What is a mechanism of direct-acting skeletal muscle relaxants such as Dantrolene?

• A. Decrease the amount of calcium released
• B. Act directly on CNS
• C. Provide sedative effects
• D. Decrease the muscle's response to stimuli

Answer: (A)

Direct-acting skeletal muscle relaxants like dantrolene work by acting on the muscle cell itself to limit calcium release from the sarcoplasmic reticulum. Contraction in skeletal muscle depends on a rise in intracellular calcium; dantrolene binds to the ryanodine receptor, inhibiting calcium release, which lowers cytosolic calcium and reduces actin–myosin cross-bridge cycling. That’s why the mechanism is described as decreasing the amount of calcium released. These drugs do not act in the brain to sedate or dampen CNS activity, nor do they simply lessen the muscle’s responsiveness to stimuli; they specifically blunt the calcium trigger for contraction within the muscle fiber. This mechanism underpins their use, notably in malignant hyperthermia, where uncontrolled calcium release drives dangerous hypermetabolism.