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Muscle Tissue. Geoffrey T. Meyer. Muscle - Prefixes. Myo (Greek) = muscle eg. Myo logy = the study of muscle Myo sitis = inflammation of muscle Sarco (Greek) = “flesh” eg. Sarco plasm = the cytoplasm of muscle Sarco mere = basic contractile unit of muscle. Contractile mechanisms.
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Muscle Tissue Geoffrey T. Meyer
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
Contractile mechanisms This is fundamental to many cell types -not just “muscle” eg. Macrophages
Contractile mechanisms Macrophages = phagocytes which move freely to engulf (phagocytose) cell debris & micro-organisms Macro = big Phage = swallow Cyte = cell
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
Specialised contractile proteins Muscle is a concentration of such proteins Myosin Actin Troponin Tropomysin & many structural proteins
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
Slow contracting packages of muscle proteins Common in tubes of the body Arteries & veins Intestine Lungs Urinary system Reproductive tubes
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
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
Skeletal muscle Muscles which move the skeleton need 1. Much more power 2. Tougher connective tissue support 3. Much faster contraction
Skeletal muscle - mass Much more power = mass – many Kg Geoff in his early athletic career
Skeletal muscle –Connective tissue Tougher connective tissue support - fascial layers & tendons Epimysium -- Perimysium Endomysium
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
Skeletal muscle- contraction Much faster contraction, highly ordered contractile filaments and a very rapid nerve supply Cross striations
Skeletal muscle Design characteristics Large cells = syncytium of fused myoblasts to form long multinuclear muscle fibres Highly organised contractile protein myofilaments
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.
Skeletal muscle Design characteristics Large cells = syncytium of fused myoblasts to form long multinuclear muscle fibres Highly organised contractile protein myofilaments
Myofibrils Myofilaments Skeletal muscle – cell = fibre Packaging Myofilaments (contractile proteins) into small bundles myofibrils
Z Z Sarcomere
Sliding myofilaments Much faster contraction
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
Skeletal muscle – tubulesComplex system of tubes within fibres (cells) for internal transport Transport Problem 1. External 2. Internal
Skeletal muscle - TS Large fibres & peripheral nuclei
Skeletal muscle – large cells Comparison of Smooth & Skeletal muscle
Skeletal muscle – Nerve supply Muscle Spindle
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
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
Cardiac Muscle Heart Left Ventricle muscle
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
Cardiac Muscle - size Smooth – Cardiac Skeletal Peripheral nuclei 5 µm 15-25 µm Central nuclei 50 µm
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
Cardiac Muscle - LS Intercalated disc