Neuro Flashcards
(174 cards)
<p>Describe the neurologic visual pathway anterior to posterior </p>
<p>Optic nerve → chiasm → optic tract → lateral geniculate body → optic radiation → occipital lobe</p>
<p>How many nerve fibers are found in an adult optic nerve?</p>
<p>composed of 1.2 million nerve fibers</p>
<p>What is the average diameter of the optic nerve?</p>
<p>approximately 1.5 mm in diameter</p>
<p>What is the diameter of the optic nerve at the lamina cribrosa? Why is it larger?</p>
<p>enlarges to 3.5 mm posterior to lamina cribrosa due to myelin sheath</p>
<p>How far is the optic nerve from the fovea (approximately)?</p>
<p>located 3–4 mm from fovea</p>
<p>Where is the physiologic blind spot (due to the optic nerve) located?</p>
<p>absolute scotoma is15° temporal to fixation and slightly below horizontal meridian</p>
<p>What is the total length of the optic nerve?</p>
<p>approximately 45-50 mm in length</p>
<p>What is the intraocular length of the optic nerve?</p>
<p>1mm</p>
<p>What is the intraorbital length of the optic nerve?</p>
<p>25mm</p>
<p>What is the intracanalicular length of the optic nerve?</p>
<p>9mm</p>
<p>What is the intracranial length of the optic nerve?</p>
<p>10-15mm</p>
<p>At which location does the optic nerve begin to aquire myelin?</p>
<p>psoterior to the lamina cribrosa</p>
<p>Which layer of the meninges merges with the sclera?</p>
<p>dura mater - outer layer</p>
<p>Which layer of meninges is fused to the surface of the nerve?</p>
<p>pia mater- inner layer</p>
<p>Between which two layers of meninges is the space that contains CSF?</p>
<p>space between arachnoid and pia contains cerebrospinal fluid (CSF)</p>
<p>Through which structure does the optic nerve run before entering the optic canal?</p>
<p>annulus of Zinn (ring of tendinous origins of the rectus muscles)</p>
<p>What are the dimensions of the optic canal?</p>
<p>9 mm long and 5–7 mm wide</p>
<p>Which wall of theoptic cannal isthinnest?</p>
<p>medially, adjacent to ethmoid and sphenoid sinuses</p>
<p>Where does the dura of the optic canal fuse in the optic canal?</p>
<p>dura of ON fuses with PERIOSTEUM of canal</p>
<p>Where doesthe interal carotid artery emerge from the cavernous sinus?</p>
<p>laterally</p>
<p>What artery supplies the orbital portion of the optic nerve?</p>
<p>ophthalmic artery with meningeal anastomoses</p>
<p>Which blood vessels supplythe INTRACANALICULARportion of the optic nerve?</p>
<p>pial branches from ophthalmic artery</p>
<p>possibly internal carotid artery (ICA)</p>
<p>Which blood vessels supply the INTRACRANIAL portion of the optic nerve?</p>
<ul> <li>small vessels from ICA</li> <li>anterior cerebral and anterior communicating arteries</li></ul>
<p>Where is the optic chiasm located?</p>
<p>10 mm above pituitary gland</p>
What percentage of optic nerve fibers decussate at the chiasm?
55% of ON fibers cross in chiasm
Which retinal fibers decussate at the chiasm (nasal or temporal)?
nasal retinal fibers cross in chiasm to contralateral optic tract (decussating nasal fibers); temporal fibers remain uncrossed; macular fibers run posteriorly (posterior compression leads to bitemporal defect)
Which retinal fibers course through Willebrand's knee? What type of scotoma is produced?
- inferonasal retinal fibers cross in chiasm and course anteriorly approximately 4 mm into contralateral ON before running posteriorly
- produces junctional scotoma
where are the carotid arteries located relative to the chiasm?
Carotid arteries course on either side of chiasm
What is the main blood supply to the chiasm?
ICA; occasionally by anterior cerebral and anterior communicating arteries
Where are teh lower retinal fibers found in the optic tract?
lower fibers lie laterally (90° rotation of fibers)
around which structure does the optic tract course?
tract courses laterally around cerebral peduncle
Why does damage to the optic tract result in a contralateral rAPD?
Damage to optic tract results in contralateral relative afferent pupillary defect (RAPD) because 55% of fibers cross (greater quantity of nasal fibers [nasal to fovea]), including the large monocular crescent (which corresponds with the extreme nasal retina)
How does vision contribute to control of diurnal rhythms?
Special fibers run to the hypothalamus, contributing to neuroendocrine systems that control diurnal rhythms
What type of reflexes is the superior colliculus involved in?
involved in foveation reflexes (receives input from pupillary fibers); injury disrupts eye movements but does not cause visual field (VF) defect
What is the blood supply of the optic tract?
- anterior choroidal artery
- branches from posterior communicating artery
the Lateral geniculate body is a part of which neuroanatomical structure?
part of the thalamus
To which layers in the LGB do crossed fibers project?
Crossed fibers (contralateral eye): project to layers 1, 4, and 6
To which layers in the LGB do uncrossed fibers project?
Uncrossed fibers (ipsilateral eye): project to layers 2, 3, and 5
In which layers of the LGB are magnocellular (M-cell) neurons found?
layers 1 and 2
What visual role do Magnocellular (M) cells play?
- motion detection
- stereoacuity
- contrast sensitivity
To wich layer of the visual cortex do M cells project?
project to layer 4C alpha of visual cortex
In which layers of the LGB are Parvocellular neurons (P cell) found?
layers 3 to 6
What visual role do Parvocellular (P) cells play?
- fine spatial resolution
- color vision
To which layer of the visual cortex do P cells project?
layer 4C beta of visual cortex
In which areas of the LGB do the Koniocellular neurons (k cells) reside?
sit in interlaminar zones and superficial layers
From which 2 structures do K cells receive input?
receive input from both retinas and the superior colliculus
What is the blood supply to the LGB?
anterior communicating artery and choroidal arteries
What structure in the visual pathway connects the LGB to the occipital cortex?
optic radiations
How do superior retinal fibers travel through the optic radiations?
Superior retinal fibers (inferior VF) travel in white matter underneath parietal cortex to occipital lobe
How doe the inferior retinal fibers travel through the optic radiations?
Inferior retinal fibers (superior VF) travel around ventricular system into temporal lobe (Meyer’s loop)
Where is Meyer's loop located relative to the temporal lobe?
Meyer’s loop is about 5 cm from tip of temporal lobe
What visual field defect can be seen with an injury to Meyer's loop?
temporal lobe injury causes incongruous homonymous superior quadrantanopia, or a ‘pie-in-the-sky’ VF defect
Where do the macular fibers travel through the optic radiations relative to the retinal fibers?
travel more centrally than do inferior retinal fibers
What is the blood supply to the optic radiations?
middle cerebral arteries
Where is the primary visual cortex located?
medial face of occipital lobe
Which structure divides the primary visual cortex?
divided horizontally by calcarine fissure
Does the visual cortex contain infromation from the contralateral or ipsilateral eye?
Visual cortex contains a topographic map of the contralateral hemifield
Where is the macular region foudn in the primary visual cortex?
Macular region is posterior, extending slightly onto lateral aspect of occipital lobe
Where is th eperipheral visual field located in the visual cortex?
Peripheral VF is located anteriorly along calcarine fissure
Which is the only site posterior to the chiasm that if injured would cause a monocular VF defect?
Temporal crescent
- each VF (from 55° to 100°) is seen only by nasal retina of ipsilateral eye; located most anteriorly
- may also be the only portion of VF spared after occipital lobe damage
What is the blood supply to the primary visual cortex?
middle and posterior cerebral arteries
Where do the sympathetic fibers from the hypothalmus synapse? Where is this located?
CILIOSPINAL CENTER OF BUDGE
located at level C8–T2
Where do the 2nd order sympathetic fibers synapse?
SUPERIOR CERVICAL GANGLIA
Is the ciliary ganglia sympathetic or parasympathetic?
parasympathetic
Where is the ciliary ganglia located?
1 cm from optic foramen between ON and lateral rectus muscle
Name the 3 nerve fiber roots that are received by the ciliary ganglion:
Which ones synapse?
- Long sensory
- Short parasympathetic (synapse)
- Sympathetic (do not synapse)
What is the role of the long sensory nerves?
sensory from:
- cornea
- iris
- ciliary body
What is the role of the short parasympathetic fibers of the ciliary ganglion?
motor to ciliary body and iris sphincter
What is the role of the sympathetic fibers of the ciliary ganglion?
conjunctival vasoconstrictor fibers and iris dilator
What ganglia is traversed by the geniculate nucleus?
Geniculate nucleus
What is the role of the fibers from the geniculate nucleus?
contains cell bodies that provide taste from anterior ⅔ of tongue
Which ganglion has parasympathetic fibers to the lacrimal gland?
Sphenopalatine
Which side of gaze does the horizontal gaze center control?
ipsilateral side
Where is the horizontal gaze center located? At the level of which nucleus?
located in paramedian pontine reticular formation (PPRF) at level of CN 6 nucleus
to which cranial nerve nuclei does the horizontal gaze center project?
Via which structure does it connect with these nuclei?
projects to ipsilateral CN 6 nucleus and (via medial longitudinal fasciculus [MLF]) to contralateral CN 3 nucleus
From which two structures does the medial longitudinal fasciculus extend?
extends from anterior horn cells of the spinal cord to the thalamus
Which cranial nerve nuclei are connected by the MLF?
connects CN 3 nuclei and gaze centers (ipsilateral CN 3 and contralateral CN 6)
Where does the vertical gaze center originate?
originates in frontal eye fields or in superior colliculus
What is required for the vertical gaze center to function?
requires bilateral cortical input
Where do the projections of the vertal gaze center travel?projections travel to rostral interstitial nucleus of the MLF (riMLF) located behind red nucleus in midbrainprojections travel to rostral interstitial nucleus of the MLF (riMLF) located behind red nucleus in midbrain
- projections travel to rostral interstitial nucleus of the MLF (riMLF) located behind red nucleus in midbrain
- travel to nuclei of CN 3 and 4
What is upgaze controlled by?
lateral portion of riMLF
- stimulates CN 3 nucleus (superior rectus (SR) and inferior oblique (IO))
What controls downgaze?
medial portion of riMLF
stimulates CN 3 nucleus (inferior rectus (IR)) and CN 4 nucleus
What signal sends signals for the torsional eye movements?
interstitial nucleus of Cajal
Name the 3 types of glial cells
- Oligodendrocytes
- Astrocytes
- microglial cells
What is the role of oligodendrocytes
myelination
Where do oligodendrocytes work with myelination?
begins at LGB and reaches lamina cribrosa after birth
What is the role of astrocytes?
support and nutrition
What is the role of microglial cells?
phagocytosis
Name three different color vision tests
- Ishihara pseudoisochromatic
- Hardy-Rand-Ritter plates
- Farnsworth tests
Which colors are usually deficient in congenital color vision defects?
usually red/green
Which colors are deficient in acquired macular disease?
- may diminish blue/yellow in early stages (blue cones concentrated in perifoveal ring)
How can color plates differentiate macular vs. optic nerve disease?
-
Fovea has mostly red/green cones, so red/green defects are detected in optic nerve diseases.
-
Perception of red object indicates gross macular function
What is the photostress recovery test and how does it work?
- determine best-corrected vision
- shine bright light into eye for 10 seconds
- record time for vision to recover within 1 line of best-corrected vision
- test each eye separately
- invalid for eyes with vision worse than 20/80
What is the photostress recovery time seen in optic nerve diseases?
normal recovery time (<60 seconds)
What is the photostress recovery time seen in macular diseases?
prolonged time (>90 seconds)
Name 3 tests that can be used to test contrast sensitivity
- Pelli-Robson chart
- Regan contrast sensitivity chart
- VectorVision chart
What do Visually evoked cortical potentials/responses (VEP, VER) measure?
- macular visual function
- integrity of primary and secondary visual cortex
- continuity of optic nerve and tract radiations
Where are the macular and peripheral retinal areas represented in the occipital cortex?
- fovea has large area in occipital cortex
- smaller area representing more peripheral retina lies deep within calcarine fissure
How can you test vision in pre verbal infants?
Visually evoked cortical potentials/responses (VEP, VER)
What is the difference between a flash VER and a pattern VER?
- Flash VER: strobe light
- Pattern VER: checkerboard pattern or bar grating
What retinal cell types are tested by the pattern VER?
amacrine and ganglion cell layer of retina
What is the p100 wave?
positive deflection at 100 ms
amplitude is height from peak to trough, latency is time from onset of flash to peak of wave
what happens to the VER in toxic or compressive optic neuropathies?
reduction of amplitude more pronounced than prolongation of latency
What happens to the VER in demyelination?
latency is prolonged; amplitude may be only mildly reduced
What areas of vision does the amsler grid test?
- tests central 10° of the visual field (held at 35 cm)
- 10 cm × 10 cm grid composed of 5-mm squares
- primarily used to evaluate foveal pathology
What does the presence of optokinetic nystagmus indicate?
presence suggests visual input is present
Which direction is the slow phase of optokinetic nystagmus?
slow phase is noted in direction of moving stimulus
What areas control the slow pursuit and saccades of optokinetic nystagmus?
- Parieto-occipital area controls slow pursuit
- frontal lobe controls saccades
Which direction does OKN pursuit movements move?
- Pathway in visual association area terminates in ipsilateral pontine gaze center
- resulting in pursuit movements to the same side
- i.e. right visual association area controls pursuit to the right
What does a normal symmetric OKN response indicate?
occipital lobe, temporal lobe, LGB, or optic tract lesions do not interfere with pursuit
What does an assymetric OKN test with deficient pursuit movements to the right indicate?
right sided parietal lobe lesion (Deficient pursuit movements to side of lesion)
What does Cogan's dictum for homonomous hemianopia indicate?
- asymmetric OKN indicates parietal lobe lesion
- symmetric OKN indicates occipital lobe lesion
In which type of nystagmus can you see a reversal of OKN response?
60% of patients with CONGENITAL MOTOR NYSTAGMUS
What would be the OKN response seen in dorsal midbrain syndrome?
downward moving OKN drum causes convergence–retraction nystagmus
Describe the OKN findings of Congenital ocular motor nystagmus?
- abnormal OKN (fast phase absent)
- loss of voluntary horizontal gaze (vertical gaze intact)
- maintained tonic deviation
- requires neuroimaging
What is the red glass test used for?
evaluation of diplopia
How does a potential acuity meter work?
projects image of letter chart onto retina to test macular potential in patients with media opacities (cataract or corneal problem)
What does the Purkinje vascular phenomena and blue field entopic test
- visualization of retinal vasculature
- indicates gross retinal function
Name the Visual field defect:
Blind spot: physiologic due to ON; 15° temporal to fixation and slightly below horizontal midline
What is meant by baring of the blind spot? When is this seen?
- reduced sensitivity directly around the optic nerve head
- glaucoma, normal patients
Name the visual field defect:
Cecocentral scotoma:
involves blind spot and macula (within 25° of fixation)
In which conditions can a cecocentral scotoma be seen?
can occur in any condition that produces a central scotoma:
- dominant optic atrophy
- Leber’s optic atrophy
- toxic/nutritional optic neuropathy
- optic pit with serous retinal detachment
- optic neuritis
Name that visual field defect:
Central scotoma
Which conditions can cause a unilateral central scotoma?
- optic neuritis
- compressive lesion of ON
- retinal lesion [macular edema, disciform scar]
Which conditions can cause a bilateral central scotoma?
- toxic optic neuropathy
- nutritional deficiency
- macular lesions
Name the visual field defect:
Arcuate scotoma
What are the conditions that can cause an arcuate scotoma (6)?
- glaucoma
- optic neuritis
- anterior ischemic optic neuropathy (AION)
- branch retinal artery occlusion (BRAO)
- branch vein occlusion (BVO)
- ON drusen
name the visual field defect:
Altitudinal defect: damage to upper or lower pole of optic disc
In which conditions can an altitudinal defect be seen?
- optic neuritis
- AION
- hemiretinal artery
- vein occlusion
What does this type of visual field indicate?
Spiraling of VF: suggests malingering/functional visual loss
Name the visual field defect:
This is Pseudobitemporal hemianopia
slope and cross-vertical meridian
What conditions can cause a Pseudobitemporal hemianopia (7)?
- uncorrected refractive error
- tilted optic disc
- enlarged blind spot (papilledema)
- large central or cecocentral scotoma
- sector retinitis pigmentosa (nasal quadrant)
- overhanging lid
- coloboma
Name the visual field defect:
Binasal defect:
In which conditions can a binasal defect be seen?
most nasal defects due to arcuate scotomas (glaucoma)
- Also, pressure on temporal aspect of ON
- pressure on anterior angle of chiasm
- aneurysm
- pituitary adenoma
- infarct
Name the visual field
Ring scotoma (constricted visual field)
In which conditions can a ring scotoma be seen (8)?
- retinitis pigmentosa
- advanced glaucoma
- thyroid-related ophthalmopathy
- ON drusen
- vitamin A deficiency
- occipital stroke
- panretinal photocoagulation
- functional visual loss
How can you tell if a visual field defect is likely neurologic in etiology?
bilateral and respects vertical midline
To which location does this visual field defect localize?
Hemichiasmal defect
To which location does this visual field defect localize?
Junctional scotoma localized to the chiasm (specifically Willebrand’s knee)
What is anterior chiasmal syndrome?
- lesion at junction of ON and chiasm
- involves fibers in Willebrand’s knee (contralateral nasal retinal loop)
- causes junctional scotoma (central scotoma in 1 eye and superotemporal defect in the other)
To which location does this visual field defect localize?
Bitempral hemianopia localizes to the chiasm
To which location does this visual field defect localize?
Incongruous right homonymous hemianopia localizes to the optic tract
To which location does this visual field defect localize?
- Incongruous homonymous superior hemianopia localizes to Meyer's loop
- ‘pie-in-the-sky’ (denser superiorly, spares central)
To which location does this visual field defect localize?
Central bitemporal hemianopia localizes to the posterior chiasm
To which location does this visual field localize?
Left homonymous horizontal sectoranopia localizes to the area of the LGN near the end of the optic tract
To which location does this visal field defect localize?
Right parietal lobe lesion
Denser inferiorly
What viusal field defects may indicate a nerve fiber layer defect?
- arcuate
- papillomacular
- temporal wedge
What visual field defect may be seen in an occipital lobe lesion?
congruous homonymous hemianopia macular sparing
In retrochiasmal lesions, what does the congruity of the defect indicate?
the more congruous the defect, the more posterior is the lesion
What is the pathway that produces the superior visual field?
anterior retinal ganglion cells → lateral portion of optic tract → temporal lobe (Meyer’s loop) →inferior bank of calcarine fissure
What are some of the lesions that can cause a bitemporal hemianopia?
- pituitary tumor
- pituitary apoplexy
- craniopharyngioma
- meningioma
- ON glioma
- aneurysm
- trauma
- infection
- metastatic tumor
- MS
- sarcoid
Optic tract lesions cause what type of visual field defect? What causes it? What other sign can be seen?
- homonymous hemianopia
- posterior sellar or suprasellar lesions
- contralateral RAPD
What disease causes 90% of isolated homonymous hemianopias
Retro-LGB lesions: 90% of isolated homonymous hemianopias due to stroke
What other side effects can be seen with a temporal lobe lesion causing a "pie-in-the-sky" VF defect?
- formed visual hallucinations
- seizures
What symptoms are seen in Gerstmann's Syndrome?
- lesion of dominant parietal lobe
- acalculia
- agraphia
- finger agnosia
- left–right confusion
- associated with inferior homonymous hemianopia if optic radiation involved
An infarct in which artery would result in the following visual field?
- suggests infarct in area supplied by posterior cerebral artery
- macular region receives dual supply from both middle cerebral artery and posterior cerebral artery
Name the visual field:
Checkerboard visual field
- bilateral incomplete homonymous hemianopias
- superior on 1 side and inferior on opposite side (left upper and right lower homonymous quadrant defects)
A lesion where could cause the following visual field defect:
infarction or trauma to both occipital lobes, above or below calcarine fissure
A lesion in which location would result in the following visual field?
Monocular temporal crescent defect:
- anterior occipital infarct
- far temporal field is seen by only 1 eye
What causes cortical blindness? What other features are seen?
- bilateral occipital lobe destruction
- pupillary response intact
- blindsight (rudimentary visual capacity)
- unformed visual hallucinations
What is the Riddoch phenomenon?
perceive moving targets but not stationary ones; may deny blindness (Anton’s syndrome)
Describe the pathway that controls saccades-
contralateral frontal eye fields (frontal lobe) →superior colliculus → pontine paramedian reticular formation (PPRF) → horizontal gaze center (CN 6 nucleus) → ipsilateral lateral rectus l (LR) and contralateral medial rectus (MR) (via MLF)
Describe the pathway that controls smooth pursuit?
ipsilateral parieto-occipital lobe →superior colliculus (SC) → PPRF → horizontal gaze center → ipsilateral LR and contralateral MR (via MLF)
What eye movements are generated by the saccadic system?
fast eye movements (FEM) (refixation); 300-700°/s
What tests can be used to test the saccadic system?
- refixation
- rotation
- calorics
- optokinetic nystagmus (fast saccadic return phase)
Which diseases can cause abnormalities in the saccadic system?
- progressive external ophthalmoplegia
- myasthenia gravis
- Wilson’s disease
- Huntington’s disease
- ataxia-telangiectasia
- spinocerebellar degeneration
- progressive supranuclear palsy
- olivopontocerebellar atrophy
- Whipple’s disease
- Gaucher’s disease
- MS
- Pelizaeus-Merzbacher disease
What is ocular motor apraxia?
failure to initiate a saccade
Which eye movements are generated by the smooth pursuit system? Which areas of th brain control these movements?
- slow eye movements (SEM)
- ipsilateral parieto-occipital junction (horizontal)
- interstitial nucleus of Cajal (vertical)
what tests can be used to test the smooth pursuit system?
- Doll’s head
- rotation
- OKN (pursuit movement)
What abnormalities are seen in the smooth pursuit system?
- demyelination (young patients)
- microvascular disease (older patients)
What is the vergence system used for?
maintains foveal fixation on approaching object
What areas of the brain control the vergence system?
controlled by frontal and occipital lobes, and possibly midbrain
Name the 3 types of vergence
- voluntary
- accommodative
- fusional
How do you test vergence?
look from distance to near
