Connective tissue MUSCLE TISSUE

Transcription

1 Connective tissue MUSCLE TISSUE Part 1

2 General features of MT Develop from mesoderm Many cells, less intercellular matrix Function contraction (shortening)

3 Skeletal (striated, voluntary) Types of MT Cardiac (striated, involuntary) Smooth (nonstriated, involuntary)

4 Structure of skeletal muscle Unit of SM muscle cell (fiber) Muscle fibers form muscle fascicle Muscle fascicles form muscle

5 Connective tissue of skeletal muscle Epimysium (covers muscle from the outside) Perimysium (surrounds muscle fascicles) Endomysium (surrounds muscle fibers)

6 Connective tissue of skeletal muscle Black arrows - perimysium; green arrows - endomysium

7 Terminology Sarx (greek) - meat Sarcolemma plasma membrane of muscle fiber Sarcoplasm cytoplasm of muscle fiber Sarcoplasmic reticulum - SER of muscle fiber Sarcomere structural unit of myofibril

8 Muscle fiber (Cell) Consist of myofibrils Myofibrils consist of myofilaments: actin and myosin Many nuclei on the periphery (syncytium)

9 Skeletal muscle fiber structure Muscle fiber Myofibrils Myofilaments

10 Myofilaments Actin (thin filament) Myosin (thick filament) Responsible for band like structure of skeletal muscle Interaction between actin and myosin results in contraction

11 Thin actin filaments Composed of 3 major proteins: - F (fibrous) actin - Tropomyosin - Troponin Two strands of F actin make a double helix F actin consists of G (globular) actin monomers Tropomyosin winds along the groove of F actin double helix Troponin composed of 3 subunits: -Tn-I: binds to actin -Tn-T: binds troponins to tropomyosin -Tn-C: binds Calcium ions

12 Actin filament

13 Thick myosin filaments Consist of myosin protein Has a golf club shape Two heavy myosin chains make the tail Two heads that extend laterally Hinge region in between

14 Skeletal muscle fiber structure Muscle fiber Myofibrils Myofilaments

15 Sarcomere Part of myofibril between two Z-lines

16 Z-line connection of actin filaments in the middle of I-band M-line connection of myosin filaments in the middle of the sarcomere

17 A-band (anisotropic, dark) - contains both myosin and actin filaments I-band (isotropic, light) contains only thin actin filaments H-band contains only thick myosin filaments

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19 Sarcoplasmic reticulum Network of tubules and cylinders surrounding each myofibril Resembles smooth endoplasmic reticulum Stores Calcium ions

20 Transverse tubule (T-tubule) invagination of the sarcolemma at the level of I- and A-band junction, surrounding the myofibril Terminal cisterns - extensions of sarcoplasmic reticulum on the sides of T-tubules Triade of skeletal muscle = 1 Т-tubule + 2 terminal cisterns of sarcoplasmic reticulum

21 Motor unit = efferent (motor) neuron + all muscle fibers innervated by it The more precise the work of the muscle, the more motor units in it (and less muscle fibers per one motoneuron)

22 Neuromuscular junction (synaps) Terminal bud of motor neuron (presynaptic membrane) Sarcolemma of muscle fiber (postsynaptic membrane) Synaptic cleft between them Function: Nervous impulse transmitting from neuron to muscle fiber

23 Release of neurotransmitter (acetylcholine) into the synaptic cleft Impulse conduction Binding of acetylcholine with receptors on the postsynaptic membrane leads to changing of the membrane charge firing of the Action potential

24 Skeletal muscle contraction 1. Action potential is spread along the sarcolemma onto the T-tubules and than terminal cisterns 2.Са ++ ions are realized into the sarcoplasm

25 Skeletal muscle contraction 3. Са ++ binds to troponin С 4. Movement of TnI away from the myosin-binding sites on the actin filaments

26 Skeletal muscle contraction 5. Binding of the myosin heads to the actin filaments 6. Activation of myosin ATPasa producing energy and ADP 7. Power Stroke: conformational change in myosin at hinge region pulling attached actin filaments toward the center of the sarcomere 8. Shortening of the sarcomeres (I bands narrow, A bands do not) 9. Shortening of the entire muscle fiber 10. New ATP molecule binds to myosin and it gets ready again to bind to actin (step 5) 11. End of neural stimulation Са ++ sequestration back to the sarcoplasmic reticulum, TnI returns to its position covering the tropomyosin binding sites

27 Skeletal muscle contraction

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29 Types of skeletal muscle fibers

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31 Cardiac muscle Consist of cardiomyocytes Striated Involuntary Diads instead of triades (1 T-tubule + 1 terminal cistern) Conducting system

32 Cardiomyocytes Branched cells One central nucleus Intercalated disc connections of cardiomyocytes allowing rapid transmission of impulses

33 Three types of cardiomyocytes Typical cardiomyocytes predominant type, function - contraction Atypical cardiomyocytes less myofibrils, function impulse generation and conduction Secretory cardiomyocytes located in right atrium, secrete hormone atrial natriuretic factor, which causes sodium and water loss, reducing blood pressure

34 Conducting system of the heart impulse generation and transmission Autonomous nervous fibers only slow down or speed up the intrinsic beat

35 Purkinje cells

36 Intercalated discs Specialized junctional complexes Consist of: - desmosomes - gap junctions

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38 Smooth muscle Spindle shaped cells with gap junctions Involuntary One central nucleus

39 No sarcomeres Dense bodies on the membrane analogous to the Z lines Thin filaments (actin) are attached to dense bodies Thick filaments (myosin) are unstable and dispersed in the cytoplasm Intermediate filaments (desmin, vimentin)

40 Smooth muscle contraction 1. Influx of Ca into the cytoplasm 2. Binding of Ca with Calmodulin (instead of troponin) 3. Ca-Calmodulin complex activates myosin light chain kinase 4. Phosphorilation and activation of myosin 5. Myosin binds to actin = initiation of contraction

41 Sliding actin filaments pull dense bodies close together, contracting the cell Contraction of smooth muscle cells is slow and wavelike

42 Smooth muscle Transverse section Longitudinal section

43 Regeneration Skeletal muscle fibers regeneration is possible due to satellite cells Smooth muscle cells regeneration is possible due to the division of mature myocytes Cardiomyocytes do not regenerate, only intracellular renewal is possible

44 Satellite cells Stem cells of skeletal muscle Lay between the sarcolemma and the basal lamina Activated in case of injury of muscle or excessive exercising

45 Skeletal muscle regeneration

46 Smooth muscle regeneration

47 Cardiomyocytes regeneration???

48 Thank you for attention