Human Eye and Ear Anatomy: Structures, Functions, and Pathways

Fibrous tunic

sclera (outer white layer), cornea.

Vascular tunic

choroid (dark middle layer), ciliary body, iris.

Neural tunic

retina (innermost sensory layer).

ciliary muscle, ciliary processes, suspensory ligaments

Three Parts of the Ciliary Body

Ciliary muscle

changes lens shape for accommodation.

Ciliary processes

produce aqueous humor.

Suspensory ligaments (zonular fibers)

connect ciliary body to lens.

Fovea centralis

highest visual acuity; highest cone density.

Macula lutea

region around fovea for sharp central vision.

Optic disc

blind spot (no photoreceptors).

Near vision

ciliary muscle contracts → zonular fibers relax → lens becomes rounder/thicker.

Distant vision

ciliary muscle relaxes → zonular fibers tighten → lens flattens/thins.

Memory aid

Contract = Close, Relax = Remote.

Myopia

image focuses in front of retina (nearsighted).

Hyperopia

image focuses behind retina (farsighted).

Lacrimal gland → lacrimal canals → lacrimal sac → nasolacrimal duct → nasal cavity

Lacrimal Drainage Pathway

CN III (Oculomotor)

Superior rectus, Inferior rectus, Medial rectus, Inferior oblique are innervated by...

CN IV (Trochlear)

Superior oblique is innervated by...

CN VI (Abducens)

Lateral rectus is innervated by...

Rectus Muscles

move eye in cardinal directions

Superior rectus (CN III)

Elevates & adducts eye

Inferior rectus (CN III)

Depresses & adducts eye

Medial rectus (CN III)

Adducts eye (most powerful adductor)

Lateral rectus (CN VI)

Abducts eye (isolated CN VI test!)

Superior oblique (CN IV)

Depresses, abducts, & medially rotates eye

trochlea

Passes through connection tissue loop

Inferior oblique (CN III)

Elevates, abducts, & laterally rotates eye

collect, transmit, and transform sound waves into nerve impulses for hearing and balance

Three regions of the ear function

Auricle (pinna)

funnels sound into ear canal

External auditory canal (meatus)

contains ceruminous glands → earwax (protection)

Tympanic membrane (eardrum)

vibrates in response to sound waves

auricle, external acoustic meatus, tympanic membrane

Collects and directs sound waves → vibration of tympanic membrane.

malleus, incus, stapes, tensor tympani, oval window, round window, auditory tube

Middle Ear (Tympanic Cavity)

Tensor tympani & stapedius muscles

dampen loud sounds

Oval window

stapes footplate pushes vibrations into inner ear

Round window

releases pressure from inner ear fluid movement

Auditory tube (Eustachian tube)

equalizes pressure between middle ear & nasopharynx

short horizontal Eustachian tube

Middle ear infections (otitis media) are common in children

cochlea, vestibule, semicircular canals, endolymph and perilymph

parts of the Inner Ear (Labyrinth)

Cochlea

hearing (spiral organ of Corti)

Vestibule

static equilibrium (utricle & saccule; detect linear acceleration)

Semicircular canals

rotational equilibrium (ampullae detect angular acceleration)

Endolymph & perilymph

specialized inner ear fluids

Vestibulocochlear nerve (CN VIII)

what nerve carries hearing & balance signals to brainstem.

External ear

Auricle, auditory canal, tympanic membrane Collect sound

Middle ear

Malleus, incus, stapes, oval & round windows Amplify & transmit vibrations

Inner ear

Cochlea, vestibule, semicircular canals Hearing, balance & acceleration

Tympanic membrane → ossicles → oval window → cochlear fluid → hair cells → vestibulocochlear nerve → brain

Sound path