Prof En 1 - Physiology

A 35-year-old patient exhibits muscle weakness with no signs of sensory loss. Nerve conduction velocity is normal. Which of the following is the MOST likely physiological explanation?

• Demyelination of peripheral nerves

• Inhibition of acetylcholinesterase

• Decreased calcium release from the sarcoplasmic reticulum

• Damage to the dorsal root ganglia

During high-intensity resistance training, which muscle fiber type undergoes the MOST hypertrophy?

• Type I

• Type IIa

• Type IIb

• Type III

Which of the following BEST explains why rigor mortis occurs after death?

• Excess calcium is pumped into the SR post-mortem

• Lack of ATP prevents detachment of myosin from actin

• Increased ATP causes sustained contraction

• Inhibition of acetylcholine release at the neuromuscular junction

In a case of muscular dystrophy, what is the PRIMARY pathophysiological mechanism that leads to progressive muscle weakness?

• Loss of troponin binding

• Overactivation of myosin ATPase

• Defective dystrophin protein affects sarcolemma integrity

• Excessive accumulation of acetylcholine in the synapse

Which molecular event occurs IMMEDIATELY AFTER the action potential reaches the T-tubule?

• Cross-bridge detachment

• Opening of ryanodine receptors on the SR

• Binding of calcium to troponin C

• Release of acetylcholine from the axon terminal

A 45-year-old athlete complains of fatigue during endurance activities. Which enzyme deficiency would MOST likely impair aerobic ATP production in skeletal muscle?

• Creatine kinase

• Myosin ATPase

• Citrate synthase

• Lactate dehydrogenase

Which of the following scenarios BEST demonstrates the concept of the length-tension relationship in skeletal muscle?

• A muscle contracts more forcefully when overstretched

• Maximum force is generated when actin and myosin overlap optimally

• Muscle force is independent of initial muscle length

• Greater passive tension always leads to greater active tension

A researcher inhibits ATP synthase in a skeletal muscle cell. What is the MOST immediate physiological consequence during contraction?

• Increased cross-bridge cycling

• Inability to release calcium from the SR

• Reduced detachment of myosin from actin

• Increased mitochondrial calcium uptake

In isometric contraction, which of the following BEST describes the muscle's behavior?

• Muscle length increases while tension remains constant

• Muscle length remains constant while tension increases

• Muscle shortens without generating force

• Muscle produces movement without neural input

A drug that blocks voltage-gated calcium channels at the axon terminal would MOST likely cause which of the following effects on skeletal muscle contraction?

• Enhanced acetylcholine release and stronger contractions

• No effect on muscle function

• Decreased acetylcholine release and weakened contractions

• Prolonged depolarization of the muscle fiber