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Describe the 3 histological types of muscle
- Smooth-fusiform cells without striations
- -vessels, uterus, gut, iris, etc...
- Striated (skeletal and cardiac)
- -cylindrical cells with densely packed arrays of contractile proteins visibly striated
- -Actin and myosin; titin (a structural protein)
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Describe the major morphological and functional characteristics of SMOOTH muscle
- small fusiform cells with CENTRAL nuclei
- individual cells arranged in sheets and tubes
- contractile proteins- only visible on TEM
- -Actin (smooth muscle actin)
- - TropoMyosin, Myosin II
- Intermediate filaments: desmin, vimentin
- Dense body (desmosome attachments)
- Gap Junctions (connexions)
- Autonomic Innervation (stretch)
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describe the major morphological and functional characteristics of striated Cardiac muscle
- Central nuclei
- branching myofibres
- Intercalated discs between cells (= anchorage region of cytoskeleton and rich in gap junctions)
- relatively short length (50-100 microns)
- rich in mitochondria (aerobic metabolism)
- extensive SER- sarcoplasmic reticulum
- vagus and purkinje fibre system innervation
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Describe the major morphological and functional characteristics of striated skeletal muscle
- eccentric nuclei, long (10-50cm)
- syncytial cell -trains of cells
- prominent arrays of cytoskeletal contractile proteins- banding (birefringent)
- abundant mitochondira
- Extensive SER (smooth endoplasmic reticulum) aka sarcoplasmic reticulum
- -contains many voltage gated Ca++ channels
- Extensive invaginations of plasma membrane
- -t tubules
- -triads include plasma membrane (the sarcolemma) and sarcoplasmic reticulum
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What are all the parts of the banding pattern
- I band (gap between a bands)
- A band (end of overlap zone to next end of overlap zone)
- H zone: no overlap
- Z line: z line to z line = sarcomere
- M line: middle of sarcomere
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When a muscle fiber is stretched what happends?
- increased distance between z lines
- decreased zone overlap
- increased width of H zone
- A band remains constant
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What forms a triad?
- T- tubules (sarcolemma invaginations)
- sarcoplasmic reticulum
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Describe the morphological and functional specializations of the neuromuscular junction
- ***Found in striated skeletal muscle
- motor endplate: alpha motor neuron, releases ACh, R activated Na+ channel
- site of BOTOX action (chemical neurectomy)
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Describe the morphological and functional characteristics of intrafusal muscle fibres
- Individual striated skeletal muscle can be modified intrafusal muscle fibers
- Proprioception (where you sense your position in space): sense stretch, indicate length/position
- Reflex arc: sensory TYPE1A, motor (gamma motor neurons)
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List the connective tissue envelopes of skeletal muscle
- epipysium: satellite cells, vessels, nerves
- perimysium
- endomysium
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What is a collagenous fibre network?
- End to end
- fuses to make tendon (myotendinous junction)
- Golgi tendon organ stretch R (at R jxn determines tension)
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What is dystrophin?
- Cytoplasmic rod-like protein
- part of a protein complex that connects the myofibrils to the extracellular connective tissue components
- important in transmitting loads from cells to tendon
Absence/insufficiency = muscular dystrophy
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What is Myostatin
- growth factor important in limiting muscle mass during development
- mutations that make this protein non-functional are found in animals with exceptionally large muscles (double muscling eg Belgian blue cattle)
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What type of meat is fast twitch and which is slow twitch?
- Light meat = fast twitch muscle (low myoglobin)
- dark meat = slow twitch (endurance muscle, lots of myoglobin)
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