Smooth Muscle Flashcards
What are gap junctions’ roles in smooth muscle?
couple smooth muscle cells so the AP can spread
What do pacemaker cells do to contribute to contraction of smooth muscle?
induce spontaneous action potential, which can be spread to other nonpacemaker cells
in smooth muscle, calcium binds to what?
calmodulin
what does activated calmodulin do?
activates myosin light chain kinase enzymes
What most directly triggers release of calcium from SR of smooth muscle cells?
calcium influx into sarcoplasm
why doesn’t cross bridge require as much ATP as skeletal muscle?
myosin and actin “latch” to one another more strongly
Actin is anchored to Z-discs in skeletal muscle. What is actin anchored to in smooth muscle?
dense bodies, which are also anchored to intermediate filaments
How are myosin and actin arranged differently in smooth muscle?
Myosin heads are not on multiple sides except in the middle, because actin is not on all sides of thin filaments
describe actin, dense bodies, and intermediate filaments in one contracted smooth muscle cell
actin pulls on dense bodies, and dense bodies pull on intermediate filament network, which shortens the cell like a corkscrew
Why are MLCK sluggish?
have to remove phosphate from ATP to put it on myosin head groups
What steps are involved in relaxing smooth muscle? Use the words calcium, SR, and dephosphorylation
Calcium detaches from calmodulin
Active transport of calcium into SR and back out of cell
Dephosphorylation of myosin to inactive myosin
Discuss why the same neurotransmitter could have different effects on different smooth muscles
Different muscles have different NT receptors, so the same NT could cause contraction or relaxation depending on the receptor it binds to
Discuss how g-protein coupled receptors affect contraction of smooth muscle in the stomach
gastrin released by g-cells in stretched stomach after eating binds to g-protein coupled receptors, which stimulates higher force and rate of stomach’s smooth muscle
Name two special features of smooth muscle
1) Response to stretch - automatically contracts when stretched, but quickly adapts to new length and relaxes, contracts on demand even when very stretched
2) Length and tension changes - can contract when between half and twice its resting length because of the myofilament arrangement
Basically, it handles stretch a lot better than skeletal muscle
Name the two types of smooth muscle and state which one is more common
Multi-unit smooth muscle (only large airways and arteries, arrector pili, and internal eye)
Single-unit (unitary) smooth muscle (a lot more common)
