muscle relaxant, an agent that reduces the contractility of muscle fibers. Curare derivatives and succinylcholine compete with acetylcholine and block neural transmission at the myoneural junction. These drugs are used during anesthesia, in the management of patients undergoing mechanical ventilation, and in shock therapy, to reduce muscle contractions in pharmacologically or electrically induced seizures. Several drugs that relieve muscle spasms act at various levels in the central nervous system: baclofen inhibits reflexes at the spinal level; cyclobenzaprine acts primarily in the brainstem; and the benzodiazepines reduce muscle tension, chiefly by acting on mechanisms that control muscle tone. Dantrolene acts directly on muscles in reducing contraction and apparently achieves its effect by interfering with the release of calcium from the sarcoplasmic reticulum.
