The Extraocular muscles. The semicircular canals 14.02.23

Question 1

What does conjugate movements allow?

Answer 1

Allows us to form one image; paralysis of muscles results in diplopia W

Question 2

What is diplopia?

Answer 2

Double vision

Question 3

What shape is the orbit?

Answer 3

Cone shaped

Question 4

Where do the muscles in the orbit originate from?

Answer 4

The apex, at one central point, then they fan out and there is a connection between the axis of the eyeball when looking straight ahead

Question 5

What muscle lifts the upper eyelid?

Answer 5

The LPS (levator palpabrae superioris)

Question 6

What are the 4 recti muscles?

Answer 6

• Medial
• Lateral
• Superior
• Inferior
  (these insert onto the sclera and are straight muscles)

Question 7

What are the 2 obliques?

Answer 7

• Superior
• Inferior

Question 8

What are the three cranial nerves that innervate the muscles of the eyes?

Answer 8

• CN III: Oculomotor
• CN IV: Trochlear
• CN VI: AbducensW

Question 9

What Cranial nerve innervates the Superior oblique?

Answer 9

Trochlear

Question 10

What cranial nerve innervates the lateral rectus?

Answer 10

abducens

Question 11

Where do the muscles originate and insert?

Answer 11

• Attach to orbital bones
• Insert into the sclera
  (except the LPS which inserts into the upper eyelid)

Question 12

As well as the oculomotor nerve what else innervates the LPS?

Answer 12

Sympathetic fibres
- So even if IIIrd cranial nerve is injured the sympathetic fibres still keep eyelid open a little bit but there is some drooping

Question 13

What is drooping of the eyelid?

Answer 13

Ptosis (to-sis)

Question 14

What does an oculomotor nerve lesion look like?

Answer 14

• Medial rectus is weak/ paralysed
• Unopposed pull of lateral rectus
• Eye deviates laterally
  (patient will experience double vision)

Question 15

What does an abducens nerve lesion look like?

Answer 15

• Lateral rectus weak/ paralysed
• Unopposed pull of medial rectus
• Eye deviates medially
  (patient will experience double vision)

Question 16

What movement is caused by the contraction of the superior and inferior recti?

Answer 16

When they contract, the direction of pull is backwards

Question 17

How do we test for medial and lateral recti?

Answer 17

• Move finger horizontally across their field of vision and look for medial and lateral movement of the eye

Question 18

How do we test the superior and inferior recti?

Answer 18

• Move finger laterally so the eye is in the abducted position
• Ask the patient to look up (SR) and down (IR)

Question 19

How do we test the superior and inferior obliques?

Answer 19

• Move finger medially so eye is an adduction position
• Ask the patient to look up (IO) and down (SO)

Question 20

What is the function of the cochlea and the vestibular apparatus?

Answer 20

• Sound (C)
• Balance (VA)

Question 21

What are the structures of the vestibular apparatus?

Answer 21

• Contains the utricle and saccule
• 3 semicircular ducts containing fluid

Question 22

How are the semicircular ducts orientated from each other?

Answer 22

• They are at right angles to each other

Question 23

Which fluid do the semicircular ducts contain?

Answer 23

endolymph

Question 24

Where does the fluid in the semicircular ducts empty?

Answer 24

Into a sac called the utricle

Question 25

What is the function of the semicircular ducts?

Answer 25

• Detect movement of the head
• When the head moves in one direction…
• The endolymph, capula and hair cells in the ampulla move in the opposite direction
• Info is sent centrally from right and left SC ducts
• Via 8th Cranial nerve
• To nuclei in the medulla

Question 26

What happens when signals reach the vestibular nuclei?

Answer 26

VN is in the brainstem
Connections here control:
- posture
- balance
- conscious awareness of position
The nuclei make connections with the nuclei of CNs III, IV, VI

Question 27

What is the oculocephalic reflex?

Answer 27

The ability to maintain a fixed gaze when the head is moving
When the head rotates:
- eyes move in the opposite direction
- Gaze remains fixed