Visual System

started 5/8 (ended on slide 22)

the optic cup develops from ___, while the lens develops from ___

diencephalon outgrowth, invaginated epithelium

the opening by which light enters the eye

pupil

the ___ can vary the size of the pupil and gives the eye its color

iris

the transparent external surface that is continuous with the sclera

cornea

the membrane that folds back from the inside of the eyelids and attaches to the sclera

conjunctiva

the ___ serve to move the eyeball

extraocular muscles

contains axons that carry visual information to the brain

optic nerve

what are the three tunics of the eye?

fibrous - cornea and sclera

vascular - iris, lens, ciliary body, choroid

neural - retina

how do the eyes adduct?

with the medial rectus muscle, innervated by CN III oculomotor

how do the eyes abduct?

by the lateral rectus muscle, innervated by CN VI abducens

what muscles are innervated by CNs III, IV, and VI?

CN III oculomotor → medial rectus, superior rectus, inferior rectus, inferior oblique

CN IV trochlear → superior oblique (intorsion)

CN VI abducens → lateral rectus (abduction)

radial fibers are innervated by ___ neurons to dilate the pupil

sympathetic

circular (sphincter) fibers are innervated by ___ neurons to constrict the pupil

parasympathetic

Which pupillary muscles are the edinger-westphal nucleus involved with?

circular (sphincter) fibers

the long ciliary nerve is associated with ___

the short ciliary nerve is associated with ___

long ciliary - radial fibers to dilate

short ciliary - sphincter fibers to constrict

how can the difference between a damaged optic nerve and a damaged oculomotor nerve be seen with pupil reflexes?

with a damaged optic nerve: the eye constricts when light is shone in the other eye, but not when the light is shone in the affected eye.

with a damaged oculomotor nerve: the eye does not constrict

what are the three main layers of the retina?

from back of retina forward: photoreceptor layer, bipolar cell layer, ganglion cell layer

___ cells fire action potentials that are relayed to the brain via the optic nerves

ganglion

___ cells transmit signals from the photoreceptor cells to the ganglion cells

bipolar

what do horizontal and amacrine cells do?

horizontal cells modify responses of bipolar cells

amacrine cells modify responses of ganglion cells

all cell types in the retina except ___ generate only graded potentials

ganglion cells

what are the photopigments present in rods and cones

rods - rhodopsin

cones - iodopsin

there are many more (rods/cones) than (rods/cones)

more rods than cones

rods are present in the ___, while cones are present in the ___

rods - peripheral retina

cones - fovea

what is the macula?

a region of high visual acuity, containing the fovea at the center. shows on fundus as the area around the dark retina

what is the blind spot of the eye?

the optic disk

the three stages of vision processing take place in:

LGN of the thalamus

Visual cortex (V1) - striate

Secondary visual cortex - extrastriate

What are the 3 cell types of the LGN? describe each.

parvocellular - small cells, small receptive fields. make up the four dorsal layers

magnocellular - large cells, large receptive fields. make up the two ventral layers

koniocellular - layers with very small cells, in between the main layers

What LGN layers are associated with each LGN cell type?

1-2 (the two ventral layers): magnocellular

3-6 (the four dorsal layers): parvocellular

macular vision is most (anterior/posterior)

posterior

Inferior visual field goes to the ___ gyrus via the ___ radiation, while the superior visual field goes to the ___ gyrus via the ___ radiation.

inferior: calcarine by the parietal optic radiation

superior, lingual by the temporal optic radiation (Myer’s loop)

define each: unilateral field loss, bitemporal hemianopia, homonymous hemianopia

unilateral field loss - lesion to the optic nerve, no input from one eye

bitemporal field loss - lesion near the chiasm, nasal retina info (lateral visual field) does not cross, person only sees inner field

homonymous hemianopia - a visual field is lost, must be after chiasm.

superior quadrantanopia involves ___

inferior quadrantanopia involves ___

superior: temporal optic radiation (myer’s loop)

inferior: parietal optic radiation

___ perceives objects so it is needed to form all visual images

V1, primary visual cortex

___, ___, and the ___ lobe all perceive complex form

V2, V4, inferior temporal lobe

___ is specialized for motion perception

V5

___ fires before ___, meaning your brain asks if an object is moving before it asks what it is

V5 before V4

the ___ pathway is the “what” pathway

ventral

the ___ pathway is the “where” pathway

dorsal

Describe a normal fundus exam, and what abnormalities to look out for

normal fundus - can see vasculature, a defined light optic disk, a dark macula.

looking for cloudiness, blurriness, bulging of the optic disk, etc

if vision issue is monocular, the lesion must be ___ to the optic chiasm

anterior

if the visual issue is one field, the lesion must be ___ to the chiasm

posterior

If the visual issue affects a quadrant, the lesion must involve either ___ or ___

the temporal lobe or the parietal lobe

what is prosopagnosia? where is the lesion?

face blindness. the lesion is to the fusiform gyrus