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MSK > Physiology > Flashcards

Physiology Flashcards

1
Q

what types of muscles are striated

A

skeletal and cardiac

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2
Q

what is skeletal muscle contraction initiated by

A

motor neuron stimulation

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3
Q

what are the physiological functions of skeletal muscles

A

maintenance of posture

purposeful movement in relation to external environment

respiratory movements

heat production

contribution to whole body metabolism

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4
Q

what innervates skeletal muscles

A

the somatic nervous system

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5
Q

what innervates cardiac and smooth muscles

A

the autonomic nervous system

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6
Q

what muscles are involuntarily controlled

A

cardiac and smooth

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7
Q

what causes the striation of cardiac and skeletal muscles

A

alternating dark bands (thick myocin filaments)

and light bands (thin actin filaments)

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8
Q

what initiates and propagates contraction of cardiac muscle cells

A

myogenic (originating within muscle tissue- pacemaker potential)

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9
Q

do cardiac muscles have motor units

A

no

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10
Q

which type of striated muscle has a neurovascular junction

A

skeletal

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11
Q

which type of striated muscle has gap junctions

A

cardiac muscle

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12
Q

where is skeletal muscle Ca++ from

A

entirely from sarcoplasmic reticulum

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13
Q

where is cardiac muscle Ca++ from

A

from extra cellular fluid and sarcoplasmic reticulum (Ca++ induced Ca++ release)

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14
Q

what determines the gradation on skeletal muscle contraction

A

motor unit recruitment

summation of contractions

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15
Q

what determines the gradiation of cardiac muscle contraction

A

depends on the the extent of the heart filling with blood (pre-load, frank sterling mechanism)

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16
Q

is there continuity of cytoplasm between nerve and skeletal muscle cells

A

NO need neurotransmitters

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17
Q

what is the neurotransmitter at neurovascular junctions

A

acetylcholine

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18
Q

what is a motor unit

A

a single alpha motor neuron and all the skeletal muscle fibres it innervates

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19
Q

where do motor neurons come from

A

spinal chord

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20
Q

what does the number of muscle fibres per motor unit depend on- explain

A

the function served by the muscles- fine movement (eye, facial, hand muscles) have fewer fibre per unit (aprox ten). powerful muscles have more units eg thigh muscles (100-1000s)

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21
Q

what makes up muscle fibres (aka muscle cells)

A

myofibril (contractile intracellular structure) which make up sarcomere (functional unit)

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22
Q

what are the protein molecules contained within myofibril and sacromeres

A

myocin and actin

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23
Q

how are skeletal muscles usually attached to the bone

A

by tendons

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24
Q

how are the protein filaments arranged in skeletal myofibrils

A

alternating actin (light) and myocin (dark) make sarcomeres (functional units)

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25
Q

what is a functional unit

A

the smallest component capable of performing all the functions of the organ

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26
Q

what is the functional unit of skeletal muscle

A

sarcomere

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27
Q

what separates sarcomeres

A

two Z lines (between adjacent sarcomeres)

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28
Q

what are the four zones of the sarcomere

A

A- band, H-zone, M-line and the I-band (i)

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29
Q

what is the A band of a sarcomere

A

made of thick filaments along with portions of thin filaments that overlap in both ends of thick filaments

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30
Q

what is the H zone of a sarcomere

A

lighter area within the middle of the A band where thin filaments dont reach

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31
Q

what is the M line of the sarcomere

A

extends vertically down middle of the A band within the centre of the H zone

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32
Q

what is the i-band of the sarcomere

A

the remaining portion of thin filaments that do not project in A band (near to Z line)

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33
Q

what produces muscle tension

A

the sliding of actin filaments on myocin filaments

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34
Q

what can crossbridges between myosin and actin not form without

A

ATP and Ca++

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35
Q

why is Ca++ important

A

required to switch on cross bridge formation

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36
Q

is ATP required for contraction or relaxation

A

both contraction and relaxation

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37
Q

what is the excitation contraction coupling

A

the process whereby the surface action potential results in activation of the contractile structures of the muscle fibres

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38
Q

in skeletal muscle fibres when is Ca++ released from lateral sacs of the sacroplasmic reticulum

A

when the surface action potential spreads down the transverse (T)- tubules

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39
Q

what are T-tubules

A

extensions of the surface membrane that dip into the muscle fibre

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40
Q

what generates the action potential that travels down T-tubules

A

acetylcholine released by axon of motor neuron

41
Q

what do the calcium ions released from the sarcoplasmic reticulum do

A

bind to troponin on actin filaments, pulling troponin-tropomyosin complex aside to expose cross-bridge binding site (cross bridge binding occurs)

42
Q

how are cross bridges formed

A

myosin bind to actin and pulls actin filament toward centre of sarcomere

43
Q

when does ATP detact from myosin

A

when bending occurs

44
Q

when does ATP bind to myosin and what happens to it

A

after detachment (bending), is dephosphorlyated, energising the myosin for binding (or resting state if no Ca++ present)

45
Q

what happens to calcium after there is no longer an action potential

A

is re taken up by sarcoplasmic reticulum

46
Q

what covers the cross bridging site on actin in the resting state

A

the troponin-tropomyosin complex

47
Q

what is the link between excitation and contraction

A

Ca++

48
Q

why is ATP needed in relaxation

A

to release cross bridges

to pump Ca++ back into sarcoplasmic reticulum

49
Q

what causes rigor mortis

A

no atp left relax muscles

50
Q

what influences the tension developed by a skeletal muscle

A

the number of muscle fibres contracting
and
the tension developed by each contracting muscle fibre

51
Q

how is a stonger contraction achieved

A

by stimulation of more muscle units (motor unit recruitment)

52
Q

what is asynchronous motor unit recruitment

A

during submaximal contraction, some motor units are recruited, some are not to prevent muscle fatigue

53
Q

what does the tension developed by each contracting muscle fibre depend on (4)

A

frequency of stimulation

summation of contractions

length of muscle fibre at the onset of contraction

thickness of muscle fibre

54
Q

what is longer in skeletal muscle: the duration of the action potential or the duration of the resulting twitch

A

twitch

55
Q

what is the latent period

A

time between action potential starting and muscle twitch starting

56
Q

what is the summation of twitches

A

when the repetitive stimulation of skeletal muscles produces a stronger contraction (second twitch added on to first twitch)

57
Q

what is tetanus

A

when a muscle fibre is stimulated so rapidly that it does not have an opportunity to relax at all between stimuli creating a maximal sustained contraction

58
Q

can cardiac muscle be tetanised, explain

A

no- long refractory period prevents generation of tetanic contraction

59
Q

what is a twitch

A

when skeletal muscle is stimulated once

60
Q

when is maximum tetanic contraction achieved

A

when the muscle is at its optimum length before the onset of contraction

61
Q

when is contraction less when muscle fibre are longer or shorter than optimum

A

as less binding sites are exposed to make cross bridges (the sliding filament mechanism)

62
Q

what is the optimal skeletal muscle length

A

length of resting muscle

63
Q

how is skeletal muscle tension transmitted to the bone

A

via the stretching and tightening of muscle connective tissue and tendon (elastic component)

64
Q

what are the two types of skeletal muscle contaction and what makes them different

A

isotonic= body movements, moving objects. muscle tension remains constant as the muscle length changes

isometric contraction= supporting objects in fixed positions and maintaining body posture. muscle tension develops at constant muscle length

65
Q

what happens to the velocity of muscle shortening as the load increases

A

it decreases

66
Q

what makes skeletal muscles different from one another

A

their enzymatic pathways for ATP synthesis

67
Q

describe different types of skeletal muscles resistance to fatigue

A

muscle fibres with greater capacity to synthesise ATP are more resistant to fatigue

68
Q

how does the activity of myosin ATPase affect different muscle fibres

A

determines the speed at which energy is made available for cross bridge cycling (e.i. the speed of contraction)

69
Q

how many types of muscle fibres does one motor unit contain

A

one type

70
Q

what are the three metabolic pathways that supply ATP in muscle fibres

A

transfer of high energy phosphate from creatine phosphate to ADP- immediate source for ATP

oxidative phosphorylation- main source when O2 is present

glycolysis- main source when O2 is NOT present

71
Q

what are the three types of skeletal muscle fibres called

A

slow oxidative (type I)

fast oxidative (type IIa)

fast glycolytic (type IIx)

72
Q

what are slow oxidative fibres (type I) and what do they do

A

slow twitch fibres

used mainly for prolonged relatively low work aerobic activities (walking, maintenance of posture)

73
Q

what are fast oxidative fibres (type IIa) and what are they used for

A

intermediate twitch fibres

use both aerobic and anaerobic metabolism, useful in prolonged relatively moderate work activities

74
Q

what are fast glyoclytic (Type IIx) fibres and what do they do

A

fast twitch fibres

use anaerobic metabolism, mainly used for short term, high intensity activities (jumping)

75
Q

motor nerves receive inputs from where

A

the brain and a variety of receptors- can be excitatory or inhibitory input

76
Q

what is a reflex action

A

stereotypes response to a specific stimulus

77
Q

what are the neural pathways for reflexes important in locating

A

lesions in the motor system

78
Q

what type of reflex in the stretch reflex

A

monosynaptic spinal reflex

79
Q

what is the role of the stretch reflex

A

serves as a negative feedback that resists passive change in muscle length to maintain optimal resting length of muscle- help maintain posture e.g. while walking

80
Q

what is activated by muscle stretch and what happens

A

the sensory receptor is the muscle spindle- stretching the muscle spindle increases firing in the afferent neurons resulting in contraction of stretch muscle

81
Q

where do the afferent neurons synapse

A

in the spinal chord, with the alpha motor neurons (efferent limb of the stretch reflex)

82
Q

what coordinates the stretch reflex

A

simultaneous relaxation of antagonist muscle

83
Q

what peripheral nerve (and spinal segment) is target with the knee jerk reflex

A

femoral nerve (L3,L4)

84
Q

what peripheral nerve (and spinal segment) is target with the ankle jerk reflex

A

tibial nerve (S1, S2)

85
Q

what peripheral nerve (and spinal segment) is target with the biceps jerk reflex

A

musculocutaneous nerve (C5,C6)

86
Q

what peripheral nerve (and spinal segment) is target with the brachioradialis reflex

A

radial nerve (C5, C6)

87
Q

what peripheral nerve (and spinal segment) is target with the triceps jerk reflex

A

radial nerve (C6,C7)

88
Q

what are muscle spindles

A

sensory receptors for stretch reflex- a collection of specialised muscle fibres called intrafusal fibres

89
Q

what are extrafusal fibres

A

normal muscle fibres

90
Q

where are muscle spindles found

A

within the belly of muscles and run parrallel to ordinary muscle fibres

91
Q

what are annulospiral fibres

A

sensory nerve endings found in muscle spindles

92
Q

what nerve supply do muscle spindles get

A

have their own efferent nerve supply called gamma motor neurons

93
Q

what is the role of gamma motor neurons

A

adjust the level of tension in the muscle spindles to maintain their sensitivity when the muscle shortens during contraction

94
Q

what can cause impairment of skeletal muscle function

A

intrinsic disease of muscle

disease of neuromuscular junction

disease of lower motor neurones

disruption of input to motor nerves

95
Q

name 7 causes of intrinsic muscle disease

A

genetically determined myopathies

  • congenital
  • chronic degeneration of contractile elements (muscular dystrophy)
  • abnormalities in membrane ion channels (myotonia)

acquired myopathies

  • inflammatory(polymyositis)
  • non innflammatory (fibromyalgia)
  • endocrine (cushing syndrome, thyroid disease)
  • toxic myopathies (alcohol, statins)
96
Q

what is myotonia

A

delayed relaxation after voluntary contraction

97
Q

what is myalgia

A

muscle pain

98
Q

what are 5 usefu investigations into neuromuscular disease

A

electromyography (EMG)

nerve conduction studies

muscle enzymes (CK)

inflammatory markers (CRP, PV)

muscle biopsy

MSK (71 decks)

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