Week 5 - Skeletal Muscle Physiology Flashcards
what tissue is muscle separated by?
connective
what does collagenous connective tissue comprise of?
epimysium, perimysium, endomysium, fasiculi
what are myofibrils made from?
actin and myosin
what excitable membrane surrounds muscle cells?
sacrolemma
what is the cellular fluid within muscle fibre?
sarcoplasm - contains enzymes, organelles, myofibrils
what membranous network runs through muscle fibre?
sarcoplasmic reticulum - stores and releases Ca and contains ATP pumps
what invaginations run from sacrolemma through muscle cell?
tranverse tubules - they speed up transmission of AP, reducing electrical delay
what in muscle membranes are crucial in conversion of electrical impulse to CA2+?
dihydropyrodine
what are thick myofilaments comprised of?
200 myosin subunits containing actin and Ca2
= binding site
what are thin myofilaments comprised of?
200 actin molecules with tropomyosin
what is troponin-tropomyosin Tr-T complex essential for?
regulation of muscle contractions
how does Tr-T complex regulate muscle contraction?
blocking of myosin binding siteson actin thin filaments
what disables Tr-T complex?
influx of Ca2+ into cell
what are myofibrils made of?
thin and thick filaments
what is the smallest unit of a myofibril?
sacromere
describe structure of sacromere
I bands surround the middle A band
the I bands are thin filaments, A is thick filaments in centre
M line is the anchoring of thick filament in centre of H-Zone (centre of A band)
Z-disc (anchors thin filaments in both I bands)
what is the largest protein in the body?
titin
function of titin in relation to skeletal msucle?
acts as a scaffold to sacromere
what happens in the sliding filament theory?
myosin motor heads move from one actin to the next
thin filamnets slide past thick filaments
myosin heads pull Z-lines closer together
acromere shortens
H-zone and I band shorten, reducing Z-disk difference
A band stays same length
what is cross-bridge cycling?
1) ATP binds to mysoin head - myosin dissociates from actin
2) hydrolysis of ATP to ADP + P - weak binding of myosin head to actin
3) P is released - conformational change of myosin heavy chain head ‘power stroke’
this results in pulling of thin filaments
4) ADP is released - tight myosin to actin binding ‘rigor’
cycle goes again - pull and push motion
name the 3 types of muscle fibre
I, IIa and IIx
what 2 muscle fibres are oxidative?
I and IIa
what muscle fibres are anaerboic/ glycolytic?
IIx
how do you determine muscle fibre types in muscle sample?
muscle biopsy and staining
homogenise a sample and measure denisty of myosin and actin
which muscle fibre is most fatiguable?
IIx (fast)
which muscle fibre is least fatiguable?
I (slow)
which muscle fibre has few mitochondria?
IIx
which muscle fibre is high in myoglobin?
I (slow)
what is muscle plasticity?
muscles have ability to change their form and function to suit environment
what are the 3 mechanims for undergoing muscle plasticity?
change in fibre size, number and type
what is wolfs law?
bones will adapt based on mechanical stress placed on them, if no stress it will weaken
what is muscle atrophy?
a reduction in muscle mass - protein degradation
what is muscle hypertrophy?
a gain in muscle mass - protein anabolism
‘an increase in the mass or cross sectional area of a single fibre’
what occurs when there is a change in fibre size?
muscle atrophy and hypertrophy
what is muscle hyperplasia?
an increase in muscle fibre number - does not occur in humans
how many isoforms (I, IIa and IIx) can an adult express?
usually 50% type 1 and type II
what isoforms are present in an endurance athlete?
> 90% type I
what isoforms are present in a track sprinter?
> 80% type II
in relation to isforms, what happens during high activity levels?
type IIx converts to IIa
in relation to isoforms, what happens during low activity levels?
type IIa to IIx
what are hybrid fibre types?
unique forms of fibres that express more than one myosin isoform
