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WINDSOR UNIVERSITY SCHOOL OF MEDICINE . Smooth Muscle Dr.Vishal Surender.MD. Smooth Muscle: Properties. Each fibre is much smaller than in skeletal muscle Found in walls of hollow organs and tubes. Usually found in two different layers:

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Windsor university school of medicine

WINDSOR UNIVERSITYSCHOOL OF MEDICINE

Smooth Muscle

Dr.VishalSurender.MD.


Smooth muscle properties

Smooth Muscle: Properties

  • Each fibre is much smaller than in skeletal muscle

  • Found in walls of hollow organs and tubes.

  • Usually found in two different layers:

  • Circular – to squeeze or dilatee.g-blood vessels.

  • Longitudinal – to stretch or shortene.g-GI tract.

    Metabolic economy-Uses less energy, Low oxygen consumption thus allows to Maintain force for long periods, e.x-urinary and esophageal sphincters.


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  • Smooth muscle is different:-

    • It has more variety

    • Anatomy is different.

    • It is controlled by hormones, paracrines, and neurotransmitters.

  • Unitary and Multiunit Smooth Muscle

  • There are two distinct categories of smooth muscle determined by the processes they use to coordinate contraction with their neighboring cells


Single unit visceral smooth muscle

Single unit/Visceral smooth muscle

  • This represents the majority

  • Made up of groups of cells joined together by gap junctions

    • FUNCTIONAL SYNCYTIUM

    • may be innervated but does not always require nervous stimulation for contraction

  • Allows for coordinated contractions

    • Uterus, GIT


Types of smooth muscle

Types of Smooth Muscle

Figure 12-25a


Multi unit smooth muscle

Multi unit smooth muscle

  • Found in large blood vessels, large airways and ciliary muscle

  • Made up of discrete units

    • Similar to skeletal muscle

  • Must be separately stimulated by nerves

  • Autonomic stimulation


Types of smooth muscle1

Types of Smooth Muscle

Figure 12-25b


Smooth muscle

Smooth Muscle

  • Has actinand myosin filaments but Lacks the Regular Sarcomere Structure of Skeletal Muscle.

  • Myosin light chain hasregulatory role

  • Have intermediate filaments- dense bodies, analogous to Z-line

  • Has less sarcoplasmic reticulum

    • IP3-receptor channel is the primary calcium channel.

    • Calcium storage function of sarcoplasmic reticulum is supplemented by Caveolae analogous to ….. In skeletal muscle?


Caveolae in smooth muscle

Caveolae in Smooth Muscle

Figure 12-26


Anatomy of smooth muscle

Anatomy of Smooth Muscle

Figure 12-27a–b


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  • Molecular Mechanism of Smooth Muscle Contraction.

  • In order for smooth muscle to contract there must be some connection between the myofilaments and the cell (to have the same role as the Z line in skeletal muscle).

  • This connection is provided by the dense bodies found within the smooth muscle cells.

  • The thick filament is made of myosin as in skeletal muscle (though of a different form) and so has two heavy chains, including the crossbridge region with the 4 light chains found on the heads. These light chains have an important role to play in smooth muscle contraction because it is phosphorylation of the regulatory light chains found on the myosin heads that initiate contraction.

  • When the myosin is phosphorylated it binds to the thin filaments and pulls them towards the center of the thick filament moving the two dense bodies connected to the thin filaments closer together, shortening the smooth muscle cell.


Smooth muscle contraction

ECF

Ca2+

Sarcoplasmic

reticulum

1

Intracellular Ca2+

concentrations increase

when Ca2+ enters cell

and is released from

sarcoplasmic reticulum.

1

Ca2+

Ca2+

Pi

CaM

2

Pi

2

Ca2+ binds to

calmodulin (CaM).

Ca2+

CaM

Inactive

MLCK

3

3

Ca2+–calmodulin

activates myosin light

chain kinase (MLCK).

Active

MLCK

ATP

4

P

ADP +

4

MLCK phosphorylates

light chains in myosin

heads and increases

myosin ATPase activity.

P

Inactive myosin

Active myosin

ATPase

Actin

Active myosin

crossbridges slide

along actin and create

muscle tension.

5

5

Increased

muscle

tension

Smooth Muscle Contraction

Figure 12-28


Smooth muscle contraction1

ECF

Ca2+

Sarcoplasmic

reticulum

1

Intracellular Ca2+

concentrations increase

when Ca2+ enters cell

and is released from

sarcoplasmic reticulum.

1

Ca2+

Ca2+

Smooth Muscle Contraction

Figure 12-28, step 1


Smooth muscle contraction2

ECF

Ca2+

Sarcoplasmic

reticulum

1

Intracellular Ca2+

concentrations increase

when Ca2+ enters cell

and is released from

sarcoplasmic reticulum.

1

Ca2+

Ca2+

Pi

CaM

2

Pi

2

Ca2+ binds to

calmodulin (CaM).

Ca2+

CaM

Smooth Muscle Contraction

Figure 12-28, steps 1–2


Smooth muscle contraction3

ECF

Ca2+

Sarcoplasmic

reticulum

1

Intracellular Ca2+

concentrations increase

when Ca2+ enters cell

and is released from

sarcoplasmic reticulum.

1

Ca2+

Ca2+

Pi

CaM

2

Pi

2

Ca2+ binds to

calmodulin (CaM).

Ca2+

CaM

Inactive

MLCK

3

3

Ca2+–calmodulin

activates myosin light

chain kinase (MLCK).

Active

MLCK

Smooth Muscle Contraction

Figure 12-28, steps 1–3


Smooth muscle contraction4

ECF

Ca2+

Sarcoplasmic

reticulum

1

Intracellular Ca2+

concentrations increase

when Ca2+ enters cell

and is released from

sarcoplasmic reticulum.

1

Ca2+

Ca2+

Pi

CaM

2

Pi

2

Ca2+ binds to

calmodulin (CaM).

Ca2+

CaM

Inactive

MLCK

3

3

Ca2+–calmodulin

activates myosin light

chain kinase (MLCK).

Active

MLCK

ATP

4

P

ADP +

4

MLCK phosphorylates

light chains in myosin

heads and increases

myosin ATPase activity.

P

Inactive myosin

Active myosin

ATPase

Smooth Muscle Contraction

Figure 12-28, steps 1–4


Smooth muscle contraction5

ECF

Ca2+

Sarcoplasmic

reticulum

1

Intracellular Ca2+

concentrations increase

when Ca2+ enters cell

and is released from

sarcoplasmic reticulum.

1

Ca2+

Ca2+

Pi

CaM

2

Pi

2

Ca2+ binds to

calmodulin (CaM).

Ca2+

CaM

Inactive

MLCK

3

3

Ca2+–calmodulin

activates myosin light

chain kinase (MLCK).

Active

MLCK

ATP

4

P

ADP +

4

MLCK phosphorylates

light chains in myosin

heads and increases

myosin ATPase activity.

P

Inactive myosin

Active myosin

ATPase

Actin

Active myosin

crossbridges slide

along actin and create

muscle tension.

5

5

Increased

muscle

tension

Smooth Muscle Contraction

Figure 12-28, steps 1–5


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Calcium Plays a Critical Role in Smooth Muscle Activation


Smooth muscle contraction6

Smooth Muscle Contraction

Activating

MLCK

Ca2+

myosin-Pi

myosin

+ATP/actin

CONTRACTION


Relaxation in smooth muscle

Ca2+

Ca2+

Na+

ECF

ATP

Free Ca2+ in cytosol decreases when

Ca2+ is pumped out of the cell or back

into the sarcoplasmic reticulum.

1

Sarcoplasmic

reticulum

1

Na+

Ca2+

ATP

Ca2+

Ca2+ unbinds from calmodulin (CaM).

2

CaM

2

Myosin phosphatase removes

phosphate from myosin, which

decreases myosin ATPase activity.

3

Ca2+

CaM

Myosin

phosphatase

3

ATP

Less myosin ATPase results in

decreased muscle tension.

4

P

ADP +

P

Inactive myosin

Myosin ATPase

activity decreases.

4

Decreased

muscle

tension

Relaxation in Smooth Muscle

Figure 12-29


Relaxation in smooth muscle1

Ca2+

Ca2+

Na+

ECF

ATP

Free Ca2+ in cytosol decreases when

Ca2+ is pumped out of the cell or back

into the sarcoplasmic reticulum.

1

Sarcoplasmic

reticulum

1

Na+

Ca2+

ATP

Ca2+

Relaxation in Smooth Muscle

Figure 12-29, step 1


Relaxation in smooth muscle2

Ca2+

Ca2+

Na+

ECF

ATP

Free Ca2+ in cytosol decreases when

Ca2+ is pumped out of the cell or back

into the sarcoplasmic reticulum.

1

Sarcoplasmic

reticulum

1

Na+

Ca2+

ATP

Ca2+

Ca2+ unbinds from calmodulin (CaM).

2

CaM

2

Ca2+

CaM

Relaxation in Smooth Muscle

Figure 12-29, steps 1–2


Relaxation in smooth muscle3

Ca2+

Ca2+

Na+

ECF

ATP

Free Ca2+ in cytosol decreases when

Ca2+ is pumped out of the cell or back

into the sarcoplasmic reticulum.

1

Sarcoplasmic

reticulum

1

Na+

Ca2+

ATP

Ca2+

Ca2+ unbinds from calmodulin (CaM).

2

CaM

2

Myosin phosphatase removes

phosphate from myosin, which

decreases myosin ATPase activity.

3

Ca2+

CaM

Myosin

phosphatase

3

ATP

P

ADP +

P

Inactive myosin

Myosin ATPase

activity decreases.

Relaxation in Smooth Muscle

Figure 12-29, steps 1–3


Relaxation in smooth muscle4

Ca2+

Ca2+

Na+

ECF

ATP

Free Ca2+ in cytosol decreases when

Ca2+ is pumped out of the cell or back

into the sarcoplasmic reticulum.

1

Sarcoplasmic

reticulum

1

Na+

Ca2+

ATP

Ca2+

Ca2+ unbinds from calmodulin (CaM).

2

CaM

2

Myosin phosphatase removes

phosphate from myosin, which

decreases myosin ATPase activity.

3

Ca2+

CaM

Myosin

phosphatase

3

ATP

Less myosin ATPase results in

decreased muscle tension.

4

P

ADP +

P

Inactive myosin

Myosin ATPase

activity decreases.

4

Decreased

muscle

tension

Relaxation in Smooth Muscle

Figure 12-29, steps 1–4


Smooth muscle relaxation

Smooth Muscle Relaxation

Myosin light

chain phosphatase

predominates

Deactivating

MLCK

Ca2+

myosin-Pi

myosin

RELAXATION


Smooth muscle regulation

Smooth Muscle Regulation

  • Many smooth muscles have dual innervation

    • Controlled by both sympathetic and parasympathetic neurons

  • Hormones and paracrines also control smooth muscle contraction

    • Histamine constricts smooth muscle of airways

    • Nitric oxide affects regulation of diameter of blood vessels


Muscles summary

Muscles: Summary


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