Central Visual Pathways

Question 1

What is the central pathway of visual info?

Answer 1

optic n –> optic chiasm –> optic tract –> LGN –> primary visual cortex

Question 2

What are the destinations for axons of the optic tract?

Answer 2

1. Lateral Geniculate Nucleus (main tract) - thalamic relay nuc. for vision
2. pretectal nuclei - pupillary light reflex
3. superior colliculus - axons in tectospinal tract to coordinate visual grasp reflex
4. hypothalamus - regulates circadian rhythm
5. reticular formation - does many things, can direct attn. of cx. to visual stimuli

Question 3

visual field

Answer 3

view seen by eyes without moving head

Question 4

binocular vision

Answer 4

• part of visual field viewed by both eyes - it is located in the center, and is excluding the peripheral vision
• Optic tracts carry this info from contralateral visual fields
• Cortex receives info from contralateral visual fields

Question 5

monocular vision

Answer 5

= part of visual field viewed only by 1 eye

- this is the peripheral vision, and is a “temporal crescend” shape

Question 6

visual hemifields

Answer 6

if draw a line down the center of the visual field projection, it can be divided into right and left halves.
- this does not correspond to right and left eyes.

Question 7

left temporal hemiretina

Answer 7

receives info from nasal half of right visual field

Question 8

left nasal hemiretina

Answer 8

receives info from the left temporal visual field

Question 9

temporal lobe damage

Answer 9

shows damage to superior visual fields because meyer’s loop goes out laterally/anteriorly in the temporal lobe. The Meyer’s loop carries information for the superior visual world.

Question 10

damage at left optic nerve

Answer 10

results in loss of the ipsilateral visual world (complete blindness of left eye)

Question 11

pituitary tumor

Answer 11

damage to optic stalk, results in damage of the peripheral visual fields = tunnel vision

Question 12

damage to right optic tract

Answer 12

loss of contralateral visual world = complete blindness of left eye

Question 13

where do axons go from LGN?

Answer 13

• axons head out anteriorly, loop out over 4th ventricle (meyer’s loops = superior visual field) to lingual gyrus
• axons head more medial/posterior over trigone and posterior horn of ventricle (inferior visual field) to cuneaus
• all optic radiations project back to primary visual cortex, BA 17
• optic radiations sometimes called “geniculostriate tract”

Question 14

primary visual cortex, other names?

Answer 14

BA 17
and
lingual gyrus and cuneus
- often called striate cortex, because it loosk striate.

Question 15

maculae

Answer 15

has a huge number of neurons dedicated to it

• this provides information for the center of vision.
• this is the region of highest acuity

Question 16

calcarine sulcus

Answer 16

divides the superior and inferior visual fields (the more caudal portion is reserved for the maculae, high acuity fibers)

Question 17

what do pretectal nuclei do?

Answer 17

control pupillar light reflexes through synapsing on edinger-wetphal nucleus, which projects through oculomotor n. to the pupillar sphincter muscle

Question 18

control pupil size?

Answer 18

through autonomic (GVE control)

• constriction = PS = oculomotor n.
• dilation = sympathetic = superior cervical ganglia

Question 19

what travels in posterior commisure

Answer 19

decussation of fibers that are traveling bilaterally to reach the edinger wesiphal nucleus

Question 20

what is located in edinger wesiphal nuclei?

Answer 20

location of preganglionic PS neurons that will head out via occulomotor n. to synapse on ciliary ganglion.

Question 21

what happens with pupillary light reflex?

Answer 21

• Collaterals are given off that bypass the LGN, and travel in the brachium of the superior colliculus to synapse on pretectal nuclei.
• they then run bilaterally (decussate via posterior comissure) to synapse on preganglionic PS neurons of edinger wesiphal nucleus
• pre ganglionic PS neurons will then travel ipsilaterally to ciliary ganglion via CN III, to synapse on short ciliary n.
• short ciliary nn. will carry post-ganglionic PS fibers and will innervate the pupillary sphincter muscle for pupillary contraction.

Question 22

what is non-cortical projection of central pathway?

Answer 22

to hypothalamus (suprachaistmatic nucleus) = regulates circadian rhythms

• helps regulate 24hr internal clock
• Melanopsin system

Question 23

higher order processing? what are two streams?

Answer 23

primary visual cortex projects to BA 18/19 for higher order processing and interpretation.

1. Dorsal Pathway: parietal region, analyzes movement, “where is it?”
2. Ventral Pathway: temporal region: analyzes colors, “what is it?”

Question 24

temporal lobe lesion

Answer 24

cannot see colors, can’t distinguish objects

- prosagbognia: inability to distinguish people and faces

Question 25

dorsal lobe lesion?

Answer 25

can't detect movement, can't distinguish where things are located "motion blindness"