014 muscle histology Flashcards
what are the 3 connective tissue sheets on muscle?
- epimysium = outside of muscle
- perimysium = around each muscle bundle/fasicle
- endomysium = around each individual muscle fibre/cell
what does the epimysium cover?
- outside of muscle
what does the perimysium cover?
- each muscle bundle/fascicle
what does the endomysium cover?
- each individual muscle cell/fiber
what is the breakdown of the structure of skeletal muscle?
- myofilaments (actin, myosin) —>
- sarcomere —>
- myofibril —>
- muscle cell/fibre —>
- muscle fascicle —>
- skeletal muscle
give 7 key features of skeletal muscle cells
- 1 muscle cell = 1 muscle fibre
- very wide, 100 micrometers diameter
- very long 30cm
- many nuclei on periphery
- no special junctions between cells
- many mitochondria
- sarcolemma, sarcoplasm, sarcoplasmic retitculum
where are the nuclei in skeletal muscle?
- on periphery of muscle cells
what does this transmssion electron micrograph (TEM) show?
- skeletal muscle fibres
- you can see the sarcomeres Sa
- SR = sarcoplasmic reticulum
- ZL = Z line
- A = dark A band = myosin and actin overlap
- I = light I band = actin
- Hzone = myosin only
what happens to the sarcomere during contraction?
- myosin pulls the actin filaments towards each either
- Z lines get closer together
- light I band shortens
- dark A band = same
- sarcomere shortens
- sliding filament theory
what is A?
sarcolemma
what is b?
terminal cisternae
what is c?
transverse tubules / T-tubules
what is d?
sarcoplasmic reticulum
what is e?
mitochondria
what is f?
myofibrils
what is g?
- dark A band myosin
what is h?
- light I band actin
what is i?
- Z line
what is j?
- nucleus
what is the triad in skeletal muscle?
- 1 T tubule and 2 terminal cisternae
what are the 2 different muscle fibre types?
- type 1 = slow
- type 2 = fast
what colour do type 1 muscle fibres appear?
- red = rich in myoglobin
what colour do type 2 muscle fibres appear?
- white = rich in glycogen, less myoglobin
what are type 1 muscle fibers used for?
- small, slow, aerobic exercise
- e.g. marathon
- related to continuous weak contractions e.g. postural muscles
what are type 2 muscle fibres used for?
- large fast anaerobic exercise
- e.g. sprint
- related to intense sporadic contraction, e.g. biceps
what does this image show?
- neuromuscular junction
- motor unit with multiple motor end plates on different myofibrils
what does this image demonstrate?
- muscle spindles
what do golgi tendon organs detect?
tension
what is myasthenia gravis and what is its pathophysiology?
- rare autoimmune disease that causes weakness of muscles
- caused by auto-anitbodies attacking ACh receptors on post-synaptic membrane of muscle
- also flattens junctional folds
= weaker less frequent nerve transmission = wealer muscle contractions
what is Duchenne’s muscular dystrophy?
- genetic disorder characterized by progressive muscle degeneration and weakness due to the alterations of a protein called dystrophin that helps keep muscle cells intact
what is Duchenne’s muscular dystrophy caused by?
- mutation in dystrophin gene which is responsible for connecting cytoskeleton of each muscle fibre to the basal lamina
- when dystrophin is mutated, excess Ca can penetrate the sarcolemma = excess water entry = cells burst and die
= muscles waste away
what does this picture show in terms of Duchenne muscular dystrophy?
dystrophin immunofluorescence stain shows absence of functional dystrophin in muscle membrane in MD
what are satellite cells?
- stem cells of the muscle
= proliferate to form new muscle fibres or replace damaged muscle fibres
where are satellite cells found in muscle?
- on the outside of skeletal muscle cells/fibres
what are satellite cells activated/stimulated by?
- muscle cells breaking/over stretching
what is this a picture of ?
satellite cell
