physiology of sight and hearing

Question 1

what parts of eye are made of type 1 collagen

Answer 1

cornea

sclera

Question 2

how is aqueous humor made and drained. what is its function

Answer 2

made by ciliary body
drained by trabecular meshwork

nourishes anterior eye, removes debris from avascular anterior segments of eye, maintains the IOP (glaucoma)

Question 3

vitreous humor function

Answer 3

to provide structural support to eyeball

Question 4

outer segment of photoreceptors is where ABSORPTION of light occurs. what is the difference between outer segments of rods/cones

Answer 4

the outersegment consists of a STACK OF MEMBRANEOUS DISKS which contain the photo-pigments

rods= long, cylindrical outer segment with MANY disks

cones= short, tapering, with FEW disks

Question 5

what is the muller cell of the retina + its function

Answer 5

a glial cell of the retina found in the neuronal layer of retina

it ensheathes ALL retinal neurones –> mediates their function

Question 6

TOTAL colour blindness is called

Answer 6

achromatoposia

rare, GENETIC, cones are effected rods will work thus wont see any colour

Question 7

what is DICHROMACY

Answer 7

when one of the 3 basic colour mechanisms (red, green, blue) ARE NOT FUNCTIONING due to a MUTATION in one of the OPSINS for cones

Question 8

specific names for the three types of dichromacy

Answer 8

dueteranopia = green opsin mutated

protanopia = red opsin mutated

tritanopia = blue opsin mutated

red and green opsin genes are on the X-chromosome thus red-green colour blindness is x-linked

Question 9

conductive hearing loss is a result of

Answer 9

outer ear/ bone around outer ear is affected

Question 10

middle ear: impediance matching is what

Answer 10

1. 3 ossicles are connected in a way to act as a lever- 1:1:3 ratio
2. the oval window has smaller area than the tympanic membrane, causes an 18:1 increase in intensity of vibrations

Question 11

middle ear: attenuation reflex

Answer 11

tensor tympani = pulls the MALLEUS inwards, and stapedius muscle pulls the STAPES away from the oval window

protects against loud sound but 40-80ms delay
masks background noise
reduces sensitivity from our own voices

Question 12

function of the eustachian tube

Answer 12

connects the middle ear to the nasopharynx = equilibrates the pressure in the middle ear with the ATMOSPHERIC pressure. this is important because pressure differences cause decreased motion of the tympanic membrane thus reduction in hearing

Question 13

the stapes bone connects to which region of the cochlea

Answer 13

the oval window

Question 14

describe the dimensions of the cochlea with that of the basilar membrane

Answer 14

cochlea base is wide and apex is narrow. opposite is for BM

Question 15

difference in K+ concentration of the endolymph found in SM and the perilymph found in SV and ST

Answer 15

perilymph= low k+, found in SV and ST
endolymph= high k+, found in scala media

Question 16

function of the BM is to

Answer 16

differentiate between different sound frequencies BY allowing different frequencies to travel different DISTANCES along the BM

Question 17

organ of corti has how many hair cells

Answer 17

1 inner

3 outer

Question 18

features of cornea

Answer 18

a -vascular
transparent
continuos with sclera
made of type 1 collagen

Question 19

features of iris

Answer 19

thin
vascular
pigmented
has muscles which change diameter of pupil

Question 20

feature of lens

Answer 20

biconvex
its curvature is controlled by ciliary body (cillary muscles and zonule fibres)
clouding of lens= cataracts

Question 21

feature of aqueous humor

Answer 21

transparent gel like fluid which fills the anterior part of eye between lens and cornea
formed by the cillary body
drained by trabecular meshwork
function= to maintain the intra-ocular pressure (IOP)

increase in IOP due to degeneration of trabecular meshwork= Glaucoma

Question 22

features of sclera

Answer 22

white
opaque
made of type 1 collagen
continious with cornea

Question 23

features of vitreous humor/ body

Answer 23

tranparent gel

provides structure to eyeball, but we do not need it

Question 24

features of choroid

Answer 24

vascular connective tissue
contains melanin pigment
nourishes the outer 1/3 of retina
continous with the cillary body

Question 25

characteristics of rods and the rod system

Answer 25

rods:

1. high sensitivity to light (specialised for night vision)
2. 20x more common/ more photopigment (capture more light)
3. high amplification
4. low temporal resolution (slower response)
5. more sensitive to SCATTERED light

rod system:

1. low acuity, not present in fovea, highly convergent pathway
2. achromatic (one type of rod pigment)

Question 26

characteristics of cones and the cone system

Answer 26

cones:

1. lower sensitivity (because specialised for day vision)
2. less photopigment
3. lower amplification
4. high temporal resolution (fast response)
5. more sensitive to DIRECT light rays

cone system:

1. high acuity, concentrated in fovea with a 1:1 ratio of cones to GANGLION cells, dispersed pathway
2. trichromatic (3 types of cone pigment, each with a different wavelength preference)

Question 27

what are thought to be the 2 cortical streams of visual processing

Answer 27

1. striate cortex towards the parietal lobe (visual motion)

2. striate cortex towards the temporal lobe (for recognition of objects)