Genetic studies have found that Charcot-Marie-Tooth may be caused by a mutation in the gene Mitofusin-2 (MFN2), which causes mitochondria to form large clumps. In what area of a neuron are these clumps most likely to cause a problem?

Question

Charcot-Marie-Tooth is the most commonly inherited peripheral neuropathy, and has no known cure. Patients suffer damage to motor and sensory neurons, leading to degeneration of muscles and gradual loss of motor control.

A.  axon
B.  synapse
C.  soma
D.  dendrite
E.  myelin

Clarify Question
· What is the key concept addressed by the question?
· What type of thinking is required?

Gather Content/Choose Answer
· What do you already know about components of the nervous system? What other information is related to the question?

Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
 

Answer 1

A.  axon

Clarify Question
· What is the key concept addressed by the question?
        o The question is asking you to evaluate which part of an neuron would be prone to disfunction because of mitochondrial clumping.
· What type of thinking is required?
        o This question is asking you to judge which part of an neuron would be the most vulnerable to blockage of neural transmission.

Gather Content/Choose Answer
· What do you already know about components of the nervous system? What other information is related to the question?
        o To solve this problem, you’ll need to apply your knowledge of the morphology and physiology of a neuron. The long thin structure of the axon makes it vulnerable to “traffic jams” from clumps of proteins or organelles. This can block fast axonal transport of neurotransmitters and their precursors to the synaptic terminal. Without neurotransmitters chemical synapses cannot function.

Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
        o If you figured out the correct answer, wonderful! If not, where in your thought process did things go wrong? Did you think that dendrites are thin and could be blocked by clumped proteins? That is a possibility, but dendrites are usually much smaller and shorter than axons. Also, transport of neurotransmitters and their precursors occur along axons, not dendrites, so blocking axons would be more detrimental to the working of the neuron than the blocking of a few of many dendrites. Mitochondria do come from the soma, but the soma is so large that mitochondrial clumping would probably not inhibit action potentials. Myelin is an important part of the axon, but it occurs outside the neuron and so does not have contact with mitochondria (with its potential clumping) from the soma.