Botulinum toxin is lethal at a dose of 1 µg/kg, making it one of the most toxic

Question

Botulinum toxin is lethal at a dose of 1 µg/kg, making it one of the most toxic substances known. It functions by inhibiting acetylcholine release from the motor neuron at the neuromuscular junction. Therefore, in presence of the toxin, we expect that:

a. The action potential from the motor neuron is normally transmitted across the synaptic cleft and into the nearby muscle cell, eventually leading to muscle contraction

b. The action potential from the motor neuron is transmitted across the synaptic cleft and into the nearby muscle cell, but it fails to propagate within the muscle cell

c. No action potential can be generated in the neuron itself, therefore no action potential ever reaches the muscle cell

d. The action potential from the motor neuron cannot be transmitted across the synaptic cleft, therefore the muscle cell never receives any signal from the neuron

e. The action potential, when triggered in the motor neuron, weakens as it propagates down the axon, such that no signal ever reaches the neuromuscular junction

Explanation / Answer

Botulinum toxin (BTX) is a neurotoxic protein produced by the bacterium Clostridium botulinum and related species.[1] It is also produced commercially for medical, cosmetic, and research use. There are two main commercial types: botulinum toxin type A and botulinum toxin type B.[2]

Infection with the bacterium may result in a potentially fatal disease called botulism. Botulinum is the most acutely lethal toxin known, with an estimated human median lethal dose (LD50) of 1.3–2.1 ng/kg intravenously or intramuscularly and 10–13 ng/kg when inhaled.[3]

Botulinum toxin types A and B are used in medicine for, among others, upper motor neuron syndrome, focal hyperhidrosis,blepharospasm, strabismus, chronic migraine and bruxism. It is also widely used in cosmetic treatments. The U.S. Food and Drug Administration requires a boxed warning stating that when locally administered the toxin may spread from the injection site to other areas of the body, causing botulism. The warning was the result of deaths associated with its uses. The commercial form is marketed under the brand name Botox, among others. Botox is made by Allergan

the correct option would be

the action potential from the motor neuron is transmitted across the synaptic cleft and into the nearby muacle cell,but it fails to propagate within the muscle cell

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