Anatomy: Pupillary Reflexes and Eye Movement Flashcards
List the cranial nerves involved in eye movements.
Oculomotor (3)
Trochlear (4)
Abducens (6)
Name the important nuclei for III, IV and VI
III - oculomotor nucleus, edinger westphal (general visceral motor)
IV - trochlear nucleus
VI - abducens nucleus
All other nuclei = general somatic motor
Name the extraocular eye muscles.
Inferior oblique Superior oblique Superior rectus Inferior rectus Lateral recuts Medial rectus
Name the innervation of the muscles.
Lateral rectus - 6
Superior oblique - 4
All the others - 3
What is the name of the levator muscle of the upper eyelid and which cranial nerve innervates it?
Levator palpebrae superioris
Cranial nerve 3 - oculomotor
What position of the eye do the oblique muscles have the major effects on?
Adducted eye
Where does the 6th cranial nerve exit?
At the ponto-medullary junction near the ventral midline
Where does the abducent motor nucleus lie?
Caudal pons, beneath the facial colliculus in the floor of the 4th ventricle
What does a LMN lesion of Abducens produce?
Inability to move the eye laterally - eye wonders medially due to non-functioning lateral rectus
Diplopia is worse when looking at impaired side
Medial squint in affected eye at rest
Where is the trochlear nucleus found?
In midbrain at the level of the inferior colliculus
Why is the pathway of the nerve fibres of the trochlear nerve unusual?
Fibres decussate before exiting the brainstem
Nerve exits dorsally
What is the function of the superior oblique muscle?
Depresses the eye (strongest when eye is adducted)
What does a LMN of the trochlear nerve result in?
Problems with vision when looking downward with an adducted eye
- blurred vision when looking medially downwards
Where are the two oculomotor nuclei found?
Sit together in the periaqueductal grey matter of the midbrain at the superior colliculus level
Describe how the oculomotor nuclear complex innervates many muscles.
Within the nuclear complex, there are sub-nuclei. Each sub-nuclei is devoted to an individual muscle.
There is an unpaired central nucleus which supplies the levator palpebrae superioris
Describe the layout of fibres of the parasympathetic edinger westphal component of cranial nerve 3.
Edinger Westphal nucleus contains preganglionic parasympathetic neurons.
Fibres from these neurons pass with the somatic motor component of III to the ciliary ganglion in the orbit.
The ciliary ganglion sends postsynaptic fibres to the pupillary constrictor muscle of the iris and the ciliary muscle (accommodation)
Name the two pupillary reflexes.
Light and accommodation reflexes
Does the pupillary light reflex require cortical consciousness?
No
What is the function of testing the pupillary light reflex?
Test integrity of brainstem
Describe what happens when you shine light in one eye.
Shine light in one eye = constriction in stimulated eye (direct response) and in contralateral eye (consensual response)
Describe the afferents involved in the pupillary light reflex.
Afferents in CN II on way to thalamus (lateral geniculate nucleus) synapse with EDW on both sides.
Activates both pupillary constrictor muscle via III and ciliary ganglion.
Describe how image is seen from the temporal field.
Temporal field projects onto nasal retina.
Fibres from nasal retina need to cross over to other side
Fibres have to go via lateral geniculate nucleus to cortex to allow vision to be seen.
What would an absence of the light reflex mean?
Retinal blindness or lesion of optic nerve
Lesion of 3rd nerve
Damaged brainstem
What is the accommodation reflex?
Part of the near reflex for close focus
What three things happen during the accommodation reflex?
Accommodation - lens focuses
Eyes medially
Pupil constriction
** requires blurring on the retina = cortical reflex
What would a pituitary tumour result in?
Loss of vision of both temporal visual fields = bitemporal hemianopia
What effects does a LMN lesion have on the oculomotor nerve?
Eye directed laterally at rest (medial rectus no longer working)
Restricted eye movement (innervates so many muscles)
Severe diplopia
Ptossi (severe droop of eyelids)
Fixed dilated pupil (mydriasis) due to unopposed action of sympathetic dilators
Will an eye affected by LMN lesion of III show a direct pupillary constriction?
No
However there will still be a consensual response in the other eye that is unaffected
What do we need to coordinate eye movements with?
6 muscles
Movements of head and body
Movements of objects in visual field
Where are eye movements initiated?
Cortical Areas - Primary Motor Cortex
What is the function of the frontal eye field?
Voluntary eye movements
Conjugate movement of eyes to opposite side
Always saccadic
What is the function of the occipital eye field?
Involuntary eye movements
Fixation and smooth pursuit keep fovea fixed
Primary visual cortex and surrounding visual association areas
Where does coordination of eye movements occur?
In the brainstem
How do motor nuclei receive commands from cortical initiation centres since there are no connections between the two?
Receive input from gaze centres via the median longitudinal fasciculus
What is the median longitudinal fasciculus?
Common pathway linking III, IV and VI and also receives input from vestibular nuclei for coordination with head rotation.
Extends from midbrain down to cervical spine levels
What is the Paramedian Pontine Reticular Formation (PPRF) used for?
Centre for lateral gaze
What input does the PPRF receive and what does it coordinate?
Receives input from cortex via corticobulbar tract
Also receives input from vestibular nuclei for adjusting gaze to match head movement
Coordinates excitation of muscles involved in lateral gaze movement (medial and lateral rectus)
What does the PPRF inhibit?
Inhibition of antagonist muscles by interneurons from abducens.
Where is the vertical gaze centre located?
Pretectal region
What happens if there is damaged to the frontal eye field?
Gaze cannot be voluntarily directed to the opposite side
At rest the gaze is fixed towards the side of the lesion
What does damage to the occipital cortex lead to?
Blindness
