Sarcomere Structure Flashcards Preview

MD2002 > Sarcomere Structure > Flashcards

Flashcards in Sarcomere Structure Deck (51):
1

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

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

2

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

Sarcolemma

3

What is the specific skeletal muscle cell term for cytoplasm?

Sarcoplasm

4

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

Sarcoplasmic reticulum

5

What are muscle fibres arranged in?

Fasciculi

6

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

Epimysium

7

What structure lies between fasciculi?

Perimysium

8

What structure separates the muscle fibres?

Endomysium

9

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

50 - 100 micrometers

10

Define sarcolemma

True cell membrane and encloses the muscle fibre

11

Define sarcoplasm

Intracellular fluid that fills spaces between myofibrils

12

What are myofibrils predominantly composed of?

Actin and myosin filaments

13

What is a sarcomere?

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

14

What is the width of a sarcomere?

1 - 2 micrometers

15

What are the different areas/sections of a sarcomere?

+ A band
+ M line
+ I band
+ H zone
+ Z disk

16

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

Myosin

17

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

Actin

18

What structures make up myosin?

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

19

What does the tail of myosin consist of?

Two intertwined heavy chains

20

What are features of the globular heads of myosin?

+ Extend out forming cross-bridges

+ Contain heavy and light chains

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

21

What size is myosin?

1.6 micrometers

22

What size is actin?

1 micrometer

23

What are features of actin?

+ Contractile protein
+ Each G actin has a binding site for myosin

24

What are the proteins associated with actin?

Tropomyosin and troponin

25

What are features of tropomyosin?

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

26

What are features of troponin?

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

27

What happens when troponin binds Ca2+?

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

28

What is the effect of Ca2+ binding to troponin?

It regulates skeletal muscle contraction

29

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

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

30

What are the structural proteins in a sarcomere?

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

31

What are the contractile proteins in a sarcomere?

+ Actin
+ Myosin

32

What properties does titin provide?

+ Elasticity
+ Stabilises myosin

33

What is the role of nebulin?

It helps align actin

34

What are myofibrils?

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

35

What are striations the result of?

The orderly arrangements of thick and thin filaments

36

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

Thin filaments only

37

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

Thick filaments only

38

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

Thick filaments linked with accessory proteins

39

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

Thick and thin filament overlap

40

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

Primarily myosin filaments in region of overlap

41

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

Actin filaments bisected by Z-line

42

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

Region of A-band which contains only myosin filaments

43

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

+ I-bands and H-zones shorten
+ A-band remains constant

44

What are features of T-tubules?

+ Walls are continuous with the sarcolemma

+ Fluid within is continuous with external environment

45

What is sarcoplasmic reticulum?

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

46

How are T-tubules and SR connected?

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

What are features of the T-tubule protein?

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

48

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

Ryanodine receptor

49

What does the ryanodine receptor form?

Ca2+ channels

50

What does sarcoplasmic reticulum store?

Ca2+

51

Where do T-tubules bring action potentials?

Into anterior of muscle fibre

Decks in MD2002 Class (85):