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EOMs Flashcards

1
Q

What muscle type are EOMs?

A

Skeletal muscle

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2
Q

What are thick myofibrils composed of?

A

Hundreds of myosin subunits.

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3
Q

Describe the structure of a myosin fibril.

A

Composed of two-headed filaments, with heads arranged in a spiral.

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4
Q

Describe the structure of an actin myofibril.

A

Composed of double-helix filament to which troponin-tropomyosin complex is attached.

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5
Q

Thin myofibrils are formed by what?

A

By a protein called actin

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6
Q

What is a sarcomere?

A

The contractile unit of striated muscle

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7
Q

Name the regions of the sarcomere, and what they contain.

A

I band

  • Only actin (thin) myofibrils
  • Light band

A band

  • Contains both myosin AND acting
  • Runs the entire length of myosin (thick) myofibrils

H zone
- Contains only myosin (thick) myofibrils

Z line
- Dark stripe bisecting the I band

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8
Q

During muscle contraction, ___ filaments slide past the ____ filaments.

A

Actin, myosin

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9
Q

During muscle contraction, which part(s) of the sarcomere decrease in size?

A

The H zone, the sarcomere itself, and the I band.

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10
Q

During muscle contraction, what part(s) of the sarcomere stay the same in size?

A

The A band and the lengths of the myosin/actin.

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11
Q

Select the incorrect statement. EOMs:

A. Have a denser blood supply than other skeletal muscle
B. Have a denser innervation than other skeletal muscle
C. Have a range of fiber sizes
D. Have slow and fast twitch fibers
E. Are among the fastest but fatigue prone muscles of striated muscle

A

E is incorrect.

EOMs are among the fastest and most fatigue-resistant of striated muscle.

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12
Q

Describe the innervation of EOMs

A

EOMs contain fewer muscle fibers in a motor unit.

Whereas in a the striated muscle of the leg which has the innervation of 1 axon per several hundred muscle fibers, in EOMs each axon innervates 3-10 fibers.

EOMs get innervation a lot quicker.

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13
Q

What advantages does the dense innervation afford?

A
  • Precise fine motor control
  • High velocity ocular movements, necessary in saccades
  • Very accurate pursuits
  • Fixations
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14
Q

Slow twitch fibers allow which type of movement?

A

Slow fibers produce slower pursuit movements and provide muscle tone.

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15
Q

Fast twitch fibers produce which type of movement?

A

Quick saccadic movements.

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16
Q

Describe Fick’s Axes

A

x-axis: horizontal or transverse axis; nasal to temporal

y-axis: sagittal axis; anterior to posterior pole

z-axis: vertical axis; superior to inferior

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17
Q

Describe the primary position of gaze

A

Eyes are focused for infinity.

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18
Q

Describe the secondary positions of gaze

A

Rotations around either the vertical axis or horizontal axis

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19
Q

Describe the tertiary positions of gase

A

Rotations around BOTH the vertical AND horizontal axes

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20
Q

What are ductions?

A

Movements of ONE eye

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21
Q

Define adduction

A

The rotation of the eye medially

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22
Q

Define abduction

A

The rotation of the eye laterally

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23
Q

Define elevation (supraduction)

A

The rotation of the eye up

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24
Q

Define depression (infraduction)

A

The rotation of the eye down

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25
What are torsions/cyclorotations?
Rotations around the sagittal axis (y-axis) in relation to a point at the 12-o'clock position on the superior limbus Intorsion (incyclorotation): Rotation of that point nasally Extortion (excyclorotation): Rotation of that point temporally
26
Why do torsional movements occur?
In an attempt to keep the horizontal retinal raphe parallel to the horizon
27
What are vergence movements?
When the eyes move in OPPOSITE left-right directions (DISCONJUGATE) to maintain fixation - Convergence: Each eye is adducted - Divergence: Each eye is abducted
28
What are version movements?
CONJUGATE movements that occur when the eyes move in the SAME direction. - Dextroversion - Levoversion - Supraversion - Infraversion
29
Dextroversion
A version movement. | Right gaze.
30
Levoversion
A version movement. | Left gaze.
31
Supraversion
A version movement. | Both eyes are elevated.
32
Infraversion
A version movement. | Both eyes are depressed.
33
List the EOMs from longest to shortest.
Superior rectus, medial rectus, lateral rectus, inferior rectus
34
What is the common tendinous ring?
An oval band of connective tissue located at the apex of the orbit. It is origin of recti muscles (attachment site). Forms a muscle cone!
35
Describe the parts that make up the common tendinous ring.
- Upper tendon (of Lockwood) > Arises from the body of the sphenoid > Origin to MR, LR, and SR - Lower tendon (of Zinn) > Attached to the inferior root of the lesser wing of the sphenoid > Origin to MR, LR, IR
36
Recti muscles attach where in relation to the equator?
Anterior
37
Obliques attach where in relation to the equator?
Posterior
38
Superior and inferior recti are located ___ degrees from the visual axis.
23
39
Superior and inferior obliques are located ___ degrees from the visual axis.
54
40
What is the clinical importance of recti insertions?
Insertion points are a landmark during strabismuc surgery. The sclera is the thinnest at the site of recti insertions (think blunt trauma).
41
True or False: Obliques attach laterally.
True.
42
What is the origin of the inferior oblique?
The maxillary bone
43
Which EOMs does the superior (lateral) branch of the ophthalmic artery supply?
- SR - LR - SO - LP (levator palpebrae)
44
Which EOMs does the inferior (medial) branch of the ophthalmic artery supply?
- IR - MR - IO
45
The lacrimal artery contributes to which EOMs?
- SR | - LR
46
The supraorbital artery contributes to which EOMs?
- SR - SO - LP
47
The infraorbital artery contributes to which EOMs?
- IR | - IO
48
The arteries to the four rectus muscles gives rise to _____.
The anterior ciliary arteries
49
How many anterior ciliary arteries emerge from each tendon?
2, except for the lateral rectus muscle which only has 1
50
What is the vestibulo-ocular reflex (VOR)?
- Reflex eye movement - Stabilizes image on the retina during head movements - Makes eye movements in the direction opposite to head movement
51
Does vestibulo-ocular reflex only work when there is light present?
No, it works in total darkness or when eyes are closed, too.
52
If there is sustained head rotation (i.e., > 30 sec), does the vestibulo-ocular reflex (VOR) continue to be responsive?
No
53
Which system is active when there has been sustained head motion (i.e., >30 sec)
The optokinetic system (OKN)
54
What does the optokinetic system (OKN) do?
It stabilizes image if there is long term head rotation.
55
The OKN drum tests for ___ then ____.
Pursuit, saccade
56
If a person cannot follow the OKN drum, what does this indicate?
If the patient cannot track, they may have decreased VA or parietal lobe lesion.
57
Head movements < 30 seconds. Which vestibular control system is in play?
Vestibulo-ocular reflex (VOR)
58
Head movements > 30 seconds. Which vestibular control system is in play?
Optokinetic system (OKN)
59
What structure is involved with the vestibulo-ocular reflex (VOR)?
The inner ear
60
What role does the inner ear have with the VOR?
It converts mechanical vibrations into a neural signal - It is innervated by CN VII - The vestibulocochlear organs maintain balance, receive sound, and contribute to eye reflex actions
61
What is the bony labyrinth of the inner ear comprised of? What do these structures do?
1. Cochlea: controls hearing 2. Vestibule: ultricle and saccule for balance 3. Semi-circular canal: ampullae
62
The utricle and saccule together are called _____.
Olithic organs
63
Which structures are responsible for linear acceleration (side-to-side)/linear vestibulo-ocular reflex?
The vestibule (utricle and saccule)
64
Which structure is responsible for angular acceleration (rotational movements)/angular vestibulo-ocular reflex?
The semi-circular canal
65
What are saccades?
Rapid eye movements to maintain fixation
66
What are saccades controlled by? (*)
1. Contralateral frontal eye fields in the frontal lobe | 2. Superior colliculus
67
If a patient has a defect in saccades, what area(s) do we suspect to have a problem?
1. Contralateral frontal eye fields | 2. Superior colliculus
68
What are pursuits?
Smooth tracking to follow slow moving objects.
69
What are pursuits controlled by? (*)
The ipsilateral parietal lobe
70
If a patient cannot pursue your finger or track the OKN drum, what do we suspect?
There is an issue with the parietal lobe.
71
What is the vergence system controlled by?
The brainstem
72
Describe Hering's Law of Equal Innervation
Agonist-Antagonist Relationship - Muscles work in pairs to move the eye; synergistic - YOKED muscles receive equal innervation. For example: LR and MR, SR and IO, SO and IR
73
Describe Sherrington's Law
Agonist and antagonist EOMs of the SAME EYE are reciprocally innervated.
74
What is Grave's Disease?
An autoimmune disorder characterized by the immune cells attacking the thyroid gland. This results in excessive secretion of hormones, increasing metabolism.
75
What effect does Grave's disease have on the eyes?
IgG causes inflammation of the EOMs (pleomorphic cellular infiltration). - The muscles become enlarged - Subsequent degeneration of muscle fibers (fibrosis)
76
What is the end result of Grave's disease on the eyes?
Myopathy and diplopia

Ocular Pathophysiology (4 decks)

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