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Muscles - Anatomy & Physiology (view source)

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<big><center>[[Musculoskeletal System - Anatomy & Physiology|'''BACK TO MUSCULOSKELETAL ANATOMY AND PHYSIOLOGY''']]</center></big>
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===Introduction===
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*Skeletal muscle includes muscles of:
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**Posture
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**Movement
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**Respiration
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*Two basic types of skeletal myofibre:
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**<u>'''Type I'''</u>
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***Grossly '''red'''
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***'''High''' myoglobin level
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***'''Slow''' rate of contraction
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***High '''oxidative''' activity
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***Function - postural
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**<u>'''Type II'''</u>
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***Grossly '''white'''
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***'''Low''' myoglobin level
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***'''Fast''' rate of contraction
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***High '''glycolytic''' activity
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***Function - exercise
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*Each muscle is composed of multiple '''fascicles'''
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**Each fascicle is composed of multiple polygonal '''myofibres'''
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===Response to injury===
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*Limited array of ways in which to respond to injury
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**[[Muscles - degenerative#Degeneration|Degeneration]]
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**[[Muscles - degenerative#Necrosis|Necrosis]]
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**[[Muscles - normal#Regeneration|Regeneration]]
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**[[Muscles - degenerative#Atrophy|Atrophy]]
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**[[Muscles - hyperplastic and neoplastic#Hypertrophy|Hypertrophy]]
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*Large number of factors indicing the changes above, e.g.:
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**Trauma
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**Toxins
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**Infectious agents
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**Nutritional deficiencies
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**Ichaemia
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**[[Muscles - developmental|Hereditary diseases]]
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*Specific diagnosis is often not possible based on morphological or histological features alone
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*Additional tests, clinical information and history are often required
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===Regeneration===
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[[Image:Muscle regeneration.jpg|right|thumb|100px|<small><center>Muscle regeneration (Image sourced from Bristol Biomed Image Archive with permission)</center></small>]]
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*Skeletal muscle myofibres have substantial regenerative ability
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*Success depends on:
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**An intact '''sarcolemmal tube''' - to act as a support and guide
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**Availability of '''satellite cells''' - to act as progenitor cells for new sarcoplasm production
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**Macrophages to clear up cell debris
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**If these conditions are not met (e.g. severe thermal damage) '''fibrosis''' will occur
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*Stages:
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#Nuclei in [[Muscles - degenerative#Necrosis|necrotic segement]] disappear, hyalinased sarcoplasm due to loss of normal myofibrillar structure, may separate from adjacent normal myofibrils and/or [[Muscles - degenerative#Calcification|mineralise]]
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#Monocytes from capillaries -> macrophages in necrotic portion, satellite cells swell -> vesicular with prominent nucleoli -> mitosis (within 1-4 days after initial injury)
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#Satellite cells move to centre
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#Macrophages clear the sacrolemmal tube, plasmalemma disappears, shape maintained by basal lamina
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#Satellite cells -> myoblasts (contain myosin) -> fuse forming myotubes with row of central nuclei; cytoplasmic processes fusing
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#Growing and differentiating fibre, striations appear - formation of sarcomeres
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#Nuclei move to peripheral position (2-3 weeks after initial injury)
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*Regeneration by '''budding'''
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**When conditions are not optimal, disrupted sacrolemma
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**E.g. injection of irritating substance, trauma, [[Muscles - degenerative#Ischaemia|infarction]]
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**Myoblasts proliferate -> sacrolamma bulges from cut part -> club-shaped with numerous central nuclei = muscle giant cells
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*Monophasic lesions - all at same phase above
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**Damage occured at one time, e.g. trauma or one toxin exposure
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*Multiphasic lesions - different stages as described above
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**Ongoing damage, e.g. vitamin E - selenium deficiency, continuous exposure to toxin
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===Rigor Mortis===
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*Muscles remain biochemically active after the death of an animal
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*Following a period of relaxation, contraction and stiffening occurs
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*Due to deficiency of ATP releasing myosin heads from their binding sites at end of power stroke
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*Onset faster in ATP deprived animals (starvation, hunting, tetanus...)
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*May be absent in cachetic animals
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*Disappears due to autolysis or putrefaction
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*See [[General Pathology - Post-Mortem Change#Rigor Mortis|general pathology]]
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<big><center>[[Musculoskeletal System - Anatomy & Physiology|'''BACK TO MUSCULOSKELETAL ANATOMY AND PHYSIOLOGY''']]</center></big>
 
<big><center>[[Musculoskeletal System - Anatomy & Physiology|'''BACK TO MUSCULOSKELETAL ANATOMY AND PHYSIOLOGY''']]</center></big>
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