Muscle 2 Flashcards
location of smooth muscle
walls of hollow organs
T/F smooth muscle is multinucleated
false. single nucleus
T/F; smooth muscle is voluntary
false. involuntary.
2 LAYERS OF MUSCLE in the tubular organs
1) longitudinal ; fibers running the length of the tubular organ
2) circular; fibers oriented around the organ.
which connective tissue layers are present in smooth muscle
perimsysium and endomysium, but NO EPIMYSIUM (around entire muscle)
T/F: smooth muscle has T tubules
false, they just have an SR as a loose network throughout the sarcoplasm
instead of the troponin/tropomyosin complex, what does smooth muscle utilize instead?
a Ca2+-calmodulin complex that activates myosin light chain kinase to phosphorylate myosin heads so they bind to actin and facilitate contraction
thin filaments of actin are attached to __ ___.
dense bodies.
what kind of intermediate filament is associated with smooth muscle? What do they connect to? what do they form?
Desmin IF.
anchored to dense bodies, which are anchored to sarcolemma to act as adhesive junctions
2 different modes of smooth muscle activation
1) single unit: nervous system innervates a single cell within a sheet or bundle and the action potential is propagated by gap junctions to neighboring cells such that the whole sheet contracts
Ex. Peristalsis
2) multiunit: all cells are innervated – allows for more control and gradual response
little evidence of propagation from fiber to fiber via gap junctions
Ex. iris, ciliary muscles
Explain the steps of a smooth muscle contraction
1) ca2+ is released from the Sr upon stimulation of acetylcholine at the neuromuscular junction
2) Ca2+ binds to calmodulin protein
3) this activate protein activates Myosin Light Chain Kinase.
4) MLCK phosphorylates the myosin heads to bind with actin
5) random sliding of filaments results in contraction where the fiber twists and gets rounder, compared to its relaxed state.
