U N I T II
Textbook of Medical Physiology, 11th Edition
GUYTON & HALL
Copyright © 2006 by Elsevier, Inc.
Chapter 8:Contraction and Excitation of Smooth Muscle
by
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.
Copyright © 2006 by Elsevier, Inc.
MULTI-UNIT AND UNITARY SMOOTH MUSCLES
Copyright © 2006 by Elsevier, Inc.
MULTI-UNIT AND UNITARY SMOOTH MUSCLES
• Location• Type of NM Junctions• Arrangement• Control• Membrane potential.
Copyright © 2006 by Elsevier, Inc.
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
Copyright © 2006 by Elsevier, Inc.
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.
Copyright © 2006 by Elsevier, Inc.
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
Copyright © 2006 by Elsevier, Inc.
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
Copyright © 2006 by Elsevier, Inc.
MULTI-UNIT AND UNITARY SMOOTH MUSCLES
5: 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.
Types of potential in unitary smooth muscles
Copyright © 2006 by Elsevier, Inc.
EXCITATION-CONTRACTION COUPLING OF SMOOTH MUSCLE FIBERS
Copyright © 2006 by Elsevier, Inc.
EXCITATION-CONTRACTION COUPLING OF SMOOTH MUSCLE FIBERS
Copyright © 2006 by Elsevier, Inc.
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
Copyright © 2006 by Elsevier, Inc.
Mechanisms That Increase Intracellular Ca2+ Concentration in Smooth Muscle
Copyright © 2006 by Elsevier, Inc.
Copyright © 2006 by Elsevier, Inc.
Copyright © 2006 by Elsevier, Inc.
