Smooth Muscle DSA Flashcards
in which ways is SM different in each organ?
- physical dimensions
- organization into bundles or sheets
- response to different types of stimuli
- characteristics of innervation
- function
what are the two types of SM?
- multiunit SM
- unitary SM
multiunit SM
- discrete, separate SM fibers
- they operate independently of each other, so they each contract independently of one another
- each fiber is innervated by a single nerve ending
- have thin layers of basement membrane on outer surface–mixture of fine collagen and glycoprotein that helps insulate separate fibers
example of multiunit SM
- ciliary muscle of eye
- iris muscle of eye
- piloerector muscles that cause erection of hairs when stimulated by sympathetic nervous system
what else is unitary SM called?
- synctial SM
- visceral SM
unitary SM
- mass of many fibers that contract together as a single unit
- fibers arranged in bundles or sheets
- cell membrane adhere to one another so that a force generated in one fiber is transmitted to next
where is unitary SM found?
in the walls of viscera including GI tract, bile ducts, uterus, ureters, and many blood vessels
how is the force generated in one muscle fiber transmitted to next?
gap junctions allow ions to flow freely from one cell to the next so that AP can travel b/w cells and they can contract together
actin in SM
-twice as much as in skeletal muscle
-anchor to dense bodies on SM cell membrane rather than Z disc
tropomyosin is found in SM but not doing the same thing as in skeletal muscle
myosin in SM
-about 1/4 as many myosin filaments in SM as in skeletal muscle
what is used to stimulate contraction in SM?
- calcium ions
- ATP degraded to ADP for energy for contraction
dense bodies
- actin filaments attach to these
- dense bodies can be found throughout inside of cell and some on cell membrane
- bonded together by intercellular protein bridges which allow contraction to be sent from one cell the next
stress relaxation and reverse stress relaxation
- when volume is suddenly decreased, pressure fall drastically at first, then rises in another few seconds to near original level
- allows hollow organ to maintain same amount of pressure inside its lumen
what does SM have in place of troponin?
calmodulin protein which initiates contraction by activating myosin cross bridges
SM contraction sequence
- Ca conc in cytosolic fluid of the SM increases as a result of influx of Ca from extracellular fluid and/or release of Ca from SR
- Ca ions bind reversibly with calmodulin
- calmodulin-Ca complex then joins with and activate MLCK
- one of light chains of each myosin head (called the regulatory chain) becomes phosphorylated in response to myosin kinase
- when not phosphorylated, the attachment detachment cycling of myosin head with the actin filament doesn’t occur
- when regulatory chain is phosphorylated, the head has capability of binding repetitively with actin filament and proceeding through entire cycling process
- binding of M-ADP-Pi to active site (b/c phosphorylated myosin light chain causes the 2 to have high affinity towards each other)
- ADP and Pi leave myosin head
- powerstroke
- ATP must bind to myosin head before actomyosin can dissociate
- once dissociated, the myosin ATPase hydrolyzes the ATP and uses energy to re-cock the myosin head back to ready
