ch 12 – central visual pathways

sensory systems

information collected by the retina allows for:

• perception of the scene

• induces reflexes

  • pupil dilation

  • turning eyes towards object of interest

• influences behaviors linked to circadian rhythms

occipital

primary visual cortex is in the _______ lobe

occipital, parietal, and temporal

what lobes are involved in vision?

parietal

lobe for motion and location

temporal

lobe for object recognition

optic nerve

where do axons of ganglion cells bundle to exit the retina?

optic chiasm

• 60% of neurons cross to the other hemisphere and enter the optic tract

optic tract

• contains neurons from both sides

dorsolateral geniculate nucleus (DGN)

where do ganglion cell axons project to?

thalamus

where is the DGN located?

thalamus

• relay for several sensory systems to the cortex

primary visual cortex

where do thalamic neurons send axons to?

optic radiation

• how thalamic neurons send axons to primary visual cortex

30

how many different types of retinal ganglion cells (RGCs)?

different functions of RGCs:

• send info about objects/writing that requires high-resolution

• send info about circadian rhythms/pupil adjustment

  • need to assess changes in light intensity

• sense light changes without rods and cones

inverted and left-right reversed

how are images projected onto retina?

binocular visual field

• two symmetrical hemifields

right hemifield

• right temporal visual field and left nasal visual field

temporal field

• larger

• peripheral vision

peripheral vision

• monocular

shape of nose blocks them more

why are inferior fields smaller than superior fields?

nasal

an object in the temporal visual field will be perceived in the _____ part of the retina

cross through optic chiasm

RGC axons on nasal side will cross through optic chiasm or stay on same side?

stay on same side

RGC axons on temporal side will cross through optic chiasm or stay on same side?

fovea

what delineates the boundary between nasal and temporal axons?

object on left of visual field

• nasal retina of left eye

• temporal retina of right eye

• all axons go through right optic tract

object on right of visual field

• nasal retina of right eye

• temporal retina of left eye

• all axons go through left optic tract

retinotopic maps

RGC projections are maintained as __________ _____ in the brain

DGN and striate cortex

where are the maps of contralateral field maintained?

striate cortex

• presence of myelinated layer around the calcarine sulcus (groove)

superior visual field

• below the calcarine sulcus

inferior visual field

• above the calcarine sulcus

fovea

• posterior (most occipital) of the visual cortex

peripheral retina

• anterior parts of the visual cortex

density of photoreceptors and sensory axons

what does the area in the visual cortex correlate with?

highest acuity (highest density of photoreceptors and sensory axons)

why is the area of the fovea/macula disproportionally large?

retina

stimulation of neurons in the DGN elicits responses similar to ones triggered in the ______

bars with distinct orientations

(spatiotemporal tuning) in the visual cortex, the neurons respond to different stimuli than the DGN + retina; instead, they respond to:

preferred orientation

each neuron is sensitive to a _______ ________

Fourier transform

• images are decomposed in frequency components

• each neuron only passes on a part of the total information of a scene

• other neurons in the visual cortex respond the the motion of the stimulus

oriented receptive field

• model: orientation selectivity in the visual cortex results from the integration of previous steps

• thalamic neurons with aligned concentric perceptive fields project to a neuron in the primary visual cortex

• the ________ ________ _____ comes from the receptive field alignment of the inputs

spiny neurons (dendrites) and aspinous (smooth) neurons

what types of neurons are in the primary visual cortex?

spiny neurons (dendrites)

• neurons in the primary visual cortex

• use glutamate as a neurotransmitter

• consist of pyramidal neurons and stellate neurons

pyramidal neurons

• spiny neurons in the primary visual cortex

• have dendrites

• in all layers except 4C

stellate neurons

• neurons in the primary visual cortex

• don’t have dendrites

• use GABA as a neurotransmitter

aspinous (smooth neurons)

• spiny neurons in the primary visual cortex

• have dendrites

• in all layers except 4C

layer 4C

what layer do DGN axons terminate in the primary visual cortex?

electrode inserted perpendicular to P.V cortex surface:

• neurons form radial columns centered on the same field with similar orientation preferences

electrode inserted tangential to P.V cortex surface:

• encounters neurons with different receptive fields and orientations that shift progressively

functional imaging

orientation maps are drawn from ________ _______

separate; monocular

in the DGN, inputs from both eyes arrive in ________ layers, and the neurons are _________

layer 4; ocular dominance columns; convergent

in the striate cortex, neurons of ______ receive inputs in separate _______ ________ _______, and then send ________ outputs in other layers

respond to one eye

do outputs on neurons at the center of ocular dominance columns respond to one eye or have equal contribution from both eyes?

have equal contribution from both eyes

do outputs on neurons at the borders between ocular dominance columns respond to one eye or have equal contribution from both eyes?

outside of the striate cortex

where is vision processed?

MT (middle temporal area)

• processes movement of an object, not color

V4

• processes color of an object, not movement

cerebral akinetopsia

• damage to MT area

• patient can’t pour liquid easily

  • fluid looks frozen

  • can’t detect that liquid has reached the top

• when crossing the street, cars appear far away and suddenly appear very near