smooth muscle Flashcards
function of smooth muscle
- propels contents
- maintains pressure
- regulates internal flow (by changing tube diameter)
describe a smooth muscle cell
spindle-shaped cells with single nucleus
how are smooth muscle cells arranged
sheets in a diamond shaped lattice
*there are no striations (No sarcomeres)
compare myosin and actin filaments between smooth and skeletal muscle
- thick myosin filaments are longer than those in skeletal muscle
- thin actin filaments contain tropomyosin but lack troponin
- smooth muscles also contain filaments of intermediate size that form part of cytoskeletal framework that supports cell shape
smooth muscle innervation is delivered via what mechanism
varicosity: vesicle containing neurotransmitter
*no motor end plates
name the two major types of smooth muscle
- single-unit smooth muscle (unitary)
- multiunit smooth muscle
characteristics of multiunit smooth muscle
- each fiber behaves seperately (like a seperate motor unit)
- little or no coupling between cells
- units must be seperately stimulated by nerves to contract
characteristics of single-unit smooth muscle
- myogenic: self-excitable (does not require nervous stimulation for contraction)
- also called visceral smooth muscle
- fibers become excited and contract as a single unit
- cell are electrically linked by gap junction
Which type of smooth muscle contains gap junctions? Function of gap junctions in smooth muscle.
- found in single-unit smooth muscle
- allow for “full recruitment”
- conduct Na+ and Ca2+ electrically couple cells
action potential of smooth muscle cells are dependent on what ion
calcium
what type of smooth muscle cells fire action potentials
single unit smooth muscle cells
- spontaneous depolarization
pacemaker potential
membrane potential gradually depolarizes until it reaches threshold for firing a single action potential
slow wave potential
membrane potential alternately depolarizes and hyperpolarizes. When the threshold is reached, the cell fires a burst of action potentials
unlike skeletal muscle, regulation of crossbridge cycling in smooth muscle occurs where?
on the thick myosin filament
difference between contraction of smooth muscle and skeletal muscle
smooth muscle lacks
- distinct striations
- T-tubules
- sarcomeres
- troponin
- contains fewer SR
list steps of calcium activation of myosin cross bridge in smooth muscle
- Ca2+ binds to calmodulin -> CA2+-calmodulin
- CA2+-calmodulin binds to inactive myosin kinase -> active myosin kinase
- active myosin kinase phosphorylates inactive myosin
- phosphorylated myosin can bind to actin
a single excitation in smooth muscle does not fully activate smooth muscle cells. What must happen to increase tension
as CA2+ concentration increases, more cross-bridges are brought into play and greater tension develops
name the 3 different mechanisms of increasing intracellular calcium for usein smooth muscle cell
- G protein; PLC; IP3 causes CA2+ release from SR
- ligand gated CA2+ channel -> CA2+ induced CA2+ release from SR
- voltage gated CA2+ channel -> CA2+ induced CA2+ release from SR
list steps for relaxation of smooth muscle
- decrease in cytosolic calcium concentration
- MLCK(Myosin light-chain kinase) returns to inactive form
- enzyme myosin phosphatase removes phosphate from myosin
- cross-bridge is inhibited
name the 3 mechanisms for decreasing intracellular calcium in smooth muscle
- SERCA (SR CA2+ ATPase)
- Sarcolemmal Na+/Ca2+ exchanger
- Sarcolemmal Ca2+ ATPase
how does the Sarcolemmal Na+/Ca2+ exchanger work
- energy for the extrusion of calcium against its concentration gradient is from the inward driving force for Na+
- the Na+/K+ ATPase maintains the sodium gradient
