Human Eye and Ear Anatomy: Functions and Structures

Eyebrow

Prevents sweat and debris from entering the eye

Eyelid

Protects and moistens the eye

Eyelashes

Protect the eye from debris and trigger blink reflex

Lacrimal sac

Collects tears from lacrimal canaliculi

Medial commissure

Corner of the eye near the nose where eyelids meet

Lacrimal caruncle

Small pink nodule at medial commissure containing sweat and sebaceous glands

Lacrimal gland

Produces tears

Lateral commissure

Outer corner of the eye where eyelids meet

Lacrimal canaliculus

Drains tears from eye surface to lacrimal sac

Nasolacrimal duct

Carries tears from lacrimal sac into nasal cavity

Superior oblique muscle

Rotates eye downward and laterally

Trochlea

Pulley-like structure for superior oblique muscle tendon

Superior rectus muscle

Moves eye upward

Lateral rectus muscle

Moves eye laterally (abduction)

Inferior oblique muscle

Rotates eye upward and laterally

Retina

Inner layer of the eye containing photoreceptors

Choroid

Middle vascular layer providing blood supply to retina

Sclera

White outer fibrous layer protecting the eye

Cornea

Transparent anterior portion of sclera that refracts light

Pupil

Opening in the iris that controls light entry

Iris

Colored part of the eye; regulates pupil size

Ciliary muscle

Changes shape of the lens for focusing

Lens

Transparent structure that focuses light on retina

Macula

Area of retina for detailed central vision

Fovea centralis

Small depression in macula with highest visual acuity

Optic disc

Blind spot; where optic nerve exits the eye

Optic nerve

Transmits visual signals from retina to brain

Anterior segment (aqueous humor)

Fluid-filled space between cornea and lens

Posterior segment (vitreous humor)

Gel-filled space between lens and retina

Rods

Photoreceptors for dim light and peripheral vision

Cones

Photoreceptors for color vision and sharp detail

External ear

Collects and funnels sound waves to tympanic membrane

Middle ear

Air-filled space with ossicles that amplify sound

Inner ear

Contains sensory organs for hearing and balance

Auricle

External ear structure that funnels sound into auditory canal

External acoustic meatus

Ear canal; conducts sound to tympanic membrane

Tympanic membrane

Eardrum; vibrates with sound waves

Malleus

First ossicle; transmits vibrations from tympanic membrane to incus

Incus

Middle ossicle; transmits vibrations from malleus to stapes

Stapes

Last ossicle; transmits vibrations to oval window

Auditory tube

Equalizes air pressure between middle ear and throat

Semicircular canals

Detect rotational equilibrium (dynamic balance)

Vestibule

Detects static equilibrium and linear acceleration

Cochlea

Contains organ of Corti; responsible for hearing

Vestibulocochlear nerve

Carries hearing and balance signals to brain

Round window

Relieves pressure in cochlea after sound waves pass through

Oval window

Receives vibrations from stapes into cochlea

Scala vestibuli

Upper chamber of cochlea; filled with perilymph

Cochlear duct

Middle chamber; contains endolymph and organ of Corti

Scala tympani

Lower chamber of cochlea; filled with perilymph

Vestibular membrane

Separates scala vestibuli from cochlear duct

Tectorial membrane

Gel-like membrane above hair cells in organ of Corti

Basilar membrane

Membrane that supports hair cells in organ of Corti

Organ of Corti

Hearing receptor organ containing hair cells