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32 terms

Smooth muscle function and structure

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Smooth muscles loc
Walls of tubular structures and hollow organs such as blood vessels, stomach, intestines, uterus, and bladder
What is the function of smooth muscle?
to change the volume of the organ they surround
What is skeletal muscle bound to and what by?
bone via ligaments
What is smooth muscle bound to and what does it connect it to?
Smooth muscle cells are attached to a matrix of CT
What are the two layers of smooth muscle
Outer layer-oriented in long axis of organ
Inner layer- circular
What shape of smooth muscle fibers and what does it allow?
Spindle-shaped cells that have gap junction between them allowing for synchronous activity
What is the difference in diameter and length of the muscle fibers in smooth and skeletal muscle?
Smooth- shorter and thinner
What part of the nervous system innervates skeletal muscle?
Somatic Nervous System
What part of the nervous system innervates smooth muscle?
Autonomic Nervous System
Are the thick and thin filaments organized into myofibrils like they are in skeletal muscle?
NO
Are the contractile filaments aligned into sacromeres?
NO= no cross striation appearance
Z lines in smooth muscles
none
What are the thin filaments inserted into in smooth muscle?
dense bodies
Are there t-tubules, or lateral sacs?
no
What is responsible for smooth and skeletal muscle contraction?
the sliding-filament mechanism
What is the maximal tension/ unit of cross-section area for smooth muscle in comparison to skeletal muscle?
Similar
What happens as a result of smooth muscle being an adaptive mechanism for volume change?
Large tension can be generated over a relatively WIDE RANGE of muscle lengths
Does troponin trigger cross-bridge cycling in smooth muscle?
NO
What is the difference between the function of tropomyosin in smooth muscle and its' function in skeletal muscle?
Smooth muscle- a structural protein; NOT involved
Skeletal muscle- responsible for a twitch
Excitation-coupling; what triggers excitation in smooth muscle?
Ca mediated myosin phosphorylation triggers cross bridge cycling
What is the path of excitation of smooth muscle?
1. Inactive calmodium (a Ca binding protein)
2. Calmodium activated by increase in Ca (HIGH)
3. Activated calmodium binds to inactivated myosin light-chain kinase and activates MLCK
4. Active Ca calmodium MLCK converts ATP to ADP
5. MLCK phosphorylates myosin head so that it forces movement of the X bridge toward actin
6. Myosin phoshporlyated head binds to actin and releases PO4
7. Cross-bridge cycle produces tension and shortening
8. Myosin light chain phosphotase dephosphorylates myosin head so that the cross bridge cycling stops- occurs when there are low levels of Ca and Ca goes back into the SR
What is major difference between the role of cystolic calcium in skeletal and smooth muscle?
Smooth muscle- induces a chemical change (phosphorylation)
Skeletal muscle- induces a physical change (conformational change of tropnonin that shifts tropomyosin to the side)
Which excitation coupling is faster phosphorylation or conformational changes?
conformational changes in skeletal muscle
Latch state (tonic isometric tension)
Steady tensions at the expense of very little ATP; level of myoplasmic Ca declines despite the sustained stimulus; tension is maintained as long as the stimulus continues and the level of Ca is above relaxed levels; slow cycling of X bridges
What are the functions of ATP in smooth muscle?
Phosphorylation- moves myosin head closer to actin
Hydrolysis- non-covalent bond b/t ADP and PO4; it energizes the myosin head
Breaking the bond b/t actin and myosin
What does low Ca trigger?
Deposphorylation that ends the X bridge cycling
What determines the level of phosphorylation vs. dephosphorylation?
the ratio of activity between the LCM kinase and the LCM phosphotase
What causes Ca rise in the cytosol
Ca influx through voltage-gated Ca channels
Ca influx in response to e.c. chemicals (e.g. hormones and nts)
Ca release from diffusion through SR
Ionotropic receptor
Direct action; ligand-gated channel opens when NT binds; FAST transmission; NICOTONIC AchR
Metabotropic recpetor
Indirect action; goes through 2nd messenger; binding of neurotransmitter releases another protein (intracellular 2nd messenger) that opens up the next channel; SLOW transmission
Why is contraction slower in smooth muscle?
Enzymatic reaction slower than physical change (phosphorylation)
no T-tubule system -> A.P. can't propagate
SR densely packed -> no instaneous release of Ca
What can the contractile activity of smooth muscle be modulated by?
1. neurotransmitters released by ANS
2. hormones
3. intrinsic properties that produce spontaneous electrical activity
4. changes in local chemical comp
5. stretch