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Muscle microstructure and contraction * Flashcards

1
Q

Is smooth muscle under voluntary or involuntary control?

A

Involuntary

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2
Q

Is skeletal muscle under voluntary or involuntary control?

A

voluntary

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3
Q

What system controls smooth muscle?

A

ANS

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4
Q

Does cardiac muscle contract autonomously?

A

Yes

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5
Q

What systems is cardiac muscle under influence (not control) of?

A

ANS, and circulating chemicals

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6
Q

What is skeletal muscle usually attached to?

A

Bones

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7
Q

What system is skeletal muscle under the control of?

A

Somatic NS

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8
Q

What is the purpose of skeletal muscle contracting?

A

To bring about movement

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9
Q

What are the 7 arrangements of muscle fibres and what do they look like?

A

Triangular
Parallel
Pennate
Multipennate
Bipennate
Unipennate
Fusiform

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10
Q

Describe the structures of muscle from macroscopic to microscopic.

A

Fascicles (bundles of myofibres)
Myofibres
Myofibrils
Myofilaments

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11
Q

What is the plasma membrane that covers the myofibre called?

A

Sarcolemma

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12
Q

What is the cytoplasm in myofibres called and what two things does it contain?

A

Sarcoplasm and it contains myoglobin and mitochondria

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13
Q

What is the network of fluid filled tubes in the myofibres called?

A

Sarcoplasmic reticulum

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14
Q

What are the tubes that tunnel into the centre of the myofibrils called?

A

T-tubules

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15
Q

What is the diameter of a myofibril?

A

1-2 micrometres

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16
Q

What 2 types of protein are myofibrils composed of?

A

Actin and myosin

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17
Q

What appearance do light and dark bands give myofilaments?

A

Striated (striped) appearance

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18
Q

Do myofilaments extend over the whole length of the myofibrils?

A

No

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19
Q

Do myofibrils extend over the whole length of the myofibres?

A

Yes

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20
Q

Do myofilaments overlap?

A

Yes

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21
Q

What are the compartments myofilaments are arranged in called?

A

Sarcomeres

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22
Q

What separates sarcomeres?

A

Dense protein Z discs

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23
Q

What are the dark bands called and what are they made of?

A

A band, thick and made of myosin

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24
Q

What are the dark bands called and what are they made of?

A

I band, thin and made of actin

25
Q

Do myosin and actin filaments overlap?

26
Q

Describe the structure of myosin

A

Two globular heads
Single tail formed by two alpha helices

27
Q

What forms one myosin filament?

A

Tails of several hundred myosin molecules

28
Q

What shape are actin molecules twisted into?

29
Q

What binding site does each actin molecules contain?

A

Myosin binding site

30
Q

What other 2 proteins are found in actin filaments?

A

Troponin and tropomyosin

31
Q

During contraction, does the I band get longer or shorter?

32
Q

During contraction, does the A band get longer or shorter?

A

Stays the same length

33
Q

During contraction, does the H zone get longer or shorter?

A

Much smaller

34
Q

Describe how muscle contraction is initiated (synaptic transition). (8 points)

A
  1. Action potential opens voltage gated Ca2+ channels
  2. Ca2+ enters presynaptic terminal
  3. Ca2+ triggers exocytosis of vesicles
  4. Acetylcholine diffuses across cleft
  5. Acetylcholine binds to acetylcholine receptors and induces action potential in muscle
  6. Local currents flow from depolarized region and adjacent region
  7. Action potential spreads along surface of muscle fibre membrane
  8. Acetylcholine broken down by acetylcholine esterase. Muscle fibre response to that molecule of acetylcholine ceases
35
Q

Describe how muscle contraction is initiated (muscle activation). (8 points)

A
  1. Action potential propagates along surface membrane and into T tubules
  2. DHP receptor in T tubule membrane senses change in voltage and changes shape of protein linked to ryanodine receptor and opens ryanodine receptor Ca2+ channel in the sarcoplasmic reticulum
  3. Ca2+ released from sarcoplasmic reticulum into space around the filaments
  4. Ca2+ binds to troponin and tropomyosin moves allowing cross bridges to attach to actin
  5. Ca2+ actively transported into SR continuously which action potentials continue- ATP driven pump so uptake rate < or = release rate
36
Q

Define excitation contraction coupling.

A

Physiological process of converting an electrical stimulus to a mechanical response

37
Q

Describe the process of excitation contraction coupling. (6 points)

A
  1. In the presence of Ca2+ movement of troponin from tropomyosin chain
  2. Movement exposes myosin binding site on surface of actin chain
  3. ‘Charged’ myosin heads bind to exposed site on actin filament
  4. This binding & discharge of ADP causes myosin head to pivot (the ‘power stroke’)  pulling actin filament towards centre of sarcomere
  5. ATP binding  releases myosin head from actin chain
  6. ATP hydrolysis  provides energy to ‘recharge’ the myosin head
38
Q

What is a motor unit?

A

Name given to a single motor neuron together with all the muscle fibres that it innervates.
Stimulation of one motor unit causes contraction of all the muscle fibres in that unit.

39
Q

How many muscle fibres in each motor unit?

A

Average of 600

40
Q

What are the 3 types of motor unit?

A

Slow (S, type 1)
Fast fatigue resistant (FR, type IIa)
Fast fatigable (FF, type IIb)

41
Q

Describe 4 characteristics of S motor units

A
  1. Smallest diameter cell bodies
  2. Small dendritic trees
  3. Thinnest axons
  4. Slowest conduction velocity
42
Q

Describe 4 characteristics of FR and FF motor units compared to S units

A
  1. Larger diameter cell bodies
  2. Larger dendritic trees
  3. Thicker axons
  4. Slowest conduction velocity
43
Q

How are muscle fibre types distributed throughout the muscle?

44
Q

Are proportions of fast and slow twitch muscles the same or different between muscles?

45
Q

What is the myoglobin content of each muscle type?

A

S- high
FR- high
FF- low

46
Q

What is the colour of each muscle type?

A

S= red
FR= pink
FF= white

47
Q

What is the aerobic capacity of each muscle type?

A

S= high
FR= moderate
FF= low

48
Q

What is the anaerobic capacity of each muscle type?

A

S= low
FR= high
FF= high

49
Q

What is the fatigue rate of each muscle type?

A

S= fatigue resistant
FR= fatigue resistant
FF= high fatigue

50
Q

What are the 2 mechanisms the brain can use to regulate amount of force a single muscle can produce?

A

Recruitment and rate coding

51
Q

How is recruitment used by the brain?

A

“Size principle”- smaller units recruited first, as more force is required, more units are recruited, allowing fine motor control

52
Q

How is rate coding used by the brain?

A

Motor units fire at range of frequencies. Slow units fire at lower frequency. As firing rate increases, force produced increases. Summation occurs when units fire too fast, allowing muscle to relax between arriving action potentials

53
Q

What are neurotrophic factors and what do they do?

A

Type of growth factor that prevents neuronal death and promotes growth of neurones after injury

54
Q

What are motor unit and fibre characteristics dependent on?

A

The nerve that innervates them

55
Q

If a fast and slow twitch muscle are cross innervated, what happens?

A

The slow one becomes fast and fast becomes slow

56
Q

What are the 3 types of skeletal muscle contraction?

A

Isometric- length of muscle stays the same with contraction
Concentric-length of muscle decreases with contraction
Eccentric- length of muscle increases with contraction

57
Q

What can cause muscle to switch from type 1 to 2?

A

Spinal cord injury

58
Q

What affects does aging have on type 1 and 2 fibres?

A

Decrease in both t1 and t2 but more decrease in t2, so larger proportion of t1 as shown in slower contraction times

BRS (16 decks)

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