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Parts of the Eye
The pupil is a circular opening located in the center of the iris of the eye that controls the amount of light that
enters the eye.
The lens is a transparent, biconvex structure in the eye that, along with the cornea, helps to refract light to be
focused on the retina. The lens, by changing shape, functions to change the focal distance of the eye so that it
can focus on objects at various distances, thus allowing a sharp real image of the object of interest to be
formed on the retina. This adjustment of the lens is known as accommodation . It is similar to the focusing of a
photographic camera via movement of its lenses.
The iris is a membrane in the eye, responsible for controlling the amount of light reaching the retina. The iris
consists of two layers, the front pigmented fibro vascular tissue known as a stroma and beneath the stroma are
pigmented epithelial cells. The iris can be green, blue, or brown
The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Together
with the lens, the cornea refracts light, accounting for approximately two-thirds of the eye's total optical power.
The ciliary body is the circumferential tissue inside the eye composed of the ciliary muscle and ciliary
processes.[1] It is triangular in horizontal section, and is coated by a double layer, the ciliary epithelium. The
inner layer is transparent and covers the vitreous body, and is continuous from the neural tissue of the retina.
The outer layer is highly pigmented, continuous with the retinal pigment epithelium, and constitutes the cells of
the dilator muscle.
The choroid, also known as the choroidea or choroid coat, is the vascular layer containing connective
tissue, of the eye lying between the retina and the sclera. In humans its thickness is about 0.5 mm. The
choroid provides oxygen and nourishment to the outer layers of the retina . Along with the ciliary body and iris,
the choroid forms the uveal tract.
The vertebrate retina is a light sensitive tissue lining the inner surface of the eye. The optics of the eye create
an image of the visual world on the retina, which serves much the same function as the film in a camera. Light
striking the retina initiates a cascade of chemical and electrical events that ultimately trigger nerve impulses.
These are sent to various visual centers of the brain through the fibers of the optic nerve.
The fovea, also known as the fovea centralis, is a part of the eye, located in the center of the macula region
of the retina. [1] [2] The fovea is responsible for sharp central vision (also called foveal vision), which is
necessary in humans for reading, watching television or movies, driving, and any activity where visual detail is
of primary importance.
The optic nerve, also called cranial nerve II. The optic nerve transmits visual information from the retina to
the brain. It connects to the back of the eye near the macula. When examining the back of the eye, a portion
of the optic nerve called the optic disc can be seen.
Parts of the Ears
The Auricle is the outer part of the ear, it is also called Pinna. The purpose of the Auricle is to collect sound. It
does so by acting as a funnel, amplifying the sound and directing it to the ear canal. While reflecting from the
Auricle, sound also goes through a filtering process which adds directional information to the filtering effect of
the human Auricle preferentially selects sounds in the frequency range of human speech. In various species,
the Auricle can also signal mood and radiate heat.
The ear canal (external auditory meatus, external acoustic meatus), is a tube running from the outer ear to
the middle ear. The human ear canal extends from the Auricle to the eardrum and is about 26 mm in length
and 7 mm in diameter.
The tympanic membrane (also called Eardrum), is a thin membrane that separates the external ear from the
middle ear. Its function is to transmit sound from the air to the ossicles inside the middle ear. The malleus bone
bridges the gap between the eardrum and the other ossicles. Rupture or perforation of the eardrum can lead to
conductive hearing loss.
The semicircular canals are three half-circular, interconnected tubes located inside each ear. The three
canals are the horizontal semicircular canal (also known as the lateral semicircular canal), superior
semicircular canal (also known as the anterior semicircular canal), and the posterior semicircular canal.
The ossicles (also called auditory ossicles) are the three smallest bones in the human body. They are
contained within the middle ear space and serve to transmit sounds from the air to the fluid-filled labyrinth
(cochlea). The absence of the auditory ossicles would constitute a moderate-to-severe hearing loss. The term
"ossicles" literally means "tiny bones" and commonly refers to the auditory ossicles, though the term may refer
to any small bone throughout the body.
The Eustachian tube (or auditory tube) is a tube that links the pharynx to the middle ear. In adults the
Eustachian tube is approximately 35 mm long. It is named after the sixteenth century anatomist Eustachius.
Some modern medical books call this the pharyngotympanic tube.
The cochlea is the auditory portion of the inner ear. Its core component is the Organ of Corti, the sensory
organ of hearing, which is distributed along the partition separating fluid chambers in the coiled tapered tube of
the cochlea.
The Eighth Nerve (also known as the vestibulocochlear nerve) is the eighth of twelve cranial nerves, and is
responsible for transmitting sound and equilibrium (balance) information from the inner ear to the brain.