PVS 2100 Chapter Notes - Chapter 9: Endoplasmic Reticulum, Membrane Potential, Neuromuscular Junction
19 Jan 2020
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Chapter 9: microscopic anatomy and physiology of muscle. Immediately beneath the outer cell membrane (sarcolemma) are numerous nuclei, reflecting the end-to-end fusion of shorter primitive muscles cells during development. Staining for the activity of myosin adenosine triphosphate (atpase), the enzyme that splits adenosine triphosphate (atp) to yield energy for muscle contraction, reveals that some muscle fibers stain darkly (type ii fibers), others lightly (type i fibers). These histochemical results correlate with the physiologic properties of the muscle fibers themselves: type i fibers contract slowly (slow twitch) but can contract for long periods. Type ii fibers contract quickly (fast twitch) but are more susceptible to fatigue. The electron microscope shows the striations only in the myofibrils and not in the sarcoplasm (cytoplasm of muscle cell). The light zones, or bands, called i bands, consist of thin filaments only; the darker regions, called a bands, are composed of overlapping thick and thin filaments.
