Neuro Visual Tracts

Question 1

What is accommodation

Answer 1

Adjustment of the eye for seeing objects at various distances
This is accomplished by the ciliary muscle, which flattens or thickens the lens of the eye for distant or near vision

Question 2

Presbyopia

Answer 2

Loss of lens elasticity with age

Question 3

Optic disc

Answer 3

Blind spot in retina where optic nerves from ganglion layer exit the eye
Located medially to the macula

Question 4

Visual fields

Answer 4

Light passes from objects in the visual field, through the pupil to subtend an image upon the retina, creates a retinal field
Image formed on retina is inverted in both lateral and vertical dimensions
Object of attention is focused and centered at the location of the fovea centralis and macula lutea

Question 5

Retinal fields

Answer 5

Location on the retina that an object in visual field is projected
Each visual field is divided into retinal hemifields and each hemifield is divided into quadrants

Question 6

L/R visual field in comparison to retina

Answer 6

The left half of the visual field forms an image upon the nasal half of the left retina and the temporal half of the right retina, visa versa

Question 7

Decussation of CN II

Answer 7

The optic nerves partially decussate in the optic chiasm
Nasal half of each retina = contralateral optic tract
Temporal half of each retinal field = ipsilateral optic tract
This brings together comparable areas of both retinas creating depth perception

Question 8

Optic tract and LGN

Answer 8

Optic tract curves posteriorly around the cerebral peduncle to terminate in the LGN
Fibers terminate in precise retinotopic pattern

Question 9

LGN organization

Answer 9

Ventral base of the nucleus is formed by the incoming optic tract fibers
Dorsal and lateral borders are formed by the outgoing optic radiations

Question 10

LGN magnocellular layers

Answer 10

Magnocellular layers: contain large cells
Consist of ventral layers 1 and 2 of LGN, receive ganglion cell inputs relaying from rods
Larger receptive fields and thick, rapidly conducting axons, sensitive to moving stimuli

Question 11

LGN parvocellular layers

Answer 11

Dorsal layers 3-6
Contain small cells
Receive ganglion cell inputs relaying from cones
Small receptive fields, slower conducting axons, tonically responsive to stationary stimuli, high-acuity color vision

Question 12

Ganglion cell axons arising in temporal retina in relation to layers

Answer 12

Fibers remain uncrossed and terminate in layers 2, 3, 5 of the ipsilateral LGN

Question 13

Ganglion cell axons arising in nasal retina in relation to layers

Answer 13

Fibers cross and terminate in layers 1, 4 and 6 of the contralateral LGN

Question 14

List the layers and side of LGN that the nasal and temporal regions of the right visual field would terminate in

Answer 14

Nasal portion of right eye- layers 1, 4, 6 of left LGN
Temporal portion of left eye- layers 2, 3 and 5 of left LGN
Try the same with left visual field

Question 15

Optic radiations

Answer 15

Secondary neurons from LGN give off a bundle of fibers- the optic radiation
These relay to the primary visual cortex, located on the upper and lower banks of the calcarine sulcus
Also referred to as the geniculostriate or geniculocalcarine pathway

Question 16

Fibers from lower quadrant of the contralateral hemifields

Answer 16

Originate from dorsomedial portion of LGN
Arch caudally to pass through the retrolenticular limb of the internal capsule
Target superior bank of the calcarine sulcus, on the cuneus

Question 17

Fibers from upper quadrant of the contralateral hemifields

Answer 17

Originate from ventrolateral portion of LGN
Arch rostrally, passing into the white matter of the temporal lobe to forma a broad U-turn, the Meyer loop
Target inferior bank of the calcarine sulcus, on the lingual gyrus

Question 18

Fibers conveying info from the macula and fovea

Answer 18

Originate from central regions of the LGN and pass to caudal portions of the visual cortex

Question 19

Temporal lobe damage and visual field defects

Answer 19

Can produce a superior visual field deficit because of Meyers loop

Question 20

Macula representation in cortex

Answer 20

Macula is represented by disproportionately large volumes (relative to size) of the LGN and visual cortex
It is represented most posteriorly, in the region of the occipital pole

Question 21

Projection of visual field in cortex

Answer 21

The upper left quadrant of the visual field is represented in the lower right quadrant of the visual cortex and so on
Inferior visual fields project above the calcarine sulcus, superior visual fields below
Macula is represented more posteriorly, and peripheral fields more anteriorly

Question 22

Calcarine sulcus - broadmanns area

Answer 22

Bordmanns area 17 - calcarine sulcus/primary visual cortex
Also known as striate cortex, because you see numerous myelinated fibers within a discrete layer, giving a striped appearance

Question 23

Visual association cortex

Answer 23

Area 17 is surrounded by areas 18 (immediately superior and inferior to 17) and 19 (immediately superior and inferior to 18)
Includes parieto-occipito-temporal area:
Heavily interconnected with 17, receives targets from LGN and helps interpret location, motion, form and color

Question 24

Superior colliculus

Answer 24

Spatially directs head movements and visual reflexes
Receives input from the retina/optic tract as well as area 17
Important for directing eye movements
Also receives spinotectal and auditory inputs

Question 25

Pretectal/pretectum area

Answer 25

Located near midbrain/forebrain junction
Receives input from optic tract, LGN and suprachiasmatic nucleus
Important in the pupillary light reflex

Question 26

Pupillary reflex arc

Answer 26

Retinal axons terminate in the olivary pretectal nucleus
Bilateral projections to Edinger-westphal nucleus
Parasympathetics exit with CN III, synapse in ipsilateral ciliary ganglion
Postganglionic fibers (short ciliary nerves) excite pupillary constrictor muscle
Decussation of retinal fibers permits consensual response in opposite eye

Question 27

Optic nerve damage and pupillary light reflex

Answer 27

Shining a light into that eye will produce diminished direct and consensual responses, but both will be present when the undamaged side is illuminated

Question 28

Total lesion of optic nerve effect on light reflex

Answer 28

Blindness in that eye

Neither a direct nor a consensual response would be elicited when the eye is illuminated

Question 29

Lesion in optic tract or pretectum effect on light reflex

Answer 29

Neither response is lost, although reflexes may be weaker

Question 30

Large lesion in posterior/dorsal midbrain effect on light reflex

Answer 30

Would weaken pupillary responses bilaterally

Question 31

Lesions in oculomotor nucleus or nerve effect on light reflex

Answer 31

Both direct and consensual responses will be lost ipsilaterally, but will be present contralaterally

Question 32

Macular sparing

Answer 32

Visual field loss that preserves vision in the center of the visual field

Question 33

Congruous visual field deficits

Answer 33

When the visual field loss of one eye can be superimposed on that of the other eye
If lesion is closer to the visual cortex, the more congruous it is likely to be
The more anterior a lesion is in the optic tract or radiations, the more likely it will be incongruous

Question 34

Overarching concept

Answer 34

Damage anterior to chiasm affects only ipsilateral eye
Damage at chiasm causes heteronymous deficits
Damage behind chiasm causes homonymous deficits

Question 35

Associative visual agnosia

Answer 35

Infarction of the left occipital lobe and posterior corpus collosum
Typically due secondary to occlusion of posterior cerebral artery
Disconnects the language area from the visual cortex
Patient cannot name or describe an object in the visual field, but he can recognize and demonstrate its use
-Visual perception is intact
Patients may also be alexic (unable to read) & writing ability my be affected (agraphia)