Senses

Question 1

fovea

Answer 1

where photoreceptors are most dense

Question 2

structure of retina

Answer 2

highly organised layered structure

light from bottom/back where ILM/muller cell endfeet
photoreceptors at opposite end

info from photoreceptors to ganglion cells, axon from ganglia cells form optic nerve

Question 3

why does light come in at opposite end to where photoreceptors are?

Answer 3

don’t want light to bounce around eye ball because won’t be able to see if light is scattered
retinal pigment epithelial is black so light can’t get reflected off so can be detected here

Question 4

photoreceptors

Answer 4

in rod cell
outer segement where photopigment is located on discs
cone cell also has outer segment

Question 5

rods

Answer 5

high sensitivity
low temporal resolution
more sensitive to scattered light
low acuity
achromatic

496nm

Question 6

cones

Answer 6

lower sensitivity
high temporal resolution
most sensitive to direct axial rays
high acuity
trichromatic

419, 531, 559nm

Question 7

rhodopsin

Answer 7

photopigment

Question 8

light hits rhodopsin

Answer 8

light turns 11-cis retinal to all-trans retinal
changes conformation of opsin (ligand binding to GPCR) - activates transducin (specialised G protein)

trans-retinal dissociates from protein and recycled back to cis via retinal pigment epithelium (which is why outer segments of photoreceptors close association with pigment epithelium)

Question 9

ganglion cells have receptive fields

Answer 9

light into central field: ganglia excited and AP

light in outer circle: inhibit AP

(off centre field has opposite effect)

Question 10

receptive fields

Answer 10

are concentric

Question 11

photoreceptors and receptive fields converge..

Answer 11

onto bipolar cell and then ganglion cell

light not on ganglion cell itself but on receptors wired to ganglion cell

Question 12

convergent signalling in retina

Answer 12

2 ganglion cells with receptive fields adjacent to each other
they share photoreceptors so receptive field contribute to both ganglion cells

Question 13

photoreceptor to bipolar cells, on-centre

Answer 13

voltage response in wrong direction
retina turns upside down
glutamate as NT but can be inhibitory in retina
more depolarisation means more glutamate (off-centre)

on centre: glutamate inhibits so light causes less glutamate so less inhibition and depolarisation in bipolar cells.

Question 14

on-centre ganglion cells

off-centre

Answer 14

signal rapid increases in light intensity

signal rapid decreases in light intensity

Question 15

lateral geniculate neurones have…

Answer 15

concentric visual fields

Question 16

M channel

P channel

Answer 16

analysis of movement

analysis of fine detail and colour

Question 17

receptive fields of simple cells in visual cortex

Answer 17

rectangle
specific retinal position
discrete excitatory and inhibitory regions
specific axis of orientation
all axes of orientation are represented for each part of the retina

Question 18

complex cells

Answer 18

no on off surround
sensitive to bar of light along long axis but has to be moving
for firing if bar not orientated properly

Question 19

general principles on eye lecture

Answer 19

convergent processing
receptive fields
hierarchial processing
ordered maps in the brain

Question 20

rods and cones are not the only photoreceptors in the retina

Answer 20

light sensitive ganglion cells (ipRGC)

Question 21

melanopsin

Answer 21

ancient opsin in ipRGC

control how pupil dilates and light entrained circadian clock

Question 22

P

Answer 22

sound pressure

Question 23

loudest tolerable sound

Answer 23

120dB SPL

Question 24

basilar membrane

Answer 24

mechanical analyser of sound
3 compartments of cochlea are filled with fluid
IHC inner hair cell
OHC - outer

width varies along its length
membrane thin and floppy at apex and thicker and taught at base
thick stiff - high frequency sounds

Question 25

vibrations of the basilar membrane

Answer 25

round window pushed out while oval window pushed in because fluid goes round
creates standing wave, created at place depending on frequency

Question 26

hair cells

Answer 26

sound transducing components of cochlea
hair cells have sterocilia - organise and in contact with tectorial membrane
hair cells vibrate and cause potential in hair cells

Question 27

vibrations of basilar membrane

Answer 27

presses against tectorial membrane and sterocilia of hair cells are deflected in a direction

Question 28

why are different hair cells in diff locations

Answer 28

look at sound frequency most efficient at activating each hair cell, so need to be in diff places to be efficient

Question 29

why must there be a way to amplify sound especially at low sound intensities?

Answer 29

sensitivity of cochlea too great and frequency selectivity too sharp to result solely from passive mechanical properties

Question 30

active mechanisms of the cochlea

Answer 30

outer hair cells change their length in response to sound
pulls on membrane
triangle vibrates
and amplifies souns because making vibrations bigger

Question 31

prestin

Answer 31

motor protein in plasma membrane
mechanosensitive ion channels in sterocilia open when sterocilia pressed
current changes membrane potential of outer hair cells and change in motor protein in membrane (conformational change)

OHC doesn’t develop without prestin

Question 32

499 prestin mutation

Answer 32

no voltage sensitive conformational change (change length)
removes electromotility from hair cells
increases threshold for hearing across the frequency range

Question 33

mechanosensitive ion channels

Answer 33

hardly any effect on hearing when knock it out
maybe few channels only in stereocilia
potassium and calcium entry

Question 34

how are potential generated in hair cells?

Answer 34

movements of cilia generate membrane potential - graded with changes in potential in stereocilia

Question 35

scala vestibuli and scala tympani have…

Answer 35

normal extracellular fluid

high sodium, low potassium

Question 36

scala media

Answer 36

high potassium in fluid

because of stria vascularis (spiral ligament)

Question 37

stria vascularis

Answer 37

contains marginal cells - with tight junctions between them

secretes potassium rich scala media

Question 38

endocochlear potential

Answer 38

80mV - 120mV
provides driving force on potassium to give inward currents into hair cells during mechanosensory transduction

potassium through gap junctions through basal cells to intermediate cells where pumped out/ion channels into space
marginal cells pumping potassium out cells so potassium can diffuse in

then through potassium ion channels to endolymph - creates endocochlear potential

like opposite resting potential

Question 39

hearing loss

Answer 39

1:800 children born with hearing impairment

> 60% of people older than 70

> 50 chromosomal loci associated with non-syndromic hearing loss

> 14 genes identified

Question 40

GJB2 (Cx26) mutation

Answer 40

most common hearing loss
K recycling
reduce endocochlear potential
interfere with cochlear development if deletion early (postnatal days)
later on deletion - doesn't affect

hair cell degeneration
less electromotility

Question 41

each spiroganglia cell inovates only 1 hair cell, why?

Answer 41

separate sound frequencies

Question 42

first place to get input from both ears

Answer 42

medial superior olive - spatial localisation of sound

Question 43

Wernicke’s area

Broca’s area

Answer 43

language comprehension

language production