Chapter 21: Visual System

Question 1

Intro

Answer 1

Sight- Recognition and location of objects
-Locate and recognize objects in visual field

• Eye movement control (point in any way we want
• Information used in postural and limb movement control

(eyes can see 180 vertically and horizontally)

Question 2

Intro

Answer 2

CN 2- Vision (bring action potential from light information from the eyes back to the brain

CN 3- Parasympathetic fibers that go back to the pupil and lens of the eye (eye movement and control of pupil and lens)

CN 4- Eye movement (in and down)

CN 6- Eye movement (straight abduction/horizontal out)

CN 3,4,6= point eyeball to where we want it to be.

Question 3

visual system

Answer 3

CN 2- what we see

CN 3- control what we see

CN 3,4,6- eye movement system

Question 4

Visual system

Answer 4

Temporal retina- part of the retina close to the temporal bone

Nasal retina- Piece of retina close to nasal bone

For every eye there is a visual field in front of the nose- NASAL VISUAL FIELD

For every eye there is a visual field out to side-TEMPORAL VISUAL FIELD

• nasal retina sees temporal visual field
• temporal retina sees nasal visual field

Question 5

Optic Chiasm

Answer 5

the crossing- axons from the nasal retina cross over the midline- puts all the information from one side of visual space into opposite occipital lobe.

Temporal retina already sees the other side- stays on that side

Question 6

conscious visual pathways

Answer 6

passes through thalamus on way to cerebral cortex. All axons end up in cortex of occipital lobe.

Question 7

Conscious visual pathway

Answer 7

passes bump (superior colliculus) to turn head towards sight

Question 8

two ways of conscious vision

Answer 8

Two streams: light bounces back dorsally and ventrally

Question 9

Dorsal stream

Answer 9

Comes into parietal to make sense and ends in motor planning area (use what I see to guide motor plan to move)

*vision guides movement

Question 10

Ventral stream

Answer 10

Used for perception- to give meaning and give a name to what I see

• Comes from occipital lobe down to inferior temporal lobe (memories stored)

Visual agnosia

Question 11

Processing of visual information

Answer 11

Bounces back to help with movement or give visual meaning

Guide movement

Visually identify objects.

Question 12

Visual field deficits

Answer 12

Classification terminology is by location of “visual field” deficit

*not necessarily clued that they are missing something
(patient does not see black)

Question 13

Blindness in one eye

Answer 13

Right eye is blind
-loss in depth perception

(eyes are capable of seeing 180- eyebrow, chin, and nose get in the way

Question 14

Bitemporal hemianopsia

Answer 14

Only nasal retina damaged- 2 temporal visual fields half vision cannot see (tunnel vision)

• most common with CVA
• loss in lateral peripheral vision

Axons from nasal retinas cut at crossing- loss in temporal visual fields.

Question 15

Homonymous Hemianopsia

Answer 15

Same side half don’t see

• All light information from one half of visual space get cut
• Line right down the middle

Question 16

Quadrantanopsia

Answer 16

One fourth don’t see

-axons that have left thalamus get interrupted only upper and lower

Question 17

Cortical blindness (blindsight)

Answer 17

do see light and dark differences

• sometimes resolve shapes
• cannot resolve into finer details (unable to give meaning)

Question 18

shine light

Answer 18

• shine light- pupil constrict

- Automatically constrict by midbrain by pretectal area (pretectal have parasympathetic neurons that go out to eye)

Question 19

CN 3 (pupillary light reflex)

Answer 19

Direct- eye that is getting light shined into it

-Consensual- other eye constricting

CN 2- provides stimulus
CN 3- provides response (parasympathetic neurons hit on cranial N 3 to adjust pupil)

Question 20

Accommodation reflex- (near triad)

Answer 20

• pupils constrict (less light information is needed)
• eyes converge (to keep objects in focus)
• lens more convex

part voluntary, part reflex

Question 21

Extraocular muscles

Answer 21

4-Down and in
6- straight abduction
3- everything else

Question 22

Medial longitudinal fasciculus (MLF)

Answer 22

wiring in brain stem connect cranial nerve 3,4,6 together on both sides of brainstem

That is how abduction of one side can go with adduction on the other (links in vestibular apparatus)

Question 23

If misalignment of eyes

Answer 23

Diplopia in the acute phase

Suppressed vision from one eye in chronic phase

• reduces double vision but,
• leads to loss of depth perception

Brain will pick one eye to pay attention of and ignore opposite

Question 24

disorders of cranial nerve 3 (oculomotor nerve)

Answer 24

Pt is looking straight ahead

• R eye is deviating laterally
• suggesting CN III is not tugging and CN VI as won with abduction

Parasympathetic pigy back is not working to dilate (R CN 3 palsy)

Question 25

Disorders of CN IV (trochlear N)

Answer 25

Trochlear is damaged because unable to look in and down. CN III is intact because eye is still able to adduct

PT with trochlear damage will start tilting head to balance

Question 26

Disorders of CN VI (abducens)

Answer 26

Palsy in this case=malfunction/damage

right eye not able to look out to the side to mirror mvmt of left eye

Question 27

Disorders of Medial longitudinal fasciculus

Answer 27

Is there damage to CN III or the MLF?

• Similarity in pupil size determines that CN III must be working.
• MLF must be broken because eyes are not working together. eyes do not move in coordination

Question 28

Eye movements

Answer 28

• Gaze Stabilization- keep the eyes focused on an object of interest while the head is moving (keeps the visual world stable through eye movement)
• Direction of Gaze- move the eyes to focus on an object of interest (follow object of interest when it is moving)

Question 29

Gaze Stabilization

Answer 29

Vestibulo-Ocular Reflex(es) (VOR)

• Inner ear FX- detect movements of head
• Both inner ears are wired to both eyes to automatically keep the visual world steady when your head moves

(like a steady cam for movies)

Question 30

VOR suppression

Answer 30

reflex can be suppressed if we want it to

-conscious overriding (follow finger with head as it moves)

Question 31

Gaze Stabilization (optokinetic reflex)

Answer 31

• stay focused on object of interest during slow head movements
• Objects moves out of central vision and moves back to track it with a smooth pursuit.
• Keeps object in focus when it is moving but you are not

Optokinetic nystagmus- occurs when eye is following something that is moving

Question 32

Nystagmus

Answer 32

nystagmus is normal until it is happening when head is not moving or when you are not focusing on moving object

-It is the involuntary back and forth movements of the eyes designed to keep the visual world as steady as possible when we are moving (especially turning or spinning)

VOR- slow- eyes lag behind
Saccade- fast- eyes catch up
Physiologic- caused by me
Pathologic- crystals may be in semicircle canals

nystagmus will always be described by the direction of its quick jump

Question 33

Saccades

Answer 33

voluntary- looking from one finger to another

Reflex- superior colliculi, eye jumps to something in peripheral vision

Question 34

Smooth pursuit

Answer 34

(used when you read)- optokinetic reflex working really well

Question 35

Vergence (convergence)

Answer 35

crossed eye movements to keep object in focus

Question 36

motion sickness

Answer 36

typically conflict between sensory systems

• some systems say “we are not moving”
• some systems say “we are moving”
• vestibular nuclei can’t decide and freak out.