Download Chapter 6 The Muscular System

The Muscular System
A. Types of muscle
1. Skeletal (voluntary; nervous control)
2. Cardiac (involuntary; nervous and endocrine control)
3. Smooth (involuntary; nervous and endocrine control)
B. Functions
1. Produce movement
2. Maintain posture and organ volume
3. Thermogenesis
The Muscular System
C. Skeletal muscle
1. Voluntary
a. Conscious control
b. Somatic nervous system
c.
So what are reflexes?
2. Gross anatomy
a. Superficial fascia and deep fascia
b. Origins and insertions
The Muscular System
C. Skeletal muscle
3. Microscopic anatomy
a. Myofiber
b. Myofibrils
c.
Myofilaments
i.
Thick myofilament (myosin)
ii.
Thin myofilaments (actin,
tropomyosin-troponin complex)
d. Sarcomere
The Muscular System
C. Skeletal muscle
4. Neuromuscular junction
a. Motor neuron
b. Synaptic cleft
c.
Motor end plate
d. Acetylcholine
e. Ach receptors
f.
Depolarization
g. Sliding filament theory
The Muscular System
C. Skeletal muscle
5. Motor unit
6. Fast- vs. slow-twitch fibers
7. Muscle tone
8. Myogram
a. Latent period
b. Contraction period
c.
Relaxation period
The Muscular System
D. Smooth muscle
1. Locations
2. Microscopic anatomy
3. Types
a. Visceral
b. Multiunit
visceral
multiunit
4. Involuntary – unconscious
5. Autonomic nervous system, hormones, local stretch
The Muscular System
E. Cardiac muscle
1. AKA - myocardium
2. Microscopic anatomy
a. Intercalated discs
b. Atrial and ventricular masses
c.
Functional syncytium
3. Autorhythmic
4. Autonomic, hormonal, chemical,
and local control
The Muscular System
F. Age-related changes in skeletal muscle
1. Reduction in total muscle mass
a. Decrease in number of fibers
b. Decrease in fiber diameters
2. Lost fibers replaced by fat
3. Factors that influence these changes
a. Exercise
b. Nutrition
c.
Heredity
The Muscular System
F. Age-related changes in skeletal muscle
4. Reduction in total muscle strength
a. 10 – 20% up to age 70
b. >70, up to 50% loss on strength
5. Lifetime activity level determines rate of strength loss
6. Low-intensity exercise for older persons leads to
increases in:
a. Strength
b. Range of motion
c.
Balance
The Muscular System
F. Age-related changes in skeletal muscle
7. Changes in fast/slow-twitch fibers
8. Anatomical changes in myofibrils
9. Loss of motor neurons
a. Leading cause of muscular atrophy and loss of tone
b. Motor units become smaller, therefore weaker
10. Decreased acetylcholine
11. Decreased response time to stimuli
The Muscular System
G. Age-related changes in smooth muscle
1. Generalized loss of tone, leading to:
a. Urinary bladder incontinence
b. GI tract diverticulosis  diverticulitis
2. In arteries:
a. Cells may accumulate fat vacuoles
b. Increased collagen between cells
The Muscular System
H. Age-related changes in cardiac muscle
1. >50, fibers decrease in diameter = loss of strength
2. Accumulated fat between fibers becomes fibrous
3. Lipofuscin accumulates (brown atrophy)
The Muscular System
I. Age-related dysfunctions
1. Parkinson’s disease
a. Dysfunction of basal ganglia of cerebrum (neural problem)
b. Tremors and rigidity
c.
Gradual loss of semi-voluntary movements
The Muscular System
I. Age-related dysfunctions
2. Myasthenia gravis
a. Autoimmune disorder directed against
acetylcholine receptors
b. Motor end plate becomes increasingly less
sensitive to ACh
c.
General results include:
i.
Weakness and fatigue, especially with repetitive motion
ii.
Drooping eyelids
iii.
Difficulty swallowing, talking, breathing
The Muscular System
I. Age-related dysfunctions
3. Muscle cramps
a. Severe, sustained contractions of one or
more motor units of skeletal muscle
b. May last seconds to hours
c.
Occurs most often in calves and feet
d. Causes:
i.
Poor circulation in extremities
ii.
Abnormal motor neuron stimulation
iii.
Low blood levels of glucose, sodium, calcium
The Muscular System
I. Age-related dysfunctions
4. Polymyositis
a. Inflammatory disease of skeletal and cardiac muscles
b. Autoimmune origin (?)
c.
General results include:
i.
Weakness in hips/thighs, making it hard to rise from a squat
or kneel, walk stairs
ii.
Weakness in neck extensors and muscles of swallowing
iii.
Difficulty breathing and dry cough
The Muscular System
I. Age-related dysfunctions
5. Polymyalgia rheumatica
a. 2 times more common in women than men
b. Incidence increases rapidly with age
c.
General results include:
i.
Bilateral pain and stiffness in shoulders and thighs
ii.
Discomfort leads to immobility, depression, weight loss,
fever
iii.
Usually resolves but may cause permanent incapacity
The Muscular System
J. Take home messages
1. Progressive loss of skeletal muscle mass, strength, and
tone with aging, much of which is related to loss of
motor neurons
2. Life-long exercise determines rate of loss
3. Muscle cells can be replaced by fat and collagen
4. Aging skeletal muscles respond more slowly
5. Cardiac and smooth muscles show similar effects
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