muscle structure and function Pt 1 - Week 4 Flashcards
what are the 4 functions of the muscles ?
force production for locomotion and breathing
force production for postural support
heat production during cold stress
acts as an endocrine organ
what is the epimysium ?
surrounds entire muscle
what is the perimysium?
surround fascicles
what is the endomysium ?
surrounds muscle fibres
what is the basement membrane ?
just below endomysium
what is the sarcolemma ?
muscle cell membrane
what are the myofibrils ?
contractile proteins
actin - thin filament
myosin - thick filament
what are the sarcomeres? (4)
z line - space between sarcomere unit
M lines - middle of sarcomere
A band - crossover between actin and myosin
I band - no cross over between actin and myosin filament
what is the sarcoplasmic reticulum ? (3)
muscles wrapped in the sarcolemma
storage sites for calcium
terminal cisternae
what are transverse tubules(2)
extend from sarcolemma to sarcoplasmic reticulum
help signal from periphery get deeper so that all fibres will contract
what is role of satellite cells ?
increase No. nuclei in mature muscle fibres - help growth and repair
myonuclear domain
more myonuclei allow greater protein synthesis
- muscle hypertrophy
what is importance of myonuclear domain and how does training effect it ? (2)
responsible for gene expression for surround sarcoplasm
training causes hypertrophy which recruits satellite cells to increase muscle fibres
What is a neuromuscular junction ?
Junction between motor neurons and muscle fibres
What is a motor end plate?
Pocket formed around motor neuron by sarcolemma
What is a neuromuscular cleft?
Short gap between neuron and muscle fibre
What is the role of acetylcholine in NMJ?
Stimulates the muscle fibre to depolarise, causing the signal to start the contractile process
Why does muscle shortening occur ?
Movement of actin filament over myosin filament
What’s is the cross bridge formation ?
Actin and myosin create a power stroke
Tropomyosin is found where ?
Calcium binding site
Where does the head of myosin attach ?
Actin binding site
Myosin : thick or thin filaments ?
Thick
Actin : thick or thin filament ?
Thin
The release of energy from ATP hydrolysis creates energy required for..?
Power stroke
___ ATPase breaks down ____ as fibre contracts
Myosin
ATP
What are sources of ATP ? (3)
Phosphocreatine
Glycolysis
Oxidative phosphorylation
Explain the repeated contraction cycle (4)
ATP binds to myosin head
ATP hydrolysed and binds to actin
Releases phosphate and ADP - causes power stroke where filaments slide over one another
ATP needs to be replenished to repeat cycle
During excitation-contraction coupling where does the signal from the motor nerve enter ? (3)
Synaptic knob
Through transverse tubules
To the sarcoplasmic reticulum
During excitation-contraction coupling what is released to receptors on sarcolemma of muscle fibre ?
Synaptic vesicles release acetylcholine across synaptic cleft
During excitation-contraction coupling, what does the release of ACh cause ?
Excitation of muscle fibre which leads to depolarisation
During excitation-contraction coupling, what does depolarisation cause ?
Opens calcium ion channels from sarcoplasmic reticulum
During excitation-contraction coupling, what do calcium ions bind to and what does this cause ?
Troponin on actin molecules
Causes tropomyosin to move away from ‘active sites’ on the actin molecule for a strong binding site for actin + myosin
During excitation-contraction coupling what happens to energised myosin crossbridges?
Binds to active site on actin and pulls on actin to produce back and forth movement
During excitation-contraction coupling, once the back and forth movement is created what happens to ACh with the muscle fibre and Calcium ?(2)
ACh release stops and muscle is repolarised
Calcium is pumped from cytosol into sarcoplasmic reticulum
What is fatigue ?
Decline in muscle power output
What is muscle fatigue(decline in muscle power output) caused by ? (3)
Decrease in force production at cross bridge level
Decrease in muscle shortening velocity
Also depends on exercise intensity
What is the lactate threshold for moderate, heavy and very heavy exercise ?
Moderate:50 -75% (up to 60% VO2 max)
Heavy: 76-85% ( 60-75 VO2 max)
Very heavy: 86- 100% (76-100 VO2 max)
What are possible causes of fatigue for max intensity exercise ? (2)
Decrease in Ca2+ release form sarcoplasmic reticulum
Accumulation of metabolites inhibiting myofilament sensitivity
What are the key metabolites contributing to fatigue at max intensity ? (3)
Pi , H+ , free radicals
Pi + free radicals modify cross bridge head + reduce No. bridges bound to actin
H+ bind to Ca2+ binding sites on troponin to prevent Ca2 binding and contraction
What are the possible causes for fatigue for moderate intensity exercise? (2)
Increased radical production
Glycogen depletion
What are the key metabolites that contribute to fatigue during moderate intensity exercise ? (3)
Accumulation of Pi and H+ don’t contribute to fatigue
Radical accumulation modifies cross-bridge head and reduce number of cross bridges bound to actin
Depletion of muscle glycogen stores reduce TCA cycle intermediates + decrease ATP production via oxidative phosphorylation
What are EAMCs cramps?
Exercise associated muscle cramps
Spasmodic , involuntary muscle contractions during exercise
Associated with prolonged high intensity exercise
What is the myth about EAMCs?
EAMCs aren’t caused by electrolyte imbalance or dehydration
Only likely in hot environments that cause electrolyte imbalance
What are EAMS likely caused by ? (3)
Altered muscle spindle and Golgi tendon organ function
Increased excitatory activity of muscle spindles and reduced inhibitory effect of Golgi tendon organ
Hyperactive motor neurons in spinal cord
What are strategies to alleviate EAMS ? (2)
Passive stretching
Activating ion channels in mouth can send inhib signals to spinal cord
