physiology of sight and hearing Flashcards
what parts of eye are made of type 1 collagen
cornea
sclera
how is aqueous humor made and drained. what is its function
made by ciliary body
drained by trabecular meshwork
nourishes anterior eye, removes debris from avascular anterior segments of eye, maintains the IOP (glaucoma)
vitreous humor function
to provide structural support to eyeball
outer segment of photoreceptors is where ABSORPTION of light occurs. what is the difference between outer segments of rods/cones
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
what is the muller cell of the retina + its function
a glial cell of the retina found in the neuronal layer of retina
it ensheathes ALL retinal neurones –> mediates their function
TOTAL colour blindness is called
achromatoposia
rare, GENETIC, cones are effected rods will work thus wont see any colour
what is DICHROMACY
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
specific names for the three types of dichromacy
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
conductive hearing loss is a result of
outer ear/ bone around outer ear is affected
middle ear: impediance matching is what
- 3 ossicles are connected in a way to act as a lever- 1:1:3 ratio
- the oval window has smaller area than the tympanic membrane, causes an 18:1 increase in intensity of vibrations
middle ear: attenuation reflex
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
function of the eustachian tube
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
the stapes bone connects to which region of the cochlea
the oval window
describe the dimensions of the cochlea with that of the basilar membrane
cochlea base is wide and apex is narrow. opposite is for BM
difference in K+ concentration of the endolymph found in SM and the perilymph found in SV and ST
perilymph= low k+, found in SV and ST endolymph= high k+, found in scala media
function of the BM is to
differentiate between different sound frequencies BY allowing different frequencies to travel different DISTANCES along the BM
organ of corti has how many hair cells
1 inner
3 outer
features of cornea
a -vascular
transparent
continuos with sclera
made of type 1 collagen
features of iris
thin
vascular
pigmented
has muscles which change diameter of pupil
feature of lens
biconvex
its curvature is controlled by ciliary body (cillary muscles and zonule fibres)
clouding of lens= cataracts
feature of aqueous humor
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
features of sclera
white
opaque
made of type 1 collagen
continious with cornea
features of vitreous humor/ body
tranparent gel
provides structure to eyeball, but we do not need it
features of choroid
vascular connective tissue
contains melanin pigment
nourishes the outer 1/3 of retina
continous with the cillary body
characteristics of rods and the rod system
rods:
- high sensitivity to light (specialised for night vision)
- 20x more common/ more photopigment (capture more light)
- high amplification
- low temporal resolution (slower response)
- more sensitive to SCATTERED light
rod system:
- low acuity, not present in fovea, highly convergent pathway
- achromatic (one type of rod pigment)
characteristics of cones and the cone system
cones:
- lower sensitivity (because specialised for day vision)
- less photopigment
- lower amplification
- high temporal resolution (fast response)
- more sensitive to DIRECT light rays
cone system:
- high acuity, concentrated in fovea with a 1:1 ratio of cones to GANGLION cells, dispersed pathway
- trichromatic (3 types of cone pigment, each with a different wavelength preference)
what are thought to be the 2 cortical streams of visual processing
- striate cortex towards the parietal lobe (visual motion)
2. striate cortex towards the temporal lobe (for recognition of objects)
