Extraocular muscles and Semi-circular canals

Question 1

How many extraocular muscles are there and what are they called?

Answer 1

7
Lateral Rectus
Medial Rectus
Superior Rrectus
Inferior Rectus
Superior Oblique
Inferior Oblique
Levator Palpabrae Superioris

Question 2

What does conjugate movement mean?

Answer 2

Co-ordinated movement of both eye to form one image

Question 3

What causes diplopia (double vision)?

Answer 3

Paralysis of muscles

Question 4

Which extraocular muscles do the oculomotor nerve (CN III) innervate?

Answer 4

Superior rectus, inferior rectus, medial rectus, inferior oblique and levator palpabrae

Question 5

What nerve innervates the Superior oblique?

Answer 5

Trochlear nerve (CN IV)

The superior oblique is held in place by a trochlea, a pulley, so think trochlear.

Question 6

Which nerve innervates the Lateral Rectus?

Answer 6

Abducens (CN VI)

The lateral rectus abducts, so think abducens

Question 7

Where does the Levator palpabrae superioris insert onto?

Answer 7

Upper eyelid

Question 8

Where do the Rectus and Oblique muscles insert to?

Answer 8

The sclera

Question 9

Why do the muscle fibres not coincide with the optical axis?

Answer 9

The orbit has an apex medially so it’s straight line forward (orbital axis) isn’t the same as what the eyeball’s straight line forward is (optic axis)

Question 10

What does injury to CN III (oculomotor) result in

Answer 10

Ptosis (drooping eyelid)

Medial Rectus becomes weak or paralysed so the eye deviates laterally. This results in double vision (diplopia)

Question 11

Is the Levator Palpabrae Superioris innervated by sympathetic or parasympathetic fibres?

Answer 11

Sympathetic fibres

Question 12

What action does the medial rectus make?

Answer 12

Moves eye medially (adducts) via CN III (oculomotor)

Question 13

What does the lateral rectus do?

Answer 13

Moves eye laterally (abducts) via CN VI (abducens)

Question 14

What does injury to CN VI (abducens) cause?

Answer 14

Lateral rectus becomes weak / paralysed. Eye deviates medially. Patient experiences double vision (diplopia)

Question 15

What does the superior rectus do?

Answer 15

Primary action: elevates eye

Secondary action: adducts and medially rotates (intorsion)

Question 16

What dos the inferior rectus do?

Answer 16

Primary action: depresses eye

Secondary action: adducts and laterally rotates

Question 17

What does the superior oblique do?

Answer 17

Primary action: medially rotates the eye

Secondary action: depresses and abducts

Question 18

What does the inferior oblique do?

Answer 18

Primary action: laterally rotates the eye

Secondary action: elevates and abducts

Question 19

Which muscle works with the inferior rectus to look down?

Answer 19

The superior oblique (cancels out the adduction and extorsion)

Question 20

Which muscle works with the superior rectus to look up?

Answer 20

The inferior oblique (cancels out the inversion and adduction)

Question 21

How do you examine the extraocular muscles?

Answer 21

Patient follows your finger. Examine the right eye. Then repeat movements and examine the left eye.

Test medial and lateral rectus, then superior and inferior recti, then oblique muscles.

To test superior and inferior recti, move finger laterally and then up to test recti not oblique. (Superior/inferior rectus causes elevation/depression and abduction whereas the obliques causes elevation/depression and adduction).

Question 22

What formula can help remember which muscle is innervated by which nerve

Answer 22

LR6 SO4 3

Lateral recuts - CN VI

Superior oblique - CN IV

All the others - CN III

Question 23

What can help to remember movements of the superior/inferior recti and obliques?

Answer 23

RAD SIN

Rectus = ADduction

Superior = Intorsion

Therefore, oblique = abduction and inferior = extorsion.

Question 24

Semicircular ducts

Answer 24

At right angles to each other.

Contain fluid (emdolymph). This fluid empties into sac called the utricle

Question 25

Which parts contain sense organs for balance?

Answer 25

Semicircular ducts and utricle

Question 26

What does the Crista ampullaris contain?

Answer 26

Cupula, endolymph, hair cells, supporting cells and sensory nerve fibres

Question 27

If your head moves in one direction…

Answer 27

Endolymph, cupula and hair cells in ampulla bend in opposite direction.

Info is sent centrally from right and left SC ducts
Via CN VIII (vestibulocochlea)

To nuclei in medulla

Question 28

Vestibular nuclei

Answer 29

When reflex not present, head moves, eyes move with it.

Can indicate brainstem lesion.