Unit 3.5: Smooth Muscle Flashcards
Where is smooth muscle found in the body?
Walls of hollow organs, not attached to bones of skeleton
Which one is more important and numerous in the body: skeletal or smooth muscle?
Skeletal is higher in terms of body weight but smooth muscle is more important
What are some important smooth muscles?
Bladder sphincter, intestine, walls of blood vessels
What are the 2 ways that smooth muscles can be arranged?
- Single unit
2. Multi unit
How are smooth muscles arranged as a single unit?
The cells are coupled by gap junctions and found on walls of internal organs (no need to electrically stimulate each individual fibre)
How are smooth muscles arranged as a multi-unit?
There are NO gap junctions, each individual muscle fibre is separately innervated
What are differences between smooth and skeletal muscles on a whole muscle level?
- Contraction of smooth muscle changes muscle shape, not just length
- smooth muscle develops tension (force) slowly
- Smooth muscles can maintain contraction longer without fatiguing (important because some are contracted most of the time like when you’re holding your pee)
Which one is smaller in size between smooth and skeletal muscles?
Smooth muscles, one smooth muscle is the same size as a single myofibril in a skeletal muscle
Are there sarcomeres in both smooth and skeletal muscles
No, actin and myosin are not arranged into sarcomeres in smooth muscles. (not striated)
How are actin and myosin arranged in smooth muscles?
They are arranged in long bundles diagonally around periphery of the cell
Where are actins anchored in smooth muscles?
They are anchored at cell membranes called dense bodies
Where are the differences in terms of T-tubules and SR between smooth and skeletal muscles?
No t-tubules in sarcolemma, not much SR
What sequesters Ca2+ in smooth muscles seeing as there is not much SR in smooth muscles?
Smooth muscles have special vesicles called caveolae that are invaginations of the sarcolemma that are specialized for cell signalling
What is the force of contraction related to?
The amount of Ca2+ released
What is the effect of not having t-tubules in smooth muscles?
No direct coupling of the action potential to Ca2+ released from the SR through DHP receptor-ryanodine reception coupling as in skeletal muscles
Instead, Ca2+ entering through the cell membrane causes Ca2+ release from the SR
Which muscle contains less myosin than actin between smooth and skeletal muscles?
Smooth muscles
Which muscle’s actin and myosin filaments are longer between smooth and skeletal muscles?
Smooth muscles
Which muscle’s ATPase activity is faster between smooth and skeletal muscles?
Skeletal muscles
What are the difference in terms of myosin heads between smooth and skeletal muscles?
Myosin heads are found all along myosin in smooth muscles
Are there any troponin in smooth muscles?
no
How do the molecular differences and properties of myosin contribute to the characteristics of the smooth muscle as a whole?
Contract more slowly and for longer periods of time than skeletal or cardiac muscle (slower ATPase activity and longer actin/myosin filaments)
How is myosin regulated in smooth muscles?
Via phosphorylation of myosin
How is actin regulated in smooth muscles?
Via tropnin/tropomyosin interaction with actin
How do smooth muscles contract?
Key: increase in cytosolic Ca2+
find the rest on p.68 course notes
What would happen to contraction if a smooth muscle cell were placed in a Ca2+-free saline solution?
No contraction as there are no Ca2+ from the extracellular environment
How do smooth muscles relax?
Find on p.69 coursenotes
What is the latch state?
Tension is maintained (myosin remains bound to actin) but with minimal ATP consumption
