Question 1

Lambert-Eaton myasthenic syndrome is an autoimmune disease in which antibodies damage which of the following?&#10;A)Acetylcholine&#10;B)Ligand-gated channels on postsynaptic membrane&#10;C)Ligand-gated channels on presynaptic membrane&#10;D)Voltage-gated channels on postsynaptic membrane&#10;E)Voltage-gated channels on presynaptic membrane

Accepted Answer

Lambert-Eaton myasthenic syndrome is characterized by the presence of antibodies that damage voltage-gated calcium channels on the presynaptic membrane, leading to a decrease in acetylcholine release and muscle weakness.

Question 2

An end plate potential in skeletal muscle could theoretically be generated by a decrease in permeability to which of the following ions?&#10;A)Ca++&#10;B)K+&#10;C)Na+

Accepted Answer

A decrease in permeability to K⁺ would lead to depolarization, as K⁺ would not leave the cell as readily, making the inside of the cell more positive and potentially generating an end plate potential.

Question 3

A 59-year-old college professor visits his physician because of muscle fatigue that worsens later in the day. The physician notices that the man has droopy eyelids and seems to have an overall weakness in his muscles. After the intravenous administration of Tensilon, which blocks degradation of acetylcholine, the droopy eyelids and symptoms of muscle weakness appear to subside. Which of the following best describes the patient's condition?

A)Encephalitis
B)Fibromyalgia
C)Flaccid paralysis
D)Myasthenia gravis
E)Poliomyelitis

D

Accepted Answer

The patient's symptoms of muscle weakness and droopy eyelids are consistent with myasthenia gravis, an autoimmune disorder that causes muscle weakness by interfering with the transmission of nerve impulses to muscles. The improvement of symptoms after the administration of Tensilon confirms the diagnosis, as Tensilon specifically works by blocking the breakdown of acetylcholine, a neurotransmitter that is decreased in myasthenia gravis. Encephalitis is inflammation of the brain, fibromyalgia is a chronic pain disorder that does not typically cause muscle weakness or droopy eyelids, flaccid paralysis is a form of paralysis characterized by limp and unresponsive muscles, and poliomyelitis is a viral infection that can cause muscle weakness but typically affects younger individuals and is rare in developed countries due to vaccination efforts.

Question 4

Electrical stimulation of a dorsal root fiber that synaptically connects with a motoneuron is observed to cause an electrotonic depolarization of the postsynaptic motoneuron. Which of the following changes in ion channels is the most likely cause for this depolarizing potential?

A)Closing of ligand-gated cation channel
B)Closing of voltage-gated anion channel
C)Opening of ligand-gated cation channel
D)Opening of voltage-gated anion channel

Accepted Answer

If an electrical stimulation causes a depolarization of a postsynaptic motoneuron, it means that there is an influx of positive charge. The only option that would cause this is the opening of a ligand-gated cation channel, which allows positive ions such as Na+ or Ca2+ to enter the cell. Closing of a ligand-gated cation channel or opening of a voltage-gated anion channel would cause a hyperpolarization, while closing of a voltage-gated anion channel would have no effect on the membrane potential.

Question 5

A 3-year-old child is admitted to the emergency department of a university hospital. The child exhibits extreme salivation, lacrimation, tremors, and tachycardia. The slight erythema and mild edema found on the child's hand suggest a spider bite. The mother acknowledges that the child has a fascination with spiders and has seen black widow spiders in the yard. The neurotoxic venom of the black widow spider (i.e., latrotoxin or latrophilin) can increase the flux of calcium ions into the presynaptic terminal. What is the likely outcome of a black widow spider bite?

A)Decreased acetylcholine release from nerve terminals
B)Hyperpolarization of postsynaptic membranes
C)Hyperpolarization of presynaptic membranes
D)Increased acetylcholine release from nerve terminals
E)Inhibition of acetylcholinesterase

Accepted Answer

The neurotoxic venom of the black widow spider causes an increased flux of calcium ions into the presynaptic terminal, leading to increased acetylcholine release from nerve terminals. This can result in the symptoms exhibited by the child, including extreme salivation, lacrimation, tremors, and tachycardia. Therefore, increased acetylcholine release from nerve terminals is the likely outcome of a black widow spider bite.

Question 6

A father and his 10-year-old daughter died suddenly of suffocation after ingesting smoked whitefish chubs from the Great Lakes. Three other family members are sick, complaining of dry mouth despite drinking copious amounts of fluids. Their upper eyelids droop. Their vision is clear, but their pupils are wide and do not narrow when a light is flashed. Two of them require artificial respiration. The suspected pathogen is botulism (Clostridium botulinum). The surviving patients begin improving soon after receiving the only treatment available, E antitoxin. The deadly effect of botulinum toxin results from which of the following?

A)Decreased release of acetylcholine
B)Decreased release of norepinephrine
C)Depletion of muscle calcium stores
D)Skeletal muscle tetany
E)Stimulation of ryanodine receptors

Accepted Answer

Botulinum toxin inhibits the release of the neurotransmitter acetylcholine, leading to muscle paralysis and respiratory failure. This is the mechanism of action that leads to the deadly effects of botulism.

Question 7

An apparently healthy 12-year-old boy dies during a minor surgical procedure while under general anesthesia. An uncle had also died during a surgical procedure. Results of a halothane contracture test indicate that the child had malignant hyperthermia. Malignant hypothermia crisis is associated with which of the following?

A)Decreased anaerobic metabolism
B)Decreased CO₂ production by muscles
C)Decreased lactic acid production by muscles
D)Defective ryanodine receptors
E)Decreased usage of adenosine triphosphate in muscles

Accepted Answer

Malignant hyperthermia crisis is associated with defective ryanodine receptors in skeletal muscles, leading to uncontrolled release of calcium ions and subsequent hypermetabolic state. This results in increased anaerobic metabolism, CO₂ production, and lactic acid production by muscles, as well as increased usage of adenosine triphosphate in muscles, leading to hyperthermia, acidosis, muscle rigidity, and potential organ failure.

Question 8

Myasthenia gravis is an autoimmune disease in which antibodies damage which of the following?&#10;A)Acetylcholine&#10;B)Ligand-gated channels on postsynaptic membrane&#10;C)Ligand-gated channels on presynaptic membrane&#10;D)Voltage-gated channels on postsynaptic membrane&#10;E)Voltage-gated channels on presynaptic membrane

Accepted Answer

Myasthenia gravis is caused by the production of antibodies against the ligand-gated channels on the postsynaptic membrane at the neuromuscular junction. These channels normally bind acetylcholine released by the presynaptic neuron, allowing the opening of ion channels that trigger muscle contraction. By blocking or reducing the function of these channels, the antibodies disrupt the neural transmission and cause weakness and fatigue in affected muscles. The other choices are not specific to myasthenia gravis or do not accurately reflect the underlying mechanism of the disease.

Question 9

Skeletal muscle and cardiac muscle contract when calcium binds to which structure or molecule?&#10;A)Active sites&#10;B)Calmodulin&#10;C)Myosin head&#10;D)Tropomyosin&#10;E)Troponin C

Accepted Answer

Calcium binds to troponin C, which causes a conformational change in the troponin-tropomyosin complex that exposes the active sites on actin filaments, allowing for myosin heads to bind and initiate muscle contraction. This is the case for both skeletal and cardiac muscle.

Question 10

A 23-year-old man loses consciousness while driving, hits a tree, and dies within 15 minutes. The police find his stiff body 5 hours later. Rigor mortis is caused by a decrease in which of the following?

A)Acetylcholine
B)Actin-myosin cross-bridges
C)Myoplasmic calcium levels
D)Interstitial lactate levels
E)Muscle adenosine triphosphate levels

Accepted Answer

Rigor mortis is caused by a decrease in muscle adenosine triphosphate (ATP) levels. After death, the body ceases to produce ATP, which is necessary for muscle relaxation. Without ATP, myosin molecules in the muscles remain attached to actin, causing the muscles to become stiff.

Question 11

A physiology experiment is conducted in which Drug X is applied to a nerve axon. The drug causes a gradual decrease in the amplitude of individual action potentials and a gradual depolarization of the resting membrane potential. Drug X is most likely to inhibit which of the following?

A)Na+ inactivation
B)Na+-K+-ATPase pump
C)Voltage-gated K+ channels
D)Voltage-gated Na+ channels

Accepted Answer

The answer of A physiology experiment is conducted in which...

Deck 7: Excitation of Skeletal Muscle: Neuromuscular Transmission and Excitation-Contraction Coupling