In contrast to these toxins, strychnine acts postsynaptically, to block glycine from binding to receptors on motor neurons. Would you expect the symptoms of strychnine poisoning to be more similar to those of botulinum or tetanus toxin?

Question

A.  botulinum
B.  tetanus toxin
C.  botulinum

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 strychnine? 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

B.  tetanus toxin

Clarify Question
· What is the key concept addressed by the question?
        o Physiological similarities and differences between tetanus, botulinum, and strychnine.
· What type of thinking is required?
        o This is an evaluate question because you need to compare and contrast the modes of action of tetanus, botulinum, and strychnine toxins.

Gather Content/Choose Answer
· What do you already know about strychnine? What other information is related to the question?
        o To solve this problem, you’ll need to remember that the question states that strychnine blocks glycine from binding to post-synaptic motor neurons. From the previous questions, recall that botulinum toxin acts to prevent ACh release at the neuromuscular junction and that tetanus blocks neurotransmitter release by stopping inhibitory interneurons. Glycine is also an inhibitory neurotransmitter, so if strychnine blocks an inhibitory effect, the result will be overly excitatory as is found in tetanus poisoning. Thus the symptoms of both would be spastic paralysis.

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, great! If not, where did you go wrong? Did you think that since both botulinum and strychnine toxins both affect neurotransmitters in the synaptic cleft that the symptoms would be the same (i.e., a lack of muscle contraction)? That is sensible but strychnine blocks glycine (which is inhibitory) instead of ACh (which is excitatory). Thus strychnine produces an excitatory output leading to too much muscle contraction, while blocking ACh (like botulism) produces too little muscle contraction.