Chapter 05: Membrane Potentials and Action Potentials

Chapter 05: Membrane Potentials and Action Potentials

Complete Chapter Questions With Answers

Sample Questions Are Posted Below

1. An 22-year-old man is admitted to the emergency department after an automobile accident. He has not lost a large amount of blood, but he suffers from a severe crush injury to his right leg. He is conscious and exhibits flaccid paralysis. Electrocardiogram results show a shortened QT interval and an increase in the P-R interval (i.e., decreased duration of action potential and decreased conduction velocity). Laboratory results indicate that his serum potassium level has increased to a value of 6.5 mEq/L (normal: 3.5 to 5.0 mEq/L). This increase in serum potassium causes which of the following?

1. A decreased net driving force for potassium from cells
2. Decreased intracellular potassium concentration
3. Hyperpolarization of the resting membrane potential
4. More negative Nernst potential for potassium
5. More negative resting membrane potential

ANS: A

2. An 88-year-old nursing home resident has diabetes mellitus and is taking diuretics for hypertension. His blood glucose concentration has recently been greater than 350 mg/dL. He is disoriented and has had limited oral intake for about five days. His vital signs include a temperature of 100.5°F, a supine blood pressure and pulse of 150/90 mm Hg and 100 beats per minute, and an upright blood pressure and pulse of 130/88 mm Hg and 118 beats per minute. The findings on examination of the heart are normal, and his axillae are dry. The table shows serum Na⁺ and K⁺ values before and after the dehydration that has occurred in this patient. The resting membrane potential of a cardiac myocyte was about −70 millivolts before dehydration occurred. What is the resting membrane potential of a cardiac myocyte after dehydration occurred, assuming no change in membrane conductance or intracellular concentrations of Na⁺ or K⁺ ions?
3. −100 millivolts
4. −50 millivolts
5. −60 millivolts
6. −70 millivolts
7. −90 millivolts

ANS: D

3. A 44-year-old man is recovering from third degree burns over 50% of his body surface area. His serum potassium level is low (2.9 mEq/L). He exhibits postural hypotension and skeletal muscle weakness. If the equilibrium potential for K⁺ in a neuron is −105 mV and the equilibrium potential for Na⁺ is +55 mV, what would be an approximate value for the resting membrane potential for a neuron in this man?

1. +20 mV
2. +48 mV
3. +80 mV
4. −25 mV
5. −48 mV
6. −96 mV

ANS: F

4. A 23-year-old man receives a crush injury to his right leg in an automobile accident. His serum potassium level is 6.4 mEq/L. The equilibrium potential for K⁺ in a motoneuron is −73 mV, and the equilibrium potential for Na⁺ is +59 mV. Which of the following best describes the resting membrane potential (in mV) for a typical motoneuron in this man?

1. +62
2. +90
3. −13
4. −67
5. −84

ANS: D

5. A 56-year-old woman is referred to the neurology clinic for evaluation of her long-term problem of a stumbling gait and a tendency to fall. Her visual acuity also seems to change periodically. Neurological findings suggest multiple sclerosis. This diagnosis is further supported by magnetic resonance imaging, which shows of areas of demyelination in the central nervous system. Other tests show the presence of oligoclonal bands in the spinal fluid. The loss of myelin from a nerve fiber has which of the following effects?

1. Decreased conduction velocity of action potential or no action potential
2. Decreased energy requirement for successful action potentials
3. Increased conduction velocity of action potential
4. Increased velocity of salutatory conduction

ANS: A