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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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slide1

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
slide2

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
slide3

The Muscular System

C. Skeletal muscle

  • 3. Microscopic anatomy
  • Myofiber
  • Myofibrils
  • Myofilaments
  • Thick myofilament (myosin)
  • Thin myofilaments (actin, tropomyosin-troponin complex)
  • d. Sarcomere
slide4

The Muscular System

C. Skeletal muscle

  • 4. Neuromuscular junction
  • Motor neuron
  • Synaptic cleft
  • Motor end plate
  • Acetylcholine
  • Ach receptors
  • Depolarization
  • Sliding filament theory
slide5

The Muscular System

C. Skeletal muscle

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

D. Smooth muscle

  • Locations
  • Microscopic anatomy
  • Types
  • Visceral
  • Multiunit
  • visceral
  • multiunit
  • Involuntary – unconscious
  • Autonomic nervous system, hormones, local stretch
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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
slide8

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
slide9

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
slide10

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
slide11

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
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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)
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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
slide14

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
slide15

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
slide16

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
slide17

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
slide18

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

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