Download Biol&241 9 Part4

Smooth Muscle
•  Spindle shaped
•  1/10th Skel. Musc. cell width
•  1/1000s Skel. Musc. cell length
•  Some endomysium (No Peri- or Epi-)
•  Organized into sheets
•  Typically two
•  outside [longi]
•  inside [circ]
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Innervation of Smooth Muscle
•  No NMJ
•  Instead Varicosities
•  bulbous swellings of nerve fibers
•  release neurotransmitter into diffuse
junctions
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Varicosities
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Innervation of Smooth Muscle
•  Reduced SR
•  No T-tubules
•  instead Caveolae (Latin “Little Caves”)
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Caveolae
Caveolae sequester Ca2+ from ECF
Striations on cell?
No
No sarcomeres
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Source: http://imgur.com/gallery/g0buc
Myofilaments in Smooth Muscle
•  Three main differences in microanatomy
1.  No troponin
•  Instead: protein calmodulin
2.  Myofilaments spirally arranged
•  contract in corkscrew manner
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Nucleus
Contracted smooth muscle fiber
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Education,
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Dense bodies
Intermediate
filament
Dense bodies
3.  Intermediate Filaments – Dense bodies network
•  Dense bodies
•  anchor intermediate filaments to sarcolemma
•  Cable-like structure
•  harnesses contraction
•  syncs all cells to each other
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Contraction of Smooth Muscle
•  Slow, low energy, synchronized contractions
•  Some pacemakers
•  Neural control
•  excitatory/inhibitory effects – depends on NT
•  Hormonal control
•  diff organs excited by diff hormones
•  i.e. gastrin à stomach; insulinà blood vessels
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Smooth M. can stretch/shorten more
•  Three characteristics of smooth m. stretching:
1.  Stretch response
•  First, stretch à contraction
•  Then, stress-relaxation response
•  important for stomach
2.  Length & Tension Δs
•  Stretched Smooth M. Tension>> Stretched Skel. M.
Tension
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Tension (percent of maximum)
Skeletal Muscle
Smooth Muscle
Sarcomeres
greatly
shortened
Sarcomeres at
resting length
Sarcomeres excessively
stretched
75%
100%
170%
100
50
0
60
80
140
100
120
160
Percent of resting sarcomere length
180
•  Why? diag. arrangement of myofilaments
Δs in volume, w/o flabbiness when empty
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2012 Result:
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Inc.
Smooth M. can stretch/shorten more
•  Three characteristics (Cont.):
3.  Hyperplasia
• 
“Over” + “formation”
• 
SM can divide to increase greatly in numbers
• 
Puberty:
• 
• 
estrogen à adult-sized uterus
Pregnancy
• 
estrogen à fit-11lb-baby uterus!
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Smooth Muscle Types
•  SM varies across organs in:
1.  fiber arrangement & organization
2.  innervation
3.  stimulus responsiveness
•  Two Types
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Smooth Muscle Types
•  Unitary SM
•  aka visceral muscle
•  very common
•  charactersitics:
•  all the stuff we’ve been talking about SM up
until now
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Smooth Muscle Types
•  Multi Unit SM
•  e.g.:
•  bronchi
•  large arteries
•  pupil adjuster muscles
•  few gap junctions
•  direct nerve connections
•  autonomic control
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Cardiac Muscle Tissue
•  Cardiac Muscle Tissue
•  striated and found only in the heart
•  cardiocytes:
•  Small
•  single nucleus
•  no terminal cisternae
•  aerobic (high in myoglobin, mitochondria)
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Cardiac muscle
cell (intact)
Intercalated disc
(sectioned)
Nucleus
Myofibrils
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Cardiac Muscle Tissue
•  Intercalated discs
•  specialized contact points between cardiocytes
•  Many gap junctions
•  coordinate cardiocytes
•  Therefore heart acts like a fused mass
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Cardiac Muscle Tissue
•  Functional Characteristics
•  Automaticity
•  pacemaker cells
•  Long contractions
•  10X skeletal muscle contraction
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mV
Skeletal:
Tension
msec
Cardiac:
mV
No summation
No tetanus
More next quarter!
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Tension
msec
Muscle Deterioration
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Developmental Aspects
•  Age > 30 y.o.
•  Normal loss of muscle mass & strength
•  Sarcopenia (remember Osteopenia?)
•  penia = poverty
•  If muscle mass ê, body é connective tissue
•  why?
•  New genes differentiate myosatellites à fibroblasts
•  strength ê
•  + atherosclerosis à intermittent claudication
•  (claudicare = “limp”)
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Developmental Aspects
•  Sarcopenia can be slowed or reversed with
exercise
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Abnormal Muscle Loss
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Abnormal muscle loss
•  Myopathies
•  muscular diseases, muscle fibers do not
function
•  Many reasons
•  acquired
•  drugs – Glucocorticoids
•  alcohol – Acute; chronic
•  impact accidents
•  genetic
•  many types, let’s focus on Dystrophies
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Muscular Dystrophy
•  Dystrophy = degeneration of tissue
•  Mostly appear in childhood
•  Fat and connective tissue deposits
Eventually fibers atrophy
and degenerate
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Gastrocnemius M.
Muscular Dystrophy
•  Duchenne muscular dystrophy (DMD):
•  Most common and severe type
•  Inherited, sex-linked
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Sex-linked…wut???
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What happens if one X is damaged on mom?
Daughter OK! (carrier)
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What happens if one X is damaged on mom?
Son NOT OK!
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Muscular Dystrophy
•  Incidence: 1/3500 boys
•  Damaged code for largest human gene:
dystrophin
•  cytoplasmic protein
•  stabilizes sarcolemma
•  anchors cytoskeleton
Dystrophin
So, structural role
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http://www.ncbi.nlm.nih.gov/books/NBK6193/
Muscular Dystrophy
•  Fragile sarcolemma tears/dammaged à
•  ECF Ca2+ entry à
•  damaged contractile fibers à
•  inflammatory cells à
•  muscle mass drops
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Duchenne’s Muscular Dystrophy Weak hip extensors à
“Wabble”
extra lordosis
Tip toe walking?
Tibialis anterior m.
wastes away before
Gastrocnemius m.
walking stops by 3 – 7 y.o.
Death of respiratory failure in 20s
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Muscular Dystrophy
•  No cure
•  Prednisone
•  émuscle strength and function
•  immunosuppressant cancer drug
•  problems?
•  Gene Therapy:
•  ‘infuse’ genomes of viruses with human
dystrophin
•  infect human with virus
•  problems?
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Muscular Dystrophy
•  Produce more utrophin
•  successful in mice
•  NOW shift gears
•  LEVERS
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