Vision Iii: Central Visual Pathways

Front 1

What happens to images as they are projected onto retina?

Back 1

Flipped

Images on superior visual field --> inferior retina

Temporal visual field --> nasal half of the retina

Front 2

What is one feature proximal retinal ganglion cell axons?

Where do they penetrate the posterior part of the globe?

Back 2

Unmyelinated

At the level of the optic disc

Front 3

What do optic discs lack?

Back 3

Lack photoreceptors or other retinal neurons --> blind spots

Front 4

What happens to ganglion cell axons once they penetrate the sclera?

Back 4

Become associated with oligodendroglial cells, acquire a myelin sheath

Front 5

What system does the optic nerve belong to?

What is it invested by externally?

Back 5

CNS

Invested by dura and arachnoid matter

Front 6

What is subarachnoid space around the optic nerve continuous with?

Back 6

Subarachnoid space of the brain

Front 7

What is papilledema?

Back 7

Increased intracranial pressure --> increased pressure in subarachnoid space around optic nerve --> optic disc swelling

Front 8

What visual field do ganglion cells in nasal portions of each retina carry?

Temporal regions?

Back 8

Nasal region of retina = temporal visual field

Temporal region of retina = nasal visual field

Front 9

What is the optic chiasm?

Where does it form?

Back 9

Crossing of ganglion cell axons from the nasal portions of each retina

Just in front of the pituitary stalk

Front 10

What forms the optic tracts?

Back 10

Crossed fibers of nasal retina axons join uncrossed axons from temporal portion of each retina

Front 11

Where do optic tracts carry axons?

Back 11

Lateral geniculate nucleus on each side

Front 12

How are the layers of the lateral geniculate arranged?

Back 12

1-6, ventrally to dorsally

Front 13

What projects to neuron layers 2,3, and 5?

Back 13

Ipsilateral (temporal) retina projections

Front 14

What projects to layers 1,4, and 6?

Back 14

Contralateral (nasal) retina projections

Front 15

What is the Magnocellular layer?

What does it contain?

Back 15

Layers 1 and 2 of lateral geniculate nucleus

Contains projections from large retinal ganglion cells

Front 16

What is the Parvocellular layer?

What does it contain?

Back 16

Layers 3-6 of lat. geniculate nucleus

Receives projections from small retinal ganglion cells

Front 17

What do M neurons respond to?

P neurons?

Back 17

M neurons = movement, location, contrast

P neurons = color, form, visual acquity

Front 18

What is the magnocellular system?

Back 18

Magnocellular neurons in lat. geniculate send axons to primary visual cortex --> respond to movement and contrast

Front 19

Parvocellular system?

Back 19

Parvocellular neurons in lat. geniculate send axons to primary visual cortex --> respond to color and fine structural detail

Front 20

What is another source of input to the lateral geniculate besides those coming from retinal projections?

Back 20

Reciprocal connections from the visual cortex

Front 21

What are optic radiations?

Back 21

Sweeping tracts through which axons from neurons in the lat. geniculate travel to primary visual cortex

Front 22

What is the superior optic radiation?

Back 22

Pathway through which axons carry information from superior retina --> medial occipital lobe through the parietal lobe

Front 23

What is the inferior optic radiation?

Back 23

Pathway through which axons carry information from inferior retina --> Meyer's loop --> occipital lobe

Front 24

What is Meyer's Loop?

Back 24

Curved path through temporal lobe in the inferior optic radiation pathway

Front 25

What occurs with a lesion to the temporal lobe?

Parietal lobe?

Back 25

Temporal lobe lesion --> loss of vision in contralateral superior visual quadrant

Parietal lobe lesion --> loss of vision in the contralateral inferior visual quadrant

Front 26

What are other names for the primary visual cortex?

Where is it located?

Back 26

Calacrine cortex, striate cortex, Brodmann 17

Medial surface of occipital lobe, above and below the calacrine sulcus

Front 27

What is Gennari's line?

Back 27

Prominent, myelin-rich band that divides the primary visual cortex into superficial and deep layers

Front 28

Where do axons from the lateral geniculate nucleus synapse in the visual cortex?

Back 28

Synapse with neurons in layer 4 of visual cortex

Front 29

What does it mean that neurons in the visual cortex receive monocular inputs?

Back 29

Monocular - receives input from signals from ipsilateral or contralateral eye, not both

Front 30

What is the structure of the primary visual cortex?

Back 30

Arranged in a series of repeating, vertically-oriented modules that are in turn, composed of vertically-oriented columns

Front 31

What does it mean that the vertically-oriented columns of cells in the visual cortex exhibit ocular dominance?

Back 31

Some columns respond to inputs from ipsilateral retinal projections, while others respond to inputs from contralateral projections

Front 32

What defines the center of an ocular dominance column?

Back 32

The monocular preference of layer 4 and the neurons directly surrounding the receptive neurons

Front 33

How are areas of monocular inputs separated by areas of binocular input?

What does this create?

Back 33

Additional neurons in visual cortex outside of layer 4 receive both divergent and convergent input from layer 4

creates graded transition of columns receiving input from one eye to columns receiving input from the other eye

Front 34

What is binocular input?

Back 34

varying mixtures of input from both ipsilateral and contralateral eyes

Front 35

What are vertical orientation columns?

Back 35

Arrangement of striate cortex

neurons in a given column respond preferentially to stimuli presented in a particular orientation

Front 36

How do vertical orientation columns of the striate cortex contribute to binocular vision?

Back 36

Create graded transition between areas that respond to horizontally- and vertically-oriented inputs

Front 37

What are 3 ways in which primary visual cortex can be subdivided?

Back 37

1. Monocular and Binocular inputs
2. Horizontally and vertically oriented inputs
3. Magnocellular vs. Parvocellular inputs

Front 38

In general, where does information from the primary visual cortex go?

Back 38

Association areas in the occipital, parietal, and temporal cortex

Front 39

What types of information is sent to areas from the primary visual cortex dorsally, eg. parietal lobe?

Back 39

Information about movement, contrast, and orientation of an object
--> Magnocellular stream

Front 40

What types of information is sent to areas from the primary visual cortex ventrally, eg. temporal lobe?

Back 40

Information on color, form, and obect recognition
--> parvocellular stream

Front 41

Where do reciprocal connections between magno and parvocellular neurons meet?

Back 41

Pulvinar nucleus of the thalamus

Front 42

What would be the result of a lesion in the right optic nerve?

Back 42

Same as if loss of right eye
--> monocular blindness

Front 43

What would be the result of a lesion in the optic chiasm?

Back 43

Bitemporal heminanopsia = no vision in either temporal visual field because lesion affects fibers coming from nasal half of each retina

Front 44

What would be the result of a lesion in the right optic tract or right lateral geniculate?

Back 44

Left homonymous hemianopsia = loss of left visual field of each eye

Lose temporal retina of right eye (carrying nasal visual field of right eye) and nasal retina of left eye (carrying temporal visual field of left eye)

Front 45

What would be the result of a lesion in the left inferior optic radiation (Meyer's loop) of the left temporal lobe?

Back 45

Contralateral superior quadrantanopsia = lose right superior visual field of each eye

Fibers from right nasal and left temporal hemiretinal have split, only signals from right inferior nasal quadrant and left inferior temporal quadrant in tract

Front 46

What would be the result of a lesion in the right superior optic radiation?

Back 46

Contralateral inferior quadrantanopsia = left inferior visual field loss

Lesion in parietal lobe interrupt info from superior temporal retina of right eye and superior nasal quadrant of left eye

Front 47

What would be the result of a lesion in the primary visual cortex?

Back 47

Contralateral hemianopsia = loss of vision in the contralateral visual field

Front 48

Besides the lateral geniculate and visual cortex, where else do ganglion cells in retina project into the brain (3)?

Back 48

Superior colliculus
Prectectal region of brainstem
Hypothalamus

Front 49

Where does the superior colliculus lie?

Back 49

Dorsal midbrain

Front 50

What do the superior and inferior colliculi combine to form?

Back 50

Midbrain tectum

Front 51

From what parts of the retina does the superior colliculus receive projections?

What is the pathway to the superior colliculus called?

Back 51

Separate subset of retinal ganglion cells carrying projections from the ipsilateral temporal retina and the contralateral nasal retina

Brachium of the superior colliculus

Front 52

What are 3 other sources (non retinal) of inputs to the superior colliculus?

Back 52

1. Cerebral cortex - visual cortex
2. Somoatosensory system
3. Auditory system

Front 53

What are 5 targets for efferent projections from the superior colliculus?

Back 53

1. Cervical spinal cord (tectospinal tract)
2. Inferior colliculus
3. Reticular formation
4. Lateral geniculate nucleus
5. Pulvinar nucleus

Front 54

What is the function of the superior colliculus?

Back 54

Controls movements of the head and eyes in rapid responses to sudden visual, auditory, and other sensory stimuli

Front 55

What is the pretectal pathway?

Back 55

Retinal ganglion cells --> brachium of the superior colliculus --> synapse w/ pretectal neurons --> Edinger-Westphal nuclei bilaterally --> ciliary ganglion --> ciliary body and pupillary constrictor

Front 56

Where do pretectal neurons lie?

Back 56

Just anterior to the superior colliculus at the junction of the midbrain and the diencephalon

Front 57

Where do pretectal neurons cross to project to Edinger-Westphal nuclei bilaterally?

Back 57

Cross ventrally and dorsally to cerebral aqueduct

Dorsal fibers cross the posterior commissure

Front 58

What are the hypothalamic pathways?

Back 58

photic stimulation --> suprachiasmatic nucleus of hypothalamus --> PVN nucleus of hypothalamus --> autonomic centers in brainstem and cord --> lateral column sympathetic neurons to superior cervical ganglia --> pineal gland, melatonin released

Front 59

What does the suprachiasmatic nucleus of the hypothalamus do?

Back 59

Regulates circadian rhythms in mammals