Explain how a muscle fiber contracts
What will be an ideal response?
Each muscle fiber is connected to a single nerve cell at the neuromuscular junction. When the electrical impulse reaches the end of the nerve cell, the nerve cell releases the neurotransmitter acetylcholine. Acetycholine is a chemical messenger that moves across the neuromuscular junction and acts as a key to unlock receptors on the muscle fiber. This changes the permeability of the cell membrane and allows calcium ions to flow into the muscle fiber. Calcium ions cause the thin filaments to slide between the thick filaments, shortening the muscle and producing a muscle contraction.
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The standing toe touch causes excessive strain on the _____.
A. shoulders and spine B. neck and shoulders C. lower back and knees D. intervertebral disks E. spine, knees, and shoulders
An inflammation of the inner lining of the heart is known as ____________________
Fill in the blank(s) with correct word
Which of the following is TRUE concerning asthma?
A) It is not influenced by genetics or family history. B) It is the most common chronic illness in adults over age 35. C) It has increased in prevalence over the last 20 years. D) It is essentially hay fever affecting the lungs.
Disk-shaped blood cells without nuclei are called:
A) leukocytes. B) platelets. C) erythrocytes. D) thrombocytes.