Muscle Tissue

1. Muscle Tissue Geoffrey T. Meyer

2. Muscle - Prefixes Myo(Greek) = muscle eg. Myology = the study of muscle Myositis = inflammation of muscle Sarco (Greek) = “flesh” eg. Sarcoplasm = the cytoplasm of muscle Sarcomere = basic contractile unit of muscle

3. Contractile mechanisms This is fundamental to many cell types -not just “muscle” eg. Macrophages

4. Contractile mechanisms Macrophages = phagocytes which move freely to engulf (phagocytose) cell debris & micro-organisms Macro = big Phage = swallow Cyte = cell

5. Muscle Packaging of contractile proteins is related to the functions required Thus there are different such arrangements These are classified into different “types” of MUSCLE

6. Specialised contractile proteins Muscle is a concentration of such proteins Myosin Actin Troponin Tropomysin & many structural proteins

7. Packaging of muscle proteins Depends on the force required eg. Slow steady contraction of tubes in the body - to maintain “tonus” or steady contractions Use individual cells with orientated packages of contractile proteins

8. Slow contracting packages of muscle proteins Common in tubes of the body Arteries & veins Intestine Lungs Urinary system Reproductive tubes

9. Slow contracting packages of muscle proteins PROPERTIES Cells contract slowly Often rhythmically – eg. peristalsis in gut tube Have tonic and slowly changing tensions Under nervous control of the Autonomic Nervous System (involuntary) Called then INVOLUNTARY muscle

10. Slow contracting packages of muscle proteins Contractile proteins arranged in a dispersed pattern - not in regular parallel arrays as in muscle which moves the skeleton ie. Skeletal muscle is “striped” in appearance INVOLUNTARY muscle is not striped & is thus then called Smooth muscle

11. Skeletal muscle Muscles which move the skeleton need 1. Much more power 2. Tougher connective tissue support 3. Much faster contraction

12. Skeletal muscle - mass Much more power = mass – many Kg Geoff in his early athletic career

13. Skeletal muscle – anatomical forms

15. Skeletal muscle –Connective tissue Tougher connective tissue support - fascial layers & tendons Epimysium -- Perimysium Endomysium

16. Skeletal muscle – Connective tissue Aponeurosis A fibrous or Membranous sheet-like tendon Fascia Fibrous sheet binding skin to underlying muscles or supporting/ separating muscles Tendon Band of connective tissue that attaches muscle to bone

17. Skeletal muscle- contraction Much faster contraction, highly ordered contractile filaments and a very rapid nerve supply Cross striations

18. Skeletal muscle Design characteristics Large cells = syncytium of fused myoblasts to form long multinuclear muscle fibres Highly organised contractile protein myofilaments

19. Why multi-nucleation? From a physical perspective? Contractile force can be efficiently generated by the shortening of a long tube From a regulatory view? It takes fewer neurons to synchronise contraction of a few large cells versus many individual smaller cells But there are problems with having such a large cell When cells become very large, signals from the cell membrane would not be able to efficiently reach a single nucleus. Also a single nucleus cannot efficiently regulate a very large cell So large cells become multinucleated with each nucleus controlling a given volume of cytoplasm = DNA unit.

20. Skeletal muscle Design characteristics Large cells = syncytium of fused myoblasts to form long multinuclear muscle fibres Highly organised contractile protein myofilaments

21. Myofibrils Myofilaments Skeletal muscle – cell = fibre Packaging Myofilaments (contractile proteins) into small bundles myofibrils

22. Z Z Sarcomere

23. Sliding myofilaments Much faster contraction

26. Skeletal muscle - LS

27. Skeletal muscle - tubules Transport problem because of huge cells 1. To transport wave of depolarisation into contractile filaments – T Tubes, which are extensions of the sarcolemma 2. Internal tubules to hold calcium - Sarcoplasmic reticulum

28. Skeletal muscle – tubulesComplex system of tubes within fibres (cells) for internal transport Transport Problem 1. External 2. Internal

29. Skeletal muscle - TS Large fibres & peripheral nuclei

30. Skeletal muscle – large cells Comparison of Smooth & Skeletal muscle

31. Skeletal muscle – Nerve supply

32. Skeletal muscle – Nerve supply

33. Skeletal muscle – Nerve supply Muscle Spindle

34. Skeletal muscle – Capillaries

35. Skeletal muscle – Blood supply Large muscle fibres & metabolically active & need a large amount of blood = oxygen But some muscles can work without oxygen for short times

36. Skeletal muscle – Blood supply These are Fast twitch muscles as in sprinters Most muscles use oxygen & can work for a long time – with an adequate blood supply These are Slow Twitch muscles

37. Skeletal muscle - Types

38. Cardiac Muscle Heart Left Ventricle muscle

39. Cardiac muscle A variant of skeletal muscle- Striated or striped Very fast contraction – but critical relaxation Internal tubular system Differences: Individual cells joined very tightly at Intercalated discs Branched individual fibres Central nuclei – like smooth muscle

40. Cardiac Muscle - size Smooth – Cardiac Skeletal Peripheral nuclei 5 µm 15-25 µm Central nuclei 50 µm

41. Cardiac Muscle - TS

42. Cardiac Muscle - LS

43. Cardiac muscle A variant of skeletal muscle- Striated or striped Very fast contraction – but critical relaxation Internal tubular system Differences: Individual cells joined very tightly at Intercalated discs Branched individual fibres Central nuclei – like smooth muscle

44. Cardiac Muscle - LS Intercalated disc