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The Muscular System Chapter 9

The Muscular System Chapter 9. Anatomy of skeletal muscles. Anatomy of the Muscular System. Origin - Muscle attachment that remains fixed Insertion - Muscle attachment that moves

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The Muscular System Chapter 9

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  1. The Muscular System Chapter 9

  2. Anatomy of skeletal muscles

  3. Anatomy of the Muscular System • Origin - Muscle attachment that remains • fixed • Insertion - Muscle attachment that moves • Action - What movement a muscle produces. Movement usually occurs at joints i.e. flexion, extension, abduction, etc.

  4. For muscles to create a movement, they can only pull, not push • Muscles in the body rarely work alone, & are usually arranged in groups surrounding a joint • A muscle that contracts to create the desired action is known as an agonist or prime mover • A muscle that helps the agonist is a synergist. Some synergists act as fixators • A muscle that opposes the action of the agonist, therefore undoing the desired action is an antagonist

  5. Fascicle arrangement within skeletal muscles

  6. To understand how muscles move the body (their actions), you must understand the attachments of the muscles (origin & insertion), and the arrangement of fascicles within the muscle (parallel, circular, etc.)

  7. To describe the actions of skeletal muscles, most of the time you describe the specific motions that occur at the moving joint Exceptions: muscles of facial expression

  8. Skeletal muscle movements (see chap. 8 – motions occurring at synovial joints) Flexion/extension/hyperextension Lateral flexion (spinal joints) Abduction/adduction (extremity joints) Rotation – left/right (spinal joints); internal(medial)/external(lateral) (extremity joints) Pronation/supination (proximal radio-ulnar joint) Dorsiflexion/plantarflexion (ankle joint) Inversion/eversion (tarsal joints) Elevation/depression (TMJ; scapulothoracic junction) Protraction/retraction (TMJ; scapulothoracic junction)

  9. Naming of Skeletal Muscles

  10. The primary tissue found within the muscular system is muscle tissue • Characteristics associated with muscle tissue: • Excitability • Contractility • Extensibility • Elasticity - Tissue can receive & respond to stimulation - Tissue can shorten & thicken - Tissue can lengthen - After contracting or lengthening, tissue always wants to return to its resting state

  11. Functions of muscle tissue: • Movement – both voluntary & involuntary • Maintaining posture • Supporting soft tissues within body cavities • Guarding entrances & exits of the body • Maintaining body temperature

  12. Types of muscle tissue: • Skeletal muscle tissue • Associated with & attached to the skeleton • Under our conscious (voluntary) control • Microscopically the tissue appears striated • Cells are long, cylindrical & multinucleate

  13. Cardiac muscle tissue • Makes up myocardium of heart • Unconsciously (involuntarily) controlled • Microscopically appears striated • Cells are short, branching & have a single nucleus • Cells connect to each other at intercalated discs

  14. Smooth (visceral) muscle tissue • Makes up walls of organs & blood vessels • Tissue is non-striated & involuntary • Cells are short, spindle-shaped & have a single nucleus • Tissue is extremely extensible, while still retaining ability to contract

  15. Organization of Skeletal Muscles (cell)

  16. Microanatomy of a Skeletal Muscle Fiber (cell)

  17. Microanatomy of a Muscle Fiber (Cell) transverse (T) tubules sarcoplasmic reticulum sarcolemma terminal cisternae myoglobin mitochondria thick myofilament thin myofilament myofibril triad nuclei

  18. Muscle fiber sarcomere Z-line myofibril Thin filaments Thick filaments Myosin molecule of thick filaments Thin filament

  19. Thin Myofilament Z-line (myosin binding site)

  20. Thick myofilament M-line (has ATP & actin binding site)

  21. Sarcomere A band Z line Z line H zone I band Zone of overlap Zone of overlap M line Thin myofilaments Thick myofilaments

  22. Sliding Filament Theory • Myosin heads attach to actin molecules (at binding (active) site) • Myosin “pulls” on actin, causing thin myofilaments to slide across thick myofilaments, towards the center of the sarcomere • Sarcomere shortens, I bands get smaller, H zone gets smaller, & zone of overlap increases

  23. As sarcomeres shorten, myofibril shortens. As myofibrils shorten, so does muscle fiber • Once a muscle fiber (cell) begins to contract, it will contract maximally • This is known as the “all or none” principle

  24. Physiology of skeletal muscle contraction • Skeletal muscles require stimulation from the nervous system in order to contract • Motor neuronsare the cells that cause muscle fibers to contract cell body dendrites Synaptic terminals (synaptic end bulbs) axon telodendria motor neuron axon hillock End bulbs contain vesicles filled with Acetylcholine (ACh)

  25. Anatomy of the Neuromuscular junction telodendria Synaptic terminal (end bulb) Synaptic vessicles containing Ach Synaptic cleft Motor end plate of sarcolemma

  26. Basic Physiology of Skeletal Muscle Contraction

  27. Skeletal muscles are made up of thousands of muscle fibers • A single motor neuron may directly control a few fibers within a muscle, or hundreds to thousands of muscle fibers • All of the muscle fibers controlled by a single motor neuron constitute a motor unit

  28. The size of the motor unit determines how fine the control of movement can be – • small motor units  precise control (e.g. eye muscles) • large motor units gross control (e.g. leg muscles) • Recruitmentis the ability to activate more motor units as more force (tension) needs to be generated

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