C2: Vision

when light comes into the eye it hits the retina which synapse onto .....

photoreceptors --> ganglion cells --> optic nerve

Why is the optic nerve unmyelinated at the eye?

- because myelin would reflect light

- becomes myelinated it leaves the eye

the ganglion cells exit the eye to form the .....

optic nerve

axons from the retinal ganglion cells relay visual signals as _______ via the _____ and ____

action potentials

optic nerve

optic tract

AP --> optic tract --> optic nerve --> where?

1. lateral geniculate nuclei

2. superior colliculi

3. pre-tectal area

visual pathway projections to the LATERAL GENICULATE NUCLEUS

- main subcortical region that processes visual information for perception

- majority of retinal axons terminate here

- signals sent to the primary visual cortex (V1); fibers to the occipital cortex

visual pathway projections to the SUPERIOR COLLICULI

- saccadic or fast eye movements

- visual, somatic, and auditory information

- adjust head/eyes toward the stimulus

draw the primary visual pathway

do it

visual pathway projections to the PRE-TECTAL AREA

- pupillary light reflexes

- light accommodation reflex

R visual field of L eye goes to what part of the retina

temporal retina

L visual field of L eye goes to what part of the retina

nasal retina

L visual field of R eye goes to what part of the retina

temporal retina

R visual field of R eye goes to what part of the retina

nasal retina

information from R visual field of R eye projects ....

ACROSS (contralateral) to LEFT LGN and LEFT V-1

information from L visual field of R eye projects ....

contralateral to right LGN RIGHT V-1

information from L visual field of L eye projects ....

ACROSS (contralateral) to RIGHT LGN and RIGHT V-1

information from R visual field of L eye projects ....

LEFT V-1

a lesion of the LEFT optic nerve would cause what?

left eye blindness

a lesion of the RIGHT optic nerve would cause what?

right eye blindness

lesion of optic chiasm

- bitemporal heteronymous hemianopsia

- loss of L visual field of L eye

- loss of R visual field of R eye

lesion of LEFT optic tract

- right homonymous hemianopsia

- loss of both RIGHT visual fields

lesion of RIGHT optic tract

- LEFT homonymous hemianopsia

- loss of both LEFT visual fields

lesion of LEFT optic radiations

- LEFT homonymous hemianopsia

- loss of both RIGHT visual fields

lesion of RIGHT optic radiations

- LEFT homonymous hemianopsia

- loss of both LEFT visual fields

lesion of LEFT V-1

RIGHT homonymous hemianopsia with macular sparing

lesion of RIGHT V-1

LEFT homonymous hemianopsia with macular sparing

macular sparing is characteristic of what type of lesion?

V-1
primary visual cortex

anopsia

loss of vision

hemianopsia

blindness in half the visual field

quadrantanopsia

blindness of one quadrant of the visual field

heteronymous lesion

visual field losses are NOT THE SAME in both eyes

homonymous lesion

affecting the SAME SIDE of the visual field of both eyes

draw the pupillary light reflex

do it

direct light reflex

constriction of pupil that light is shining in

consensual light reflex

shining a light into one eye causes the pupil of the other eye to contract

what can be used to distinguish an optic tract lesion from a lesion more distal in the visual pathway?

light reflex

with lesions distal to optic tract, a small beam of light into only the blind half of each retina results in?

pupillary constriction because the visual pathway is interrupted beyond the optic tract and pretectum

optic nerve lesion interrupts the _____ limb of the pupillary light reflex

it abolishes what light reflexes?

are light reflexes in the good eye still active?

Would both pupils react when increased light is shown in the good eye?

afferent

direct and consensual from the blind eye (both eyes would not dilate)

yes

yes

oculomotor nerve lesion interrupts the ____ limb of the pupillary light reflex

resulting in ...

efferent

mydriasis (dilation); loss of direct and consensual responses in the ipsilateral eye

result of an incomplete LEFT optic radiation lesion

right homonymous quadrinopsia

result of an incomplete RIGHT optic radiation lesion

LEFT homonymous quadrinopsia

acromegaly

rare disease cause by pituitary gland tumor

elevated GH (pituitary) levels stimulate excess amounts of IGF-1 (liver)

PRESSURE on surrounding brain tissue

extra IGF-1 in acromegaly is responsible for .....

slow but progressive GROWTH and swelling of various tissues, bones, and organs

what is the occurrence of acromegaly?

6 per 100,000 people

2-3 new cases each year per 1,000,000 people

T/F acromegaly effects men and women at different rates

FALSE

what age group is most commonly diagnosed with acromegaly?

middle aged adults

complications of acromegaly

high blood pressure
cardiomyopathy
osteoarthritis
diabetes
sleep apnea
spinal cord compression
headaches
vision loss***

is there a cure for acromegaly?

what about treatments?

no

drug therapy, radiation therapy, surgery

what happens when you leave acromegaly untreated?

death

growth of the pituitary tumor common in acromegaly often leads to pressure on the ...

leading to ...

optic chiasm

loss of peripheral vision (tunnel vision)

LEFT optic NERVE lesion ...
left eye:
direct =
consensual = light in R eye

right:
direct =
consensual = light in L eye

left eye:
direct = no, blockage of afferent signal
consensual = yes, uninterrupted

right eye:
direct = yes, uninterrupted
consensual = no, blockage of afferent signal

RIGHT optic NERVE lesion ...
left eye:
direct =
consensual = light in R eye

right:
direct =
consensual = light in L eye

left eye:
direct = yes, uninterrupted
consensual = no, blockage of afferent signal

right eye:
direct = no
consensual = yes

RIGHT optic TRACT lesion ...
left eye:
direct =
consensual = light in R eye

right eye:
direct =
consensual = light in L eye

left:
direct = yes, still innervation of edinger-westphal
consensual = yes, loss of only one pathway

right:
direct = yes
consensual = yes

OPTIC CHIASM lesion ...
left eye:
direct =
consensual = light in R eye

right eye:
direct =
consensual = light in L eye

left:
direct = yes, still innervation of edinger-westphal
consensual = yes, loss of only one pathway

right:
direct = yes
consensual = yes

LEFT oculomotor nerve lesion:
left eye:
direct =
consensual = light in R eye

right eye:
direct =
consensual = light in L eye

left:
direct = no, loss of innervation of sphincter muscle
consensual = no, loss of efferent nerve

right:
direct = yes
consensual = yes

RIGHT oculomotor nerve lesion:
left eye:
direct =
consensual = light in R eye

right eye:
direct =
consensual = light in L eye

left:
direct = yes
consensual = yes

right:
direct = no, loss of innervation of sphincter muscle
consensual = no, loss of efferent nerve

what would happen in a LEFT or RIGHT optic radiation lesion?

none of the afferent or efferent nerves would be affected so everything would still work

projection from the pretectal nucleus are

bilateral

what performs the first stage of visual processing?

retina

in the retina, stimulation of light activates?

photoreceptors with the production of electrical signals (AP)

what are the two classes of photoreceptors?

rods = absent in fovea

cones = concentrated in fovea

cones and rods:
high vs low threshold

cones = high threshold
rods = low threshold

rods function under conditions of _____ illumination

scotopic (low)

cones function under conditions of ___ illumination

photopic (daylight)

how many cones are in the eye?

10 million

how many rods are in the eye?

100 million

are rods present in the fovea?

no bitch

are cones present in the fovea?

f*ck yeah

rods contain what photo-pigment?

rhodopsin

are rods or cones poor in detail?

rods

do you use rods or cones in night vision?

rods

Are the cones or rods responsible for color vision?

cones

Are the cones or rods responsible for visual acuity?

cones

what photopigment do cones contain?

opsin

3 types - red, blue, green

at night, there is not enough _____ to stimulate opsin in cones

light energy to generate an electrical signal (NO AP)

is rhodopsin in rods or opsin in cones lower threshold?

rhodopsin in rods

is there enough light energy at night to stimulate rhodopsin in rods?

yes

during the day, rhodopsin in rods is ...

fully saturated so they are unable to generate an AP

what happens to rods when you walk into a dark room after being outside on a sunny day?

rhodopsin takes a bit to desaturate from lack of white light

action potentials generated by cones and rods are relayed to ...

V-1

within the retina, rods and cones synapse onto ...

which then synapse onto ...

which then exit the eye to form ...

bipolar cells

ganglion cells

optic nerve

axons from the retinal ganglion cells relay visual signals principally to the .....

lateral geniculate nuclei

color processing involves a series of _____ steps that begin in the ___ with ____ which then go through the ____ to ___

heirarchial
retina
three classes of cones
LGN
V-1

in V-1, color cells are clustered and project to ____ which in turn to project to _____ and the final stage takes place in the _____

V-2

posterior inferior temporal (PIT) cortex

inferior temporal cortex (V4)

stages in hierarchal processing of color>

retina (cones)
LGN
V-1
V-2
posterior inferior temporal (PIT) cortex
inferior temporal cortex (V4)

what is the function of the inferior temporal cortex (V4)?

final stage of color processing takes place here
help shape decision making

what are the functions of V1-V3a?

processing information, shapes, and textures

what is the function of V4?

color recognition

most common cause of color blindness

genetic fault in development of one or more of the three sets of cones

is there a cure for color blindness?

no

other causes of color blindness

brain or retinal damage
accidents or trauma (occipital lobe)
damage to retina from UV light
degenerative diseases of the eye
deficiency of vitamin K

about _____% of males and _____% of females are color blind

8%

.5%

it total or partial color blindness more common?

partial

more than 95% of all variations in human color vision involve what receptors in male eyes?

red and green

color blindness is _____ linked

X chromosome

because color blindness is X linked, ______% of women have a ____ th color cone and can be considered ______

2-3
4
tetrachromats

Ishihara color test

most common test used to diagnose color deficiencies

prosopagnosia

face blindness, inability to recognize faces

prosopagnosia affects ____% of the US population

2.5%

are there any treatments for prosopagnosia

no