muscles Flashcards
components of sarcomere?
Z disc, I+A band, H zone, M line and myosin+actin
Z disc
between I band
desmin binds to Z disc
thin helical actin filaments (I) anchored perpendicularly to Z disc via alpha actinin
have opp polarity
I band
I band- G and F actin fil
1um and 8nm wide
isotropic
thin/light
accessory proteins
tintin- 3700kDa, largest protein in body scaffolding+ elastic properties help stretch +recoil to maintain space between thin fil in sarcomere during contraction
nebulin- 600-900kDa, bind thin filaments laterally+ anchor to alpha actinin
A band+ M line
A band- myosin II, 1.6um to 15nm
anisotropic- birefringence
thick/dark
tintin recenter A band to prevent overtwisting
lighter zone= H zone has no actin and bisects A band
M line between h zone and
myomesin- holds A in place
creatine kinase transfer PO4 from phosphocreatine to make ATP
actin
F actin
long filamentous polymer that has 2 globular monomers that are twisted w other pair= double helix
troponin- 3 subunits TnC: Ca, TnT: tropomyosin and TnI: mediate interaction actin+myosin
tropomyosin: 40nm, 2 glycoproteins that in groove of 2 actin strands
myosin
500kDa
composed of rod-like motor proteins: light and heavy chain(longer polypeptide+ binding site for ATP and actin)
150nm long 2/3 nm thick
globular projections w 4 light chains w myosin head in each; binds to actin= cross-bridge between thin+thick fil (use ATP) hexagonal in shape
muscle spindle
intro: striated m+ myotendinous j contain sensory receptors=act as proprioreceptors to provide data to cns.
muscle spindle 1mm-0.1mm has capsule: modified perimysium(fascicle) contains concentric layer of flattened cells
afferent sensory nerve fibres: are terminal new endings formed by
intrafusal fibres: contain satellite cells in external lamina
- has fewer myofibrils
- nuclei can be closely aligned (nuclear chain fibres) OR piled in central dilation (nuclear bag fibres)
fine motor nerve fibres: motor neurons terminate in small MEP at pole of muscle fibres
process:
- sensory nerve penetrates the muscle spindle + wraps around intrafusal fibre
- when body moves (change length of extrafusal m fibre which is detected by spindles; sensory n relays info to spinal cord
Golgi tendon organ
small, encapsulated structure that encloses the sensory axon
- penetrates collagen bundles at myotendinous junction (epimysium continuous w dense reg tissue of tendon)
1) organs detect change in tension
2) inhibit motor n activity if tension too high; prevent damage
3) helps reg amount of effort to make movement+ control F
embryonic muscle development
mesenchymal myoblast fuse= myotubes w nuclei which differentiate into striated muscle fibres
align into chain-like arrays which don’t fuse but form a complex junction between interdigitating process
essential components of smooth m tissue that striated m don’t have
no troponin instead, has: calmodulin and Ca2+ sensitive light-chain kinase for contraction (use filament sliding theory)
has thin F: has actin, an isoform kind of tropomyosin+ specific protein CALDESOM+CALPONIN (Block myosin binding site).
caveolae- small membrane invagination that have ion channels
organelles concentrated around nucleus
have cadherins of desmosomes
- thin filaments on dense bodies embedded in desmin (vimentin for vessels) which supplement activity of fibroblast, elastin, collagen and proteoglycans
contraction in smooth muscle
no MEP motor end plate so relies on autonomic nerves and hormones
whether contracts by small groups or whole muscle fibre it depends on degree of autonomic innervation+ density of gap junctions(high density more efficient + speed = more unison contraction)
uses adrenergic (epinephrine released binds to alpha+beta adrenergic receptors which cause contraction or can relax muscle: resp tract, unitary tract and cardiovascular system) +cholinergic nerve ending (release ACh to promote contraction (GIT, reproductive organs and urinary bladder)
muscle innervation-sk
1) myelinated motor nerves branch out from within perimysium. each nerve makes unmyelinated terminal twig, pass through endomysium to form synapse w m fibre.
2) Schwann cell enclose around small axon branches+external lamina of schwann cell fuse w sarcolemma. Axonal branch form dilated termination in trough of surface of m cell (site of synapse/synaptive contact NMJ/MEP)
3) within axon terminal, has mitochondria +synaptic vesicles w Ach. Between axon+muscle =synaptic cleft; adj to it has junctional folds (increase ACh receptor+post synaptic SA).
4) nerve AP reaches MEP-release ACh binds to receptor on folded sarcolemma (has cation channel) ->release Na = depolarization, makes muscle AP.
- dissociation of ACh to receptor (free NT removed) acetylcholanase to prevent prolonged contact. Axon release Ca from cistern in T tubule …(which penetrates sarcollema and encircles myobifirl near aligned I+A band. Ca bind to troponin for bridge to form…
5) motor unit- forms many MEP w many muscle fibres to inn them. The more fibres, the less precise and more coarse mov. to find how much a motor unit inn- send fire single motor neuron generates tension proportional to number of m fibre it inn
6) striated m contract all the way or none at all. F of contraction varied by not having all simultaneously contract.
