vision

Question 1

Review: tongue

Answer 1

taste cells (roughly 100) are composed of a taste bud. taste buds are on papillae. more taste buds = stronger discernment of taste

Question 2

Review: taste cells

Answer 2

NON-NEURONAL but can transduce molecules in food to electrical signals that synapse onto gustatory aferent axons via chemical synapses.
Neurotransmitter mechanism is unknown.
Most taste cells respond to >tastants

Question 3

Review: olfactory neurons

Answer 3

cilia protrude into mucus layer that senses volatile molecules and transduce that signals to the olfactory bulb (through specialized epithelium, and pores in the cribiform plate). Utilizes special GPCR that promotes Na+ and Ca2+ influx as well as Cl- efflux

Question 4

Review: olfactory sensory neurons

Answer 4

Neural encoding of odorants, the role of olfactory interneurons and the transduction of smells by the olfactory receptor cells -> olfactory bulb -> many brain regions (thalamus/hypothalamus/amydala) -> olfactory cortex

Question 5

Properties of light

Answer 5

reflection, absorption, and refraction

Question 6

Anatomy of eye

Answer 6

pupil, sclera, iris, cornea, and optic nerve

Question 7

Pupil

Answer 7

opening where light enters the eye (the black center)

Question 8

Iris

Answer 8

gives color to eye

Question 9

sclera

Answer 9

white of the eye

Question 10

cornea

Answer 10

glassy transparent external surface of the eye (the part you put your contacts on)

Question 11

optic nerve

Answer 11

bundle of axons from the retina (behind the eye)

Question 12

refraction of light by the cornea

Answer 12

incoming light is refracted, focused on the retina, and transduced into an image

Question 13

fovea

Answer 13

a small depression in the retina of the eye where visual acuity is highest. Center of field of vision is focused in this region, where retinal cones are particularly concentrated
does sharp central vision (useful for things like reading and driving)

Question 14

Direct (vertical) pathway of retinal signal transduction

Answer 14

photoreceptors -> bipolar cells -> ganglion cells

Question 15

Retinal signal transduction

Answer 15

retinal processing influenced by: lateral connections, ie: horizontal cells and amacrine cells

• the only light-sensitive cells in retina are photo receptors EXCEPT for intrinsically photosensitive retinal ganglion cells
• • the ganglion cells are the only source of output from the retina

Question 16

Horizontal cells

Answer 16

receives input from photoreceptors and projects laterally to influence surrounding bipolar cells and photoreceptors

Question 17

amacrine cells

Answer 17

receives input from bipolar cells and projects to ganglion cells, bipolar cells, and other amacrine cells

Question 18

photoreceptor structure

Answer 18

converts light to neural structure via the four main regions:
outer segment
inner segment
cell body
synaptic terminal

Question 19

types of photoreceptors

Answer 19

rods and cones (“classic” retinal ganglion cells)

intrinsically photosensitive retinal ganglion cells (ipRGCs)

Question 20

rods

Answer 20

100 million in the human retina
1 type
exquisitely sensitive to a photon of light
more discs = more sensitivity
responsible for night vision (scotopic conditions)
contains rhodopsin (retinal+opsin)

Question 21

cones

Answer 21

6 million in the human retina
3 types (L = long wave; M = medium waves; and S = short wave)
less sensitive to light, but faster to respond
responsible for daytime color vision (photopic conditions)
contains photopsin

Question 22

photopsin

Answer 22

retinal and an opsin variant (distinguished by its absorption spectrum, rhodopsin is red when there is no light, reason why our eyes get redder)

Question 23

phototransduction

Answer 23

photons leading to closing of constitutively active cation channels in photoreceptor outer segments
this causes hyperpolarizing potential and decreasing neurotransmitter release

Question 24

single photon amplification

Answer 24

a rhodopsin molecule that absorbs a photon has 67% chance of being photoisomerized, which triggers electrical response with >80% reliability
each R molecule activates 100 molecule of transducin
2 T per one phosphodiesterase
1 phosphodiesterase capable of hydrolyzing >1000 molecules of cGMP per second

cGMP sink closes hundreds of the ten thousand channels that are open; this causes 10 MILLION na+ ions to be prevented from entering outer segment
**TL;DR: tight control of amplification process, amplifies v big

Question 25

mechanism of phototransduction

Answer 25

light absorbing retinal (aldehyde form of vit A undergoes conformatoinal change from absorbing photon of light from 11-cis retinal to all-trans retinal) retinal is covalently attached to opsin and because all-trans isomer fits differently inside opsin (specifically not in 11-cis binding site) opsin undergoes conformational change this change triggers visual transduction by way of GPCR

Question 26

regional differences in retinal structure

Answer 26

cones found primarily in central retina near fovea central retina has lower ratio of photoreceptors to ganglion cells = better resolution peripheral retina has higher ratio of photoreceptors to ganglion cells = better at detecting dim light

Question 27

dark adaptation

Answer 27

dark: takes roughly 20 minutes to stabilize, pupils dilate - more light enters eye and hits retina; regeneration of unbleached rhodopsin can increase sensitivity to light by >1,000,000x

Question 28

light adaptation

Answer 28

~5 minutes to stabilize pubils constrict - less light reaches retina cones transition from maximally hyperpolarized to gradually depolarized Na+/Ca2+ channels gradually reopen, establishes new baseline; absolute light level is lost but relative changes can now be sensed

Question 29

ON and OFF bipolar cells

Answer 29

ON bipolar cells: GPCR, responds to glutamate by hyperpolarizing and releasing less glutamate OFF bipolar cells: ionotropic (glutamate gated Na+ channel); responds to glutamate by depolarizing and releasing more glutamate

Question 30

retinofugal projection

Answer 30

neuronal pathway that projects away from retina

Question 31

image forming vision

Answer 31

right and left hemifields small number of optic tract axons connect to hypothalamus ~10% form connections in the midbrain most ~88% innervate lateral geniculate nucleus (LGN) of the dorsal thalamus neurons in LGN project to primary visual cortex via optic radiation

Question 32

macular degeneration

Answer 32

degeneration of macula, including fovea and surrounding region loss of central region

Question 33

retinitis pigmentosa

Answer 33

heretidary disease, initially affects rods and peripheral vision progresses to cones and then blind

Question 34

lateral geniculate nucleus (LGN)

Answer 34

little or no information process beyond this structure done in retina two hypothesis as to why this does information processing: 1. brings retinotopic maps from both eyes into register to make easy for the cortex to combine inputs from both eyes 2. only 10% of inputscome from the retina, and the other 90% are modulatory inputs from the cortex and brainstem - if instead all of these modulatory inputs fed back to the retina you'd have a blind spot 10x bigger due to huge increase in neuronal matter

Question 35

retinal input into lgn

Answer 35

structure in each hemisphere receives input from temporal retina of ipsilateral eye and the nasal retina of contralateral eye

Question 36

dorsal pathway

Answer 36

visually guided movement

Question 37

ventral pathway

Answer 37

object recognition

Question 38

what is the role of the inferior temporal cortex

Answer 38

facial recognition