The ocular motor nuclei and nerves Flashcards
What is the ocular motor system compromised of?
> EOM - 6 per eye
3 pairs of cranial nerves ( 3, 4, 6)
3 paired ocular motor nuclei in the brainstem
Numerous higher brain centres
What divisions are there in the higher hierarchical system?
Infra nuclear
Nuclear
inter nuclear
supra nuclear
What is inside the infra nuclear?
The EOM
What is inside the Nuclear?
Ocular motor neurones
What is inside the inter nuclear?
axons pathway
What is in the supra nuclear?
Brainstem nuclei generators
Control by higher centres
What does the 3rd nerve innervate and where is the third nerve ?
Oculormotor nerve from upper midbrain innervated the MR, SR, IR, IO
What does the 4th nerve innervate and where is the fourth nerve?
Trochlear nerve from the lower midbrain innervates the SO
What does the 6th nerve innervate and where is the sixth nerve ?
Abducences nerve from the mid caudal pons enervates the LR
What three axons take which course and where ?
The short intra cerebral course before exiting the brainstem
The long intra cranial course to reach the superior orbital fissure
The long intra orbital course to reach and innervate the target muscles
What do all nerves pass and go through?
All nerves pass along some arteries and some bones but all 3 nerves go through the superior orbital fissure and through the cavernous sinus
Where is the ocular motor nuclei located?
Ocular motor nuclei located at the midline in upper midbrain at the level of superior colliculus
What does the ocular motor nuclear complex contain?
4 somatic motor neurone pools
1 midline somatic motor neurone pools
2 autonomic motor neurone pools
What is the function of 4 somatic motor neurone pools?
Innervate the oculorotatory muscles (MR SR IR IO)
What is the function of 1 midline somatic motor neurone pools?
Innervates the LPS
What is the function of 2 autonomic motor neurone pools?
innervate different neurones in ciliary ganglion, which supply the sphincter pupillae and ciliary muscles
What is the name of 1 midline somatic motor neurone pool?
Caudal central nucleus
What is the 2 autonomic motor neurone pools?
Edinger westphal and anteromedian nuclei
Which is the largest of all nerves?
Oculormotor (3rd) nerve
What axons does 3rd nerve have?
Both somatic and parasympathetic axons
-mojority are voluntary motor axons to (MR, SR, IO, IR and LPS) occupy the centre of the nereve
-The rest pre ganglionic autonomic axons (to ciliary ganglion ) which are superficial in the nerve
What are these axons?
Uncrossed, but supplying the SR projects contra laterally- their axons cross in the upper midbrain just as they exit the nucleus
How do the SR axons project?
Contra laterally crossed in the upper midbrain just as they exit the nucleus
What is the intra cerebral 3rd nerve course?
Via Red nucleus and medial part of cerebral peduncle into the spinal chord
How do axons emerge into the fossa?
The nerve exits ventral midbrain :
>into subarachnoid space at the inter pedunculur fossa
>passes between the PCA &SCA then inferno lateral to the PCoA
>Travels forward in sub-arachnoid space
>To enter dural sheath forming the lateral wall of the cavernous sinus
enters the orbit via superior orbital fissure
What does PCA stand for?
Posterior cerebral artery
What does SCA stand for?
Superior cerebellar artery
What does PCoA stand for?
Posterior communicating artery
What are cells of arachnoid membrane called ?
Meningiothelial cells
What does the PCA supply ?
Occipital lobe
What does the SCA supply ?
Superior cerebellum
What is the basilar artery?
Two vertible arteries uniting to form large artery that runs along midline of the pons
What is the Intra cerebral 6th nerve course?
Through the basal pons and pyramidal tract
Where is the trochlear nuclei located?
At the midline in lower midbrain at the level of inferior colliculus
What are the two unique distinguish features of 4th nerve?
Emerges from dorsal surface of the brainstem
Carries axons that cross completely inside the brain
- nuclei supplies the opposite SO muscle
- nerve outside the brain supplies the SO muscle on same side
What is the smallest diameter of the 4th nerve?
3000-4000 axons
but longest intra cranial course
Intra cerebral 4th nerve course?
Around the Peri aqueductal grey PAG and across the superior medullary velum SMV
Where is the abducens nuclei located?
Located close to midline of middle of pons just below the facial colliculi
Intra cerebral 6th nerve course>?
Through the basal pons and pyramidal tract
what arteries are trochlear close to?
Superior cerebellar artery
basilar artery
What arteries is abducens nerve close to?
AICA- anterior inferior cerebellar artery
Basilar artery
What is part of spenoid bone?
Apex of petrous temporal bone
What else does the 6th nerve pass in intra orbital nerve course ?
Annular of tendon
MCQ: The abducens nerve passes close to which of the structures during its course from the brainstem to the orbit?
Pyramidal tract
