visual system I&II - Raj

Question 1

retina

Answer 1

encodes visual info. to optic nerve to travel to brain

Question 2

optic nerve

Answer 2

hemidecussation at optic chiasm to project to lateral geniculate nucleus of thalamus

Question 3

thalamocortical neurons

Answer 3

take info. from lateral geniculate nucleus to primary visual cortex

Question 4

where do optic nerve and retina come from?

Answer 4

prosencephalic primary brain vesicle

Question 5

internal refractive media

Answer 5

bend light rays as they pass through the photoreceptors

-refracted before reaching retina

Question 6

fibrous (outer) layer of eye

Answer 6

consists of sclera and cornea

• sclera - maintains shape, attach external ocular muscles
• cornea - translucent, avascular

Question 7

middle (vascular) layer of the eye

Answer 7

contains choroid or uvea

• focus light and regulate intensity
• choroid proper - vascular and pigmented
• ciliary body - produce aqueous humor (sometimes vitreous); lens held by suspensory ligament; contract to relax suspensory ligament and focus light
• iris - has pigments and forms rim of pupil; constrictor and dilator muscles to control size of pupil

Question 8

inner (retinal) layer

Answer 8

1. pigmented (external stratum) - single layer

2. cerebral (internal stratum) - 9 layers

Question 9

cornea

Answer 9

different refractory index than air - bending of light rays

-main refractive structure of eye

Question 10

aqueous humor

Answer 10

• posterior chamber –> anterior chamber
• drains into spaces of fontana –> canal of schlemm –> episcleral veins
• increase intraocular pressure w/o drainage –> can lead to glaucoma (leading cause of blindness)

Question 11

lens

Answer 11

focusing bc its refractile power can be altered by suspensory ligament

• relax suspensory –> lens thickens
• presbyopia = lens becomes harder with age
• cataract = opacification of lens

Question 12

reina

Answer 12

1. non-neural - light absorbing pigmented cells
2. neural - the deep layer photoreceptors

• transmit light energy to electrical energy
• more rods on periphery than cones in the middle

Question 13

retinitis pigmentosa

Answer 13

failure of pigmented epith. to take up debris –> damage to photoreceptors

Question 14

retinal detachment

Answer 14

separation of pigment and photoreceptor layers –> blurred vision

Question 15

rods vs. cones

Answer 15

1. rods
   - sensitive to light - night vision, dim light
   - peripheral part - decrease towards macula
2. cones
   - bright light - color vision and high visual acuity
   - middle part - fovea and macula

Question 16

neurons of retina

Answer 16

• 1st order neuron –> bipolar cells in retina
• 2nd order neuron –> ganglion cells forming optic nerve
• interneurons - 1. horizontal cell (b/w photoreceptor and bipolar) 2. amacrine cell (b/w bipolar and ganglion)

Question 17

central area of the eye

Answer 17

1. fovea - contains cones, area for acute vision, foveola for light focusing to cones
2. macula lutea

Question 18

optic disc

Answer 18

• where unmyelinated nerve fibers coming from ganglion exit to head to brain
• fibers become myelinated when exiting
• blind spot - no photoreceptors

Question 19

rods vs. cones pigment

Answer 19

• rods - rhodopsin pigment –> broken down to retinal and opsin and restored by vit. A after absorption
• cones - iodopsin pigment
• outer segment of photoreceptor cells –> transduce light rays to electrical energy
• inner segments –> contain mitochondria for energy

Question 20

what causes night blindness?

Answer 20

vitamin A deficiency reduces nocturnal vision bc it cannot restore rhodopsin

Question 21

what is the effect of intracranial pressure via CSF?

Answer 21

can compress optic nerve –> disc edema, papilledema, choked disc

Question 22

fibers from temporal and nasal side of eye

Answer 22

• temporal fibers - travel to LGN w/o decussation

- nasal fibers - travel to opposite LGN after decussation

Question 23

route for left visual field

Answer 23

left visual field –> right optic tract –> right LGN –> right visual cortex

Question 24

route for right visual field

Answer 24

right visual field –> left optic tract –> left LGN –> left visual cortex

Question 25

where do some optic nerve fibers go instead of LGN?

Answer 25

pretectal area - mediate the pupillary light reflex

Question 26

central visual pathway of info.

Answer 26

LGN (contains 3rd order neuron) --> thalamocortical neurons to primary visual cortex in occipital lobe

Question 27

primary visual cortex ***

Answer 27

- located above and below calcarine sulcus - upper visual field --> lower retina --> fibers travel ventrally in temporal lobe to terminate BELOW calcarine sulcus (lingual gyrus) - lower visual field --> upper retina --> fibers travel dorsally in parietal lobe to terminate ABOVE calcarine sulcus (cuneus) - surrounded by visual association cortex (complex info.)

Question 28

macula of the eye

Answer 28

post. in visual cortex - center of eye - more visual acuity - image also flipped

Question 29

ex. of nasal/temporal side - visual field

Answer 29

right visual field - nasal side of right eye - temporal side of left eye - vice versa for left

Question 30

what do upper visual fields have to travel around?

Answer 30

around inferior horn forming loop (Meyer's loop) | -lesion in temporal lobe --> affect UPPER visual field

Question 31

field of vision

Answer 31

- fixation point - where vision is focused - quadrants - projected on retina in reversed, inverted by lens - visual pathways past optic chiasm carry fibers from contralateral halves of visual fields

Question 32

anopsia

Answer 32

complete loss of vision

Question 33

homonymous defect aka contralateral homonymous hemianopsia

Answer 33

affect same parts of visual fields in both eyes - lesion distal to optic chiasm - lose entire opposite field of vision in both eyes

Question 34

heteronymous defect aka bitemporal hemianopsia

Answer 34

affect different parts of visual field of both eyes - lesions of optic chiasm - usually affect crossing fibers (nasal) - ex. affect left visual field of left eye and right visual field on right eye bc of decussation

Question 35

dorsal vs. ventral fiber lesions

Answer 35

dorsal fiber lesion --> affect lower visual field | ventral fiber lesion --> affect upper visual field

Question 36

light/pupillary constriction reflex

Answer 36

direct light reflex, can involve PNS - light exposure --> pupil constricts - consensual light reflex --> indirect pupil constriction in opposite eye - optic tract --> superior colliculus --> pretectal area --> edinger Westphal --> oculomotor nerve --> ciliary ganglion --> short ciliary nerve --> constrictor muscle of iris

Question 37

pupillary dilation reflex

Answer 37

passively by decreased PNS or actively by increased SNS (in hypothalamus) - post. hypothalamus --> ciliospinal center in spinal cord --> ventral route --> white rami communicating --> superior cervical ganglion --> carotid plexus --> nasociliary and long ciliary nerves to dilator muscles of iris - miosis if SNS is affected

Question 38

accommodation reflex

Answer 38

maintain clear image when shifting from far to near object - near triad: convergence, pupillary constriction, thicken lenses - increase curvature of lens (bulge), contract ciliary body relaxing suspensory lig. - increase visual acuity by convergence and constriction of pupil

Question 39

accommodation reflex pathway

Answer 39

stimulated by perception of object - occipital cortex --> corticotectal tract --> accomodation center --> oculomotor nuclei --> edinger westphal (pupil constriction --> oculomotor nerve --> ciliary ganglion --> short ciliary nerves --> iris constrictor muscles - OR...accomodation center --> oculomotor somatic nuclei (for convergence) --> medial rectus

Question 40

where is upper left visual field info. found?

Answer 40

found in lower right quadrant in visual cortex

Question 41

retinitis pigmentosa

Answer 41

inherited disease of photoreceptors and retinal pigment epith. cells --> night blindness -need to remove pigment

Question 42

Horner syndrome

Answer 42

from tumors or vascular lesions - miosis, ptosis, anhydrosis - loss of smooth muscle innervation in upper eyelid and SNS innervation to sweat glands