Muscle Motility Flashcards
What is the name of the tissue between skeletal muscle fibres?
Endomysium
What is the name of a group of skeletal muscle fibres and what is each group surrounded by?
Fascicle
Perimysium
What is the name of the tissue surrounding a group of fascicles?
Epimysium
Explain the process of myoblast determination
Somites - embryonic mesodermal cells
Signals from surrounding tissues act on somites - form myoblasts - precursor skeletal muscle cells - committed, not differentiated
Explain the process of myoblast proliferation
Signals from surrounding tissues act on myoblasts - form premuscle masses
Explain the process of myoblast differentiation
Myoblasts fuse
Activation of myogenes - 4 transcription factors
Forms multinucleate skeletal muscle fibre
What are the signs of commitment of a myoblast?
ACh receptors spread over sarcolemma
Formation of actin and myosin - but no sarcomeres
What are the 2 types of skeletal muscle fibres and what are their key characteristics?
Slow - long duration contraction - high endurance
Fast - high velocity contraction - short duration - low endurance
What are the 3 main types of skeletal muscle fibres?
Slow oxidative
Fast oxidative-glycolytic
Fast glycolytic
What are the characteristics of slow oxidative fibres and what is their use?
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
What are the characteristics of fast oxidative-glycolytic fibres?
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
What are the characteristics of fast glycolytic fibres?
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
Define oxidative capacity
µl of O2 consumed per g of muscle per hour
What does oxidative capacity depend on?
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
What is the concentration of ATP in a muscle cell?
~5mM
What are the ATP regeneration pathways and what are their characteristics?
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
What is the order of recruitment of ATP regeneration pathways with intense muscle activity?
1st - direct ADP phosphorylation
2nd - glycolysis
3rd - oxidative phosphorylation
What is VO2 max?
Maximal O2 consumption - maximal ATP made
What is O2 debt/EPOC and what is its role?
Amount of additional O2 required by muscle after exercise
Allows phosphocreatine restoration, lactic acid oxidation, glycogen restoration, and replenishment of myoglobin with O2
What is the structure of myosin?
Hexamer - 2 heavy chains, 2 regulatory light chains, 2 essential light chains
Globular head domain is actin-binding ATPase
What are the different myosin heavy chain isoforms and where are they found?
MHCI - slow fibres
MHCIIa and IId - intermediate fibres
MHCIIb - fast fibres
What causes the different contraction speed differences of the different muscle fibre types?
DIfferent myosin isoforms - due to different myosin heavy chain isoforms
Define muscle fatigue
Decline in muscle tension due to previous contraction
What are the causes of muscle fatigue?
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
What are the characteristics of MNs for fast fibres?
Large axon Fast conduction High threshold Late recruitment Phasic discharge
What are the characteristics of MNs for slow fibres?
Small axon Slow conduction Low threshold Early recruitment Tonic discharge
Which type of motor units are recruited first?
Small motor units
What are the effects of endurance training on muscle?
Augmentation of oxidative phosphorylation
Increased capillary density and mitochondria
No effect on fibre diameter
Increases slow oxidative and fast oxidative-glycolytic fibre number
What are the effects of strength training on muscle?
Increased pale fast fibre diameter
Higher glycolytic enzyme levels
Increases fast glycolytic fibre number
