Smooth Mucle

Question 1

What are the characteristics of smooth muscle?

Answer 1

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

Question 2

What are the three types of filaments in smooth muscle?

Answer 2

Thick myosin filaments (long)
Thin actin filament (tropomyosin but NO troponin)
Intermediate filaments (mainly forms cytoskeletal framework not for contraction)

Question 3

What is the regulatory protein if smooth muscle?

Answer 3

Calmodulin (CaM)

Question 4

What are the two major types of muscle?

Answer 4

Multiunit smooth muscles- neurogenic

Single unit smooth muscle-myogenic

Question 5

What is the meaning of neurogenic?

Answer 5

The motor neurons nerve fiber stimulates one cell and the AP is propagated through gap-junctions
Autoexcitable

Question 6

What is the meaning of myogenic?

Answer 6

Each cell is stimulated by an axon to create contraction

Question 7

Where can multiunit smooth muscle be found?

Answer 7

Walls of large blood vessels
Large airways to lungs
Ciliary muscles if eye
Iris of eye
Pilo-erector muscle

Question 8

Where can Single unit smooth muscles be found?

Answer 8

Wall of GIT
Large blood vessels
Utefter
Bile duct
Uterus

Question 9

What are the arrengement of singleunit smooth muscle?

Answer 9

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

Question 10

What are the arrangement of multiunit smooth muscle?

Answer 10

Individual fibers

Each fiber is independently excited

Question 11

What type of NM junctions do multiunit have?

Answer 11

Contact junction between autonomic nerves and muscle fiber and release NT as nor-epinephrine

Question 12

What type of NM junction to singleunit have?

Answer 12

Diffuse junction, no contact with nerve cell

NT is released near the muscle fiber

Question 13

How is the multiunit controlled?

Answer 13

Mainly through nervous stimuli (ANS)

No spontaneous contraction

Question 14

How is the singleunit controlled?

Answer 14

Mainly non-nervous stimuli

Spontaneous contractions

Question 15

What are the mechanism of smooth muscle contraction?

Answer 15

Corkscrew like

Dense Bodies and the filaments forms a “net” around the cell

Question 16

Describe the activation of myosin cross-bridge in smooth muscle

Answer 16

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

Question 17

What is the mechanism of smooth muscle contraction?

Answer 17

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

Question 18

What is the mechanism of smooth muscle relaxation?

Answer 18

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

Question 19

Why is dephosphorylation of MLC needed?

Answer 19

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

Question 20

What are the main differences in Ca++ activity of smooth vs skeletal muscle?

Answer 20

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