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Tissues > Muscle > Flashcards

Muscle Flashcards

1
Q

What are the three major muscle types?

A

Skeletal
Cardiac
Smooth

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2
Q

What do muscles develop from?

A

Mesoderm - somites - myotome

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3
Q

How do myoblasts differentiate, what do they differentiate to?

A

Myoblasts withdraw from the cell cycle and express transcription factors MyoD and Myf5 to activate genes for myocyte formation.

The myoblasts fuse to form multinucleate myotubes which develop into mature myofibres.

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4
Q

What are contractile elements of all muscle?

A

Actin and myosin

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5
Q

Do all muscle cells have permanently oriented contractile machinery?

A

Yes

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6
Q

What are the role of muscles?

A

Change body position

Act as mechanical pumps

Move viscera

Regulate blood pressure.

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7
Q

What is the role of skeletal muscle?

A

Voluntary movement

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8
Q

How does skeletal muscle attach to bones?

A

Via tendons

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9
Q

Describe the nuclei number and position of skeletal muscle cells

A

Multinucleate with the nuclei peripherally located

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10
Q

Why are skeletal muscle nuclei peripherally located?

A

Fibrils fill the central part of the cell

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11
Q

What cells surround the surface of skeletal muscle cells?

A

Satellite cells

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12
Q

What is the role of satellite cells?

A

Stem cells with regenerative capacity

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13
Q

What are single skeletal muscle cells called?

A

Muscle fibres

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14
Q

What do muscle fibres contain (contraction)?

A

Myofibrils

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15
Q

What makes up a myofibril?

A

Myofilaments (actin and myosin)

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16
Q

What are T-tubules?

A

Invaginations of the sarcolemma that go deep into the cell to surround each myofibril. T-tubules are associated with SR cisternae.

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17
Q

What gives the striated banding pattern to skeletal muscle?

A

Thin actin filaments and thick myosin repeat along the length of the myofibril. Repeating sarcomeres

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18
Q

What is actin structure?

A

Actin is a globular protein which polymerises into a fibres, it has a myosin binding site

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19
Q

What is myosin structure?

A

6 twisted polypeptides which forms a fibrous helix with globular ends (heads) that will bind to the binding site on actin.

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20
Q

What is the structure of tropomyosin?

A

Fibre like proteins which wraps around the actin filament. Blocks the attachment side for myosin cross-bridge

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21
Q

What is the structure of troponin C?

A

Fibre like proteins which wraps around the actin filament. Blocks the attachment side for myosin cross-bridge

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22
Q

What is a sarcomere?

A

Repetitive subunits of contractile apparatus including the filaments along with the associated proteins

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23
Q

Describe a sarcomere?

A

Z-line at each end attached to actin filaments, I band is actin only, light striation

Actin overlaps with myosin filaments

Myosin alone at A-band dark striation

M line is centre

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24
Q

What happens to regions of the sarcomere when myofibril contracts?

A

Z discs move closer together

I and A band widths are reduced

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25
Q

How many actin surrounds each myosin?

A

6

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26
Q

What is the role of titin?

A

Connects the Z line to the M-line, acts as a molecular spring for passive elasticity of muscle. It is the largest known protein.

27
Q

What is the largest known protein?

A

Titin

28
Q

What is nebulin?

A

Actin binding protein localised to actin regulating its length.

29
Q

What makes up the Z line?

A

Alpha actinin

30
Q

What is the endomysium?

A

Connective tissue layer that surrounds each muscle fibre. Reticular fibres and basal lamina.

31
Q

What is the perimysium?

A

Connective tissue layer that surrounds the cell bundles (fascicles) of muscle fibres, derived from the epimysium.

32
Q

What is the epimysium?

A

Connective tissue layer that surrounds the entire muscle and is dense and irregular connective tissue.

33
Q

What are bundles of muscle fibres called?

A

Fasicles

34
Q

How is the cytoskeleton of muscles attached to the ECM?

A

By a protein complex called dystrophin-associated glycoprotein complex (DGC).

Dystrophin maintains mechanical integrity of cell during contraction by anchoring cytoskeletal elements.

35
Q

What leads to muscular dystrophy?

A

Genetic defects in DGC proteins leads to muscular dystrophy.

As force is no longer transmitted from myocytes to bones and so cannot move at joint.

36
Q

Is cardiac muscle striated?

A

Yes

37
Q

What gives rise to the cardiac epicardium and myocardium?

A

Splanchnic mesenchyme and myoepicardium mantel cells

38
Q

What gives rise to the endocardium?

A

Vascular endothelial progenitors

39
Q

What are cardiomyocytes?

A

Specialised branched striated muscle cells

40
Q

Describe the number and position of nuclei in cardiomyocytes

A

Single centrally located nuclei, one or two per cell

41
Q

How are cardiomyocytes arranged?

A

Layers

42
Q

What is a distinguishing feature of cardiomyocytes?

A

Intercalated discs

43
Q

What are intercalated discs?

A

Darkly stained transverse lines that are regions of complex cell junction networks

44
Q

What is the role of intercalated discs?

A

Support synchronised contraction

45
Q

What are the three elements of intercalated discs?

A

Fascia adherens - Anchoring sites between cells of actin filaments.

Desmosomes - Cell to cell adherens junctions - using desmin filaments

Gap junctions - Provide chemical continuity between cells allowing ions to pass through. Bind cells together with connexins that form connexons.

46
Q

What do fascia adherens do?

A

Anchoring sites between cells of actin filaments.

47
Q

What are purkinje fibres?

A

Specialised cardiac muscle to enable synchronisation of vesicle contraction.

48
Q

How do purkinje fibres look different to cardiomyocytes?

A

Stain much paler as they contain less contractile elements, no t-tubule system and more mitochondria and glycogen.

49
Q

What is the innervation of cardiac muscle?

A

Autonomic

50
Q

What is the innervation of skeletal muscle?

A

Somatic

51
Q

What is the innervation of smooth muscle?

A

Autonomic

52
Q

Describe the shape of smooth muscle cells?

A

Elongated, spindle shaped (fusiform) shape

53
Q

Are smooth muscle cells striated?

A

No

54
Q

Describe the nuclei of smooth muscle cells

A

Centally located, mononucleate

55
Q

What are the two ways smooth muscle can act?

A

Unitary syncytium with gap junctions for mass control

Multiunit (isolated) for finer control

56
Q

Why is smooth muscle non-striated?

A

Not aligned in parallel/regular arrays

Instead lattice like network

57
Q

What are distinguishing features of smooth muscle?

A

Focal densities
Dense bodies
Caveolae
Gap junctions

58
Q

What are focal densities?

A

Attachment junctions, actin to the sarcolemma.

59
Q

What are dense bodies?

A

Attachments between intracellular actin filaments (like the Z-line) maintain the alignment of thin filaments.

60
Q

What are caveolae?

A

Depression of the plasma membrane in the system, act a bit like t-tubules involved in transport of the depolarisation signal.

61
Q

What muscle cell type has the greatest regenerative capacity?

A

Smooth muscle

62
Q

Specialised structures in skeletal muscle cells found roughly at the boundary of the A and I bands

A

Triads

63
Q

During contraction, which of the following remains constant in length?

A

A band

Tissues (13 decks)

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