BIO 264 Lecture Notes - Lecture 5: Endoplasmic Reticulum, Sarcolemma, Cell Membrane
18 Jun 2018
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● Muscles are covered in membrane: Epimysium, outer cover of muscle, becomes tendon
● Fascicle: parts of muscles, bundle of skeletal muscles
○ Covered by perimysium: endomysium covers each of these
○ Muscle fibers: bundles of myofibers, run length of cell
● Myofibril: contain actin and myosin myofilaments arranged in sarcomeres
● Sarcolemma: cell membrane of striated muscle fiber cell
Properties of muscle cells
1. Contractility: ability to contract where proteins in cells draw closer together, does not
necessarily involve shortening
2. Excitability: response to stimulus
3. Conductivity: ability of a cell to conduct electrical changes across entire plasma
membrane
4. Extensibility: stretching without rupturing
5. Elasticity: return to original length after stretching
● Sarcolemma: myocyte plasma membrane
● Sarcoplasm: myocyte cytoplasm
● Sarcoplasmic reticulum (SR): myocyte modified endoplasmic reticulum
● Myofibril: bundles of specialized protein that allow for contraction
○ Other organelles are packed between
○ Made of actin and myosin
● Skeletal muscle fibers are formed by fusion of many embryonic myoblasts giving each
fiber multiple nuclei
● T-tubules: deep inward extensions of sarcolemma that surround each myofibril
○ Form tunnel like network within muscle fibers, continuous with exterior of cell,
extracellular fluid
● Terminal cisternae: enlarged sections of SR found flanking each T-tubule
● Muscle contractions rely on flow of ions
○ Relies on presence of channels
○ Calcium is essential and is stored on SR (sarcoplasmic reticulum)
● Dystrophin: structural protein found in striated muscle fibers that anchors the
sarcolemma to the surrounding connective tissue andn to myofibrils
● DMD (Duchenne Muscular Disorder): degenerative muscular disease occuring in almost
exclusively boys coded on X
● Sarcomere: repeating functional units of myofilaments, between Z lines
● Thick filaments: made of myosin
○ Globular heads
○ Active site binds with actin
● Thin filaments: actin, tropomyosin, troponin
○ Two intertwined chains of actin monomers with myosin head binding sites
● Categories of Proteins:
○ Contractile: generate tension
○ Regulatory: dictate fiber contraction
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Document Summary
Muscles are covered in membrane: epimysium, outer cover of muscle, becomes tendon. Fascicle: parts of muscles, bundle of skeletal muscles. Covered by perimysium: endomysium covers each of these. Muscle fibers: bundles of myofibers, run length of cell. Myofibril: contain actin and myosin myofilaments arranged in sarcomeres. Sarcolemma: cell membrane of striated muscle fiber cell. Sarcoplasmic reticulum (sr): myocyte modified endoplasmic reticulum. Myofibril: bundles of specialized protein that allow for contraction. Skeletal muscle fibers are formed by fusion of many embryonic myoblasts giving each fiber multiple nuclei. T-tubules: deep inward extensions of sarcolemma that surround each myofibril. Form tunnel like network within muscle fibers, continuous with exterior of cell, extracellular fluid. Terminal cisternae: enlarged sections of sr found flanking each t-tubule. Muscle contractions rely on flow of ions. Calcium is essential and is stored on sr (sarcoplasmic reticulum) Dystrophin: structural protein found in striated muscle fibers that anchors the sarcolemma to the surrounding connective tissue andn to myofibrils.
