PSL- CNS (Part 5, 6, 7, 8 )

Question 1

why does colour depend on wavelength of light

Answer 1

that is because light has a wavelength and a wavelength is a distance from one wave peak to another and different wavelengths correspond to different colours and wavelengths we normally see ranges from 400 nm for violet to 700 nm for red

Question 2

is our ability to see light restricted between 400nm and 700 nm

Answer 2

for most yes, but we can also see powerful infrared light and people with their lenses removed, they cna see ultraviolet

Question 3

why did evolution give us eyes that cna see 400-700 nm

Answer 3

because of the power in the sunlight peaks there and earth’s atmosphere is most transparent to these wavelengths

Question 4

what are the three types of cones that allow us to sense color

Answer 4

the three types are called based on the light they sense and they are red, green,and blue and amount of each in people vary but is is around 63% for red cones, 31% for green and only 6% for blue

Question 5

what is the reason that allow each cone type to sense different wavelengths

Answer 5

that is because each type has its own visual pigment just like rhodopsin for rods and each pigment will absorb different amount of light at each wavelength

Question 6

what is evolution behind the cones

Answer 6

blue cones evolved first and can be due to blue light penetrating sea water better than longer wavelengths while red and green evolved from common ancestor

Question 7

what is the light that each cone type prefer

Answer 7

red and green cone pigments prefer yellow and yellow-green light while blue prefer blue light and melanopsin pigments prefer blue as well

Question 8

how does brain infer colour from these three cones

Answer 8

it does so by comparing data from the three,
yellow light affect both red and green cones but not blue ones, so yellow light will hyperpolarize the red and green cones but not the blue cones so brain will interpert that activity as yellow
but brain cna be fooled that is why green and red lights will produce same activity so brain gets tricked and u see yellow even if there is no yellow light

Question 9

does that mean we can produce any colour just by mixing the 3 wavelengths

Answer 9

yes, because any colour we see correspond to pattern of activity in these 3 types of cones

Question 10

what is difference between spectal and extraspectal colours

Answer 10

spectal colours are the ones that can be evoked by light of a single wavelength, they are the rainbow colours
extraspectal are ones like purpule or white where they can be evoked only by mix of wavelengths

Question 11

what is example of ganglion cells that are combinations of cone signals

Answer 11

the R+G cells or yellow channels, are ganglion cells excited by red light and by green light
the R-G cells are ganglion cells excited by red light and inhibited by green, others can be G-R cells where they are inhibited by red and excited by green, and these two types are the red-green opponenet channels
some get excited by blue light and inhibited by green and red so they are the B-R-G cells which is same as B-(R+G) where R+G=yellow, and otehr are the yellow minus blue so R+G-B and these two types make the blue-yellow opponent channels

Question 12

what is the theory behind the opponent channels and after images

Answer 12

it is thought taht as you stare at something green, the G-R cells will gradually fatigue and when u look away, those fatigued lines will be less active than the R-G ones so you end up seeing red and similiar case for blue vs. yellow
however, the responsible cells aren’t sure if they are in retina, LGN or visual cortex

Question 13

what is teh common type of colour blindness

Answer 13

that would be the red-green colour blindness also known as daltonism as people have trouble distinguishing between those two colours

Question 14

how is colour blindness linked to chromosomes

Answer 14

it was the first human trait linked to chromosomes where the inheritance pattern for daltonism is that colour blind fathers will have colour blind sons and colour normal daughters as the genes for red and green cones visula pigment lie in X-chromosome and problem in these loci are cause of 95% of all variations in colour vision

Question 15

what is meant by reflectance for colour constancy

Answer 15

that intrinsic colour of surface is its reflectance as reflectance of surface is its tendancy to reflect certain wavelengths of light and absorb others and this reflectance carries information of teh object

Question 16

what is meant by colour constancy

Answer 16

that our brains usually infer reflectance so we see ripe banana as yellow even in green light

Question 17

what are the two main functions of our ear

Answer 17

hearinga nd equilibrium

Question 18

what is teh structural components of teh ear

Answer 18

external ear consist of pinna and ear cannal, it is sealed at its end by tympanic membrane(eardrum)
after eardrum comes the middle ear which is air filled space connected to pharynx by eustachian tube
the inner ear is the one that contain teh sensores: cholera is for hearing and vestibular apparatus is for equilibirum

Question 19

what is it that our ear preceive as sound

Answer 19

that is teh pressure waves where at peaks of teh waves, moelcules are crowded together and pressure is high and at the troughs the molecules are far apart and pressure is low

Question 20

what is frequency

Answer 20

frequency is number of waves peaks per second, we preceive frequency as pitch where low frequencies are low pitched sounds and high frequencies are high pitched
we as humans can hear sounds in range of 16-20000 Hz

Question 21

what is amplitude

Answer 21

teh pressure difference between peak and trough and it ius the main factor that determines our perception of loudness as larger amplitude mean louder sound
but loudness also depend on frequency because if sound is over the range then it wouldn’t sound loud

Question 22

what is role of eardrum

Answer 22

they get vibrated by sound waves and are what seperate the outer ear from middle ear

Question 23

if eardrum is seperating middle and outer ear, how does vibrations of sound waves reach inner ear

Answer 23

there are small bones that convey these vibrations through the middle ear as teh middle ear will vibrate malleu bone first which moves the incus and then the incus moves stapes and stapes push against teh oval window like piston

Question 24

what are the ossicles bones

Answer 24

they consist of these three small bones: malleus, incus, and stapes and are the smallest bones in the human body but they act as the lever system that carry vibration from eardrum to oval window

Question 25

where is the oval window

Answer 25

it is membrane between middle and inner ear

Question 26

where does oval window lead to

Answer 26

to choclea which contains the receptor cells

Question 27

what are the components of cochlea

Answer 27

it has teh vestibular duct and tympanic duct which contain the perilymph and these two ducts are resposnible for communication at helicotrema
it also contain the endolymph

Question 28

what happens in cochlea when oval window vibrates

Answer 28

it will setup waves in the perilymph as teh wave energy eneters cochlea and as it is moving through cochlea, it shakes the cochlear duct which contains the receptor cells and that wave will also exit into middle ear through another membrane called round window

Question 29

what is organ of corti and where is it found

Answer 29

it sits on the basilar membrane and under tectorial membrane
it contains the auditory receptor cells which are mechanoreceptores and they are known as hair cells as tehy aren’t neurons but epitherlial cells
these hair cells also have stiff hairs that are called stereocilia which extends ino tectorial membrane and they bend when waves in perilymph deform basilar and tectorial membrane

Question 30

how do these hair cells send signals to brain

Answer 30

when the cilias bend toward the lonest cilium, they excite its neuron as the hair cell depolarizes and releases neurotransmitter which activtaes primary snensory neuron and these axons form auditory nerve called cochlear nerve which is branch of cranial nerve eight

Question 31

what happens when cilia of hair cell bend away

Answer 31

when that happens the hair cell release less transmitter which causes hair cell to hypoerpolarize and release less neurotransmitter so it doesn’t excite the neuron as much

Question 32

why does basilar membrane respond to different frequencies at different points

Answer 32

because membrane is narrow and stiff near round and oval windows and wider and more flexible at the otehr end
so high frequency waves maximally displace membrane at oval window end, whiel low frequency waves maximally displace the other end
the brain will deduce frequency by notion of which hair cells are most active

Question 33

how do auditory signals pass to brain

Answer 33

there is one from each ear to both sides of the brain and the primary auditory cortex is A1 in temporal lobe

Question 34

how does brain localizes sounds

Answer 34

based on the loudness and timing as if teh sound is louder in right ear than left that emans sound is coming from right side of the head and if soudness reach right ear first, that means it is coming from right side

Question 35

what are teh three kinds of hearing loss

Answer 35

conductive hearing loss- sound can;t be transmitted through external or middle ear
sensorineural hearing loss- damage to hair cells or elsewhere in inner ear
central hearing loss- damage to cortex or pathway from cochlea to cortex

Question 36

how is conductive hearing loss distinguished from senorineural hearing loss

Answer 36

using Rinne test, hold the tuning fork against mastoid boen and then beside ear and ask when sound is louder as normally it is louder through the ear canal but if it is louder through bone then it is conductive loss
in Weber test, hold the tuning fork to patient’s forehead and in midline and ask which ear is it louder: in senorineural loss=louder in good ear, in conductive loss= louder in bad ear since it doesn’t ahve to compete with sounds heard through the ear canal

Question 37

how is equilibrium sensed by our ears

Answer 37

different parts of vestibular apparatus sense head position and motion
utricle and saccle contain hair cells that are activated when head tilts relative to gravity
semicircular canals are fluid filled hoops that detect head rotation as when head turns right the fluid in tubes sloshes leftward

Question 38

where do equilibirum pathways project to

Answer 38

mainly to cerebellum as vestibullar hair cells activate teh primarly sensory neurons of vestoibular nerve which branches of cranial nerve 8
these neurons may pass directly to cerebellum or synapse in medullar and tehn they procced to cerebellum or up through thalamus to cortex
the brain uses vestibullar information to infer position and motion and keeps us upright