Prior to intubation for a surgical procedure, the anesthesiologist administered a single dose of the neuromuscular blocking agen
t, succinylcholine, to a 23-year-old female to provide muscular relaxation during surgery and to facilitate the insertion of the endotracheal tube. Following this, the inhalation anesthetic was administered and the surgical procedure completed. A. Beginning with depolarization at the neuromuscular junction, describe the normal sequence of events which lead to muscle contraction.
B. What prevents acetylcholine (ACh) from accumulating in the neuromuscular junction and causing a sustained contraction in a normal individual?
C. Succinylcholine acts as a depolarizing agent that prevents repolarization of the nerve. Therefore, no further ACh is released until the drug is cleared. Name another site within the neuromuscular junction that might be affected to prevent muscle contraction. (Hint: curare acts by this mechanism.)
A. During general anesthesia drugs are administered to provide hypnosis, ensure analgesia, and skeletal muscle relaxation. The degree of relaxation is assessed by supramaximal train-of-four stimulation of the ulnar nerve and measuring the electromyogram response of the adductor pollicis muscle.
B. ACh is hydrolyzed by the enzyme acetylcholinesterase, which is on the postsynaptic membrane, with its active site facing the synaptic cleft. Succinylcholine acts as a depolarizing agent that prevents repolarization of the nerve. Therefore, no further ACh is released until the drug is cleared. Name another site within the neuromuscular junction that might be affected to prevent muscle contraction. (Hint: curare acts by this mechanism.) Curare competes with ACh for the receptor proteins on the muscle cell membrane, thus reducing the size of the end-plate potential. Thus, curare can be used as a muscle relaxant during anesthesia.
C.Thus, curare can be used as a muscle relaxant during anesthesia.
