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MD2002 > Sarcomere Structure > Flashcards

Sarcomere Structure Flashcards

1
Q

What are the 5 defining characteristics of a skeletal muscle cell (fibre)?

A
  1. Multinucleated
  2. Contains many mitochondria
  3. Has special structures called Transverse (T) tubules
  4. Has myofibrils and sarcomeres
  5. Has specific terms for some intracellular structures
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2
Q

What is the specific skeletal muscle cell term for plasma membrane?

A

Sarcolemma

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3
Q

What is the specific skeletal muscle cell term for cytoplasm?

A

Sarcoplasm

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4
Q

What is the specific skeletal muscle cell term for smooth ER?

A

Sarcoplasmic reticulum

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5
Q

What are muscle fibres arranged in?

A

Fasciculi

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6
Q

What is the name of the structure that is a dense sheath that lies on the surface of the muscle?

A

Epimysium

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7
Q

What structure lies between fasciculi?

A

Perimysium

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8
Q

What structure separates the muscle fibres?

A

Endomysium

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9
Q

What is the width of a muscle fibre (muscle cell)?

A

50 - 100 micrometers

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10
Q

Define sarcolemma

A

True cell membrane and encloses the muscle fibre

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11
Q

Define sarcoplasm

A

Intracellular fluid that fills spaces between myofibrils

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12
Q

What are myofibrils predominantly composed of?

A

Actin and myosin filaments

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13
Q

What is a sarcomere?

A

The portion of a myofibril that lies between two successive Z disks

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14
Q

What is the width of a sarcomere?

A

1 - 2 micrometers

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15
Q

What are the different areas/sections of a sarcomere?

A 
\+ A band
\+ M line
\+ I band
\+ H zone
\+ Z disk
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16
Q

What is the THICK filament that myofibrils are predominantly composed of?

A

Myosin

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17
Q

What is the THIN filament that myofibrils are predominantly composed of?

A

Actin

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18
Q

What structures make up myosin?

A

+ Tail
+ Two globular heads
+ Chains (head and tail)

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19
Q

What does the tail of myosin consist of?

A

Two intertwined heavy chains

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20
Q

What are features of the globular heads of myosin?

A

+ Extend out forming cross-bridges

+ Contain heavy and light chains

+ Contain binding sites fro actin and ATP (myosin-ATPase)

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21
Q

What size is myosin?

A

1.6 micrometers

22
Q

What size is actin?

A

1 micrometer

23
Q

What are features of actin?

A

+ Contractile protein

+ Each G actin has a binding site for myosin

24
Q

What are the proteins associated with actin?

A

Tropomyosin and troponin

25
Q

What are features of tropomyosin?

A

+ Regulatory protein
+ Overlaps binding sites on actin for myosin
+ Inhibits interaction when in the relaxed state

26
Q

What are features of troponin?

A

+ Regulatory protein
+ Forms a complex with the other proteins of the thin filament (actin and tropomyosin)
+ Binds Ca2+ reversibly

27
Q

What happens when troponin binds Ca2+?

A

Once bound, it changes conformation to pull tropomyosin away from the myosin interaction sites

28
Q

What is the effect of Ca2+ binding to troponin?

A

It regulates skeletal muscle contraction

29
Q

How does Ca2+ binding to troponin regulate skeletal cardiac muscle?

A

It moves tropomyosin away and allow myosin to interact with the actin

30
Q

What are the structural proteins in a sarcomere?

A

+ Titin (connectin)
+ Z-line (alpha-actinin)
+ M-line (myomesin, M-protein)
+ Nebulin

31
Q

What are the contractile proteins in a sarcomere?

A

+ Actin

+ Myosin

32
Q

What properties does titin provide?

A

+ Elasticity

+ Stabilises myosin

33
Q

What is the role of nebulin?

A

It helps align actin

34
Q

What are myofibrils?

A

The structures that give skeletal (and cardiac) muscle their characteristic striated appearance

35
Q

What are striations the result of?

A

The orderly arrangements of thick and thin filaments

36
Q

What type of filaments form I-bands in a cross section through a sarcomere

A

Thin filaments only

37
Q

What type of filaments form H-zones in a cross section through a sarcomere

A

Thick filaments only

38
Q

What type of filaments form M-lines in a cross section through a sarcomere

A

Thick filaments linked with accessory proteins

39
Q

What type of filaments form the outer edges of A-bands in a cross section through a sarcomere?

A

Thick and thin filament overlap

40
Q

What is the ultrastructural basis of sarcomere banding for A-bands?

A

Primarily myosin filaments in region of overlap

41
Q

What is the ultrastructural basis of sarcomere banding for I-bands?

A

Actin filaments bisected by Z-line

42
Q

What is the ultrastructural basis of sarcomere banding for H-zones?

A

Region of A-band which contains only myosin filaments

43
Q

What happens to the zones of a sarcomere when it shortens (muscle is contracted)?

A

+ I-bands and H-zones shorten

+ A-band remains constant

44
Q

What are features of T-tubules?

A

+ Walls are continuous with the sarcolemma

+ Fluid within is continuous with external environment

45
Q

What is sarcoplasmic reticulum?

A

In muscle, it is homologous to the endoplasmic reticulum found in most cells - Ca2+ is stored and released following membrane excitation

46
Q

How are T-tubules and SR connected?

A

With junctions - they involve two integral membrane proteins, one in the T-tubule membrane and the other in the membrane of the sarcoplasmic reticulum

47
Q

What are features of the T-tubule protein?

A

It is a modified voltage-sensitive Ca2+ channel known as the dihydropyridine (DHP) receptor, which acts as a voltage sensor

48
Q

What is the protein embedded in the SR membrane known as?

A

Ryanodine receptor

49
Q

What does the ryanodine receptor form?

A

Ca2+ channels

50
Q

What does sarcoplasmic reticulum store?

A

Ca2+

51
Q

Where do T-tubules bring action potentials?

A

Into anterior of muscle fibre

MD2002 (85 decks)

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