Question

skeletal muscle contractions ___.

a. are stimulated by sensory neurons' serotonin release

b. require the release of Na+ and K+ from a motor neuron's synaptic terminals

c. occur when acetylcholine stimulates calcium release from the sarcoplasmic reticulum

d. are more vigorous when the parasympathetic nervous system is regulating body functions

Answer 1

c) occur when acetylcholine stimulates calcium release from the sarcoplasmic reticulum

Multistep molecular processing within the muscle fiber begin with acetylcholine binding to receptors on the muscle fiber membrane. Proteins inside the muscle fibers are organized into long chains which interact with each other, reorganizing to shorten and relax. When acetylcholine reaches receptors on the membranes of muscle fibers, membrane channels open and the process that contracts a relaxed muscle fibers begins:

• Open channels allow an influx of sodium ions into the cytoplasm of the muscle fiber.
• The sodium influx also sends a message within the muscle fiber to trigger the release of stored calcium ions.
• The calcium ions diffuse into the muscle fiber.
• The relationship between the chains of proteins within the muscle cells changes, leading to the contraction.