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Histology > Skeletal Muscle > Flashcards

Skeletal Muscle Flashcards

1
Q

How is skeletal muscle formed

A

Fusion of myoblasts to form multi-nucleated cells - muscle fibres

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2
Q

Where are the nuclei of muscle fibres

A

At the edge of the fibres just beneath the plasma membrane (plasmalemma)
Appear alongside the pink-stained fibre

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3
Q

What forms the striations of skeletal muscle

A

Myofibrils lie in parallel with one another and are joined side by side with the sarcomeres in register

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4
Q

Endomysium

A

Specialised connective tissue between muscle fibres

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5
Q

Permysium

A

Bundles of muscle fibres are bound together to form fasciculi by a sheath of connective tissue

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6
Q

Epimysium

A

Groups of fasciculi are bound together to form muscles by more connective tissue

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7
Q

Myofibrils

A

A linear series of sarcomeres connected by Z lines

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8
Q

2 major contractile proteins of sarcomere

A

Myosin
Actin

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9
Q

Myosin

A

Bipolar thick filaments

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10
Q

What is the maximum amount of shortening of the sarcomere

A

30%

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11
Q

Extrinsic work

A

Thin actin filaments slide deeper within the A band bringing the Z lines closer together and shortening the sarcomere

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12
Q

Intrinsic work

A

Shortening of the sarcomere is minimal but tension within the muscle increases

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13
Q

Function of titin

A

Maintaining the structural integrity of the myofibrils

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14
Q

Which part of the sarcomere is darker staining

A

A bands

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15
Q

Which part of the sarcomere is lighter staining

A

I band

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16
Q

Khonheim’s fields

A

A refractory optical feature
A slightly oblique cut involving more than one band of the sarcomere

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17
Q

What stain is commonly used to resolve the bands of a sarcomere

A

Iron haematoxylin

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18
Q

3 types of muscle fibres

A

Type 1
Type 2A
Type 2B

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19
Q

Type 1 muscle fibres

A

Slow twitch
Oxidation in terms of energy supply
Fatigue resistant

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20
Q

Where are type 1 muscle fibres found in highest numbers

A

Postural muscles

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21
Q

Type 2A muscle fibres

A

Fast twitch
Use a mixture of oxidative and glycolytic processes to obtain energy
Moderately fatigue resistant

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22
Q

Type 2B muscle fibres

A

Fast twitch
Dependent on glycolytic processes for energy
Fatigue sensitive

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23
Q

Where are type 2B muscle fibres predominantly found

A

Sprint muscles

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24
Q

Structure of type 1 muscle fibres

A

Large mitochondria that lie in rows between myofibrils
Fat droplets alongside mitochondria - use as a source of triglyceride for production of ATP

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25
Q

Structure of type 2 muscle fibres

A

Fewer and smaller mitochondria
Large reserves of glycogen

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26
Q

Mysium

A

Connective tissue that connects muscles to bone

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27
Q

Sharpey’s fibres

A

Numerous small collagen bundles that surrounds the muscle fibres

28
Q

What do the collagen bundles of Sharpey’s fibres merge with

A

Fibrous periosteum of bone and collagenous matrix of bone itself

29
Q

Examples of Sharpey’s fibres

A

Origins of rotator cuff muscles on the blade of the scapula

30
Q

Advantage of Sharpey’s fibres

A

Spreads force of the muscle over a wide area

31
Q

Advantage of Tendons

A

Exert force over a smaller, more defined area

32
Q

Example of tendons

A

Tendinous insertions of the rotator cuff muscles on the head of the humerus

33
Q

What composes tendons and aponeuroses

A

Condensed parallel bundles of collagen fibres interspersed with fibroblasts

34
Q

What happens at the end of muscle

A

Fasciculi split becoming smaller but more numerous
Connective tissue between becomes more prominent

35
Q

Structure of tendon

A

Continuation of the peri and Epimysium of the muscle which becomes highly condensed to form tough inelastic bands

36
Q

Structure of muscle spindles

A

A small number of muscle fibres (intrafusal fibres) isolated from the surrounding extrafusal fibres by a connective tissue sheath

37
Q

Intrafusal fibres

A

Have nerve fibres wound around them

38
Q

Function of muscle spindles

A

Relay information about the degree of contraction of the surrounding muscle

39
Q

Which muscles have more muscle spindles

A

Muscles with fine movements with small motor units have more than larger motor units concerned with course movements

40
Q

Are bundles of muscle fibres in the tongue small or large

A

Generally quite small

41
Q

What do small fascicles denote

A

Smaller motor units
- greater the level of fine movement and control

42
Q

Are all skeletal muscle anchored to bone

A

No - some are interconnected by fibrous connective tissue eg a raphe

43
Q

Dystrophin

A

Binds actin to the plasmalemma of muscle cells

44
Q

Mechanism of muscular dystrophy

A

Dystrophin fails to bind actin successfully to the plasmalemma causing weakness in the muscles

45
Q

What is the major protein of Z lines

A

Alpha actinin-
(60% lipid which electrostatically binds the proteins together)

46
Q

Which type of collagen composed tendons and Sharpey’s fibres

A

Type 1

47
Q

How is a torn tendon repaired

A

Tearing causes inflammation which stimulates the fibroblasts to synthesise actin and collagen

48
Q

Approximately how many actin filaments are there to each myosin filament in a sarcomere

A

6 (hexagonal close packing) - each actin filaments also interacts with another adjoining myosin filament

49
Q

To what are the actin filaments within a sarcomere attached

A

Nebulin
Tropomyosin

50
Q

Nebulin function

A

Binds actin to Z line

51
Q

Tropomyosin function

A

Orients actin with respect to myosin

52
Q

What prevents a sarcomere being stretched beyond its normal limits

A

Non-contractile proteins - titin and nebulin

53
Q

What is a motor unit

A

A group of muscle fibres that receive a nerve supply from the same axon and therefore respond identically to stimulation

54
Q

Golgi tendon organs

A

Reside close to or within tendons and monitor tension within the muscle

55
Q

Muscle types

A

Smooth muscle
Skeletal muscle
Cardiac muscle
Other contractile cells - pericytes, myo-fibroblasts, myo-epithelial cells

56
Q

Where is skeletal muscle found

A

Skeletal muscles
Larynx
Diaphragm

57
Q

Syncytium

A

Myoblasts fused to form multi-celled syncytium

58
Q

Fascicles

A

Muscle fibres clumped together

59
Q

Dimensions of a muscle fibre

A

50-60 um diameter
Up to 10cm in length

60
Q

T-tubules

A

Convey Ca2+ into the cytoplasm

61
Q

Skeletal muscle overview

A

Voluntary muscle
Elongated fibres
Striated cytoplasm
Mutlinucleate
Nuclei at edges
Non-branching

62
Q

Is skeletal muscle branching

A

No

63
Q

Structure of a sarcomere

A

Z line
I band
A band
H zone
M line

64
Q

Which type of muscle fibre are richer in ATPase

A

Type 1

65
Q

Type of nerve fibres in a muscle spindle

A

Gamma efferent

66
Q

What do fibroblasts synthesise

A

Collagen

Histology (17 decks)

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