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AN ASSINGMENT ONPHYSIOLOGY OF
SENSE ORGAN : EYE
SUBMITTED BY: Sudipta Nag Himel(11/26)
UNDER THE DEPARTMENT OF PHARMACOLOGY, BIOCHEMISTRY & PHYSIOLOGY
An undergraduate student ofChittagong Veterinary and Animal Sciences University
Khulshi, Chittagong-4225.
Eyes are the paired organs that detect light and convert it into electro-chemical impulses in neurons.
EYE : The organ of VISION
Types of eye:Simple eye
is presence in all
chordates Compound eye
is presence in case of
arthopods
Parts of EYE
EYEcomponent mainly
divided into
2parts
• Three layers: – Fibrous outer layer
• Sclera• Cornea
– Vascular middle layer• Choroid, • Ciliary body and • Iris
– The inner nervous layer• Retina • Pupil
• Structures inside the eyeball are the lens, aqueous fluid and vitreous body.
1.EyeballParts of EYE
2.Accessory structures • Conjunctiva
• Eyelid
• Eyelashes
• Lacrimal gland
• Extraocular muscles
Parts of EYE
Sclera“White part of the eye”
Maintaining the shape and form
of the eye ball.
Contains BVs and insertion site
for extrinsic eye muscles.
CorneaThin, transparent epithelium
Allow the free entry of light.
Act as refractive media.
Fibrous outer layer
Iris “Colored part” of the eye which contains BVs, pigment cells, loose connective tissue and pupillary muscle.
Adjusts the pupilRegulates amount of light
Vascular middle layer
Choroid– Pigmented to absorb excess
light– Supplies the retina with
nutrients and oxygen via blood supply
Vascular middle layer
Ciliary BodyRing of smooth muscle around lens
Regulates the shape of the lens for accommodation
Suspensatory Ligaments– Attach the ciliary body to the lens
The retinaThe inner nervous layer
FunctionsIt helps in
Photopic visionScoptic visionMesopic visionSteroscopic visionAcuity of visionColor visionPerception of movement
Retinais a light-sensitive layer of tissue, lining the inner surface of the eye.
The retinaThe inner nervous layer
Cells of retina-I. Photoreceptor cellsII. Bipolar cellsIII.Horizental cellsIV.Amacrine cellsV. Ganglion cells
• The photo receptor cells are 2 types -
(1)The cone cells
(2)The rod cells
Difference betweem CONE cell and ROD cell
Property Cones Rods
Location In the fovea Outside the fovea
Resolution and visual acuity
Large Small
Total number of elements
5 million 120 million
Color sensitivity Yes No
Brightness sensitivity Small, for daylight vision
Large, for night vision
Figure
The retinaThe inner nervous layer
The macula lutea and fovea centralis
The blind spotRetinal blood vessels.
Macula luteaMacula lutea
Vein Vein
Optic disc Optic disc
Artery Artery
Special Areas of the Retina
Fovea centralis (fovea) is a depresion, located in the center of the macula region of the retina.
The macula or macula lutea is an oval-shaped highly
pigmented yellow spot near the center of the retina
The inner nervous layer
Is a hole located in the center of the iris.
It helps to pass the light into the eye.
Pupil
Structures inside the eyeball
Cavity of EYEThe lens and ciliary body
divide the eye into two cavities.The anterior cavityThe posterior cavity
LensClosely-packed concentric
columnar cellsFocuses image on the retina.
Contains aqueous humor which is secreted by ciliary body
Maintains shape of anterior eye.
Constantly produced - leaves eye thru canal that carries it to bloodstream.
Anterior Chamber of Eye
Anterior Chamber
Contains vitreous humor
Maintains shape of posterior eye.
Refracts light rays.
Is not constantly being produced. Loss of vitreous humor may mean loss of eye.
Posterior Chamber of Eye
Vitreous Chamber
Lacrimal gland The lacrimal glands are the sites of tear
production.
Tears function to keep the conjunctiva
and corneal epithelium moist and
wash away foreign material from the
eye.
Accessory structures
Lacrimal apparatusSecretes and drains tears from the eye
Accessory structures
Eyelashes
Eyelashes are short hairs of eye that
may occur in double or triple rows.
They function to protect the eye
from debris.
Lashes may also have
different lengths and
diameters to one another.
Accessory structures Conjunctiva The conjunctiva refers to the lining of the
eye.
It has 2 parts
Palpebral conjunctiva
Bulbar conjunctiva
It helps lubricate the eye by secreting
mucous, and serves as a protective
barrier again microbes.
It contains many goblet cells which
secrete a component of the tears that
bath the eye.
Accessory structures
Eyelid The main function of the eyelid
is to provide the eye with
protection. There are several
types of glands in the eyelids,
including tarsal glands that
produce a sebaceous secretion
that results in an oily surface of
the tear film to prevent the
evaporation of the normal tear
layer.
Accessory structures
Extraocular Muscles
i. Rectus dorsalis
ii. Rectus ventralis
iii. Rectus medialis
iv. Rectus lateralis
v. Obliqus dorsalis
vi.Obliqus ventralis
Functions of Extraocular MusclesIO SR IO/SR SR/IO SR IO
LR MR MR LR
SO IR SO/IR IR/SO IR SO
MR MR
CONVERGENCE
These six muscles responsible for eye movement.
Four rectus muscles control the movement of the eye in
the four cardinal directions:
Up,
Down,
Left and
Right.
The remaining two muscles control the adjustments
involved in counter acting head movement.
Light
Refraction
• Cornea and lens
Accommodation
Photo-pigments
Photo-transduction
Photoreceptor activity
• In the dark
• When exposed to light
Vision Steps of vision
Visual Pathway
Pathway of
LIGHT
Refraction is the phenomenon which makes image formation possible by the eye as well as by cameras and other systems of lenses.
The eye, is optically equivalent to the usual photographic camera.
The lens system of the eye is composed of four refractive interfaces.
Formation of an Image on the Retina.
The lens system of the eye can focus an image on the retina. The image is inverted and reversed with respect to the object. However, the mind perceives objects in the upright position because the brain is trained to consider an inverted image as the normal.
The Eye as a CameraRefraction
AccommodationThe process of changing the
shape of the lens while focusing on an object is termed as accommodation.
At rest focused on distant objects, needs to increase focal power than focus on close objects.
The ciliary muscles contract and release tension in the ligaments and the lens becomes rounder in case of close objects.
There are four types of photopigments, one in the rods and one in
each of three types of cones.
The pigment in the rods is called rhodopsin.
Rhodopsin absorbs all visible wavelengths, so that rods
provide vision only in shades of grey by detecting different
intensities rather than colours.
The three types of cones - red, green and blue
photopsin, can respond selectively to various
wavelengths of light, giving rise to colour vision.
Photopigments
Rhodopsin
๑ The photon is absorbed by rhodopsin. ๑ The light receptor molecule tightly-packed in the
disk membranes
๑ One rod contains 10 billion rhodopsin molecules, which ensures an optimum photon capture rate
Rhodopsin has 2 components Retinal- Vitamin A aldehydeOpsin- single polypeptide
containing 7 transmembrane domains
RHODOPSIN CYCLE
ROLE OF VITAMIN A FOR FORMATION OF RHODOPSIN.
Vitamin A is present both in the cytoplasm of the rods and in the pigment layer of the retina. Therefore, vitamin A is normally always available to form new retinal when needed.
Conversely, when there is excess retinal in the retina, it is converted back into vitamin A, thus reducing the amount of light-sensitive pigment in the retina.
Night blindness.
The retina therefore signals the brain
Light stimulation through an inhibitory response involving a series of
physiological reactions
Action potentials, Only originate in the ganglion cells,
The first neurons in the chain that carry the visual stimuli to the brain.
Vision occurs
This process is called phototransduction.
Phototransduction
ERRORS OF REFRACTION• Astigmatism– defective
curvature of the cornea or lens of the eye.
• Presbyopia– impaired vision of the cornea or lens of the eye, associated with aging.
• Hyperopia– can’t see close objects, rays of light focus behind retina
• Myopia- can’t see far away objects, rays of light focus in front of the retina
COMMON DISORDERS OF THE EYE
(A) Acute bacterial conjunctivitis.
(B) Anisocoria.
(C)Color Blindness Monochromacy
lack of 2 of the 3 types of
cones Dichromacy:
lack of 1 type of normally-function cones
Anomalous trichromacy shift in the normal spectrum
Visual loss
Double vision
Severe eye pain
Foreign body sensation
Some other Symptoms found in a serious
Ocular condition
Internet
ReferencesBooks
Textbook of medical physiology / C. Guyton, John E. Hall.—11th ed
Review of Medical Physiology / William F . Ganong .—22nd ed
Animal Physiology /Eckert & Randall -2nd ed
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