Muscle Structure and Function Part 1 W4 Flashcards
What are the functions of skeletal muscle?
Force production for locomotion and breathing
Force production for postural support
Heat production during cold stress
Act as an endocrine organ
What are flexors muscle actions?
Decreases joint angles
What are extensors muscle actions?
Increases joint angles
What is the sarcolemma?
Muscle cell membrane
What is the basement membrane?
Just below endomysium
What is the endomysium?
Surrounds muscle fibres
What is the perimysium?
Surrounds fascicles
What is the epimysium?
Surrounds entire muscle
What is the microstructure of myofibrils?
Contains contractile proteins:
- Actin (thin filament)
- Myosin (thick filament)
What is the microstructure of the sarcomere?
Z line
M line
H zone
A band
I band
What is the sarcoplasmic reticulum?
Storage sites for calcium
Terminal cisternae
What is the transverse tubules?
Extend from sarcolemma to sarcoplasmic reticulum
How does satellite cells play a key role in muscle growth and repair?
They increase the number of nuclei in mature muscle fibres
What is the myonuclear domain?
Volume of sarcoplasm surrounding each nucleus
Each nucleus can support a limited myonuclear domain
What is myonuclei and muscle hypertrophy relationship?
Increased myonuclei
What is myonuclei and muscle atrophy relationship?
Decreased myonuclei
What allows for greater protein synthesis?
More myonuclear
What is the neuromuscular junction?
Junction between motor neuron and muscle fibre
What is the motor end plate?
Pocket formed around motor neuron by sarcolemma
What is the neuromuscular cleft?
Short gap between neuron and muscle fibre
What is acetylcholine?
Ach is a neurotransmitter released from the motor neuron
Causes an end-plate potential (EPP)
Depolarization of muscle fibre
Signal for muscle contraction
In the sliding filament model, what causes muscle shortening to occur?
Movement of actin filament over the myosin filament
What is cross-bridge formation?
Actin and myosin form to create a “power stroke”
What is a repeated contraction cycle?
A single contraction cycle shortens the muscle by 1% of resting length
Some muscles can shorten up to 60% of resting length
What is excitation-contraction coupling?
Sequence of events where nerve impulses reaches muscle membrane and leads to muscle shortening by cross-bridge activity
What is contraction mediated by?
Calcium
What is fatigue?
A decline in muscle power output
What does a decline in muscle power output occur due to?
Decrease in muscle force production at the cross-bridge level
Decrease in muscle shortening velocity
What are the possible causes of fatigue in heavy intensity exercise?
Decreased Ca2+ release from the sarcoplasmic reticulum
Accumulation of metabolites that inhibit myofilament sensitivity to Ca2+
What are the key metabolites contributing to fatigue during heavy intensity exercise?
Pi, H+ and free radicals
- Pi and free radicals modify cross-bridge head and reduce number of cross-bridges bound to actin
- H+ ions bind to Ca2+ binding sites on troponin, preventing Ca2+ binding and contraction
What are the possible causes of fatigue in moderate intensity exercise?
Increased radical production
Glycogen depletion
What are the key metabolites contributing to fatigue?
Accumulation of Pi and H+ do not contribute to fatigue during moderate intensity exercise
Radical accumulation of modifies cross-bridge head and reduces number of cross-bridges bound to actin
Depletion of muscle glycogen reduces TCA cycle intermediates and decreases ATP production via oxidative phosphorylation
What is EAMS (Exercise-associated muscle cramps)?
Spasmodic, Involuntary muscle contractions
What is EAMS likely to cause in the spinal cord?
Hyperactive motor neurons
High-intensity exercise can alter muscle spindle and Golgi Tendon Organ function
Increased excitatory activity of muscle spindles and reduced inhibitory effect of the Golgi Tendon Organ
What strategies can be used to alleviate EAMS?
Passive stretching often relieves this type of muscle cramp
Possible that activating ion channels (transient receptor potential channels) in the mouth/ throat could send inhibitory signals to the spinal cord, and thus inhibit overactive motor neurons
