The Muscular System

1. The Muscular System

2. The Muscular System • Muscles are responsible for all types of body movement • Three basic muscle types found in the body • Skeletal muscle • Cardiac muscle • Smooth muscle

3. Skeletal Muscle • Location: • Attaches to bones or skin (face muscles) • Cell Shape and Appearance: • Multinucleated (many nuclei per cell) • Striations (stripes) • Single long cylindrical cells • Regulation of Contraction: • Voluntary • Nervous System control • Contraction Speed: • Slow to fast • Rhythmic contraction: • No

4. Cardiac Muscle • Location: • Walls of heart • Cell Shape and Appearance: • Branching chains of cells • Striated • Uninucleate (1 nucleus per cell) • Regulation of Contraction: • Involuntary; has pacemaker • Nervous System control • Hormonal control (ex: ANP) • Contraction Speed: • Slow • Rhythmic contraction: • Yes (“lub dub”)

5. Smooth Muscle • Location: • Wall of visceral organs (not the heart) • Ex: stomach, intestines, esophagus, rectum • Cell Shape and Appearance: • Single cells • No Striations • Fusiform (wide in middle; tapered at ends) • Uninucleate (1 nucleus per cell) • Regulation of Contraction: • Involuntary • Nervous System control • Hormonal control • Contraction Speed: • Slow • Rhythmic contraction: • Yes (in some)

6. Characteristics of Muscles • Muscle cells are elongated (muscle cell = muscle fiber) • Contraction of muscles is due to the movement (sliding) of microfilaments • Micro = small • All muscles share some terminology • Prefix my(o)-refers to muscle • ex. myosin • Prefix mys-refers to muscle • ex. epimysium • Prefix sarc(o)-refers to flesh • ex. sarcomere • sarcophagus • phag(o) = eat

7. Connective Tissue Wrappings of Skeletal Muscle • Endomysium • around single muscle fiber • Perimysium around a fascicle (bundle) of fibers • Epimysium covers the entire skeletal muscle Figure 6.1

8. Skeletal Muscle Attachments • Epimysium blends into a connective tissue attachment • Tendon – cord-like structure • Aponeuroses – sheet-like structure • Sites of muscle attachment • Bones • Cartilages • Connective tissue coverings

9. Function of Muscles • Produce movement • Maintain posture • Stabilize joints • Generate heat

10. Microscopic Anatomy of Skeletal Muscle • Cells are multinucleate • Nuclei are just beneath the sarcolemma Figure 6.3a

11. Microscopic Anatomy of Skeletal Muscle • Sarcolemma • specialized plasma membrane • Sarcoplasmic reticulum • specialized smooth endoplasmic reticulum Figure 6.3a

12. Microscopic Anatomy of Skeletal Muscle • Myofibril • Bundles of myofilaments • Myofibrils are aligned to give distinct bands • I band = light band • A band = dark band Figure 6.3b

13. Microscopic Anatomy of Skeletal Muscle • Sarcomere • Contractile unit of a muscle fiber Figure 6.3b

14. Microscopic Anatomy of Skeletal Muscle • Organization of the sarcomere • Thick filaments = myosin filaments • Composed of the protein myosin • Has ATPase enzymes Figure 6.3c

15. Microscopic Anatomy of Skeletal Muscle • Organization of the sarcomere • Thin filaments = actin filaments • Composed of the protein actin Figure 6.3c

16. Microscopic Anatomy of Skeletal Muscle • Myosin filaments have heads (extensions or cross bridges) • Myosin and Actinoverlap Figure 6.3d

17. Microscopic Anatomy of Skeletal Muscle • At rest, there is a bare zone that lacks actinfilaments • Sarcoplasmic Reticulum (SR)stores calcium Figure 6.3d

18. Properties of Skeletal Muscle Activity • Irritability • ability to receive and respond to a stimulus • Contractility • ability to shorten when an adequate stimulus is received

19. Nerve Stimulus to Muscles • Skeletal muscles must be stimulated by a nerve to contract • Motor unit • One neuron • Muscle cells stimulated by that neuron Figure 6.4a

20. Nerve Stimulus to Muscles • Neuromuscular junctions = association site of nerve and muscle Figure 6.5b

21. Nerve Stimulus to Muscles • Synaptic cleft – gap between nerve and muscle • Nerve and muscle do not make contact • Area between nerve and muscle is filled with interstitial fluid Figure 6.5b

22. Transmission of Nerve Impulse to Muscle • Neurotransmitter = Chemical released by nerve upon arrival of nerve impulse Skeletal muscle neurotransmitter = Acetylcholine

23. Transmission of Nerve Impulse to Muscle • 1. Neurotransmitter attaches to receptors on the Sarcolemma • 2. Sarcolemma becomes permeable to sodium (Na+) • 3. Sodium rushing into the cell generates an Action Potential • 4. Once started, muscle contraction cannot be stopped

24. The Sliding Filament Theory of Muscle Contraction • Activation by nerve causes myosin heads (cross-bridges) to attach to binding sites on the thin filament • Myosin heads then bind to the next site of the thin filament Figure 6.7

25. The Sliding Filament Theory of Muscle Contraction • This continued action causes a sliding of the myosin along the actin • The result is that the muscle is shortened (contracted) Figure 6.7