SPECIAL SENSES

Eye

the organ of sight and consist of eyeball and its accessory structures.

Extraocular muscles

Associated with the bulb of the eye are — that move it

Periorbital fascia

Surround and cushion the eye

Eyelids and conjunctivae

Protect the eye

Lacrimal apparatus

Keeps surface if the eye moist, provides the first barrier to infection, and helps to nourish the cornea.

Upper and lower eyelids (superior and inferior palpebrae)

two movable folds protecting the rostral surface of the eyeball.

Tarsus

is the fibrous plate supporting the margin of the eyelid. It contains the tarsal (meibomian) gland.

Cilia or eyelashes

hairs coming out of the eyelids.

Lateral and medial commissures or canthi

point where the eyelids meet.

Lacrimal caruncle

triangular prominence in the medial angle

Lacrimal puncta

openings into the lacrimal canals on upper and lower eyelids near the medial angles

Conjunctiva

special mucous membrane lining the eyelid and eyeball.

Palpebral conjunctiva

Lines the inner surface of the eyelid.

Bulbar conjunctiva

is the reflection of the palbebral conjunctiva onto the eyeball.

Nictitating membrane

third eyelid, fold of conjunctiva located between the eyelid’s medial angle and eyeball

Fibrous tunic

outer coat of the eyeball. It is divided into sclera and cornea.

Sclera

the white part of the eye. It is the caudal part of the fibrous coat consisting of fibrous tissue. It gives shape and protects the inner structures of the eye

Cornea

transparent anterior coat of the fibrous coat that lets light into the eyeball.

Limbus

junction between the sclera and cornea

Vascular tunic

middle layer of the eyeball composed of the ciliary body, choroid and iris. They are composed mainly of blood vessels and smooth muscles that supply the nutrition to the eyeball.

Choroid

posterior part of the vascular tunic. It is a thin, dark, highly vascular membrane inside the sclera.

Tapetum lucidum

is a specialized refractive area of the choroid and the reason for the glowing of eyes when shined with light.

Ciliary body

thickest portion of the vascular tunic between choroid and iris. It consists of ciliary muscle and ciliary process.

Ciliary muscles

are smooth muscles that alter the shape of the lens (accommodation)

ciliary process

are folds on the inner surface of the ciliary body that anchor the zonular fibers.

Zonular fibers

are the suspensory ligaments that hold the lens in position.

Iris

colored part of the eye surrounding the pupil.

Pupillary constrictor

a circular smooth muscle constricting the pupil

Pupillary dilator

a radiating smooth muscle dilating the pupil.

Pupil

is the central opening of the iris that lets light into the eye.

Nervous tunic

Innermost layer of the eyeball. It is composed of the retina.

Retina

inner coat of the eye that function in image formation. It is contains 3 layers of neurons: photoreceptors, bipolar neuron and ganglion neurons

Photoreceptors

light sensitive and the first layer of retina.

Rods

dendrites sensitive to dim light (night vision) and shape while cones are dendrites

Cones

dendrites sensitive to color and sharpness of vision.

Bipolar neuron

intermediate layer of the retina which receives impulse form rods and cones and passes them to neuronal gangli

Ganglion neuron

inner layer of the retina which pass the impulse to the optic nerve

Optic disc

area on the retina where the axons from the ganglion neuron leave the eye as the optic nerve. Having no rods or cones, this is the blind spot.

Lens

transparent, biconvex body of the eye suspended behind the iris and zonular fibers.

• Anterior chamber

• Posterior chamber

• Posterior chamber

Chambers of the eye

Anterior chamber

space between the cornea and the iris

Posterior chamber

space between the iris and lens

Vitreous chamber

larger space between the lens and retina. It is filled with vitreous humorlarger space between the lens and retina. It is filled with vitreous humor

Aqueous humor

watery fluid, similar to cerebrospinal fluid, filling the posterior and anterior chamber. It is secreted by the ciliary processes into the posterior chamber and flows to the anterior chamber via the pupil. It maintains the intraocular pressure and as medium for nutrient and waste transport.

Vitreous humor

jelly-like substances that fills the vitreous chamber. It maintains the shape of the eye and holds the retina in place

Ear

the organ of balance and hearing. It is composed of three portions: outer, middle and inner ear.

Outer ear

is composed of the pinna and the external auditory meatus.

Pinna or auricle

the fleshy appendage attached to the side of the skull by muscles and ligaments. It functions to catch and direct sound waves toward the middle ear (ear drum)

Auricular cartilage

elastic framework of the pinna and external auditory meatus covered by skin.

External auditory meatus

passageway from the pinna to the ear drum

Anthelix

transverse fold of cartilage on the concave surface of the pinna

Scapha

large flat concave internal side of the auricle

Helix

entire free margin of the auricle and passing over the apex

Cutaneous marginal sac

Fold of skin at the proximal lateral portion of the helix

Tragus

thick blunt irregularly quadrangular plate of cartilage that projects from the rostral border of entrance to external auditory meatus

Antitragus

thin elongate projection of cartilage lateral to the tragus

Intertragic incisures

notch separating the tragus and antitragus

Middle ear

part of the ear inside the tympanic cavity containing the auditory ossicles and opening to the auditory tube

Tympanic membrane or ear drum

thin semi-transparent partition between the external auditory meatus and the middle ear. It is vibrated by the sound waves

Auditory ossicles

three bones extending across the middle ear from the ear drum to the oval window of the cochlear. They transmit and amplify vibrations from the ear drum

Malleus

hammer”, small bone connecting the inner surface of the inner surface of the tympanic membrane and the incus

Incus

“anvil”, ossicle between malleus and stapes

Stapes

“stirrup”, smallest bone of the body, base fits into the oval window.

Oval (vestibular window)

one of the two openings between the middle and inner ear. Filled by the base of the stapes

Round (cochlear window)

located below the oval window

Auditory (Eustachian tube)

passageway between the middle ear and the nasopharynx. It equalizes the pressure on both sides of the ear drum thus protecting it from rupture. Swallowing opens the auditory tube allowing air into the middle ear.

Inner ear

consists of bony and membranous labyrinth. The bony labyrinth, which lies within the petrous temporal bone. It is divided into three areas – the bony cochlea, bony vestibule and bony semicircular canals – each of which contains a corresponding part of the membranous labyrinth.

Perilymph

fluid within the bony labyrinth surrounding the membranous labyrinth

Endolymph

fluid within the membranous labyrinth

Cochlea

snail shell-like part of the inner ear associated with hearing. It has two channels: scala vestibule and scala tympani.

Scala vestibuli

canal of bony labyrinth communicating with the vestibule, middle ear at the oval window and scala tympani at the apex of cochlea.

Scala tympani

continuation of scala vestibule from the ape of cochlea to the round window.

Vestibule

central expanded portion of the inner ear. Consist of two sacs: saccule and utricle

Maculae

Both these structures (saccule and utricle) contain areas of sensory hair cells known as -

Otoliths

Maculae are surrounded by jelly-like material containing calcium carbonate particles or

Semicircular canal

three bony canals arising from the vestibule, arranged approximately at right angles at each other.

Ampulla

enlarged swelling at the end of each semicircular canal