Vision Flashcards
What are the extraoccular muscles?
Muscles involved in eyemovement; Lateral Rectus (6); Superior Oblique (4); superior rectus, medial rectus, inferior rectus; inferior oblique (3)
Which extraoccular muscles are innervated by the Abducens nerve?
lateral rectus
Which extraocculuar muscle is innervated by the Trochlear nerve?
Superior oblique
Which extraoccular muscles are innervated by CN III
superior rectus, medial rectus, inferior rectus, inferior oblique
Which fibre bundle is associated with communication between motor CN nuclei involved in gaze?
Medial longitudinal fasciculus
Where is the MLF at the level of the rostral pons?
Where is the MLF at the level of the caudal pons?
Where is the MLF at the level of the midbrain?
Where is the vertical gaze centre?
Midbrain - reticular formation and pretectal area
Where is the horizontal gaze centre?
Pons - paramedian pontine RF (PPRF)
How many neurons are involved in directing the gaze to the right
4 - 1) the horizontal gaze centre neurons synpapse on the abducens nucleus; IPSI CN VI terminates on the right lateral rectus (LR6); 3) another set of abducens neurons cross the midline and synapse at the OCCULOMOTOR nucleus; 4) occulomotor neurons innervate the ipsilateral medial rectus
What would happen to gaze if there was a lesion to the RIGHT abducens nerve
Ipsilateral (right) eye would fail to abduct when looking to the right; leftward gaze would be unaffected
What is a reflexive saccade?
Visually guided saccade in response to external cue (prosaccade)
What is a volitional saccade
voluntary eye movement
What is the main input for voilutional saccades?
Frontal eye fields in SMA (BA 8)
What is the main input for reflexive saccades
Superior colliculi (brainstem)
Reflexive saccades recruit which structures?
Frontal eye fields –> ipsi superior colliculus –> contralateral horizontal gaze centre –> abducens nucleus –> ipsi lateral rectus and contra occulomotor nucleus –> ipsi left medial rectus
What is found in the DESCENDING MLF?
Medial and lateral vestibulospinal tracts
Which structures are involve in smooth pursuit?
FEF and V1 –> ipsilateral pontine nuclei (cerebropontine) –> contralateral cerebellum –> ipsilateral vestibular nuclei –> contralateral abducens nucleus –> activation of ips CNVI and contra CN III via the MLF
Which direction do eyes move in the VOR
Opposite of the direction of head movement
Which structures are involved in the VOR response to leftward head rotation?
1) Left horizontal canal —> ipsi vestibular nuclei —> contra abducens nucleus —> ipsi CN VI and contra CN III via MLF and occulomotor nucleus
Which muscles are involved in the pupillary reflex?
Constrictor pupillae
Which nuclei are involved in pupillary constriction
1) Pretectal; 2) Edinger-Westphal (CN-III GVE)
What are the first step involved in pupillary constriction?
1) light reaches retina; info travels to pre-tectal nuclei in midbrain via optic nerve and optic tract (post-chiasm)
What is the role of the pretectal nuclei in pupillary constriction?
Send bilateral projections to the edinger-westphal nuclei of CN III
What is the role of the edinger-westphal nuclei in pupillary constriction
Send preganglionic efferents (GVEs) to the ciliary ganglia
What happens at ciliary ganglia during pupil constriction?
Receive pre-ganglionic input from edinger-westphal nucleus; send post-ganglionic projections (ciliary nerves) to innervate constrictor pupillae muscles
If parasympathetic fibres in the right CN III were damaged, what would happen when a light was shone into the right eye?
No pupillary constriction in right eye BUT left eye will still constrict; called “blown pupil”
Which fibres cross the optic nerve?
Fibres from the NASAL (medial) half of each retina
Which tract do fibres travel in on their way from the LGN to V1?
Optic radiation (geniculocalcarine tract)
Which fibres form Meyer’s loop?
More ventral fibres (representing info from the upper visual field)
Where do tracts from the upper and lower visual field end up in the cortex
Lower portion of calcarine sulcus (upper); upper portion of calcarine sulcus (lower)
Which portion of the visual field travels via Meyer’s loop upon exiting the LGN?
Upper visual field (“bottom” of the retina)
What is a homonymous visual field deficit?
One that affects both eyes in the same part of the visual field
Monocular vision loss is due to a lesion to ____
Optic nerve
A lesion to the optic chiasm causes ____
Loss of temporal vision in both visual fields – bitemporal hemianopia
A lesion to the optic tract causes ____
Loss of the contralateral visual field in BOTH eyes
A lesion to Meyer loop causes ____
Upper portion of the contralateral visual field in both eyes
A partial lesion to the optic radiations before they are joined by fibres from Meyer’s loop ___
Loss of lower portion of contralateral visual field in both eyes
A lesion of the entire V1 ___
Loss of the contralateral visual field on both sides
Pupillodilator reflex begins where with which type of stimulus
Lateral horn neurons in T1 receive descending input (from e.g., the hypothalamus) in response to EMOTIONAL cues
Where do preganglionic fibres travel after receiving descening input for the pupillodilator reflex
Leave SC; travel up sympathetic trunk to superior cervical ganglion
Where do postganglionic neurons from the superior cervical ganglion go to intiate the pupillodilator reflex?
Travel along internal carotid and via the opthalmic division of CN V
Which nerves innervate the dilator pupillae muscles
Long cilliary nerves (branch off of CN V-1 opthalmic)
The corneal blink reflex is mediate by WHICH cranial nerve afferent
Trigeminal (V)
Which brainstem nuclei are involved in the corneal nerve reflex
Trigeminal Sensory nucleus and facial motor nucleus
Which muscle do fibres from the facial motor nucleus innervate to cause the blinking reflex
Orbicularis oculi
Convergence of the eyes (close vengence point) involves WHICH muscles and associated motor nuclei?
Medial rectus; oculomotor nuclei
Divergence of the eyes (far vengence point) requires WHICH muscles and assocaited motor nuclei
lateral rectus (abducens)
Which area of the rostral midbrain is responsible for coordinating the accommodation reflex
Supraocculomotor Area
Which processes occur during accomodation?
1) Convergence, 2) Pupillary constriction 3) Thickening of the lens
Which brainstem nuclie does the supraocculomotor area activate to intiate accomodation
1) Oculomotor (activates the medial rectus muscles) 2) Edinger-westphal nucleus (para efferents innervate the ciliary ganglion)
Afferent component of the pupillary light reflex
retinal info to pretectal area; pretectal to EW nucleus
Efferent component of pupillary light reflex
CN III (occulomotor nerve) –> ciliarly ganglion –> ciliary nerves –> iris constrictor muscles
Afferent component of ACCOMODATION
retina (receptors and neuronal elements), optic nerves, optic chiasm, optic tracts, lateral geniculate bodies, geniculocalcarine tracts, visual cortex. Corticotectal projections to superior colliculus/pretectal area - then to oculomotor nuclear complex.
Accomodation efferent component
CNIII nerve, ciliary ganglion, short ciliary nerves, ciliary muscle andconstrictor.•CNIII nerve, medial rectus muscle.
Pupilodilator reflex afferent component
Afferent component - from posterior hypothalamus via brainstem. Reticular formation to preganglionic sympathetic neurons at C8 and T1. Information via sympathetic trunk to superior cervical ganglion.
Pupilodilator reflex efferent component
Efferent component - postganglionic sympathetic fibers via nasociliary nerve (travels in opthalmic division of V-1), which gives off long ciliary nerves to dilator muscle of iris.
Where are the trochlear (CN IV) nuclei
Caudal midbrain; anterior part of PAG
What is in the DESCENDING MLF
Vestibulospinal tract
What is in the ASCENDING MLF
Connects CN-IV with CN-III; also connect VIII (vestibular) to CN III, IV, and VI for the VOR
