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Physiology > Skeletal Muscle > Flashcards

Skeletal Muscle Flashcards

0
Q

What do the the muscles do?

A
  • they allow movement = walking
  • protect the viscera = body wall
  • heat production = 37 degrees Celsius
  • posture, fascial expression
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1
Q

What are the characteristics of muscle?

A
  • excitable = respond to stimuli and produce ATP
  • contractile = can shorten and thicken
  • extensible = they stretch when pulled
  • elastic = can go back to original after contraction and extension
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2
Q

In a neuromuscular junction, how many neurone(s) innervates each muscle fibre(cell)? Explain.

A
  • one

- the axon of a motor neurone branches out to innervate several muscle fibres

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3
Q

How many muscle fibres can a singular motor neurone innervate?

A
  • about 150 muscle fibres within the same whole muscle
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4
Q

What is a motor unit?

A
  • a single neurone + all the muscle fibres it innervates
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5
Q

Explain the structure of a motor unit.

A
  • presynaptic cell (neurone) that releases nt = ACh in vesicles
  • postsynaptic cell (muscle) membrane (sarcolemma) = specialized with ACh
  • the two membranes are separated by a synaptic cleft
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6
Q

Explain the steps of impulse transmission at a neuromuscular junction.

A

1) AP reaches the axon terminal and the synaptic end bulb
2) the voltage Ca2+ gates open and Ca2+ diffuse in
3) Rising Ca2+ causes exocytosis of nt AcH
4) AcH binds to AcH receptors on the motor end plate of the muscle cell
5) chemical gates Na+ open and Na+ diffuse in causing EPP (End Plate Potential = a depolarizing GP)
6) EPP causes Na+ voltage gates open on adjacent sarcolemma –> more Na+ diffuse in causing an AP
7) AP travels long the sarcolemma

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7
Q

In a neuromuscular junction, will an AP occur always? why

A
  • yes because it’s stimulus is always a critical stimulus due to the large concentration of AChr eleased accompanied by the abundant amount of ACh receptors found on the motor end plate.
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8
Q

So how can the skeletal muscle be inhibited?

A
  • by inhibiting the motor neurone
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9
Q

In a resting muscle, what is the state of the filaments in the muscle fibre?

A
  • tropomyosin covers the myosin binding site on the actin

- this activates the myosin head

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10
Q

In a myosin head activation, what happens.

A
  • this is still in the resting phase of the muscle,
  • ATP is found on the myosin head which later breaks down to form ADP and release energy.
  • the energy, ADP and Pi however remains in the myosin head.
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11
Q

Generally, what happens when the AP or impulse reaches the muscle fibre?

A

1) Excitation of muscle fibre (electrical event)
2) Excitation-contraction coupling (electrical to mechanical event)
3) Contraction or the Sliding Filament Mechanism (mechanical event)

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12
Q

In details, explain the excitation of the muscle fibre.

A
  • the sarcolemma gets depolarized ( EPP -> AP)

- AP travels down to the T-tubules to deep within the fibre

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13
Q

In details, explain what happens in the Excitation-Contraction coupling

A
  • the AP reaches the T-tubules causing the release of Ca2+ via mechanical gates found on the terminal cisternae of the sarcoplasmic reticulum
  • the Ca2+ binds to the troponin
  • the troponin-tropomyosin complex moves and exposes the myosin binding site on the actin
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14
Q

In details what happens in the Sliding filament mechanism?

A
  • the activated myosin head attaches to the myosin binding site on the actin, as a result a cross bridge formation occurs (myosin head becomes the bridge between the myosin and the actin)
  • the energy stored in the activated myosin head is released when the myosin head pivots (called power stroke), this causes the ADP and Pi to be released as well. As a result, the actin moves over the myosin towards the center of the sacromere (M-Line)
  • ATP attaches to the myosin head causing it to unpivot and detach from the actin (called recovery stroke)
  • the myosin head gets reactivated again and the cycle continues as long as there is high concentration of Ca2+ in the cytosol.
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15
Q

To shorten the sarcomere, the cycle has to happen _____ times.

A

many

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16
Q

What is the power stroke?

A

when the activated myosin head releases it’s energy, ADP + Pi by pivoting

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17
Q

What is a recovery stroke?

A

when ATP attaches with the myosin head to detach and unpivot it from the actin

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18
Q

Describe the state of the sarcomere during the Sliding Filament Mechanism

A
  • in a sarcomere:
    • the H zone and the I band shorten
    • A band remains the same length
    • the thick (myosin) and the thin (actin) myofilaments remain the same length
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19
Q

When the myofibril shortens during the sliding filament mechanism, what happens to the muscle?

A
  • it shortens as well
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20
Q

Explain the steps to muscle fibre relaxation.

A

1) ACh is broken down by the AChE and produces acetic acid (used in Krebs cycle as Acetyl CoA) and choline which is recycle
2) The sarcoplasmic reticulum takes up Ca2+ via Ca2+ ATPase
3) the tropomyosin covers the myosin binding site on the actin
4) ATP binds to the myosin head

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21
Q

What is the role of ATP in skeletal muscles?

A

1) fuels up Na+/K+ ATPase
2) pumps Ca2+ into to the sarcoplasmic reticulum via Ca2+ ATPase
3) deactivates cross bridge
4) Activates myosin head

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22
Q

What happens with improper canning? And what causes this?

A
  • botulism

- caused by clostridium botulinum which is very potent

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23
Q

How can botulism affect skeletal muscle?

A
  • prevents exocytosis of ACh which causes flaccid paralysis
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24
Q

what is the medical use of botulism?

A

treat uncontrolled blinking eyes and crossed eyes

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25
Q

What is the cosmetic use of botulism?

A
  • botox (wrinkles and sweating)
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26
Q

What is muscle tension?

A
  • the force exerted by a muscle or a muscle fibre
27
Q

What determines muscle tension?

A

number of cross bridges formed

28
Q

Muscle tension in a muscle fibre is affected by:

A

1) Frequency of Stimulation
2) Fatigue
3) Fibre length
4) Size of fibre

29
Q

What are some factors that affect the frequency of the stimulus?

A

a) Single Stimulus
b) 2nd stimulus arrives before complete relaxation of 1st stimulus
c) Rapid sequence of stimuli
d) High frequency of stimuli

30
Q

In a single stimulus, what happens in muscle tension

A
  • single stimulus = causes twitch (not normally occurring)
  • for 1 stimulus = 1 AP fires up which lasts 1-2 msec
  • latent period comes which lasts for about 2msec = excitation-contraction coupling
  • contraction period which lasts about 10-100 msec = muscle tension increases due to cross bridges attachment & sliding filaments
  • relaxation = decreases muscle tension
31
Q

After the single stimulus, what comes next?

A

second stimulus appears before the first stimulus completely relaxes

  • the first stimulus has not relaxed completely because uptake of Ca2+ in SR has not been finished
  • the second stimulus increases availability of Ca2+ which causes anther contraction
  • this is called wave summation
32
Q

Is there refractory period in contractions?

A

-no

33
Q

How does rapid sequence of stimuli affect muscle tension?

A
  • it increases muscle tension because it increases availability of Ca2+ which causes wave summation
34
Q

What is the partial relaxation that occurs between contractions and causes quivering?

A

incomplete tetanus

35
Q

what causes high frequency of stimuli?

A
  • all troponin have been saturated with Ca2+ and fibre warmth (from ATP synthesis) = works faster
36
Q

what is a complete tetanus?

A

no relaxation in between muscle contractions

37
Q

How does fibre length affect muscle tension?

A
  • resting fibre length is optimal because max number of crossbridges upon stimulation will maximize tension
  • tension decreases with shorter or longer fibre
    = short fibre = the thin filaments overlaps disrupting the the crossbridge attachment (min length = 70% of optimal)
    = long fibre = not all myosin head attaches with the binding sites on the actin (max length = 130% of optimal0
38
Q

How does size of fibre affects muscle tension?

A
  • the more myofibrils = the thicker the fibre is

- the thicker the fibre = the greater the tension is

39
Q

How can muscle fibre size be increased?

A
  • exercising and testosterone
40
Q

How does fatigue affect muscle tension?

A
  • muscles cannot contract because theres no ATP and low Ca2+ which causes 0 tension.
41
Q

What kind of fibre is present in muscle that contracts an relaxes rapidly?

A
  • white fibre with little myoglobin
42
Q

What kind of fibre is present in muscle that contracts slowly and relaxes slowly? give an example

A
  • red fibre with more myoglobin

- postural muscle

43
Q

In a whole muscle, what affects muscle tension?

A

1) number of fibres contracting
2) number of fibres/motor unit
3) muscle size
4) fatigue

44
Q

How does the number of fibres contracting affect muscle tension?

A
  • more number of fibres contracting the more fibres/motor unit = increased muscle tension
45
Q

How does number of fibres/motor unit affect muscle tension?

A
  • increases muscle tension
46
Q

which motor unit will have greater tension, 1 neurone innervated to 10fibres or 1 neurone innervated to 1000 fibres?

A

1 neurone innervated to 1000 fibres

47
Q

how does muscle size affect muscle tension

A
  • the bigger the muscle, the more fibres contrasting = greater muscle tension
48
Q

what causes muscle tone?

A

when low level of tension in a few fibres become a separate group of motor units are stimulated alternately overtime

49
Q

what does muscle tone do?

A

give firmness to muscle

50
Q

What are two types of muscle contraction?

A

isotonic & isometric

51
Q

What is an isotonic muscle contraction? give an example

A
  • uses ATP
  • muscle changes in length
  • tension exceeds the resistance of the load lifted
  • flexion of elbow = tension > weight of forearm
52
Q

What is an isometric muscle contraction?

A
  • uses ATP
  • the tension is lower than the whats required to move load
  • tension increases because of cross bridge formation but no shortening (no changes muscle length)
53
Q

when lifting a book what muscle contraction is taking place?

A
  • isotonic
54
Q

When holding a book, what muscle contraction is working?

A

isometric

55
Q

Where does the muscle get its energy during resting conditions

A
  • fatty acids used to make ATP (aerobic)

- use storage of glycogen and creatine phosphate

56
Q

Where does the muscle get its energy during short term exercise. eg. 1 minute or less like sprinting.

A
  • uses creatine phosphate to produce ATP (lasts about 15 secs)
  • uses glycogen –> glucose –> pyruvic acid –> via anaerobic pathway –> lactic acid (lasts about 30 sec)
  • mostly anaerobic reaction is used
57
Q

Where does muscle get its energy during long term exercise (1 min to hours)?

A
  • ATP - from aerobic pathway
  • glucose in liver
  • fatty acids - used more as exercise continues
  • O2: from blood hemoglobin and muscle myoglobin
  • but sometimes they get energy from anaerobic pathways n
58
Q

What are the kinds of muscle fatigue?

A

Physiological Fatigue & Psychological Fatigue

59
Q

What is physiological fatigue and what does it do?

A
  • the muscle’s inability to maintain tension - not widely understood
  • decreases ATP therefore crossbridges can’t be released.
60
Q

What causes physiological fatigue?

A

1) depletion of sources of energy such as glycogen
2) the build of end products
- H+ from lactic acid - muscle contractions compress blood vessels which decreases O2 = therefore remains anaerobic for periods even in long term exercise
- Pi from ATP binds to Ca2+ = less binds with the troponin and this slows down the release of phosphate from myosin and slows crossbridges release
3) Failure of APs
- increase in K+ in small T-tubules during rapid stimuli disrupts the MP, which stops the release of Ca2+ from the SR
- long term: neurone runs out of ACh

61
Q

What is psychological fatigue?

A

the failure of CNS to send commands to muscles probably due to lactic acid

62
Q

what does EPOC stand for and what is it?

A
  • Excess Post-exercise oxygen consumption

= recovery from O2 consumption (deep rapid breathing)

63
Q

What is O2 used for?

A
  • replenish storage of glycogen, creatine phosphate, O2 in hemoglobin and myoglobin
  • used convert lactic acid to pyruvic acid in Krebs cycle, or lactic acid to glucose in liver
64
Q

increase of body temperature from exercise equals _________

A

increase in O2 demand

Physiology (11 decks)

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