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The Muscular System

The Muscular System . Types of muscle. Skeletal (voluntary; nervous control) Cardiac (involuntary; nervous and endocrine control) Smooth (involuntary; nervous and endocrine control). B. Functions. Produce movement Maintain posture and organ volume Thermogenesis . The Muscular System .

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The Muscular System

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  1. The Muscular System Types of muscle • Skeletal (voluntary; nervous control) • Cardiac (involuntary; nervous and endocrine control) • Smooth (involuntary; nervous and endocrine control) B. Functions • Produce movement • Maintain posture and organ volume • Thermogenesis

  2. The Muscular System C. Skeletal muscle • Voluntary • Conscious control • Somatic nervous system • So what are reflexes? • 2. Gross anatomy • Superficial fascia and deep fascia • Origins and insertions

  3. The Muscular System C. Skeletal muscle • 3. Microscopic anatomy • Myofiber • Myofibrils • Myofilaments • Thick myofilament (myosin) • Thin myofilaments (actin, tropomyosin-troponin complex) • d. Sarcomere

  4. The Muscular System C. Skeletal muscle • 4. Neuromuscular junction • Motor neuron • Synaptic cleft • Motor end plate • Acetylcholine • Ach receptors • Depolarization • Sliding filament theory

  5. The Muscular System C. Skeletal muscle • Motor unit • Fast- vs. slow-twitch fibers • Muscle tone • Myogram • Latent period • Contraction period • Relaxation period

  6. The Muscular System D. Smooth muscle • Locations • Microscopic anatomy • Types • Visceral • Multiunit • visceral • multiunit • Involuntary – unconscious • Autonomic nervous system, hormones, local stretch

  7. The Muscular System E. Cardiac muscle • AKA - myocardium • Microscopic anatomy • Intercalated discs • Atrial and ventricular masses • Functional syncytium • Autorhythmic • Autonomic, hormonal, chemical, and local control

  8. The Muscular System F. Age-related changes in skeletal muscle • Reduction in total muscle mass • Decrease in number of fibers • Decrease in fiber diameters • Lost fibers replaced by fat • Factors that influence these changes • Exercise • Nutrition • Heredity

  9. The Muscular System F. Age-related changes in skeletal muscle • 4. Reduction in total muscle strength • 10 – 20% up to age 70 • >70, up to 50% loss on strength • Lifetime activity level determines rate of strength loss • Low-intensity exercise for older persons leads to increases in: • Strength • Range of motion • Balance

  10. The Muscular System F. Age-related changes in skeletal muscle • Changes in fast/slow-twitch fibers • Anatomical changes in myofibrils • Loss of motor neurons • Leading cause of muscular atrophy and loss of tone • Motor units become smaller, therefore weaker • Decreased acetylcholine • Decreased response time to stimuli

  11. The Muscular System G. Age-related changes in smooth muscle • 1. Generalized loss of tone, leading to: • Urinary bladder incontinence • GI tract diverticulosis  diverticulitis • 2. In arteries: • Cells may accumulate fat vacuoles • Increased collagen between cells

  12. The Muscular System H. Age-related changes in cardiac muscle • >50, fibers decrease in diameter = loss of strength • Accumulated fat between fibers becomes fibrous • Lipofuscin accumulates (brown atrophy)

  13. The Muscular System I. Age-related dysfunctions • Parkinson’s disease • Dysfunction of basal ganglia of cerebrum (neural problem) • Tremors and rigidity • Gradual loss of semi-voluntary movements

  14. The Muscular System I. Age-related dysfunctions • 2. Myasthenia gravis • Autoimmune disorder directed against acetylcholine receptors • Motor end plate becomes increasingly less sensitive to ACh • General results include: • Weakness and fatigue, especially with repetitive motion • Drooping eyelids • Difficulty swallowing, talking, breathing

  15. The Muscular System I. Age-related dysfunctions • 3. Muscle cramps • Severe, sustained contractions of one or more motor units of skeletal muscle • May last seconds to hours • Occurs most often in calves and feet • Causes: • Poor circulation in extremities • Abnormal motor neuron stimulation • Low blood levels of glucose, sodium, calcium

  16. The Muscular System I. Age-related dysfunctions • 4. Polymyositis • Inflammatory disease of skeletal and cardiac muscles • Autoimmune origin (?) • General results include: • Weakness in hips/thighs, making it hard to rise from a squat or kneel, walk stairs • Weakness in neck extensors and muscles of swallowing • Difficulty breathing and dry cough

  17. The Muscular System I. Age-related dysfunctions • 5. Polymyalgia rheumatica • 2 times more common in women than men • Incidence increases rapidly with age • General results include: • Bilateral pain and stiffness in shoulders and thighs • Discomfort leads to immobility, depression, weight loss, fever • Usually resolves but may cause permanent incapacity

  18. The Muscular System J. Take home messages • Progressive loss of skeletal muscle mass, strength, and tone with aging, much of which is related to loss of motor neurons • Life-long exercise determines rate of loss • Muscle cells can be replaced by fat and collagen • Aging skeletal muscles respond more slowly • Cardiac and smooth muscles show similar effects end

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