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Download Week 5, Muscles, Feb 12, student version
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Muscles Types of muscles- skeletal • • • • Attached to bones of skeleton Voluntary Multinucleate cells Striated Types of muscles- smooth • Internal organs/tubes • Involuntary • Lack striations Types of muscles- cardiac • • • • Only found in heart Involuntary Uninucleate cells Striated Skeletal muscle Structure of skeletal muscle Within a muscle cell • Sarcolemma- cell membrane • Myofibril- contractile proteins, actin/myosin • Wrapped by sarcoplasmic reticulum Myofibril Myosin • Creates the movement • Composed of protein chains that intertwine • Long tail, two heads, hinge to allow heads to move • 250 myosin molecules = thick filament Actin • Multiple actin molecules polymerize • Two twist to form thin filaments • One myosin head to one actin molecule Combined • Sarcomere- light/dark repeat Muscle contraction Muscle contraction • Tropomyosin- covers actin, prevents myosin from tightly binding • Troponin- gatekeeper Sliding filaments http://www.youtube.com/watch?v=jqy0i1KXUO 4&list=PL3EED4C1D684D3ADF&index=31 How much tension can be generated? Moving bone • Muscles must contract to move bones • Attachment to bone – Origin- stationary bone – Insertion- movable bone Can only pull on a bone, not push Types of contractions • Isotonic- muscle contracts and changes length • Isometric- muscle contracts but does not change length – Concentric- shortening – Eccentric- lengthening (a) Muscle contracts with force greater than resistance and shortens (concentric contraction) (b) Muscle contracts with force less than resistance and lengthens (eccentric contraction) (c) Muscle contracts but does not change length (isometric contraction) No movement Movement Movement Smooth muscle Smooth muscle • Internal organs • Many differences between skeletal and smooth muscle Communicating with neighbors Uterus Other differences • • • • • • • Operate over varying lengths (e.g., bladder) Layers run in different directions Contract slower Sustained contractions without fatiguing Responds from chemical or electrical signal Lack specialized receptor regions Lack sarcomeres • Allows for deformation Cardiac muscle Cardiac muscle • • • • Features of smooth and skeletal muscle Striated, sarcomere Uninucleate Intercalated discs (gap junctions)
