1. SMOOTH MUSCLE Dr. Ayisha Qureshi MBBS, MPhil Assistant Professor

2. CLASSIFICATION OF SMOOTH MUSCLES UNITARY/ SINGLE UNIT/SYNCYTIAL/VISCERAL 1.Muscles of visceral organs.e.g. GIT, uterus, ureters & some of the smaller blood vessels. 2.Form a sheet or bundles of tissue. 3.Cell membranes show gap junctions that allows AP to pass rapidly from cell to cell. 4.AP spreads rapidly throughout the sheet of cells – cells contract as a single unit. MULTI-UNIT 1.Iris & Ciliary body of the eye, large arteries, Piloerector muscles 2.Showing discrete, individual smooth muscle fibers. 3.Smooth muscle cells not electrically linked. Each muscle fiber innervated by a single nerve ending. NT itself can spread and lead to an AP. 4.Selective activation of each muscle fiber that can then contract independently of each other.

4. Latch mechanism It is a state in which the dephosphrylated myosin remains attached to actin for prolonged period of time. This produces sustained contraction without consuming ATP & thus enables the smooth muscle to sustain long-term maintenance of tone without fatigue. E.g. urinary bladder full of urine.

5. COMPARISON OF SKELETAL & SMOOTH MUSCLE CONTRACTION:

6. S.NOCHARACTERISTICSSKELETAL MUSCLESMOOTH MUSCLE 1.LocationAttached to the skeleton Blood vessels, hollow organs, eye 2.Mechanism of contractionSliding filament 3.Nerve supplyMotor neuronsAutonomic nervous system 4.Level of controlUnder Voluntary control Under Involuntary control 5.Presence of Thick & Thin filaments Yes 6.Presence of TropomyosinYes 7.Presence of TroponinYesNo 8.Presence of T-tubulesYesNo 9.Level of development of Sarcoplasmic Reticulum Well DevelopedPoorly Developed

7. S.noCHARACTERISTICSSKELETAL MUSCLESMOOTH MUSCLE 10.Source of CalciumSarcoplasmic Reticulum (SR)ECF & SR 11.Overlap of Actin & MyosinOverlap of actin & myosin seen only in part of the A- band Continuous overlap of actin & myosin, b/c of side-polar cross bridges 12.ATP used directly by contractile apparatus Yes 13.Myosin ATPase activity; speed of contraction Fast or slow depending on type of fiber Very slow 14.Site of Calcium regulationTroponin in thin filamentsMyosin in thick filaments 15.Mechanism of Calcium action Physically repositions troponin-tropomyosin complex to uncover actin cross-bridge binding site Chemically brings about phosphorylation of myosin cross bridges so they can bind with actin

8. S.noCHARACTERISTICSSKELETAL MUSCLESMOOTH MSUCLE 16.Duration of contraction100- 200 msecUpto 5 sec 17.Presence of Gap junctionsNoYes 18.Latch mechanismNoYes 19.NMJYesNo 20.NeurotransmitterAch onlyAch & Norepinephrine