Sense Organs Flashcards
define receptors
any specialised tissue or cell sensitive to a specific stimulus
orbits
eyes are located in these deep sockets
on the front side of the head
tear glands
at the upper sideward portion of orbit
6 to 12 glands present
function of lacrimal gland
- blinking spreads the liquid which acts as lubricant
- washing away dust
- antiseptic due to lysozyme which kills germs
- tears communicate emotions
conjuctiva
thin membrane covering front part of the eye
continuous with the inner lining of eyelids
layers of wall of eyeball
- outer sclerotic
- middle choroid
- inner retina
sclerotic layer
tough fibrous tissues
white in colour
bulges out and becomes transparent in front, where it covers the coloured part of eye, called cornea
choroid layer
blood vessels for nourishment
contains melanin which prevents light rays from reflecting and scattering inside eye
in front, choroid expands to form ciliary body
iris
extension of choroid
function of radial muscles in iris
widen the pupil- adjust amount of light entering
function of circular muscle
constrict the pupil
rod cells in retina
sensitive to dim light
do not respond to colour
contain rhodopsin/ visual purple
throughout retina
cones in retina
sensitive to bright light
responsible for colour vision
iodopsin/ visual violet
only in yellow spot
yellow spot
AKA macula lutea
at the BACK OF THE EYE, CENTRE ON THE HORIZONTAL AXIS OF EYEBALL
has maximum sensory cells
region of brightest vision
blind spot
LATERAL TO YELLOW SPOT ON NASAL SIDE
no sensory cells
all sensory cells’ nerve fibres converge and bundle together here to leave as optic nerve
lens
transparent, flexible, biconvex
just behind the pupil
contains lens fibres transparent
suspensory ligaments
lens is held in position by these fibres, and are attached to ciliary body
ciliary body
at junction of choroid and iris
contains muscles which on contraction/relaxation, change shape of lens for viewing different distances
chambers of eye
- aqueous
- vitreous
aqueous humour
between lens and cornea
- keeps lens moist
- protects from shock
- refracts light
aqueous humour is clear watery liquid
vitreous chamber (humour)
behind the lens
- helps in keeping shape of eyeball
- protects retina and its ending
vitreous humour is jelly-like thicker fluid
define accomodation
the process of focusing the eye to see objects at different distances, brought about by making a change in the curvature of elastic lens (by ciliary muscles)
dark adaptation due to
- regeneration of rhodopsin, which was earlier broken down due to light
- dilation of pupil
light adaptation due to
1.visual purple of rods is bleached
2. pupil constricts
myopia caused due to
- eyeball is lengthened from front to back
- lens is too curved
corrected by concave lens
hypermetropia due to
- shortening of eyeball from front to back
- lens is too flat
astigmatism
when some objects are seen in focus while others are blurred
- uneven curvature of cornea
corrected by cylindrical lenses
presbyopia
lens loses flexibility
cannot see near objects clearly
convex lens
cataract
- lens turns opaque, vision is cut down to blindness
use highly convex lens, remove lens, small plastic lens behind or front of the iris
night blindness
- non formation of rhodopsin
- deficiency of vit A which is required for synthesis of pigment
colour blindness
- due to genetic defect
rare in females
corneal opacities
- cornea gets scarred and turns opaque/white
can cause irritation or vision problems or blindness
defective cornea is replaced with healthy cornea
squint
two eyes converge- cross eye
two eyes diverge- wide eye
may cause double vision/ diplopia
fixed by surgery and exercise
functions of ear
- hearing
- body balance
divisions of ear
- outer
- middle
- inner
outer ear
- projecting part called pinna/ auricle
- auditory canal leading to ear drum/tympanum
middle ear
- malleus, incus, stapes
- eustachian tube connects cavity of middle ear to throat
oval window and round window
oval- membrane covered opening leading to inner ear
round- membrane covered, connects middle and inner ear
inner ear
AKA membranous labyrinth
1. cochlea
2. semicircular canals
3. vestibule
cochlea
spiral shapes, looks like snail shell
has two and a half turns
inner winding is divided into 3 parallel canals
middle canal has areas possessing sensory cells
sensory cells lie on basilar membrane
organ of Corti
lie in the middle canal of the cochlea
possess sensory cells
spiral organ
semicircular canals
set of 3
arranged at right angles to each other in three different planes (one horizontal, two vertical)
ampulla
one end of each semicircular canal is widened to form ampulla
contains sensory cells for dynamic balance while body is moving
vestibule
short stem joining the bases of semicircular canals to the cochlea have UTRICULUS and SACCULUS
contain sensory cells for static balance when body is not moving
function of eustachian tube
equalises air pressure on either side of ear drum, allowing it to vibrate freely
why is vibration of stapes amplified
due to lever like action of the first two ossicles
