish.

Step-by-step solution

Understanding Wallerian Degeneration

Wallerian Degeneration is a process that occurs when a nerve fiber is damaged or injured. The part of the axon distal to the injury site (i.e., the part away from the neuron's nucleus) degenerates, while the part proximal to the injury (connected to the neuron's nucleus) survives. Eventually, the degenerated axon is cleared away and may go through a process of regrowth and reconnection.

Evaluating Option a

"If a nerve fiber is crushed, the part proximal to the injury (i.e. the part of the axon that is connected from the neuron's nucleus) will degenerate." This statement is incorrect because it is the distal part of the axon that degenerates, not the proximal part.

Evaluating Option b

"Target tissues of the nerve (typically an innervated muscle) never atrophies." This statement is also incorrect. When the nerve connecting to the target tissue is damaged, the target tissue can indeed atrophy due to loss of innervation and diminished functionality.

Evaluating Option c

"Wallerian degeneration is named after Augustus Volney Waller who first described it in 1850, in the Zebra fish." This statement is correct. Augustus Volney Waller was a British physiologist who first described Wallerian Degeneration, and the process was named after him. He made this discovery while studying nerve degeneration in Zebra fish.

Evaluating Option d

"None of the above." This statement is incorrect, as we have determined that option c is true.

Conclusion

Based on the evaluation of each statement, the correct answer is: c. Wallerian degeneration is named after Augustus Volney Waller who first described it in 1850, in the Zebra fish.

Key concepts

Understanding Neurobiology

Neurobiology is the study of the nervous system, including how it is structured, how it functions, and how it develops. Within this field, researchers delve into the complexities of the brain and neural networks, exploring the cellular and molecular mechanisms that underlie neurological processes. Neural communication, an intricate dance of electrical and chemical signals, takes center stage here.

One fascinating aspect of neurobiology is how the system reacts to injury. A prime example is Wallerian Degeneration, where following damage to a nerve fiber, a planned dismantling of the axon occurs distal to the injury site. Understanding this phenomenon is critical because it reveals much about the potential for regeneration and repair within the nervous system, vital knowledge when it comes to treating neurological injuries and diseases.

In the context of the exercise, this understanding helps to clarify why option a is incorrect, as it mistakenly claims that the damage results in degeneration proximal to the injury rather than distal to it.

The Process of Neural Regeneration

Neural regeneration, or neuroregeneration, is the process through which neurons repair and renew themselves. It has immense therapeutic potential for recovering from neurological injuries and disorders. The central nervous system (CNS), which includes the brain and spinal cord, has a limited ability to regenerate, which is why CNS injuries often result in permanent damage. In contrast, the peripheral nervous system (PNS) has a more robust capacity for regeneration.

After injury, such as the damage described in Wallerian Degeneration, the PNS can often initiate a complex, yet remarkable, regrowth process. The remaining healthy part of the neuron can sprout axon outgrowths that may eventually reconnect with target tissues. Unfortunately, as indicated by option b, these target tissues can suffer atrophy in the interim, a detail that underscores the critical importance of timing and efficient mechanisms for regeneration.

Axon Degeneration Mechanisms

Axon degeneration refers to the process by which axons, the long thread-like parts of a nerve cell through which impulses are conducted, deteriorate and ultimately perish. This can occur due to injury or disease, and it takes place in a degenerative cascade triggered by a variety of molecular signals. Wallerian Degeneration is one specific pattern of axon degeneration that happens following a nerve injury.

During Wallerian Degeneration, the segment of the axon separated from the neuron's cell body, or the distal segment, undergoes a systematic breakdown. This is comprised of disintegration of the axon, degeneration of myelin sheath, and recruitment of glial cells for phagocytosis to clear the debris. Meanwhile, the neuron stimulates regeneration of a new axon, with the goal of restoring functionality, assuming the environment is conducive to growth. The inclusion of Augustus Volney Waller's name, as seen in option c, is an acknowledgment of his pioneering work in identifying and describing this pattern of degeneration, long before the mechanisms of regeneration were understood.