Skeletal Cardiac Smooth Muscles Skeletal Cardiac Smooth 22-Feb-19 Muscles

Muscles Specialized tissue Convert chemical energy into mechanical energy The energy obtained from nutrients Enable the muscles to contract Move different skeletal bones around joints Cardiac muscle to pump blood Smooth muscle to contract eg- GIT 22-Feb-19 Muscles

Types of Muscles There are three types of muscles Smooth Skeletal (striated) Cardiac (which is also striated) 22-Feb-19 Muscles

Types of Muscles Cardiac Muscle Skeletal Muscle Syncytial smooth Muscle Multiunit smooth Muscle 22-Feb-19 Muscles

Skeletal Muscles Structure Muscle cell (muscle fiber) Long cylindrical multinucleated cell Lie parallel to each other Force of action is directed along the fiber’s long axis Length varies from few mm to 30 cm or more Width is about 0.15 mm 22-Feb-19 Muscles

Skeletal Muscles Level of organization Fine layer of connective tissue (endomysium) Wraps each muscle fiber It separates it from neighboring fiber Endomysium Muscle fiber Perimysium Muscle fibers 22-Feb-19 Muscles

Skeletal Muscles Another layer: perimysium Surround a bundle of up to 150 muscle fibers Fascicules A fascia Fibrous connective tissue surround the entire muscle Endomysium Muscle fiber Perimysium Muscle fibers 22-Feb-19 Muscles

Skeletal Muscles Beneath the endomysium lie The sarcolema Thin elastic membrane Enclose the fiber’s cellular contents Contain the plasma membrane 22-Feb-19 Muscles

Skeletal Muscles Plasma membrane Conduct electrochemical wave of depolarization Over the surface of fiber Insulates one fibre from another during depolarization 22-Feb-19 Muscles

(Connective tissue sheath) Fascicules within sheath of perimyesium Epimysium (Connective tissue sheath) Fascicules within sheath of perimyesium Bundles of fibers. Muscles fibers are enclosed by own sheath of endomyesium Sarcoplasmic reticulum From H.Taher Sherief; Physiology Book(CD) 22-Feb-19 Muscles

Skeletal Muscles Within the muscle fiber Aqueous protoplasm (sarcoplasm) which contains Enzymes, fat, glycogen particles Nuclei (about 250 per mm length) Genes, mitochondria, organelles 22-Feb-19 Muscles

Sarcoplasmic Reticulum Nucleus Sarcoplasmic reticulum Longitudinal network of tubular channels and vesicles Allows the wave of depolarization To spread from outer surface to inner environment Myofibrils Sarcolemma Terminal cisterna (lateral sacs) Z disc sarcoplasmic reticulum (SR) Z-disc Triad 22-Feb-19 Muscles

Sarcoplasmic Reticulum Nucleus Through the T tubules To initiate muscle contraction Contain Ca++ pump in their membrane Pump Ca++ from sarcoplasm into vesicles Sarcoplasmic reticulum Myofibrils Sarcolemma Terminal cisterna (lateral sacs) Z disc sarcoplasmic reticulum (SR) Z-disc Triad 22-Feb-19 Muscles

Skeletal Muscles Chemical composition 75% water 20% proteins 5% minerals & nutrients Salts, high energy phosphates, urea, lactate Na+, Ca++, Mg++, Cl- phosphorous, Fat, carbohydrate, AA 22-Feb-19 Muscles

Skeletal Muscles Ultra-structure A single multinucleated muscle fibre contain Smaller functional units Lie parallel to long axis Myofibrils Myofibrils contain even smaller units Myofilaments Actin Troponin Tropomyosin myosin 22-Feb-19 Muscles

Ultra-structure MYOFIBRILS ARE MADE OF REPEATING ASSEMBLIES OF THICK AND THIN FILAMENTS 22-Feb-19 Muscles

(Connective tissue sheath) Fascicules within sheath of perimyesium Epimysium (Connective tissue sheath) Fascicules within sheath of perimyesium Bundles of fibers. Muscles fibers are enclosed by own sheath of endomyesium Sarcoplasmic reticulum Actin From H.Taher ; Physiology Book(CD) 22-Feb-19 Muscles

Myosin Filament Made up of 4 protein chains 2 myosin molecules Double helix Tail segment Heavy meromysin (HMM) Light meromysin Light chains Myosin globular head Light Meromysin Tail, Heavy Meromysin (HMM) Myosin globular head LMM HMM 22-Feb-19 Muscles

Myosin Filament Globular head 4 light chains Cross-bridge formation ATPase 4 light chains 2 associated with each myosin molecule globular heads Light chains Myosin globular head Light Meromysin Tail, Heavy Meromysin (HMM) Myosin globular head LMM HMM 22-Feb-19 Muscles

Myosin Filament 22-Feb-19 Muscles

Actin Filaments Made up of Double helix 2 strands of actin molecules twisted together Double helix Can exists as Globular proteins Fibrilar proteins Actin filament Tropomyosin Troponin 22-Feb-19 Muscles

Actin Filaments Troponin complex Tropomyosin Attaches tropomyosin to actin Tropomyosin Covers active sites on actin Tropomyosin Troponin 22-Feb-19 Muscles

Other Muscle Proteins Others include  -actinin distributed along Z band -actinin found in actin filament M protein C protein 22-Feb-19 Muscles

Muscle Contraction Pure myosin and actin Combine to form Actomyosin Sliding filament theory of muscle contraction 22-Feb-19 Muscles

Cross bridge Z - line Z - line Sarcomere showing the region of overlap between thick and thin filaments Sarcomere shortening in response to crossbridge formation Increase in the degree of overlap RELAXED CONTRATING FULLY CONTRACTED From: Physiology textbook CD by Hassen T. Sherief 22-Feb-19 Muscles

Mechanism of Muscle Contraction At rest Interaction between actin and myosin Prevented by troponin tropomyosin complex Active sites Inhibitor Actin filament 22-Feb-19 Muscles

Mechanism of Muscle Contraction In the presence of Ca++ Ca++ bind to troponin C Leads to conformational change of tropomyosin Uncovering of active sites Active sites Inhibitor Actin filament Ca++ 22-Feb-19 Muscles

Mechanism of Muscle Contraction Myosin bind to actin Bending of globular head While still attached to actin Moves the actin molecule Active sites Inhibitor Actin filament 22-Feb-19 Muscles

Mechanism of Muscle Contraction The bending of globular head Exposes ATP binding site ATP bind on myosin head Detachment from actin Active sites Inhibitor Actin filament 22-Feb-19 Muscles

Mechanism of Muscle Contraction ATP is hydrolyzed to ADP and energy ADP, energy Incorporated into myosin head Straightening of bent head to 900 Ready to attach to next active sight Active sites Inhibitor Actin filament 22-Feb-19 Muscles

Mechanism of Muscle Contraction 22-Feb-19 Muscles

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Excitation Contraction Coupling 22-Feb-19 Muscles

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Excitation Contraction Coupling Arrival of AP on motor end plate NMJ transmission AP along sarcolema Spread through T-tubules AP T-tubule AP Sarcoplasmic ret Ca++ Ca++ Mg++ Ca++/Mg++ ATPase Voltage gated channels Ca++ Ca++ Ca++ Ca++ 22-Feb-19 Muscles

Excitation Contraction Coupling AP Opening of voltage gated Ca++ channels Ca++ move from Sarcoplasmic reticulum Into sarcoplasm  Ca++ concentration T-tubule AP Sarcoplasmic ret Ca++ Ca++ Mg++ Ca++/Mg++ ATPase Voltage gated channels Ca++ Ca++ Ca++ Ca++ 22-Feb-19 Muscles

Actin Filaments Ca++ bind to troponin C Actin and myosin Conformational change of tropomyosin Uncovering of active sites Actin and myosin Crossbridge formation Muscle contraction Actin filament Tropomyosin Troponin Active site 22-Feb-19 Muscles

Excitation Contraction Coupling Relaxation occur Active pumping of Ca++ into sarcoplasmic reticulum Ca++/Mg++ ATPases AP T-tubule AP Sarcoplasmic ret Ca++ Ca++ Mg++ Ca++/Mg++ ATPase Voltage gated channels Ca++ Ca++ Ca++ Ca++ 22-Feb-19 Muscles

Actin Filaments There is a ↓ in the Concentration of Ca++ in the cytoplasm Closure of active sites relaxation Actin filament Tropomyosin Troponin Active site 22-Feb-19 Muscles

Excitation Contraction coupling 22-Feb-19 Muscles

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Length – Tension Relationship 22-Feb-19 Muscles

Length – Tension relationship During muscle contraction the isometric force exerted by the muscle Depend on the Actual length of the muscle fibers The force developed Related to degree of overlap between Actin and myosin 22-Feb-19 Muscles

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Cross-bridges Mechanical link The interaction between Between thick and thin filament The interaction between Myosin head and Actin filament Cause the head to Tilt towards the arm 22-Feb-19 Muscles

Cross-bridges This drags the actin filament This is the power stroke Towards centre of the sarcomere This is the power stroke The number of cross bridges determine Force produced by muscle fibre 22-Feb-19 Muscles

Cross-bridges Each of the cross-bridge Operate independently of the others The greater the number of cross-bridges Attaching to actin The greater the force of contraction 22-Feb-19 Muscles

Cross bridge Z - line Z - line Sarcomere showing the region of overlap between thick and thin filaments Sarcomere shortening in response to crossbridge formation Increase in the degree of overlap RELAXED CONTRATING FULLY CONTRACTED From: Physiology textbook CD by Hassen T. Sherief 22-Feb-19 Muscles

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Smooth Muscles 22-Feb-19 Muscles

Smooth Muscles Responsible for contractility Hollow organs Blood vessels, GIT, urinary bladder, uterus Structure differ from that of skeletal muscle Can develop isometric force per cross sectional area Equal to or greater than that of skeletal muscle Speed of contraction A fraction of that of skeletal muscle 22-Feb-19 Muscles

Smooth Muscles Does not show cross striation Under microscope It is also known as INVOLUNTARY muscle because Its function is not under our voluntary will Its activities arises spontaneously Or through the autonomic nervous system 22-Feb-19 Muscles

Smooth Muscles Smooth muscle from different tissue differ In structure Organization in sheets, bundles In property Response to different types of stimuli, innervations 22-Feb-19 Muscles

Smooth Muscles But in general individual cells Are long and spindle shaped About 50 to 500 μm long Are 5 to 10 μm wide Have one nucleus per cell Guyton Textbook of Physiology 22-Feb-19 Muscles

Smooth Muscles Are surrounded by a cell membrane Have myosin and actin Exhibit invagination (surface vesicles, caveoli) Have myosin and actin Contain sarcoplasmic reticulum Guyton Textbook of Physiology 22-Feb-19 Muscles

Multi-Unit Type Multi-unit smooth muscle Composed of individual muscle fibres Each with its own nerve inervation Can function independently www.uic.edu/classes/phyb/phyb516/smoothmusclesleu3.htm 22-Feb-19 Muscles

Multi-Unit Type Each muscle fibre is Discrete and operates independently There is no spontaneous contraction Activity controlled by the autonomic nervous system www.uic.edu/classes/phyb/phyb516/smoothmusclesleu3.htm 22-Feb-19 Muscles

Multi-Unit Type The axon terminal Found in the Makes several synaptic contacts on the membrane Found in the Iris, ciliary body Around hair follicles www.uic.edu/classes/phyb/phyb516/smoothmusclesleu3.htm 22-Feb-19 Muscles

Unitary (Single unit) Type Unitary (single unit), visceral smooth muscle Individual cells join together to form a sheet of cells When one cell is excited Then all contract as a single unit Guyton Textbook of Physiology 22-Feb-19 Muscles

Unitary (Single unit) Type Found in the walls of viscera Digestive system, urinary bladder, ureters Blood vessels Guyton Textbook of Physiology 22-Feb-19 Muscles

Unitary (Single unit) Type Cells are aggregated together into sheets or bundles The cell membranes adhere to each other at several points Tight and gap junctions Where ions can flow freely from one fibre to next Force generated in one muscle fibre can be transmitted into the next Guyton Textbook of Physiology 22-Feb-19 Muscles

The Contractile Process in Smooth Muscles: Contain both myosin and actin Not arranged in orderly way as in skeletal muscles Do not have troponin and tropomyosin Instead there is Caldesmon Calponin Guyton Textbook of Physiology 22-Feb-19 Muscles

The Contractile Process in Smooth Muscles: The actin filaments Are attached to dense bodies Contraction is achieved by the Sliding action of filaments like in skeletal muscles Guyton Textbook of Physiology 22-Feb-19 Muscles

Molecular Basis for Contraction Initiated by calcium as it is in skeletal muscles Smooth muscle Has poorly developed sarcoplasmic reticulum www.uic.edu/classes/phyb/phyb516/smoothmusclesleu3.htm 22-Feb-19 Muscles

Molecular Basis for Contraction Stimulation by nerves, or stretching Causes membrane depolarization Opening voltage gated calcium ion channels Influx of calcium ions from the extra cellular fluid Electromechanical coupling www.uic.edu/classes/phyb/phyb516/smoothmusclesleu3.htm 22-Feb-19 Muscles

Molecular Basis for Contraction Stimulation by hormones, drugs Causes activation of receptors Release of Ca++ ions from sarcoplasmic reticulum www.uic.edu/classes/phyb/phyb516/smoothmusclesleu3.htm 22-Feb-19 Muscles

Molecular Basis for Contraction Calcium ions bind to calmodulin Myosin light chain kinase (MLCK) is activated Activated MLCK Catalyses the phosphorylation of the myosin head Actin then bind with myosin Producing muscle contraction www.uic.edu/classes/phyb/phyb516/smoothmusclesleu3.htm 22-Feb-19 Muscles

Cessation of Contraction Myosin is de-phosphorylated by a phosphatase However, the cross bridges remain attached to actin This produces sustained contraction Latch mechanism (phenomenon) Relaxation of smooth muscle occurs When there is dissociation of calcium-calmodulin complex 22-Feb-19 Muscles

Control of Smooth Muscle Contraction Low levels of Ca++ Caldesmon blocks actin binding sites Muscle RELAXED High Ca++ levels Ca++ Calmodulin complex Removes caldesmon and Activates myosin light chain kinase (MLCK) Which phosphorylates myosin Promoting cycling Caldesmon bound to Ca++- calmodulin complex From: Physiology textbook CD by Hassen T. Sherief 22-Feb-19 Muscles