smooth-muscle-physiology-by-dr-roomi-ch-8
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U N I T II
Textbook of Medical Physiology, 11th Edition
GUYTON & HALL
Copyright © 2006 by Elsevier, Inc.
Contraction and Excitation of Smooth Muscleby
Dr. Mudassar Ali Roomi (MBBS, M. Phil.)
Copyright © 2006 by Elsevier, Inc.
CLASSIFICATION OF THE MUSCULAR TISSUE
Non-striated muscle (smooth muscle) Striated muscle (cardiac, skeletal
muscle)
Copyright © 2006 by Elsevier, Inc.
SMOOTH MUSCLE
No cross striations Location: in the walls of
blood vessels, hollow viscera Function: controls the size
of the lumen. Shape: each fiber is fusiform
in shape. Diameter: 3-8 um Length: 15-200 um No well developed
sarcotubular system. Caveolae are present.
Nucleus: single, rod- shaped nucleus located in the centre of each cell.
Copyright © 2006 by Elsevier, Inc.
Cytoplasm of smooth muscle fiber
E/M shows that actin and myosin are present in the cytoplasm.
Actin: diamter is 5-7 nm Myosin: diameter 12-16 nm actin/myosin ratio: 15/1 Desmin intermediate
filaments are also present in the cytoplasm. (dia= 10 nm)
Dense bodies: intermediate filaments cross over one another to form darkly staining patches.
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MULTI-UNIT AND UNITARY SMOOTH MUSCLES
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MULTI-UNIT AND UNITARY SMOOTH MUSCLES
Location Type of NM Junctions Arrangement Control Membrane potential.
MULTI-UNIT AND UNITARY SMOOTH MUSCLES
1: LOCATION: UNITARY: Wall of GIT,
ureter, bile duct, uterus and large blood vessels.
MULTIUNIT: Ciliary muscle of eye, Iris of eye and pilo-erector muscle, vas deference
MULTI-UNIT AND UNITARY SMOOTH MUSCLES
2: ARRANGEMENT: UNITARY: Sheaths or
bundles with gap junctions in between, so act as single unit. If one part is excited whole is excited.(functinal syncytium)
MULTIUNIT: Individual muscle fibers. Each fiber has insulating outer membrane with glycoprotein and collagen consistency. Independently each muscle fiber is excited.
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MULTI-UNIT AND UNITARY SMOOTH MUSCLES
3: TYPE OF NM JUNCTION:
UNITARY: Diffuse junction. No contact with nerve fiber. Neurotransmitter is released near the fiber.
MULTIUNIT: Contact junction. One of the autonomic nerves form junction with muscle fiber and releases neurotransmitter like nor-epinephrine
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MULTI-UNIT AND UNITARY SMOOTH MUSCLES
4: CONTROL: UNITARY:
Mainly non-nervous stimuli (hormonal stimuli like oxytocin and serotonin).
Nervous stimuli are less important
Show spontaneous contractions.
MULTIUNIT: Mainly through
nervous stimuli. Does not show
spontaneous contraction
MULTI-UNIT AND UNITARY SMOOTH MUSCLES
Types of potential in unitary smooth muscles5: MEMBRANE POTENTIAL:
UNITARY: 3 types: Spike potential , Action potential with
Plateau and spikes superimposed on
Slow wave. MULTIUNIT:
action potential is not produced.
Only localized depolarization in response to excitation.
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EXCITATION-CONTRACTION COUPLING OF SMOOTH MUSCLE FIBERS
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EXCITATION-CONTRACTION COUPLING OF SMOOTH MUSCLE FIBERS
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Contraction-Relaxation – myosin based regulation
Ca2+
Ca2+
calmodulin
MLCKMLC active(phosphorylated)
MLC inactive(dephosphorylated)
Relaxation
Contraction
MLCP
MLCK, myosin light chain kinaseMLCP, myosin light chain phosphatase
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Mechanisms That Increase Intracellular Ca2+ Concentration in Smooth Muscle
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Copyright © 2006 by Elsevier, Inc.
Copyright © 2006 by Elsevier, Inc.