A 47-year-old woman was admitted to the hospital afterexperiencing nausea and vomiting for about 2 days followed bysevere muscle weakness and neurologic symptoms, includingptosis and dysphagia. She indicated she had eaten at a restaurantthe evening before the symptoms began. Laboratory tests werepositive for Clostridium botulinum. The basis for the muscleweakness in this case was most likely because the toxinA. blocked the reuptake of neurotransmitter into presynapticterminals.B. bound irreversibly to the receptor on the postsynapticmembrane at the neuromuscular junction.C. reached the cell body of the motor neuron by diffusion intothe spinal cord.D. exerted its adverse effects by a direct action on the skeletalmuscle.E. prevented the release of acetylcholine from motor neurons.
Question
A 47-year-old woman was admitted to the hospital afterexperiencing nausea and vomiting for about 2 days followed bysevere muscle weakness and neurologic symptoms, includingptosis and dysphagia. She indicated she had eaten at a restaurantthe evening before the symptoms began. Laboratory tests werepositive for Clostridium botulinum. The basis for the muscleweakness in this case was most likely because the toxinA. blocked the reuptake of neurotransmitter into presynapticterminals.B. bound irreversibly to the receptor on the postsynapticmembrane at the neuromuscular junction.C. reached the cell body of the motor neuron by diffusion intothe spinal cord.D. exerted its adverse effects by a direct action on the skeletalmuscle.E. prevented the release of acetylcholine from motor neurons.
Solution
To determine the basis for the muscle weakness in this case, we need to understand the mechanism of action of the Clostridium botulinum toxin. Let's analyze each option step by step:
A. Blocked the reuptake of neurotransmitter into presynaptic terminals.
- This option suggests that the toxin prevents the reuptake of neurotransmitters back into the presynaptic neuron. However, botulinum toxin does not act by blocking reuptake mechanisms. This is more characteristic of certain other toxins or drugs.
B. Bound irreversibly to the receptor on the postsynaptic membrane at the neuromuscular junction.
- This option suggests that the toxin binds to the receptors on the muscle side of the neuromuscular junction. Botulinum toxin does not act by binding to postsynaptic receptors. Instead, it affects the presynaptic side.
C. Reached the cell body of the motor neuron by diffusion into the spinal cord.
- This option suggests that the toxin diffuses into the spinal cord and affects the motor neuron cell body. Botulinum toxin does not need to reach the cell body of the motor neuron to exert its effects. It acts at the neuromuscular junction.
D. Exerted its adverse effects by a direct action on the skeletal muscle.
- This option suggests that the toxin acts directly on the muscle itself. Botulinum toxin does not act directly on skeletal muscle; it affects the neuromuscular transmission process.
E. Prevented the release of acetylcholine from motor neurons.
- This option suggests that the toxin prevents the release of acetylcholine, a neurotransmitter essential for muscle contraction, from the presynaptic terminals of motor neurons. This is the correct mechanism of action for botulinum toxin. It cleaves specific proteins required for the fusion of neurotransmitter-containing vesicles with the presynaptic membrane, thereby preventing acetylcholine release and leading to muscle weakness.
Given the above analysis, the most likely basis for the muscle weakness in this case is:
E. Prevented the release of acetylcholine from motor neurons.
Similar Questions
Passage 3 (Questions 11 - 15)A woman began canning her own jams as a hobby. She shared several cans of her jam with her mother for lunch. The next day, her mother was found suffering from blurry vision, difficulty swallowing and troubled breathing. Given the quick progression of symptoms, associated with the new food, the ER physician suspected botulism poisoning. Due to the danger and toxicity of botulism, tests were performed immediately to determine the best course of treatment.The botulinum toxin is a neurotoxin produced by the bacterium Clostridium botulinum. Botulism is a life-threatening illness in humans, although forms of the toxin are used for various cosmetic and medical procedures. The eight distinct toxin types are designated A to H. The botulinum toxin protein is a two-chain polypeptide with a 100-kDa heavy chain joined by a disulfide bond to a 50-kDa light chain. This light chain is a protease that attacks one of the fusion proteins (SNARE protein) present in neuromuscular junctions, preventing vesicles from anchoring with the cell membrane to release acetylcholine.Figure 1 Mechanism of neuromuscular blockade by botulinum toxinThe tests employed to detect botulism include brain scans and nerve conduction tests. Toxicity testing of serum specimens, wound tissue cultures, and stool specimen cultures are the best methods for identifying botulism, though they are time-consuming. If the symptoms are diagnosed early, treatment can reduce the case fatality rate to less than 10%, while untreated botulism is fatal in nearly half of cases. A more rapid way to detect the toxin in humans utilizes mass spectrometry. Question 15The symptoms of botulism took 12-18 hours to be observed in the patient after exposure was confirmed. How is this delay best explained? A.Only growing bacteria produce the toxin.B.Botulinum toxin is immediately filtered by the kidneys and excreted.C.Toxins can be absorbed through mucous membranes or the respiratory tract.D.Most of the toxins are polar and they take time to cross the nuclear membrane
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Bacterial infection with Clostridium botulinum has a biological outcome similar to the Lou Gehrig's disease. Which body structure is directly affected?Group of answer choicessmooth muscles of the bronchiolespleuraesurfactant-producing alveolar cellsmucociliary apparatusintercostals
assage 3 (Questions 11 - 15)A woman began canning her own jams as a hobby. She shared several cans of her jam with her mother for lunch. The next day, her mother was found suffering from blurry vision, difficulty swallowing and troubled breathing. Given the quick progression of symptoms, associated with the new food, the ER physician suspected botulism poisoning. Due to the danger and toxicity of botulism, tests were performed immediately to determine the best course of treatment.The botulinum toxin is a neurotoxin produced by the bacterium Clostridium botulinum. Botulism is a life-threatening illness in humans, although forms of the toxin are used for various cosmetic and medical procedures. The eight distinct toxin types are designated A to H. The botulinum toxin protein is a two-chain polypeptide with a 100-kDa heavy chain joined by a disulfide bond to a 50-kDa light chain. This light chain is a protease that attacks one of the fusion proteins (SNARE protein) present in neuromuscular junctions, preventing vesicles from anchoring with the cell membrane to release acetylcholine.Figure 1 Mechanism of neuromuscular blockade by botulinum toxinThe tests employed to detect botulism include brain scans and nerve conduction tests. Toxicity testing of serum specimens, wound tissue cultures, and stool specimen cultures are the best methods for identifying botulism, though they are time-consuming. If the symptoms are diagnosed early, treatment can reduce the case fatality rate to less than 10%, while untreated botulism is fatal in nearly half of cases. A more rapid way to detect the toxin in humans utilizes mass spectrometry. Question 13Which molecule could be used to specifically detect toxin D in the cultures described in the passage? A.An antibodyB.A phospholipidC.A radiolabeled thymineD.An antigen
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