General and Special Senses

VISION

Eye – The organ of sight that detects light and sends visual signals to the brain.

Pupil – The opening in the center of the iris that allows light to enter the eye.

Medial and lateral canthus – The inner (medial) and outer (lateral) corners where the upper and lower eyelids meet.

Conjunctiva – A thin, transparent membrane that covers the white of the eye (sclera) and lines the inside of the eyelids.

Lacrimal gland – Produces tears that lubricate and protect the surface of the eye.

Nasolacrimal duct – Drains tears from the lacrimal sac into the nasal cavity.

Muscles that control eye movement – Extraocular muscles that move the eye in various directions.

Anatomy of the Eyeball

Fibrous layer

Sclera – The white, tough outer layer of the eyeball that provides structure and protection.

Cornea – The transparent front part of the eye that allows light to enter and helps focus it.

Vascular layer

Iris – The colored part of the eye that controls the size of the pupil.

Lens – A transparent, flexible structure behind the pupil that focuses light onto the retina.

Pupil – The adjustable opening in the center of the iris.

Sensory layer (Retina)

Retina – The light-sensitive layer of tissue at the back of the eye where visual images are formed.

Optic disc – The “blind spot” where the optic nerve exits the eye; lacks photoreceptors.

Fovea centralis – A small central pit in the retina packed with cones for sharp central vision.

HEARING AND EQUILIBRIUM

Ear

External ear

Auricle (Pinna) – The outer part of the ear that collects and directs sound waves into the auditory canal.

Auditory canal (External acoustic meatus) – The canal that channels sound waves from the auricle to the eardrum.

Middle ear

Tympanic membrane – Also known as the eardrum; it vibrates in response to sound waves.

Auditory ossicles (malleus, incus, stapes) – The three small bones in the middle ear that transmit vibrations from the tympanic membrane to the inner ear.

Oval window – A membrane-covered opening that leads from the middle ear to the vestibule of the inner ear.

Round window – A membrane-covered opening that allows for movement of fluid within the cochlea.

Auditory tube (Eustachian tube) – Connects the middle ear to the throat and helps equalize pressure.

Inner ear

Vestibule – The central part of the bony labyrinth that helps with balance.

Semicircular canals – Three looped structures that help maintain balance and detect head rotation.

Cochlea

Vestibular duct – The upper chamber of the cochlea filled with perilymph; part of the sound transmission path.

Tympanic duct – The lower chamber of the cochlea, also filled with perilymph.

Cochlear duct – The middle chamber of the cochlea filled with endolymph and contains the organ of Corti (the sensory organ of hearing).