The Extraocular muscles. The semicircular canals 14.02.23 Flashcards
What does conjugate movements allow?
Allows us to form one image; paralysis of muscles results in diplopia W
What is diplopia?
Double vision
What shape is the orbit?
Cone shaped
Where do the muscles in the orbit originate from?
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
What muscle lifts the upper eyelid?
The LPS (levator palpabrae superioris)
What are the 4 recti muscles?
- Medial
- Lateral
- Superior
- Inferior
(these insert onto the sclera and are straight muscles)
What are the 2 obliques?
- Superior
- Inferior
What are the three cranial nerves that innervate the muscles of the eyes?
- CN III: Oculomotor
- CN IV: Trochlear
- CN VI: AbducensW
What Cranial nerve innervates the Superior oblique?
Trochlear
What cranial nerve innervates the lateral rectus?
abducens
Where do the muscles originate and insert?
- Attach to orbital bones
- Insert into the sclera
(except the LPS which inserts into the upper eyelid)
As well as the oculomotor nerve what else innervates the LPS?
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
What is drooping of the eyelid?
Ptosis (to-sis)
What does an oculomotor nerve lesion look like?
- Medial rectus is weak/ paralysed
- Unopposed pull of lateral rectus
- Eye deviates laterally
(patient will experience double vision)
What does an abducens nerve lesion look like?
- Lateral rectus weak/ paralysed
- Unopposed pull of medial rectus
- Eye deviates medially
(patient will experience double vision)
What movement is caused by the contraction of the superior and inferior recti?
When they contract, the direction of pull is backwards
How do we test for medial and lateral recti?
- Move finger horizontally across their field of vision and look for medial and lateral movement of the eye
How do we test the superior and inferior recti?
- Move finger laterally so the eye is in the abducted position
- Ask the patient to look up (SR) and down (IR)
How do we test the superior and inferior obliques?
- Move finger medially so eye is an adduction position
- Ask the patient to look up (IO) and down (SO)
What is the function of the cochlea and the vestibular apparatus?
- Sound (C)
- Balance (VA)
What are the structures of the vestibular apparatus?
- Contains the utricle and saccule
- 3 semicircular ducts containing fluid
How are the semicircular ducts orientated from each other?
- They are at right angles to each other
Which fluid do the semicircular ducts contain?
endolymph
Where does the fluid in the semicircular ducts empty?
Into a sac called the utricle
What is the function of the semicircular ducts?
- 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
What happens when signals reach the vestibular nuclei?
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
What is the oculocephalic reflex?
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
