A 30-year-old woman, Isabel Yang, was brought into the emergency room. she had been dining in a restaurant, and while eating dessert she noticed the following symptoms. initially there was a tingling sensation that affected her mouth and lips, but then spread to the faced neck. then the tingling spread down her arms and legs, to the fingers and toes.

at the hospital Isabel reported numbness of the areas that previously tingled and had difficulty walking in a coordinated fashion. she was asked to describe the meal she had just eaten and stated that she had shrimp cocktail as and appetizer, followed b salad, steak, and baked potato and green beans, and apple pie and coffee for dessert. Isabel had no history of allergic response to shellfish. her superficial reflexes were almost absent, and her deep reflexes were markedly hypoactive. an extracellular electrode was placed in Isabel's ulnar nerve. then the palmer surface of her little finger was scraped with the physician's fingernail in a way that would normally be painful to the patient. the patient could not feel this stimulus, and no action potentials were detected in the ulnar nerve. when an intracellular microelectrode was placed on a sensory nerve fiber in the ulnar nerve, the resting membrane potential was found to be near -70 mV (normal). when an action potential was evoked by repeated vigorous scraping of the skin of the little finger as described earlier, the action potential was slower to rise and of shorter amplitude than that expected from measurements in normal individuals. the duration of the action potential was normal.

1. what can be concluded from the failure to elicit action potential in the ulnar nerve by vigorous scraping of the skin of the little finger

2. what can be concluded from the gross neurologic symptoms and findings taken together

3. what can be concluded from the findings that the resting membrane potential in the sensory fibers in the ulnar nerve is near normal.

4. what might explain the finding that the action potential in the sensory fiber in the ulnar nerve is slow to rise and of smaller amplitude than normal.

5. why is the action potential in the sensory fiber of normal duration

6. what may be the cause of Isabel's difficulties

7. how should Isabel's care be managed, and what is her prognosis

Answer rating: 100% (QA)

1 Isabel seems to have encountered a saxitoxin poisoning along with a certain malfunction of the sensory system of the skin The compound saxitoxin is ... View the full answer