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Flashcards in MUSCLE PHYSIOLOGY Deck (89):
1

what is the muscular system?

consists of muscle cells, responsible for movement in the body

2

what are the 3 major muscle types?

smooth muscle
cardiac muscle
skeletal muscle

3

where is smooth muscle found?

Lines the tubular and hollow structures in the body

4

what are smooth muscle cells connected by?

gap junctions

5

what shape are smooth muscle cells?

spindle shape with central nucleus

6

how are the Contractile cytoskeletal elements arranged in a smooth muscle cell?

diagonally across the cell

7

what are actin thin filaments anchored to in smooth muscle?

dense bodies

8

how are dense bodies arranged in smooth muscle?

within a network of intermediate (desmin) fibres

9

how are myosin fibres arranged in smooth muscle?

scattered throughout the cell within the network of intermediate fibres

10

what is cardiac muscle?

Striated muscle - each fibre consists of a single branched cell

11

what does a cardiac muscle cell contain?

centrally located nucleus and large numbers of mitochondria

12

how are cardiac muscle cells connected?

by specialised thickenings of the sarcolemma, the intercalated discs

13

what are found within intercalated discs?

fibre-like structures, the desmosomes (hold the muscle cells together), and gap junctions

14

what is the function of gap junctions in intercalated discs?

provide physical connections that enable electrical signals to be passed from cell to cell

15

what is skeletal muscle associated with?

with movement of bones in relation to one another

16

what is each muscle surrounded by?

by a connective tissue sheath (epimysium), beneath which can be found bundles of muscle fibres, the muscle fascicle

17

what is each fascicle surrounded by?

by a connective tissue layer (perimysium)

18

what are muscle fascicles composed of?

muscle fibres - multinucleate cells, made up of a large number of fused myoblasts

19

what are found along muscle fibres?

satellite cells – un-fused myoblasts that can enlarge and divide after muscle injury

20

what does each muscle fibre consist of?

myofibrils

21

what 2 myofilaments form myofibrils?

Thin actin filaments
Thick myosin filaments

22

what is the memb potential dependent on?

on relative permeability of membrane to Na and K

23

what is depolarisation associated with?

opening of ligand gated and voltage gated Na channels

24

what does depolarisation promote?

release of Ca from the sarcoplasmic reticulum

25

what does depolarisation mediate?

changes in K permeability and the Na/K pump

26

what are muscle fibres?

large structures – all components have to contract simultaneously

27

how is simultaneous contraction achieved?

because the signal to contract is distributed evenly by the T tubules

28

what are T-tubules?

narrow tubes that extend from the sarcolemma into the sarcoplasm of the muscle fibre, and then around myofibrils

29

what are T-tubules filled with?

with extracellular fluid and so allow a rapid conduction of potential changes throughout the muscle

30

what are T-tubules tightly bound to?

to the memb of the sarcoplasmic reticulum

31

what does the sarcoplasmic reticulum (SR) form?

a tubular network around each myofibril, either side of each T-tubule the SR enlarges and fuse forming large chambers, the terminal cisternae

32

what is a triad?

The association between an encircling T-tubule and a pair of terminal cisternae

33

what is the sarcoplasm of the muscle deficient in?

calcium

34

where is calcium stored?

in the sarcoplasmic reticulum

35

what happens when a muscle muscle cells fires an action potential?

potential change is conducted along the T-tubule system allowing the release of calcium from the sarcoplasmic reticulum into the sarcoplasm

36

how are the contractile filaments actin and myosin arranged?

into myofibrils

37

what does each myofibril consist of?

a number of contractile units, the sarcomeres

38

what is each sarcomere separated by?

by a thin line known as the Z band or Z disc

39

In the sarcomere, what do the thin actin filaments form?

the I band which attach the Z disc

40

what is found between he I bands?

a much darker band, the A band

41

what happens when the muscle contracts?

the actin filaments of the I band slide over the myosin filaments of the A band, so that the Z discs move closer together

42

what is myosin (A band) formed from?

myosin-II

43

what is myosin-II?

a protein consisting of two identical heavy chains, each of which is bound to a pair of light chains

44

what does the AA terminal of the heavy chain form?

a motor head domain

45

what does the carboxyl end of the heavy chain form?

forms an elongated tail

46

what does the elongated tail of myosin form?

an alpha helix with the second heavy myosin chain to form a dimer

47

what can the heavy chain dimers polymerise into?

stable bipolar filaments with free head groups at either end

48

what does the Actin (I band) consist of?

of a chain of globular actin molecules

49

what does each actin molecule have?

a binding site for a myosin head

50

what is the actin helix coupled to at every 6th molecule?

to two other proteins, tropomyosin and troponin

51

what is tropomyosin?

rod shaped molecule that binds via the troponin molecule to the groove of the actin helix, where it masks the myosin binding sites

52

what is troponin?

a complex of, troponin T, I, and C

53

what is troponin I?

binds to actin

54

what is troponin T?

binds to tropomyosin

55

what is troponin C?

binds calcium

56

what happens when 4 Ca2+ ions bind to troponin?

troponin goes through a conformational change moving the tropomyosin from the myosin biding site

57

what is muscle contraction a result of?

of muscle cell excitation

58

where are stored Ca2+ released from?

from the sarcoplasmic reticulum

59

what happens when Ca2+ binds to troponin C?

causes conformational change in the troponin complex

60

what happens when tropomyosin molecule moves away from actin molecule binding sites?

allows myosin heads to bind

61

what is muscle contraction driven by.?

by the conversion of ATP to ADP

62

how are skeletal muscles controlled?

under the control of the nervous system

63

how are synaptic terminals formed?

A single axon will branch within the perimysium and expand at their ends

64

what does the neuromuscular junction consist of?

Synaptic terminal + synaptic cleft + sarcolemma

65

what happens when the skeletal muscle becomes depolarised?

ACh travels across the synaptic cleft and binds to ACh receptors located in the sarcolemma

66

what does depolarisation of the skeletal muscle trigger?

opening of Na channels and the myocyte action potential. ACh is quickly broken down by AChE

67

what is the Motor end plate (MEP)?

region of sarcolemma rich in ACh receptors – MEP folded to increase surface area and number of ACh receptors

68

what is the tension generated dependent on?

on number of cross bridges formed between the actin and the myosin

69

what can modify tension?

Stretching a muscle
by varying the degree of overlap between the actin and myosin filaments

70

what is the relationship between the degree of stretch and tension?

initially positive and linear

71

what happens as the number of cross bridges between the actin and myosin filaments start to decrease?

this relationship breaks down until the relationship becomes negative

72

what is a twitch?

A single stimulation of a muscle induces a single contraction

73

what 3 main phases does a twitch consist of?

Latent period
Contraction phase Relaxation phase

74

what is a trippe?

If a 2nd stimulation arrives immediately after the end of the relaxation phase, the next contraction will be slightly bigger
Thought to be because of steadily increasing Ca conc

75

what is tetanus?

If the next stimulation occurs before the relaxation phase has ended the contractions will merge (summate) and become larger

76

what is incomplete tetanus?

Describes the summation of contractions that occurs when the 2nd stimulus arrives just after the relaxation phase has started. Subsequent stimulations applied at the same frequency will induce tension to rise until it reaches a maximum value roughly four times that achieved by Treppe

77

what is complete tetanus?

Achieved by increasing stimulating frequency, eliminating the relaxation phase. The muscle will contract smoothly up to the maximum tension

78

what are muscle fibres innovated by?

by motor neurons

79

how many muscle fibres does one motor neurone innervate?

hundreds or thousands of fibres

80

what is a motor unit?

the muscle fibres innervated by a single motor neuron

81

what is muscle tone?

In both smooth and skeletal muscle, some muscle cells or fibres are always in a state of contraction, even when the whole muscle is at rest. This resting tension is called muscle tone.

82

what does muscle tone enable?

Maintenance of posture
Diameter of tubular structures (blood vessels etc) and so resistance to flow

83

what is isotonic?

means equal tension tension rises and the muscle length changes

84

what are the 2 types of isotonic?

concentric
eccentric

85

what is concentric?

2kg weight on the muscle. To shorten the cross bridges must generate more than 2kg (the resistance) of tension before the weight can be moved. After generating 2kg of tension the weight will move but tension in the muscle will remain at 2kg

86

what is eccentric?

Tension generated is less than the resistance - weight cannot be moved - muscle lengthens. However, contraction of the muscle slows that extension. A very important mechanism – used to control muscle extension when sitting, walking etc

87

what are isometric contractions?

Tension generated in the muscle does not exceed the resistance to force

88

give examples of isometric contractions

trying to pick up a very heavy weight, or pushing against a locked door

89

what do isometric allow?

allow you to maintain posture