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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
what is the medical use of botulism?
treat uncontrolled blinking eyes and crossed eyes
25
What is the cosmetic use of botulism?
- botox (wrinkles and sweating)
26
What is muscle tension?
- the force exerted by a muscle or a muscle fibre
27
What determines muscle tension?
number of cross bridges formed
28
Muscle tension in a muscle fibre is affected by:
1) Frequency of Stimulation 2) Fatigue 3) Fibre length 4) Size of fibre
29
What are some factors that affect the frequency of the stimulus?
a) Single Stimulus b) 2nd stimulus arrives before complete relaxation of 1st stimulus c) Rapid sequence of stimuli d) High frequency of stimuli
30
In a single stimulus, what happens in muscle tension
- 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
After the single stimulus, what comes next?
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
Is there refractory period in contractions?
-no
33
How does rapid sequence of stimuli affect muscle tension?
- it increases muscle tension because it increases availability of Ca2+ which causes wave summation
34
What is the partial relaxation that occurs between contractions and causes quivering?
incomplete tetanus
35
what causes high frequency of stimuli?
- all troponin have been saturated with Ca2+ and fibre warmth (from ATP synthesis) = works faster
36
what is a complete tetanus?
no relaxation in between muscle contractions
37
How does fibre length affect muscle tension?
- 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
How does size of fibre affects muscle tension?
- the more myofibrils = the thicker the fibre is | - the thicker the fibre = the greater the tension is
39
How can muscle fibre size be increased?
- exercising and testosterone
40
How does fatigue affect muscle tension?
- muscles cannot contract because theres no ATP and low Ca2+ which causes 0 tension.
41
What kind of fibre is present in muscle that contracts an relaxes rapidly?
- white fibre with little myoglobin
42
What kind of fibre is present in muscle that contracts slowly and relaxes slowly? give an example
- red fibre with more myoglobin | - postural muscle
43
In a whole muscle, what affects muscle tension?
1) number of fibres contracting 2) number of fibres/motor unit 3) muscle size 4) fatigue
44
How does the number of fibres contracting affect muscle tension?
- more number of fibres contracting the more fibres/motor unit = increased muscle tension
45
How does number of fibres/motor unit affect muscle tension?
- increases muscle tension
46
which motor unit will have greater tension, 1 neurone innervated to 10fibres or 1 neurone innervated to 1000 fibres?
1 neurone innervated to 1000 fibres
47
how does muscle size affect muscle tension
- the bigger the muscle, the more fibres contrasting = greater muscle tension
48
what causes muscle tone?
when low level of tension in a few fibres become a separate group of motor units are stimulated alternately overtime
49
what does muscle tone do?
give firmness to muscle
50
What are two types of muscle contraction?
isotonic & isometric
51
What is an isotonic muscle contraction? give an example
- uses ATP - muscle changes in length - tension exceeds the resistance of the load lifted - flexion of elbow = tension > weight of forearm
52
What is an isometric muscle contraction?
- 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
when lifting a book what muscle contraction is taking place?
- isotonic
54
When holding a book, what muscle contraction is working?
isometric
55
Where does the muscle get its energy during resting conditions
- fatty acids used to make ATP (aerobic) | - use storage of glycogen and creatine phosphate
56
Where does the muscle get its energy during short term exercise. eg. 1 minute or less like sprinting.
- 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
Where does muscle get its energy during long term exercise (1 min to hours)?
- 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
What are the kinds of muscle fatigue?
Physiological Fatigue & Psychological Fatigue
59
What is physiological fatigue and what does it do?
- the muscle's inability to maintain tension - not widely understood - decreases ATP therefore crossbridges can't be released.
60
What causes physiological fatigue?
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
What is psychological fatigue?
the failure of CNS to send commands to muscles probably due to lactic acid
62
what does EPOC stand for and what is it?
- Excess Post-exercise oxygen consumption | = recovery from O2 consumption (deep rapid breathing)
63
What is O2 used for?
- 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
increase of body temperature from exercise equals _________
increase in O2 demand

Physiology (11 decks)

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