Week 5 - Skeletal Muscle Physiology

Question 1

what tissue is muscle separated by?

Answer 1

connective

Question 2

what does collagenous connective tissue comprise of?

Answer 2

epimysium, perimysium, endomysium, fasiculi

Question 3

what are myofibrils made from?

Answer 3

actin and myosin

Question 4

what excitable membrane surrounds muscle cells?

Answer 4

sacrolemma

Question 5

what is the cellular fluid within muscle fibre?

Answer 5

sarcoplasm - contains enzymes, organelles, myofibrils

Question 6

what membranous network runs through muscle fibre?

Answer 6

sarcoplasmic reticulum - stores and releases Ca and contains ATP pumps

Question 7

what invaginations run from sacrolemma through muscle cell?

Answer 7

tranverse tubules - they speed up transmission of AP, reducing electrical delay

Question 8

what in muscle membranes are crucial in conversion of electrical impulse to CA2+?

Answer 8

dihydropyrodine

Question 9

what are thick myofilaments comprised of?

Answer 9

200 myosin subunits containing actin and Ca2
= binding site

Question 10

what are thin myofilaments comprised of?

Answer 10

200 actin molecules with tropomyosin

Question 11

what is troponin-tropomyosin Tr-T complex essential for?

Answer 11

regulation of muscle contractions

Question 12

how does Tr-T complex regulate muscle contraction?

Answer 12

blocking of myosin binding siteson actin thin filaments

Question 13

what disables Tr-T complex?

Answer 13

influx of Ca2+ into cell

Question 14

what are myofibrils made of?

Answer 14

thin and thick filaments

Question 15

what is the smallest unit of a myofibril?

Answer 15

sacromere

Question 16

describe structure of sacromere

Answer 16

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)

Question 17

what is the largest protein in the body?

Answer 17

titin

Question 18

function of titin in relation to skeletal msucle?

Answer 18

acts as a scaffold to sacromere

Question 19

what happens in the sliding filament theory?

Answer 19

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

Question 20

what is cross-bridge cycling?

Answer 20

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

Question 21

name the 3 types of muscle fibre

Answer 21

I, IIa and IIx

Question 22

what 2 muscle fibres are oxidative?

Answer 22

I and IIa

Question 23

what muscle fibres are anaerboic/ glycolytic?

Answer 23

IIx

Question 24

how do you determine muscle fibre types in muscle sample?

Answer 24

muscle biopsy and staining
homogenise a sample and measure denisty of myosin and actin

Question 25

which muscle fibre is most fatiguable?

Answer 25

IIx (fast)

Question 26

which muscle fibre is least fatiguable?

Answer 26

I (slow)

Question 27

which muscle fibre has few mitochondria?

Answer 27

IIx

Question 28

which muscle fibre is high in myoglobin?

Answer 28

I (slow)

Question 29

what is muscle plasticity?

Answer 29

muscles have ability to change their form and function to suit environment

Question 30

what are the 3 mechanims for undergoing muscle plasticity?

Answer 30

change in fibre size, number and type

Question 31

what is wolfs law?

Answer 31

bones will adapt based on mechanical stress placed on them, if no stress it will weaken

Question 32

what is muscle atrophy?

Answer 32

a reduction in muscle mass - protein degradation

Question 33

what is muscle hypertrophy?

Answer 33

a gain in muscle mass - protein anabolism 'an increase in the mass or cross sectional area of a single fibre'

Question 34

what occurs when there is a change in fibre size?

Answer 34

muscle atrophy and hypertrophy

Question 35

what is muscle hyperplasia?

Answer 35

an increase in muscle fibre number - does not occur in humans

Question 36

how many isoforms (I, IIa and IIx) can an adult express?

Answer 36

usually 50% type 1 and type II

Question 37

what isoforms are present in an endurance athlete?

Answer 37

>90% type I

Question 38

what isoforms are present in a track sprinter?

Answer 38

>80% type II

Question 39

in relation to isforms, what happens during high activity levels?

Answer 39

type IIx converts to IIa

Question 40

in relation to isoforms, what happens during low activity levels?

Answer 40

type IIa to IIx

Question 41

what are hybrid fibre types?

Answer 41

unique forms of fibres that express more than one myosin isoform