Smooth Muscle Spindle shaped 1/10 th 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]
Innervation of Smooth Muscle No NMJ Instead Varicosities bulbous swellings of nerve fibers release neurotransmitter into diffuse junctions
Varicosities
Innervation of Smooth Muscle Reduced SR No T-tubules instead Caveolae (Latin Little Caves )
Caveolae Caveolae sequester Ca 2+ from ECF Striations on cell? No No sarcomeres
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
Nucleus Dense bodies Contracted smooth muscle fiber 2013 Pearson Education, Inc.
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
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
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
Skeletal Muscle Smooth Muscle Tension (percent of maximum) 100 50 Sarcomeres greatly shortened Sarcomeres at resting length Sarcomeres excessively stretched 75% 100% 170% 0 60 80 100 120 140 160 180 Percent of resting sarcomere length Why? diag. arrangement of myofilaments Result: large Δs in volume, w/o flabbiness when empty
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!
Smooth Muscle Types SM varies across organs in: 1. fiber arrangement & organization 2. innervation 3. stimulus responsiveness Two Types
Smooth Muscle Types Unitary SM aka visceral muscle very common charactersitics: all the stuff we ve been talking about SM up until now
Smooth Muscle Types Multi Unit SM e.g.: bronchi large arteries pupil adjuster muscles few gap junctions direct nerve connections autonomic control
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)
Cardiac muscle cell (intact) Intercalated disc (sectioned) Nucleus Myofibrils
Cardiac Muscle Tissue Intercalated discs specialized contact points between cardiocytes Many gap junctions coordinate cardiocytes Therefore heart acts like a fused mass
Cardiac Muscle Tissue Functional Characteristics Automaticity pacemaker cells Long contractions 10X skeletal muscle contraction
mv Skeletal: Tension msec Cardiac: No summation No tetanus mv Tension More next quarter! msec
Muscle Deterioration
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 )
Developmental Aspects Sarcopenia can be slowed or reversed with exercise
Abnormal Muscle Loss
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
Muscular Dystrophy Dystrophy = degeneration of tissue Mostly appear in childhood Fat and connective tissue deposits Eventually fibers atrophy and degenerate Gastrocnemius M.
Muscular Dystrophy Duchenne muscular dystrophy (DMD): Most common and severe type Inherited, sex-linked
Sex-linked wut???
What happens if one X is damaged on mom? Daughter OK! (carrier)
What happens if one X is damaged on mom? Son NOT OK!
Muscular Dystrophy Incidence: 1/3500 boys Damaged code for largest human gene: dystrophin cytoplasmic protein stabilizes sarcolemma anchors cytoskeleton Dystrophin So, structural role http://www.ncbi.nlm.nih.gov/books/nbk6193/
Muscular Dystrophy Fragile sarcolemma tears/dammaged à ECF Ca 2+ entry à damaged contractile fibers à inflammatory cells à muscle mass drops
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
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?
Muscular Dystrophy Produce more utrophin successful in mice NOW shift gears LEVERS