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Muscle Contractions and the Effects of Anesthetics

Prior to intubation for a surgical procedure, the anesthesiologist administered a single dose of the neuromuscular blocking agent, 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.

1. Beginning with depolarization at the neuromuscular junction, describe the normal sequence of events which lead to muscle contraction.

2. What prevents acetylcholine (ACh) from accumulating in the neuromuscular junction and causing a sustained contraction in a normal individual?

3. 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.

Solution Preview

1. When the action potential produced by the nerve in response to the stimulus reaches the synapse at the neuromuscular junction, the voltage causes Ca2+ voltage-gated channels in the membrane to open, allowing an influx of Ca2+ ions into the synaptic bulb. This in turn then causes vesicles in the synaptic bulb to fuse with the membrane, discharging their contents (the neurotransmitter acetylcholine) into the neuromuscular junction space. This acetylcholine attaches to receptors on the membrane of the muscle cell (sarcolemma) that act as voltage-gated channels for Na+ and produce an influx of Na+ ions into the muscle cell. The resting potential of a muscle cell is about -95mV, and the increase of Na+ ions in the interior of the cell increases this potential. When it reaches the threshold of about -50mV, this triggers a large increase in the movement of Na+ ions into the cell and an action potential is created. This action potential then ...

Solution Summary

In this solution, a discussion of the effects of anesthetics on muscle contraction is given.

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