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Binocular vision > EOMs: cell biology & physiology > Flashcards

EOMs: cell biology & physiology Flashcards

1
Q

how many EOMs does each eye possess

A

7

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2
Q

what are 6 of the 7 EOMs and what are they responsible fro

A

oculo-rotatory muscles

responsible for movements of the globe in different directions

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3
Q

if 6 of the EOMs are oculo-rotatory muscles, what is the 7th muscle

A

levator palpebrae superiors which elevates the upper eyelid

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4
Q

list what 4 of the 6 oculo-rotatory muscles are

A 
4 recti:
superior rectus 
medial rectus 
inferior rectus 
lateral rectus
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5
Q

what are 2 of the 4 oculo-rotatory muscles

A

2 obliques:
superior oblique
inferior oblique

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6
Q

what is the globe of the eyeball suspended/separated from the orbital bones by

A

network of specialised connective tissue capsules & fibrous septa (orbital fascia) which holds the eyeball in the orbit

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7
Q

what type of joint is the network of specialised connective tissue capsules & fibrous septa (orbital fascia) which holds the eyeball in the orbit similar to

A

ball & socket joint

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8
Q

what does the network of specialised connective tissue capsules & fibrous septa (orbital fascia) which suspends the eyeball from the orbital bones allow

A

allows the eye to rotate in different axes i.e. horizontally, vertically & torsionally, in a relatively low friction environment, with only minimal translational (backward-forward) movements

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9
Q

what is the action of the medial rectus

A

ADduction - towards the nose

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10
Q

what is the action of the lateral rectus

A

ABduction - away from the nose

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11
Q

what is the action of the superior rectus

A

elevation - up

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12
Q

what is the action of the inferior rectus

A

depresses - down

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13
Q

what is the action of the superior oblique

A

intorsion - top of eyeball moves towards the nose

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14
Q

what is the action of the inferior oblique

A

extorsion - top of eyeball moves away from the nose

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15
Q

what is required between the muscles in order to maintain a straight ahead primary gaze

A

well balanced contraction of paired antagonists (3 pairs)

ie MR-LR, SR-IR & SO-IO

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16
Q

what is the inner surface of the orbital bones covered by which is the same case for all bones in the body

A

a layer of tough connective tissue called periosteum or periorbital fascia

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17
Q

in addition to the orbital bones being covered by a layer of tough connective tissue called periosteum or periorbital fascia, what three additional unique substances cover the surface of the orbital bones (not found anywhere else in the body)

A
  • tenon’s capsule
  • medial and lateral check ligaments
  • suspensory ligament of lockwood
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18
Q

what is tenon’s capsule

A

fascial sheath surrounding the globe from corneal limbus which wraps itself back and goes around the optic nerve

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19
Q

what is the tenon’s capsule separated from the sclera by

A

epi-scleral space

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20
Q

what does the epi-scleral space contain inside it

A

epi-scleral fluid

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21
Q

what does epi-scleral fluid allow with tenon’s capsule

A

smooth (low-friction) rotation of the globe in tenon’s capsule i.e. little resistance

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22
Q

what can friction from movement of the eyeball within globe cause

A

heating up of eye

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23
Q

what are medial & lateral check ligaments

A

extensions of the fascial sheaths of the MR & LR muscles anchored/inserted into the periosteum of the lacrimal and zygomatic bones

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24
Q

as one side of the medial and lateral check ligaments insert into the periosteum of the lacrimal and zygomatic bones , what does the other side of the medial and lateral check ligaments insert

A

into the sleeve around the medial and lateral recuts muscles called epimyosin

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25
Q

what do the medial and lateral check ligaments prevent

A

retraction of the globe into the orbital cavity when the eye is moving in different directions

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26
Q

what is the suspensory ligament of lockwood

A

blending on tenon’s capsule with extensions of the fascial sheaths (i.e. thickening of connective tissue/suspensory ligaments) enclosing epimyosin of the inferior IR & IO muscles

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27
Q

what so the suspensory ligaments of lockwood do

A

suspends the globe ‘hammock’ style

so prevents the eye from dropping down into the globe from the force of gravity

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28
Q

what can an orbital blow which damages the suspensory ligament of lockwood cause

A

eye to fall down into orbit which causes vertical diplopia

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29
Q

what is duane’s syndrome

A

a convergence-retraction syndrome

when try to converge the eyes, they fall back into the orbit

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30
Q

what is the cause of duane’s syndrome

A

errors in muscle contraction which over powers the check ligaments causing the eyes to translate back

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31
Q

what is the difference of EOM cytology compared to skeletal muscles of the rest of the body

A
  • contain smaller muscle fibres
  • have 2 separate layers containing different fibre types with distinct contractile properties
  • possess pulleys which the outer layer is directly connected (apart from the superior oblique)
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32
Q

what size are the smaller muscle fibres diameters of the EOMs, compared to skeletal muscles of the body

A

10-20um compared to 100um

5-10x smaller

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33
Q

what is the inner layer of muscle fibre closer to

A

the globe

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34
Q

what type of fibres does the inner layer of the muscle contain

A

fast contracting muscle cells/fibres called fibrillenstrucktur

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35
Q

what is the outer layer of muscle fibre closer to

A

the orbital bones

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36
Q

what type of fibres does the outer layer of the muscle contain

A

mix of fast and slow felderstrucktur fibres

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37
Q

what is the name of the fast contracting muscle fibre in the EOMs

A

fibrillenstrucktur

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38
Q

what is the name of the slow contracting muscle fibre in the EOMs

A

felderstrucktur

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39
Q

how many % do fibrillenstrucktur fibres account for

A

80%

40
Q

what size fibres are fibrillenstrucktur

A

large fibres 20um

41
Q

what size and type of myofilaments do fibrillenstrucktur fibres have

A

small & well defined

42
Q

how much sarcoplasmic reticulum & mitochondria do fibrillenstrucktur fibres have

A

abundant

43
Q

why so fibrillenstrucktur fibres have abundant mitochondria

A

they’re energy dependent

44
Q

what do fibrillenstrucktur fibres mediate

A

fast twitch (rapid/phasic) contractions of the muscle

45
Q

how many % do felderstrucktur fibres account for

A

20%

46
Q

what size are felderstrucktur fibres

A

smaller

47
Q

what size and type of myofilaments do felderstrucktur fibres have

A

larger & less distinct

48
Q

how much sarcoplasmic reticulum & mitochondria do felderstrucktur fibres have

A

less amount

49
Q

why do felderstrucktur fibres have less mitochondria

A

they’re not as active

50
Q

what do felderstrucktur fibres mediate

A

tonic sustained contractions of the muscle in order to maintain fixation

51
Q

what other muscles are felderstrucktur fibres correspond to

A

to specialised skeletal muscle cells, abundant in axial muscles of the trunk involved in postural control

52
Q

what does a longitudinal section of the EOMS show in relation to the muscle fibres

A

small diameter felderstrucktur muscle fibres
&
larger diameter fibrillenstructur muscle fibres

53
Q

what does a transverse section of the EOMs show in relation to muscle fibres

A

felderstrucktur fibres are not as common, less organised and smaller diameter
&
fibrillenstrucktur fibres are more common, myofilaments inside them are more organised and larger diameter

54
Q

in a transverse section of the EOMs, what is found between the muscle cells/fibres

A

fine connective tissue called endomysium

55
Q

what does the inner global region of the EOM contain

A

densely packed mass of large diameter fast twitch fibrillenstrcktur fibres

56
Q

what does the outer orbital region of the EOM contain

A

less dense mixture of fast and slow twitch, fibrillensctrucktur and felderstrucktur fibres for tonic contractions

57
Q

which EOMs have pulleys

A

4 rectus & inferior oblique

58
Q

where are the pulleys located

A

close to where the muscles insert in the sclera

59
Q

what is the composition of the pulleys of the 4 rectus and IO muscles

A

rings of fibro-elastic connective tissue made of collagen and elastin & smooth muscle fibres

60
Q

what are the pulleys of the 4 rectus and IO muscles made of

A

collagen, elastin and smooth muscle fibres

61
Q

what do the outer orbital layer of felderstrucktur muscle fibres insert into

A

the pulley itself

62
Q

what does the fact that the felderstrucktur muscle fibres insert into the pulley itself allow for

A

being adjustable: they move backwards during muscle contraction, modifying the forces applied to the eye

63
Q

what do the inner global layer of fibrillenstrucktur muscle fibres insert into

A

pass through the hole in the pulley and insert into the sclera

64
Q

what is it important not to do during a squint surgery

A

do not cut the pulleys

65
Q

what is the name of the superior oblique pulley

A

trochlea

66
Q

what is the pulley (trochlea) of the superior oblique composed of

A

ring made out of cartilage

67
Q

how is the EOMs similar to skeletal muscle cells with contraction

A

their contraction is both caused by acetylcholine release from the motor-end plates of somatic (voluntary) motor neurons inside the brain stem

68
Q

what do EOMs generate much less of than skeletal muscles

A

force

69
Q

why do EOMs generate much less force than skeletal muscles

A

they only contract against a fairly constant & low-resistance load (eye only weighs 100g) and eye is suspended in orbit in a friction free environment

70
Q

what are the difference between EOM compared to skeletal muscle motor units

A

EOMs have much smaller motor units 1:100

71
Q

what significance does an EOM have in terms of smaller motor units <1:10

A

they have much finer neural control & a wider dynamic range increasing their precision of contraction

72
Q

what does the motor unit ratio refer to/mean

A

the number of muscle fibres innervated by a single motor neuron i.e. for EOMs this ratio is uniquely small

73
Q

what is meant by EOMs having a small motor neuron ratio

A

each ocular motor neuron (in the brain stem) innervates/exerts control over very few (1-10) fibres in am EOM

74
Q

what is the number of active motor neurons supplying an EOM increases known as

A

recruitment

when more and more motor neurons = need to recruit more muscle cells

75
Q

what happens to the contraction when more and more motor neurons are recruited

A

the force of the contraction increases gradually

76
Q

what happens as a result of motor neuron recruitment

A

very fine adjustments can be made to the state of EOM contraction, which are needed for accurate eye movements & stable fixation

77
Q

what does a motor neuron ratio of 1:1 refer to

A

one motor neuron in the brain stem controls one muscle cell in the EOM

78
Q

what does a motor neuron ratio of 1:100 in skeletal muscles refer to

A

one motor neuron controls a 100 skeletal muscle cells

79
Q

what did an experiment measuring frequency force relations prove about EOMs compared to skeletal muscles

A

for the same increments in nerve stimulation frequency, the force of contraction of the EOM is 10x less (a 10th of that of a diaphragm cell) & more gradual (over 20-250Hz range), compared to the typical skeletal muscle

80
Q

between EOMs and skeletal muscle, which has a wider dynamic range

A

EOM from 0-300Hz (EOM muscle exerts force more gradually)

81
Q

what is a fast twitch fibrillenstrucktur fibre innervated by

A

thick, heavily myelinated motor axons

82
Q

what type of end plate do fibrillenstrucktur fibres which are innervated by thick, heavily myelinated motor axons form

A

a single en plaque = typical motor end plate (found in all skeletal muscles)

83
Q

what is slow tonic felderstrucktur fibres innervated by

A

thinner motor axons

84
Q

what type of end plate do felderstrucktur fibres innervated by thinner motor axons form

A

grape like en grappe = unique motor end plates/endings which do not generate action potentials in the muscle, but are thought to mediate sustained contractions

85
Q

what do en grappe/grape like motor end plates of felderstrucktur fibres not generate and do mediate

A

do not generate action potentials

do mediate sustained contractions

86
Q

what is the tendon region of felderstrucktur fibres innervated by

A

unique proprioceptors (on the tendon) endings

87
Q

what is the name of the unique proprioceptor endings on the tendon of felderstrucktur fibres called

A

palisades

88
Q

what is the function of palisades, which are proprioceptors found on the tendon of felderstrucktur fibres

A

monitor muscle tension signalling eye position in the orbit to the brain

89
Q

what type of nerve is palisades proprioceptive endings of the felderstrucktur fibres

A

sensory nerve

90
Q

what do intracellular recordings to maximal nerve stimulation show about fast twitch fibrillenstrucktur fibres

A

short duration from response to end of action potential of <10ms
amplitude was large 10mv

91
Q

what do intracellular recordings to maximal nerve stimulation show about slow twitch felderstrucktur fibres

A

long slow response to end of action potential of ~200ms

amplitude was low but multiple (summating responses) with the highest to be 7.5mv

92
Q

over which bone is the medial check ligament attached

A

lacrimal

93
Q

over which bone is the lateral check ligament attached

A

zygomatic

94
Q

briefly list a summary of the slow tonic muscle fibres

A
  • thin motor nerve fibers
  • multiply innervated en grappe
  • large poorly delineated muscle fibrils (felderstrucktur)
  • no conduction of action potentials
  • slow sustained contraction (tonic)
  • predominantly in orbital layer
95
Q

briefly list a summary of fast twitch muscle fibres

A
  • thick motor nerve fibres
  • singly innervated en plaque
  • small, well-delineated muscle cell fibrils (metabolic activated cells - fibrillenstrucktur)
  • conduction of action potential
  • fast contraction (phasic)
  • predominantly in central/inner bulbar layer/global

Binocular vision (12 decks)

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