Term
| What is the location of smooth muscle? |
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Definition
In the walls of hollow organs
Vascular (Blood & Lymphatic)
-Tunica Media
Visceral
-Digestive Tract
-Respiratory Tract
-Urinary Tract
-Reproductive Tract
-Splenic Capsule
-Skin (arrector pili - attach to hair) |
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Term
| What are the two types of smooth muscle and compare/contrast them |
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Definition
Vascular Smooth Muscle (Blood & Lymphatic)
-From mesoderm surrounding developing vessels
-Intermediate filaments contain Desmin and Vimentin
Visceral Smooth Muscle
-From embryonic lateral-plate, splanchopleural mesoderm
-Intermediate filaments contain Desmin only
Desmin is in all muscle while vimentin is only present in vascular smooth muscle, not other muscle |
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Term
| How is the tissue organized in smooth muscle? |
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Definition
Forms sheets (layers) or bundles around hollow organs
Orthogonal arrangement of layers
Elongated, overlapping cells
No cross striations
Single, central, pale, nucleus/cell
Tight packing
Less vascular
very little connective tissue |
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Term
| What is the cell structure of smooth muscle cells? |
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Definition
Spindle shaped
Tight Packing
Dense Bodies - attachment sites for actin filaments, analogous to Z-line in skeletal muscle
Caveolae (near sarcolemma) - vesicles that aid in uptake and release of Ca2+
Few Mitochondria
Many, poorly organized thin filaments
Few or no thick filaments - myosin bundles only form during contraction |
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Term
| How does smooth muscle contraction compare with skeletal (and cardiac)? |
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Definition
Intrinsic rhythm
Slower contractions
No motor end plates (same as cardiac but diff.from skeletal)
Nerve endings (more in vascular than in visceral) lie nearby, but no synapses form
Gap junctions (more in visceral-unitary, than in vascular, multiunit) transmit impulses cell-to-cell |
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Term
| How does the ANS control smooth muscle? |
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Definition
The effects depend on type and location
Parasympathetic increases visceral (gut & bronchial) smooth muscle contraction, decreases vascular smooth muscle contraction
Sympathetic decreases visceral smooth muscle contraction, increases
vascular smooth muscle contraction |
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Term
| Explain the contractile apparatus in smooth muscle |
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Definition
Actin filaments radiate from dense bodies
Myosin filaments found between and overlapping actin. Form “on demand.” - before contraction they are soluble and not polymerized
Dense bodies are attached to one another by intracellular protein bridges; serve as “Z lines” |
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Term
| Explain the contraction mechanism of smooth muscle |
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Definition
Smooth muscle contraction is regulated by the phosphorylation of one of the myosin light chains
Ca2+ binds to calmodulin and the complex binds to myosin light chain kinase, activating it
MLCK-Ca2+-calmodulin complex phosphorylates myosin and activates it
Myosin then binds to F-actin
The smooth muscle thin filaments have tropomysin but not troponin |
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Term
| How does smooth muscle respond to injury? |
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Definition
In response to injury, the smooth muscle precursors proliferate and differentiate into new smooth muscle fibers
In addition to proliferation they also release inflammatory cytokines. This can lead to atherosclerosis |
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Term
| What are the distinguishing characteristics of smooth muscle? |
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Definition
Small, spindle shaped cells
one central nuclei
filament ratio of 12 thin to 1 thick
poorly organized sarcoplasmic reticulum
contain abundant caveolae
no distinct myofibrils
no T-tubules
no motor plates
involuntary contraction
no striations
no Z-lines (dense bodies instead)
cells overlap |
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