muscle structure and function Pt 1 - Week 4 Flashcards

1
Q

what are the 4 functions of the muscles ?

A

force production for locomotion and breathing

force production for postural support

heat production during cold stress

acts as an endocrine organ

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2
Q

what is the epimysium ?

A

surrounds entire muscle

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3
Q

what is the perimysium?

A

surround fascicles

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4
Q

what is the endomysium ?

A

surrounds muscle fibres

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5
Q

what is the basement membrane ?

A

just below endomysium

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6
Q

what is the sarcolemma ?

A

muscle cell membrane

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7
Q

what are the myofibrils ?

A

contractile proteins

actin - thin filament

myosin - thick filament

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8
Q

what are the sarcomeres? (4)

A

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

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9
Q

what is the sarcoplasmic reticulum ? (3)

A

muscles wrapped in the sarcolemma

storage sites for calcium

terminal cisternae

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10
Q

what are transverse tubules(2)

A

extend from sarcolemma to sarcoplasmic reticulum

help signal from periphery get deeper so that all fibres will contract

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11
Q

what is role of satellite cells ?

A

increase No. nuclei in mature muscle fibres - help growth and repair

myonuclear domain

more myonuclei allow greater protein synthesis
- muscle hypertrophy

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12
Q

what is importance of myonuclear domain and how does training effect it ? (2)

A

responsible for gene expression for surround sarcoplasm

training causes hypertrophy which recruits satellite cells to increase muscle fibres

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13
Q

What is a neuromuscular junction ?

A

Junction between motor neurons and muscle fibres

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14
Q

What is a motor end plate?

A

Pocket formed around motor neuron by sarcolemma

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15
Q

What is a neuromuscular cleft?

A

Short gap between neuron and muscle fibre

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16
Q

What is the role of acetylcholine in NMJ?

A

Stimulates the muscle fibre to depolarise, causing the signal to start the contractile process

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17
Q

Why does muscle shortening occur ?

A

Movement of actin filament over myosin filament

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18
Q

What’s is the cross bridge formation ?

A

Actin and myosin create a power stroke

19
Q

Tropomyosin is found where ?

A

Calcium binding site

20
Q

Where does the head of myosin attach ?

A

Actin binding site

21
Q

Myosin : thick or thin filaments ?

22
Q

Actin : thick or thin filament ?

23
Q

The release of energy from ATP hydrolysis creates energy required for..?

A

Power stroke

24
Q

___ ATPase breaks down ____ as fibre contracts

A

Myosin

ATP

25
What are sources of ATP ? (3)
Phosphocreatine Glycolysis Oxidative phosphorylation
26
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
27
During excitation-contraction coupling where does the signal from the motor nerve enter ? (3)
Synaptic knob Through transverse tubules To the sarcoplasmic reticulum
28
During excitation-contraction coupling what is released to receptors on sarcolemma of muscle fibre ?
Synaptic vesicles release acetylcholine across synaptic cleft
29
During excitation-contraction coupling, what does the release of ACh cause ?
Excitation of muscle fibre which leads to depolarisation
30
During excitation-contraction coupling, what does depolarisation cause ?
Opens calcium ion channels from sarcoplasmic reticulum
31
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
32
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
33
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
34
What is fatigue ?
Decline in muscle power output
35
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
36
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)
37
What are possible causes of fatigue for max intensity exercise ? (2)
Decrease in Ca2+ release form sarcoplasmic reticulum Accumulation of metabolites inhibiting myofilament sensitivity
38
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
39
What are the possible causes for fatigue for moderate intensity exercise? (2)
Increased radical production Glycogen depletion
40
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
41
What are EAMCs cramps?
Exercise associated muscle cramps Spasmodic , involuntary muscle contractions during exercise Associated with prolonged high intensity exercise
42
What is the myth about EAMCs?
EAMCs aren’t caused by electrolyte imbalance or dehydration Only likely in hot environments that cause electrolyte imbalance
43
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
44
What are strategies to alleviate EAMS ? (2)
Passive stretching Activating ion channels in mouth can send inhib signals to spinal cord