Chapter 8: Excitation and Contraction of Smooth Muscle Flashcards
Which type of smooth muscle fibers is mainly controlled by non-nervous stimuli?
unitary or single-unit muscle fibers
Which structures allow free flow of ions from one muscle cell to the next to allow unitary smooth muscle contraction?
gap junctions
Where do actin filaments attach in smooth muscle cells?
dense bodies
These bonds transmit the force of contraction from one smooth muscle cell to another
intercellular protein bridges between membrane-dense bodies
This organization allows smooth muscle cells to contract as much as 80% of their length instead of being limited to less than 30%, as occurs in skeletal muscle.
bidirectional pull of the “side-polar” cross-bridges of myosin filaments
The ________ that the cross-bridges remain attached to the actin filaments, which is a major factor that determines the force of contraction, is believed to be greatly increased in smooth muscle.
fraction of time
**the maximum force of contraction of smooth muscle is often greater than that of skeletal muscle, as much as 4 to 6 kg/cm2 cross-sectional area for smooth muscle in comparison with 3 to 4 kilograms for skeletal muscle.
What is the reason for the slow cycling time in smooth muscle fibers compared to skeletal muscles?
Smooth muscle fibers have far less ATPase activity than skeletal muscle fibers
This mechanism maintains the prolonged tonic contraction in smooth muscle for hours, with little use of energy; hence, little continued excitatory signal is required from nerve fibers or hormonal sources.
latch mechanism
**When smooth muscle has developed full contraction, the amount of continuing excitation can usually be reduced to far less than the initial level even though the muscle maintains its full force of contraction.
This phenomenon, occurring in smooth muscle fibers, allows a hollow organ to maintain about the same amount of pressure inside its lumen despite sustained large changes in volume
stress-relaxation or
reverse stress-relaxation
This regulatory protein that is activated by calcium ions to cause skeletal muscle contraction is absent in smooth muscle fibers
troponin
This regulatory protein counterpart of troponin is present in smooth muscles for binding with calcium ions
calmodulin
This is the phosphorylating enzyme activated by the calcium-calmodulin complex
myosin light chain kinase
Which chain of smooth muscle myosin filament is phosphorylated for the attachment-detachment of myosin head with the actin filament?
regulatory chain
Where is the main source of calcium ions for skeletal and smooth muscles, respectively, for the initiation of action potential?
skeletal muscle = sarcoplasmic reticulum
smooth muscle = extracellular fluid
This is the time required for the diffusion of calcium ions from the ECF into the cell before smooth muscle contraction begins
latent period