Lecture 30 - Muscle Structure, Function, Neuromuscular Transmission Flashcards Preview

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Flashcards in Lecture 30 - Muscle Structure, Function, Neuromuscular Transmission Deck (43):
1

Difference between myopathies and dystrophies

Myopathies are disorders of muscle contractile apparatus. Are normally static (don't progress)

Dystrophies are disorders of supporting structures. Often progressive.

2

What leads to variable muscle colour?

Myoglobin content (more myoglobin --> deeper red colour)

3

Feature of skeletal muscle cells

Multinucleated

4

Skeletal muscle structure
1)
2)
3)
4)
5)
6)

1) Muscle made up of bundles of muscle fibres called fasciculi.
2) Fasciculi are wrapped in perimysium
3) Fasciculi are made up of muscle fibers wrapped in endomysium
4) Each fibre made up of myofibrils wrapped in sarcolemma
5) Myofibrils and sarcolemma are surrounded by sarcoplasm
6) Each myofibril is made up of sarcomeres, which are the smallest contractile unit in muscle

5

What is wrapped around fasciculi?

Perimysium

6

What is wrapped around muscle fibers?

Endomysium

7

What makes up muscle fibres?

Myofibrils wrapped in sarcolemma

8

In striated muscle, which band is light?

I band (actin)

9

In striated muscle, which band is dark?

A band (actin and myosin)

10

Thin filament

Actin

11

Thick filament

Myosin

12

Sarcoplasm
1)
2)

1) Liquid surrounding myofibrils
2) Contains glycogen, fat particles, enzymes, mitochondria

13

Which filament has globular heads that crosslink?

Myosin

14

Sarcomere structure
1)
2)
3)
4)
5)

1) Surrounded by Z discs. Where actin attaches
2) I band - Aligned actin filaments
3) A band - Aligned actin and myosin filaments
4) H zone - Aligned myosin filaments
5) M line - Centre of sarcomere. Where myosin anchor

15

Fibre present in I band

Only actin

16

Fibre present in H zone

Only myosin

17

Part of sarcomere that only contains myosin

H zone

18

Part of sarcomere that only contains actin

I band

19

Sliding filament muscle contraction
1)
2)
3)
4)

1) At rest, tropomyosin covers myosin binding sites on actin
2) Action potential depolarises T-tubule membrane, causes Ca2+ release into sarcoplasm
3) Ca2+ binds tropomyosin, makes it unbind actin, revealing myosin binding site
4) Myosin head binds actin, begins crossbridging

20

Is crossbridge formation synchronous?

No.
If it were, all would detach at the same time, and the muscle would return to uncontracted state

21

Crossbridge formation
1)
2)
3)
4)

1) ATP binds myosin head, myosin detaches from actin
2) ATP hydrolysed to ADP + Pi, myosin head is cocked
3) Myosin head attaches to actin
4) ADP and Pi detach from myosin head. This leads to a power stroke (pulls Z discs together)

22

What causes muscle contraction?
1)
2)
3)

1) Motor neurons release ACh into neuromuscular junction.
2) ACh binds nicotinic ACh receptors, influx of Na+ into cell --> depolarisation of sarcolemma
3) Depolarisation of T-tubule membrane leads to Ca2+ influx into sarcoplasm

23

T tubules

Transverse tubules
Invaginations in sarcolemma, aligned with I and A bands

24

Supporting proteins of muscle fibers
1)
2)
3)
4)

1) Dystrophin-associated protein complex (in sarcolemma membrane)
2) Sarcoglycans (a complex) (in sarcolemms)
3) Dystrophin
4) Proteins in the nuclear envelope - emerin and lamin a

25

ATP sources for muscle
1)
2)
3)
4)

1) Within the muscle fibre
2) Creatine phosphate
3) Glucose stored in the cell as glycogen
4) Glucose and fatty acids obtained from the bloodstream

26

How long can ATP stored within a muscle maintain contraction?

A few seconds

27

Creatine phosphate

Molecule in muscles that transfers a high-energy Pi to ADP to form ATP

28

How long can creatine phosphate maintain muscle contraction?

About 15 seconds

29

Where do the fatty acids and glucose taken from the bloodstream by muscles cone from?
1)
2)

1) Glucose from glycogen broken down in the liver
2) Fatty acids from adipose cells and the liver

30

Advantages of anaerobic respiraiton

Fast
Doesn't require oxygen

31

Disadvantages of anaerobic respiration

Only generates 2 ATP
Generates lactic acid

32

Number of ATP produced by aerobic respiration

36 (including 2 from glycolysis)

33

Advantages of aerobic respiration

Produces a lot of ATP (36)

34

Disadvantages of aerobic respiration

Relatively slow
Requires oxygen

35

Timeline of cellular respiration in muscle
1)
2)
3)
4)

1) 0-30 seconds - ATP/Creatine phosphate used
2) 20-120 seconds - Anaerobic respiration
3) 110 seconds - Aerobic respiration, if contraction continues
4) Depletion of resources (ATP, oxygen, glycogen), lactic acid buildup, lead to cessation of contraction

36

How long can anaerobic respiration sustain muscle contraction at maximum capacity?

Around 30 seconds

37

Type I fibres
1)
2)
3)

1) Slow-twitch
2) Slow oxidative
3) Fatigue-resistant

38

Type I fibre features
1)
2)
3)
4)

1) Myoglobin-, mitochondria-rich
2) Many capillaries
3) Generate ATP aerobically
4) Split ATP at a slow rate --> slow contraction velocity

39

Where are many type I fibres found?

In the postural muscles of the trunk
Used in long-distance running

40

Type IIA fibres
1)
2)
3)
4)

1) Fast-oxidative fibres
2) Myoglobin-, mitochondria-rich
3) Fatigue resistant, but not as much as type I
4) Split ATP at a rapid rate --> rapid contraction velocity
5) Rich in capillaries

41

Type IIB fibres
1)
2)
3)
4)
5)
6)
7)

1) White fibres
2) Fast glycolytic fibres
3) Low in myoglobin, mitochondria
4) Few capillaries
5) Large amount of glycogen
6) Split ATP very quickly
7) Fatigue easily

42

Another name for type IIB fibres

Type X fibres

43

Age and sex differences in muscle fibre type distribution

None