in diameter and consists of tissues present in three
concentric layers :- Outermost fibrous layer consists of sclera and cornea.
- middle vascular layer (also called uvea) consists of
choroid, ciliary body and iris. - Innermost nervous layer consists of retina.
a. fibrous coat
(i) Sclera
• It is an opaque, fibro-elastic collagen capsule that
forms the outermost covering.
• It is bluish white in appearance, except at the front,
where it forms the transparent cornea.
• It forms the posterior 5/6th part of the eye ball.
• Sclera maintains the shape of the eyeball and protects
all the inner layers of the eye.
(ii) Cornea
• It is a thin transparent, front part of sclera that forms
a slight bulge (called conjunctiva) at the front, and
covers about 1/6th part of the sclera.
• It lacks blood vessels but is rich in nerve endings, and
absorbs oxygen from air.
• Stimulation of nerve endings reflexly causes blinking
and tear flow.
• The cornea is kept moist by tears and
mucus from conjunctival and lacrimal
glands.
• as cornea is avascular so its
living materials e.g., epithelium,
and endothelium get nutrition from
aqueous humour, and from super
marginal plexus of blood vessels.
Therefore, corneal transplant is
easiest, with over 90% success rate.(cilia), membranes and opening specific Na+ and K+
channels. This leads ultimately to an action potential that
is conducted to the first relay station in the olfactory
bulb.• The fibres of the olfactory nerves synapse with mitral
cells (second order neurons) in complex structures
called glomeruli (balls of yarn). When the mitral cells
are activated, impulses travel from the olfactory bulbs
via olfactory tracts to main destinations (e.g., temporal
lobe of the cerebrum).
DiSorDerS of Smell anD taSte
• Anosmia – Loss of the ability to smell.
• Hyperosmia – Increased sensitivity to odours.
• Dysosmia – Disagreeable or distorted sense of smell.
• Hyposmia – Diminished sense of smell.
• Hypogeusia – Diminished sense of taste.
• Ageusia – Loss of the sense of taste (Eg. Whales)
• Dysgeusia – Distorted sense of taste.
• Sinusitis – an infection of the sinuses (cavities, or air-
filled pockets) near the nose. These infections usually
occur after a cold or after an allergic inflammation.
• Rhinitis – Inflammation of the nasal mucous membrane.
• Rhinorrhoea – Nasal flow.
Human eye
• The organs of sight are a pair of eyes in
human. The eyes are situated in deep
protective bony cavities, called the
orbits or eye sockets of the
skull. The study of structure,
function and diseases of the
eye is called ophthalmology.
Structure of the eye
• human eyes are spherical
structures. Each eye is about 2.5 cm