Question

Which of the following statements best illustrates how Clostridium tetani affects Jackies nervous system? For the four that are false, explain why they are incorrect. Defend the one correct choice with adequate justification.

1. By blocking Na+ voltage gated channels, the bacteria disrupt resting membrane potential of motor afferent neurons so that they are more likely to fire action potentials to facial muscles.

2. The endotoxin prevents the influx of Na+ that is required during repolarization, decreasing action potentials carrying information related to face sensation.

3. Jackies neurons are firing less frequently because the endotoxin prevents the impulse from passing beyond the axon hillock of sensory and motor neurons.

4. The endotoxin affects hyperpolarization by preventing the redistribution of Na+ out of the cell during refractory period.

5. By inhibiting voltage channels, the endotoxin makes the membrane potential more positive than normal, which leads to hypersecretion of neurotransmitters such as ACh.

Answer 1

Answer: "E"

Explanation:

• Mechanism of action of tetanus toxin
• Tetanus toxin is apparently transported retrogradely to the CNS where it exerts its primary action, namely, to block release of the inhibitory amino acid transmitters gamma-aminobutyric acid (GABA) and glycine, leading ultimately to a spastic form of paralysis.
• The spastic paralysis induced by the toxin is due to the blockade of neurotransmitter release from spinal inhibitory interneurons.
• As result of inhibition of release of inhibitory neurotransmitter, the motor neurons continuously releases the Ach at neuromuscular junction resulting in spastic paralysis.

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