Neuroanatomy: Block 3, # 46? - Wang's Visual Pathways

Front 1

talk about large vs. small receptive fields and transient responses -

Back 1

if big fat receptive field, have transient response to light.

if smaller receptive field, can sustain a response if light is around.

fatty hobo.

Front 2

talk about daylight vs. starlight pathways:

Back 2

daylight is easy - use cones, no rods.

use cone bipolars to get to the ganglion cells.


starlight - use rods, no cones.
use rod bipolars and cone bipolar terminals.

also, amacrines come into play here.

then ganglion cells.

Front 3

information leaving the retina - what are some potential destinations?

Back 3

lateral geniculate nucleus for projection back to the visual cortices for conscious perception of light.

also, can go to the pretectum for the pupilary response

also, to the superior coliculus

also, to the suprachiasmatic nucleus

Front 4

describe the pathway of signaling from the retina from the medial retina (nasal side) and the lateral retain (temporal side)

Back 4

medial side crosses, temporal side doesn't. both are going to the lateral geniculate nucleus.

note that the nasal retina looks out at the periphery - so, really, peripheral vision crosses.

this is why injury to the optic chiasm = tunnel vision: you're loosing those fibers that cross, and those are peripherally looking.

Front 5

describe the layout of the lateral geniculate nucleus, what inputs go where, and the two kinds of large and small receptive fields: where do contralateral and ipsilateral retinal projections go?

Back 5

magnocellular vs. parvocellular:
magnocellular = large receptive field, parvocellular = small.

the lateral geniculate nucleus has 6 layers.

magnocellular is layers 1 and 2. parveocellular = layers 3, 4, 5, and 6.


note that ipsilateral projections are easy to remember because they add up (2, 3, and 5).

contralateral are the remaining (1, 4, and 6).

Front 6

functionally, what do the magnocellular and parvocellular pathways do?

Back 6

magnocellular, like we said, is for a large receptive field.

we know large receptive fields see transient information. it follows then that they'd be for motion and see quickly. think of old-timey black and white fat hobo going from place to place quickly.

the parvocellulars are slower conducting, sustained, and are better at seeing colors.

Front 7

magnocellular or parvocellular - which has been correlated to a disease?

Back 7

magnocellular deficits have been correlated with dyslexia or problems reading - probably problem with transient, fast motion.

Front 8

pupilary light response - what is the afferent/efferent pathway? what are some potential problems with lesions?

what happens if you cut the visual tract? what about the optic nerve

Back 8

go from the retain to the pretectal nucleus, to the edenger-westphal nucleus.

then efferent, it's EW nucleus to CN3 to the ciliary ganglion to the sphincter pupilae.

note that the afferent pathway is BILATERAL (each EW nucleus gets signals from both eyes) but EFFERENT IS IPSILATERAL (projects to ipsilateral Cn3 nucleus).

so, if one eye isn't constricting, you can assume it's an efferent problem?

if you cut the tract, the response should be intact still.

if you cut the optic nerve, the afferents from one eye will be completely destroyed - so shining a light in it won't make anything happen.
shine in the oppostie eye, and both pupils should constrict.

Front 9

fields of vision - what does one of the LGN's represent in terms of observed field?

Back 9

one LGN perceives an entire HEMIFIELD (half of vision).

for example, the right LGN is getting information from the temporal side of the right eye (observing the left field of vision) and the nasal retina of the left eye (also seeing the left side of the world) - so the right LGN is really looking at the left side of the world in both eyes.

Front 10

what is the projection from the LGN to the visual cortex called?

Back 10

meyer's loop!

Front 11

superior and inferior retinal areas - which cortical areas to they project to?

Back 11

the superior area of the retina projects to the superior side of the calcarine fissure (cuneus) - note however that the upper retina sees the LOWER FIELD of vision, so the cuneus (above calcarine fissue) sees the LOWER part of the world.

the lower retina projects back to the inferior side of the calcarine fissure (which is the lingual gyrus) - this perceives the UPPER visual field.

Front 12

what's the striate cortex?

Back 12

the striata gennari, in layer 4 of the cortex.

Front 13

talk about the what and where pathways:

Back 13

remember our magnocellular hobo - he's transient, so we need to know WHERE he is. this is also the DORSAL pathway (fat hobo has big butt). this information is destined for the posterior parietal lobe, going up the top of the brain.

all visual info goes to 17 (V1) then to 18 (V2), then some random places...then here, it's going to end up in 7a (posterior paretal lobe). it's going to tell us WHERE things are - their position in space and their acceleration/deceleration and their timing. movement.



What pathways: this is our parvocellular pathway. it's our "what" pathway, destined for the temporal lobe - it's going to tell us shape, name, etc. start again with 17, then 18, then ending up in 37. called inferior temporal cortex.

Front 14

talk about the ventral pathway:

Back 14

ventral pathway is also the "what" pathway - it's going to end up in the inferior temporal lobe, # 37.

again start at 17, then 18, then move anteriorally to #37. tell you associations, color, what the object is, give it a name, etc.

Front 15

heteromanous hemianopnia - what is it?

Back 15

tunnel vision, so lesion at the optic chaism.

Front 16

what's homonomous hemianopnia?

Back 16

problem behind the optic chiasm - as in cut one of the optic tracts. this kills the left side of vision in both eyes (if you hit the right optic tract).

Front 17

what's homonomous quadrapnosia?

Back 17

problems with radiations:

end up with killing one quarter of the visual field in one eye, the same one in fact (upper left in both eyes, for example. if you kill the right field going to the lingual gyrus, going to kill the left upper field)

Front 18

what's macular sparing?

Back 18

if you kill the area 17 on one side, get honomomyous hemianopnia with the center fields spared.