muscle Flashcards Preview

Tissues of the body > muscle > Flashcards

Flashcards in muscle Deck (122):
0

What is myalgia?

-Muscle pain

1

What is myasthenia?

-Weakness of the muscles

2

What is myocardium?

-The muscle component of the heart

3

What is myopathy?

-Any disease of the muscles

4

What is myoclonus?

-Any sudden spasm of the muscles

5

What is sarcolemma?

-The outer membrane of a muscle cell

6

What is sarcoplasm?

-Cytoplasm of muscle cells

7

What is sarcoplasmic reticulum?

-The smooth endoplasmic reticulum of muscle

8

What are two characteristics of all types of muscle?

-Contractility
-Conductivity

9

What are the three types of muscle?

-Skeletal muscle
-Smooth muscle
-Cardiac muscle

10

Which types of muscle are striated?

-Skeletal muscle
-Cardiac muscle

11

Which type of muscle is non-striated?

-Smooth muscle

12

Where are skeletal muscle cells derived from?

-Mesodermally-derived multipotent myogenic stem cells

13

How do multinucleated skeletal muscle cells develop?

-Myogenic stem cells-> myoblasts which fuse together to form primary myotube with a chain of multiple central nuclei

14

Why are skeletal muscle nuclei displaced to the periphery?

-The synthesis of actin and myosin filaments displace the nuclei

15

What are the three types of muscle fibre?

-Narrow red
-Intermediate
-Wide white

16

Which muscle fibre is small in diameter?

-Red

17

Which muscle fibre has poor vasculature?

-White

18

Which muscle cell has a poor store of myoglobin?

-White

19

Which muscle fibre has the most mitochondria?

-Red

20

What are the contractions like in red skeletal muscle fibres?

-Slow, repetitive, weak

21

What are the contractions like in white skeletal muscle fibres?

-Fast and strong

22

How do the red and white skeletal muscle fibres fatigue?

-Red-> slowly
-White-> radiply

23

Which skeletal muscle fiber has the most neuromuscular junctions?

-White

24

Give an example of where red and white skeletal muscle fibres are found

-Red-> postural muscles of the back
-White-> extraocular muscles and the fingers

25

Describe the structural organisation of muscle units from bone to myofilaments

-Bone
-Tendon
-Muscle
-Fasicle
-Muscle fibre
-Myofibrils
-Myofilaments (actin and myosin)

26

How can you tell a fascicle from a muscle fibre?

-The fibre will have multiple nuclei on its sarcolemma

27

What is epimysium?

-Connective tissue sheath which surrounds the entire muscle

28

What is perimysium?

-Connective tissue sheath which surrounds fascicles

29

What is endomysium?

-Connective tissue sheath which surrounds muscle fibres

30

What is another name for a muscle fibre?

-Muscle cell

31

What are the different anatomical arrangements of muscles?

-Circular
-Convergent
-Multipennate
-bipennate
-Unipennate
-Parallel
-Fusiform

32

What is a myotendinous junction?

-Where the muscle and tendon meet

33

How is skeletal muscle arranged at a myotendinous junction?

-The fibres interdigitate with tendon collagen bundles

34

What two types of skeletal muscle are found in the tongue?

-Extrinsic and intrinsic muscles

35

What are the extrinsic muscles of the tongue attached to?

-The have insertions into bone and cartilage

36

What are the functions of the extrinsic tongue muscles?

-To protrude, retract and move the tongue from side to side

37

What is the function of the intrinsic muscles of the tongue?

-Allow the tongue to change shape but not position

38

How are nuclei arranged in muscle fibres?

-In rows at the periphery of the cell

39

What structures does the perimysium contain?

-Nerves
-Blood vessels

40

What structures do endomysium contain?

-Capillaries
-Nerves

41

What are myofibrils made up of?

-Myofilaments (thin actin and thick myosin)

42

How are myofilaments arranged?

-In a strict banding pattern of A and I bands

43

What shade is the A band of a myofibril?

-Dark

44

What shade is an I band of a myofibril?

-Light

45

Where is the Z line located?

-In the centre of an I band

46

What is a sarcomere?

-A contractional unit from Z line to Z line

47

What myofilament(s) do the A binds contain?

-Both actin and myosin as they overlap

48

What myofilament(s) do the I bands contain?

-Actin only

49

What is the H zone?

-The segment within an A band which only contains myosin

50

Where is the M line?

-In the centre of an H zone

51

What is a pneumonic for remembering these bands?

-MHAZI (M is in H in A, Z is in I)

52

Which bands decrease in size during contraction and which stay the same length?

-I and H zones get smaller
-A remains the same

53

What happens to the size of the sarcomere during contraction?

-It decreases

54

What is the structure of an actin myofilament?

-Contains actin, troponin and tropomyosin which form a helix by troponin attaching to tropomyosin which then wraps around actin

55

What can troponin be used as a marker for?

-Cardiac ischaemia

56

Describe the structure of myosin

-An individual myosin molecule has a rod-like structure from which two heads protrude
-Each thick filament is made up many myosin molecules in such a way that the 'heads' protrude in a multidirectional way
-The filaments are devoid of myosin heads in the centre of the filament (where there is no overlap)
-The heads extend towards the actin filaments

57

What is the role of calcium in muscle contraction?

-Influx of calcium into the the muscle fibril
-Binds to troponin causing a conformational change leading to dissociation from the tropomyosin, and causing tropomyosin to change position, exposing the active site of actin
-This allows the myosin head to bind to actin and contraction to begin

58

Describe the sequence of events in the sliding filament model

-Myosin head attaches to actin filament as ATP is hydrolysed
-Working stroke-> myosin head pivots and bends as it pulls on the actin filment, sliding it towards the M line
-Release of ADP and Pi
-A new ATP molecule binds to myosin causing the myosin cross-bridge to detach
-ATP hydrolysis causes the cycle to repeat

59

What is the cause of rigor mortis?

-Lack of ATP results in myosin heads staying bound to actin

60

What is a neuromuscular junction?

-The point at which an axon meets muscle containinf a small terminal swelling of the axon and a synaptic cleft

61

Describe the mechanism of innervation of muscle and excitation contraction coupling

-Nerve impulse along motor neurone arrives at neuromuscular junction
-Influx of calcium at the synaptic bulb causes the release of acetylcholine
-Acetylcholine diffuses across the synaptic cleft and fuses with nicotinic receptors located on the sarcolemma of the muscle causing depolarisation
-This cause voltage-gated Na+ to open, causing the action potential to enter
-Action potential (depolarisation) spreads along sarcolemma down T tubules and to two sarcoplasmic reticulum
-This causes the opening of voltage gated calcium channels at the terminal cisternae of the two adjacent sarcolasmic reticulum; calcium is released into the sarcoplasm
-Resulting in the sliding filament model

62

What happens to the calcium after the action poteltial is complete?

-Returned to the sarcoplasmic reticulum by active transport

63

What is the triad in skeletal muscle contraction?

-One T tubule causes calcium release from two sarcoplasmic reticulum

64

Describe the histology of cardiac muscle in longitudial section

-Striations
-Centrally positioned nuclei(one or two per cell)
-Intercalated discs
-Branching

65

Why does cardiac muscle contain intercalated discs?

-For electrical and mechanical coupling with adjacent cells

66

Describe cardiac muscle in transverse section

-Centrally positioned nuclei
-Endomysium bearing rich supply of capillaries
-Some lobular profiles which represent branching

67

Are myofibrils arranged in bands in cardiac muscle?

-Yes however myofilaments of actin and myosin form continuous masses in cytoplasm

68

What other structures are present in the cytoplasm of cardiac muscle?

-Mitochondria
-Sarcoplasmic reticulum

69

How are intercalated discs associated with Z lines?

-Intercalated discs lay over the Z lines (Z lines become obscured in LM)

70

Why does cardiac muscle contain many gap junctions?

-For electrical coupling

71

What is the function of adherens-type junctions in cardiac muscle?

-To anchor the cells and provide anchorage for actin filaments

72

Where in skeletal muscle are the T tubules located?

-At the A I band junction

73

Where do T tubules lie within cardiac muscle?

-At the points of intercalated discs and Z lines

74

What is meant by cardiac muscle having a diad not a triad?

-One T tubule serves on sarcoplasmic reticulum

75

How does muscle contraction occur in cardiac muscle?

-Same as skeletal muscle except electrical impulse is generated from the heart itself

76

Where are purkinje fibre located?

-Ventricle walls

77

-What generates the action potential in the heart and how does this travel to the ventricles?

-SAN generates
-Passes to AVN into ventricles

78

What is the function of the purkinje fibres?

-Transmit the action potential from the AVN to the ventricles to allow rapid conduction enabling ventricles to contract in a synchronous manner

79

Describe the characteristics of the purkinje fibres

-Large cells
-Abundant glycogen
-Sparse myofilaments
-Extensive gap junctions

80

Describe the histology of smooth muscles

-Spindle-shaped (fusiform)
-Have a central nucleus
-Non striated, no sarcomeres, no T tubules

81

What is the mechanism of contraction of smooth muscle? (simply)

-Actin-myosin interactions

82

How do contractions of smooth muscle differ from cardiac and skeletal contractions?

-Slower
-More sustained
-Require less ATP

83

Which of the muscle types is capable of being stretched?

-Smooth

84

What generic stimuli cause smooth muscle to contract?

-Nerves (ach)
-Hormones
-Drugs

85

What conformation do lots of smooth muscle cells make?

-Sheets
-Bundles
-Layers

86

-Where is smooth muscle most frequently located?

-The contractile walls of passageways or cavities
eg vascular structures, the GI, respiratory and genitourinary tract

87

When can smooth muscle become clinically significant?

-High bp
-Dysmenorrhoea
-Asthma
-Atherosclerosis
-Abnormal gut mobility

88

What are myofibroblast cells?

-Specialised smooth muscle cells involved in wound healing which produce a collagenous matrix but also contract the wound

89

What are myoepithelia?

-Specialised smooth muscle cells known as satellite cells which form a basketwork around the secretory units of some exocrine glands to help secretion via contraction eg sweat, salivary, mammory and iris

90

Outline the contraction of smooth muscle

-Thick and thin myofilaments are arrananged diagonally within a cell, spiralling down the long axis
-Smooth muscle contracts in a twisting way
-Requires Ca2+ (binds to CaM, binds to MLCK, phosphorylates myosin-> sliding filament model)
-Intermediate filaments attach to dense bodies in the sarcoplasm

91

Describe the nature of repair of skeletal muscle

-Cannot divide
-Can regenerate-> mitotic activity of satellite cells result in hyperplasia after muscle injury
-Satellite cells fuse with existing muscle to increase muscle mass

92

Describe the nature of repair of cardiac muscle

-Not capable of regeneration
-Following damage fibroblasts invade, divide and lay down scar tissue

93

Describe the nature of smooth muscle repair

-Retain mitotic activity and form new smooth muscle cells
-Evident in pregnant uterus which undergoes hypertrophy and hyperplasia

94

Describe the process of skeletal muscle remodelling

-The contractile proteins actin and myosin can increase/decrease in number
-This is known as remodelling and is a continual process
-All the myofilaments can be replaced within two weeks

95

How does atrophy of skeletal muscle occur?

-Destruction of the myofilaments during remodelling is greater than replacement

96

How does hypertrophy of skeletal muscle occur?

-Replacement of the myofilaments during remodelling is greater than destruction

97

What is the cause of hypertrophy in skeletal muscle?

-Increased demand, ie exercise

98

What happens to skeletal muscle cells when they undergo hypertrophy?

-Increase metabolic demand
-Sarcoplasmic reticulum swelling
-Increased mitochondria
-Increased Z line width
-Increased ATPase
-Increased density of T tubules
-Increased contractile proteins

99

What are the main causes of atrophy?

-Immobility, age, denervation

100

How long after denervation does re-innervation need to occur for full use?

-3 months

101

What increases uptake of acetylcholine at the neuromuscular junction?

-Motor neurone is embedded into the muscle with the muscle having a highly-folded endplate to increase surface area

102

What terminates acetylcholine in the synaptic cleft?

-Acetylcholine esterase

103

What causes myasthenia gravis?

-Autoimmune destruction of the endplate ach receptors, specifically by IgG

104

What does autoimmune destruction of the achR in myasthenia gravis do to the endplate?

-Causes the loss of junctional fold resulting in widening of the synaptic cleft

105

What are the signs and symptoms of myasthenia gravis?

-Fatiguability and sudden falling
-Drooping upper eyelids (ptosis)
-Blurred vision

106

Why does sudden falling occur in myasthenia gravis?

-Muscles fail die to lack of excitation caused by the lack of AchR

107

Why are the eyes one of the first structures to be effected in myasthenia gravis?

-Have a low amount of muscle and therefore are effected easier

108

Why do the symptoms in myasthenia gravis fluctuate?

-Based on general state of health

109

What are the treatment options for myasthenia gravis?

-Acetylcholinesterase inhibitors (pyridostigmine)
-Immune suppressants
-Plasmapheresis
-Thymectomy

110

How can acetylcholinesterase inhibitors treat myasthenia gravis?

-Ach not as quickly broken down so it can stimulate muscles for longer

111

How can plasmapheresis treat myasthenia gravis?

-Removal of specific IgG from serum

112

How can a thymectomy treat myasthenia gravis?

-Thymus is producing abnormal lymphocytes, removal will stop production

113

How does botulism disrupt the neuromuscular junctions?

-Reduces acetylcholine release and thus decreases excitation of muscles

114

How does organophosphate poisoning disrupt neuromuscular junctions?

-Decreased production of acetylcholinesterases; ach stays active for longer; overexcitation of muscles

115

What type of disorder is muscular dystrophy?

-Genetic

116

How is muscular dystrophy characterised?

-By progressive muscle weakness and wasting

117

What is the cause of muscular dystrophy?

-Complete absence of the protein dystrophin (protein for stength) causing the muscles to tear apart upon contraction

118

What is the consequences of muscle fibres tearing?

-Muscle wastage
-The enzyme creatine phosphokinase is liberated into the serum causing calcium to enter the cell resulting in necrosis
-Pseudohypertrophy (swelling) occurs before fat and connective tissue replace muscle fibres

119

Outline the pathophysiology of malignant hyperthermia

-Large quantities of calcium released from sarcoplasmic reticulum of skeletal muscle due to altered calcium channel gated kinetics so ca2+ is not taken back up into SR
-Causes hypermetabolic state
-Sustained Ca2+ elevation allows excessive stimulation of glycolytic metabolism
-Causes respiratory and metabolic acidosis
-Causes rigidity due to all muscles contracting at once
-High heat generation due to hypermetabolic state

120

What type of disease and what are triggering agents of malignant hyperthermia?

-Inherited disease
-Anaesthetic gases

121

How can some people have malignant hyperthermia and never know?

-Never exposed to a trigger