Special senses II

Question 1

define accomodation

Answer 1

• automatic adjustment by which the eye adapts itself to distinct vision at different distances

Question 2

define presbyopia

Answer 2

• farsightedness due to ciliary muscle weakness and loss of elasticity in the crystalline lens

Question 3

blind spot

Answer 3

• a small area on the retina that is insensitve to light due to the interruption, where the optic nerve joins the retina, of the normal pattern of light-sensitive rods and cones

Question 4

define fovea

Answer 4

area consisting of small depression in the retina containing cones and where vision is most acute

Question 5

define binocula disparity

Answer 5

the difference in images of an object seen by left and right eye resulting from the eye’s horizontal separation

Question 6

define prosopagnosia

Answer 6

• inability or difficulty in recognizing familiar faces; may be congenital or result from injury/disease of the brain

Question 7

• define object agnosia

Answer 7

• loss of ability to recognize objects

Question 8

define scotoma

Answer 8

loss of vision in part of the visual field; blind spot

Question 9

match position in the visual field to retinal lcoation

Answer 9

• the image flipped vertically and horizontally

- upper right –> lower left on the retina

Question 10

match the retinal location to projection area

Answer 10

• Temporal (lateral visual field, medial retina crosses to contralateral cortex)
• Nasal (medial visual field, lateral retina stays IPSILATERAL

Question 11

difference between rods and cones

Answer 11

• rods have more PIGMENT and see in DIM LIGHT (rods = scotopic vision (dim light))
• cones need MORE LIGHT, for acute vision (PHOTOTOPIC vision = bright light)
• cones have 3 types of pigments (red, blue and green)
• Many rods to ONE ganglion
• ONE cone to ONE ganglion

Question 12

Distribution of photoreceptors

Answer 12

• in fovea, ONLY have CONES; no rods
• If you look directly at something in the dark, you can’t see it well (b/c you are using cones)
• if you look at object from the side, you will be able to see an outline (b/c you are using rods)
• Optic disc = no rods/cones at all

Question 13

Describe electrophysiological changes in the DARK

Answer 13

• in the dark, the RODS are DEPOLARIZED
• -> Na and Ca channels are open whenver there is enough cGMP
• -> Na and Ca keep coming in and K keeps going out
• -> causes depolarization and release of neurotransmiter in the dark

Question 14

Describe electrophysiological changes in the Light

Answer 14

• When there is light, intracellular cGMP is reduced and channels close
• -> K+ keeps leaving the cell and allows for HYPERPOLARIZATION of the cell
• -> result = decrease in release of neurotransmitter

Question 15

define receptive field for visual neurons

Answer 15

• area of retina from which the neuron can be influenced

Question 16

define photoreceptors

Answer 16

• capture photons, release NTs onto bipolar cells

Question 17

define bipolar cells

Answer 17

• receive NTs from photoreceptors, release NTs onto ganglion cells

Question 18

define ganglion cells

Answer 18

• only RETINA CELLS that produce action potentials (since their axons form the optic nerve) and are the OUTPUT CELLS of the retina

Question 19

Function of retinal projections to suprachiasmatic nuclei

Answer 19

• circadian rhythms

Question 20

function of retinal projects to pretectal nuclei

Answer 20

mediate papillary light reflexes

Question 21

function of retinal projections to LGN

Answer 21

• LGN relays to visual cortex and receives input from visual cortex (90% of axons terminate in LGN)

Question 22

function of retinal projections to superior colliculi

Answer 22

• in response to visual (or auditory or somatic) stimuli can cause eyes, head and body to turn towards stimuli
• -> part of major visual pathway (retina –> superior colliculus –> pulvinar –> cortex)

Question 23

define dorsal stream

Answer 23

• respjonsible for analysis of motion and relative psoitions of objects in visual scene
• neurons show selectivity for direction and speed of movement

Question 24

define ventral stream

Answer 24

• responsible for high-level form vision and object recognition
• neurons show selectivity for shape, color and texture
• Most selective highest order neurons can respond preferentially to faces and objects

Question 25

what is the clinical significances of the dorsal and ventral stream

Answer 25

• separate processing of different aspects of visual info

- can lose one aspect of vision without losing the rest - protective

Question 26

Describe the trichromatic theory of color vision

Answer 26

• Three types of cones - each absorb different wavelengths, need normal amounts for normal color vision
• -> short wavelength = blue cone
• -> middle wavelength = green cone
• -> long wavelength = red cone

Question 27

describe red-green color blindness

Answer 27

• missing EITHER red or green cones
• -> genes for red and green cones are on X-chromosome
• -> gene for blue is on chromosome 7
• -> rhodopsin gene on chromosome 3

Question 28

define monochromatopsia

Answer 28

• (ACHROMATIC)

- missing 2 cones/only have 1 type

Question 29

define Ishihara charts

Answer 29

• test for color blindness

Question 30

describe mechanisms for depth perception

Answer 30

• size of image of know objects on retina (know how big it should be and can judge how far away it must be
• occlusion = can judge which object is closer if one object blocks view of another
• Linear perspective = parallel lines seem to converge with distance (railroad tracks)
• Motion parallax = if you move your hand or body, nearby objects seem to move more quickly, but distant objects move slowly

Question 31

describe strabismus

Answer 31

• squint or cross-eyedness
• -> caused by failure of 2 eyes to fixate on same points
• -> causes diplopia/double vision
• -> some people with strabismus alternate which eye fixates on objects (in young children, tendency is to use one eyes for fixation and eventually supress vision from other eye; therefore important to treat early to prevent vision loss)

Question 32

what vitamin is necessary to prevent night blindness

Answer 32

• Vitamin A

Question 33

lesion of right optic nerve results in…

Answer 33

• total blindness of right eye

Question 34

lesion of midline of optic chiasma…

Answer 34

• Bitemporal hemianopsia

Question 35

lesion of right optic tract

Answer 35

• left homonymous hemianopia

Question 36

lesion of the right perichiasmal area

Answer 36

• right nasal hemianopia

Question 37

lesion to the lower right optic radiation fibers

Answer 37

• left homonymous inferior quadrantoanopia

Question 38

lesion of upper right optic radiation fibers

Answer 38

• left homonymous superior quadrantoanopia

Question 39

Lesion of right occipital lobe

Answer 39

• left homonymous hemianopia with macular sparing

Question 40

lesion of both Left optic radiation fibers or left LGN

Answer 40

• right homonymous hemianopia