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: 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 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 Ca 2+ calmodulin MLCK MLC active (phosphorylated) MLC inactive (dephosphorylated) Relaxation Contraction MLCP MLCK, myosin light chain kinase MLCP, myosin light chain phosphatase
Copyright © 2006 by Elsevier, Inc. Mechanisms That Increase Intracellular Ca 2+ Concentration in Smooth Muscle
Copyright © 2006 by Elsevier, Inc.