Smooth Mucle Flashcards
What are the characteristics of smooth muscle?
Fusiform cells Single nuclei Nonstriated Found in walls of hollow organs, blood vessels, eye, glands, uterus, skin Autorhythmicity Gap-junctions Dense Bodies, no intermidiate filaments No T-tubules, caveolae may act as these Ca++ comes from ECF Fewer mitochondria Unvoluntary Slow, wavelike contractions
What are the three types of filaments in smooth muscle?
Thick myosin filaments (long) Thin actin filament (tropomyosin but NO troponin) Intermediate filaments (mainly forms cytoskeletal framework not for contraction)
What is the regulatory protein if smooth muscle?
Calmodulin (CaM)
What are the two major types of muscle?
Multiunit smooth muscles- neurogenic
Single unit smooth muscle-myogenic
What is the meaning of neurogenic?
The motor neurons nerve fiber stimulates one cell and the AP is propagated through gap-junctions
Autoexcitable
What is the meaning of myogenic?
Each cell is stimulated by an axon to create contraction
Where can multiunit smooth muscle be found?
Walls of large blood vessels Large airways to lungs Ciliary muscles if eye Iris of eye Pilo-erector muscle
Where can Single unit smooth muscles be found?
Wall of GIT Large blood vessels Utefter Bile duct Uterus
What are the arrengement of singleunit smooth muscle?
It is unitary
Sheaths/bundles of fibres with gap-junctions between, works as a Single unit
If one fiber is excited, all are= functional syncytium
What are the arrangement of multiunit smooth muscle?
Individual fibers
Each fiber is independently excited
What type of NM junctions do multiunit have?
Contact junction between autonomic nerves and muscle fiber and release NT as nor-epinephrine
What type of NM junction to singleunit have?
Diffuse junction, no contact with nerve cell
NT is released near the muscle fiber
How is the multiunit controlled?
Mainly through nervous stimuli (ANS)
No spontaneous contraction
How is the singleunit controlled?
Mainly non-nervous stimuli
Spontaneous contractions
What are the mechanism of smooth muscle contraction?
Corkscrew like
Dense Bodies and the filaments forms a “net” around the cell
Describe the activation of myosin cross-bridge in smooth muscle
Calmodulin is avtivated by Ca++
Ca++-Calmodulin activates myosin light chain kinase (MLCK)
Through phosphorylation of ATP the phosphorylated myosin cross-bridge is activated and binds to actin
What is the mechanism of smooth muscle contraction?
The influx of Ca++ and release of Ca++ from SR increase concentration
Ca++ binds to Calmodulin
Ca++-Calmodulin activates MLCK
MLCK phosphorylates light chains in myosin heads and increase myosin ATPase activity
Active myosin cross-bridges slide along actin and creates muscle tension
What is the mechanism of smooth muscle relaxation?
The Ca++ concentration in ICF decreases due to Ca++ being pumped out of cell or reabsorbed into SR
Ca++ unbinds from CaM
Myosin phospatase removes phosphate from myosin-myosin ATPase activity decreases
Less active myosin ATPase= decreased muscle tension
Why is dephosphorylation of MLC needed?
The muscle doesnt stop contracting even if Ca++ leaves the cell since MLC been physically modified through phosphorylation, this change needs to be reversed.
Dephosphorylation is made by the enzyme MLCP- myosin light chain phosphatase
What are the main differences in Ca++ activity of smooth vs skeletal muscle?
In smooth muscle Ca++ comes mainly from ICF, in skeletal muscle ONLY from SR
In smooth muscle a serial of chemical events occurs, in skeletal muscle there is a physical remidelling of troponin and tropomyosin
In smooth muscle a phosphorylation of myosin cross-bridging in thick filaments occurs, in skeletal muscle there is an uncovering of cross-bridge binding sites on actin in thin filaments
