The masseter is the strongest muscle in the human body and is responsible for lifting the lower jaw to close the mouth. The location of the masseter can be seen in the diagram.
Which of the following is not an event which would occur in the masseter as the jaw is moved towards its closed position?
Myosin heads perform a power stroke which is driven by energy released in the hydrolysis of ATP
The sarcomeres shorten as the Z lines are pulled together but the A band remains the same length.
Calcium ions are actively pumped back into the sarcoplasmic reticulum and tropomyosin covers binding sites
Troponin complexes change shape leading to the exposure of binding sites on actin molecules
Polymyositis (PM) is an autoimmune disease of the muscles in which T-cells and B-cells are activated by antigens located on striated muscles of the body.
Which of the following statements is unlikely to result from polymyositis?
Muscle biopsies of patients shows increased levels of antibodies
Blood pressure may decrease as vascular muscle deteriorates
Patients exhibit weakening of biceps and triceps muscles
Progression of the disease may result in poor posture
Rigor mortis describes the stiffening of body muscles due to chemical change in myofibrils after death. Knowledge of the stages of rigor mortis allows pathologists to estimate the time of death accurately.
Algor mortis refers to the gradual decrease in the body's temperature after death.
The graph shows the onset of Rigor mortis and Algor mortis after death.
Which of the following options shows a valid explanation for the trends shown in the graph?
Trend
Explanation
A
Body temperature decreases from 0 to 36 hours after death
Calcium is not replenished due to lack of ATP
B
Rigor mortis peaks at 12 hours after death
ATP is no longer available to break actin-myosin cross bridges
C
Body temperature increases slightly 36 hours after death
Energy is released from hydrolysis of the remaining ATP
D
Rigor mortis increases gradually after death
ATP becomes depleted so muscles cannot remain relaxed.
