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PHOL2003 > Muscle Motility > Flashcards

Muscle Motility Flashcards

1
Q

What is the name of the tissue between skeletal muscle fibres?

A

Endomysium

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2
Q

What is the name of a group of skeletal muscle fibres and what is each group surrounded by?

A

Fascicle

Perimysium

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3
Q

What is the name of the tissue surrounding a group of fascicles?

A

Epimysium

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4
Q

Explain the process of myoblast determination

A

Somites - embryonic mesodermal cells
Signals from surrounding tissues act on somites - form myoblasts - precursor skeletal muscle cells - committed, not differentiated

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5
Q

Explain the process of myoblast proliferation

A

Signals from surrounding tissues act on myoblasts - form premuscle masses

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6
Q

Explain the process of myoblast differentiation

A

Myoblasts fuse
Activation of myogenes - 4 transcription factors
Forms multinucleate skeletal muscle fibre

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7
Q

What are the signs of commitment of a myoblast?

A

ACh receptors spread over sarcolemma

Formation of actin and myosin - but no sarcomeres

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8
Q

What are the 2 types of skeletal muscle fibres and what are their key characteristics?

A

Slow - long duration contraction - high endurance

Fast - high velocity contraction - short duration - low endurance

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9
Q

What are the 3 main types of skeletal muscle fibres?

A

Slow oxidative
Fast oxidative-glycolytic
Fast glycolytic

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10
Q

What are the characteristics of slow oxidative fibres and what is their use?

A 
Low myosin ATPase activity
High oxidative capacity
Red - high myoglobin
Slowest muscle twitch response to AP
Smallest force contraction
Longest duration contraction
Fatigue-resistant
E.g. walking
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11
Q

What are the characteristics of fast oxidative-glycolytic fibres?

A 
High myosin ATPase activity
High oxidative capacity
Red - high myoglobin
2nd fastest muscle twitch response to AP
Intermediate force contraction
Intermediate duration contraction
Fatigue slowly
E.g. walking
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12
Q

What are the characteristics of fast glycolytic fibres?

A 
High myosin ATPase activity
Low oxidative capacity
White - low myoglobin
Fastest muscle twitch response to AP
Largest force contraction
Shortest duration contraction
Fatigue quickly
E.g. jumping
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13
Q

Define oxidative capacity

A

µl of O2 consumed per g of muscle per hour

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14
Q

What does oxidative capacity depend on?

A

Rate of O2 delivery to muscle - capillary density
O2-carrying capacity of blood
Amount of O2 taken up by muscle form blood - enhanced by myoglobin
Amount of O2 used by muscles - depends of no. of mitochondria

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15
Q

What is the concentration of ATP in a muscle cell?

A

~5mM

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16
Q

What are the ATP regeneration pathways and what are their characteristics?

A

Direct ADP phosphorylation - by creatine kinase - rapid and reversible
Glycolysis - in anaerobic conditions - in cytosol - fast and low yield - causes lactic acid build-up
Oxidative phosphorylation - in aerobic conditions - in mitochondria - slow and efficient - needs myoglobin

17
Q

What is the order of recruitment of ATP regeneration pathways with intense muscle activity?

A

1st - direct ADP phosphorylation
2nd - glycolysis
3rd - oxidative phosphorylation

18
Q

What is VO2 max?

A

Maximal O2 consumption - maximal ATP made

19
Q

What is O2 debt/EPOC and what is its role?

A

Amount of additional O2 required by muscle after exercise

Allows phosphocreatine restoration, lactic acid oxidation, glycogen restoration, and replenishment of myoglobin with O2

20
Q

What is the structure of myosin?

A

Hexamer - 2 heavy chains, 2 regulatory light chains, 2 essential light chains
Globular head domain is actin-binding ATPase

21
Q

What are the different myosin heavy chain isoforms and where are they found?

A

MHCI - slow fibres
MHCIIa and IId - intermediate fibres
MHCIIb - fast fibres

22
Q

What causes the different contraction speed differences of the different muscle fibre types?

A

DIfferent myosin isoforms - due to different myosin heavy chain isoforms

23
Q

Define muscle fatigue

A

Decline in muscle tension due to previous contraction

24
Q

What are the causes of muscle fatigue?

A

Conduction failure - due to build-up of extracellular K+ in T-tubules - AP failure
Lactic acid build-up - due to anaerobic glycolysis - acidification causes conformational changes to muscle proteins

25
Q

What are the characteristics of MNs for fast fibres?

A 
Large axon
Fast conduction
High threshold
Late recruitment
Phasic discharge
26
Q

What are the characteristics of MNs for slow fibres?

A 
Small axon
Slow conduction
Low threshold
Early recruitment
Tonic discharge
27
Q

Which type of motor units are recruited first?

A

Small motor units

28
Q

What are the effects of endurance training on muscle?

A

Augmentation of oxidative phosphorylation
Increased capillary density and mitochondria
No effect on fibre diameter
Increases slow oxidative and fast oxidative-glycolytic fibre number

29
Q

What are the effects of strength training on muscle?

A

Increased pale fast fibre diameter
Higher glycolytic enzyme levels
Increases fast glycolytic fibre number

PHOL2003 (20 decks)

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