Special Senses

Pinna (Auricle)

External ear structure that directs sound into the ear canal

External Acoustic Meatus

Pathway that channels sound waves to the tympanic membrane

Tympanic Membrane (Ear Drum)

Vibrates when sound waves hit it; transmits vibrations to middle ear bones

Auditory Ossicles

Three small bones in the middle ear that amplify sound: malleus, incus, stapes

Malleus (Hammer)

Transmits vibrations from tympanic membrane to incus

Incus (Anvil)

Transmits vibrations from malleus to stapes

Stapes (Stirrup)

Transmits vibrations from incus to oval window

Oval Window

Membrane-covered opening into inner ear; stapes vibrates against it

Round Window

Flexible membrane that allows cochlear fluid to move

Cochlea

Snail-shaped inner ear chamber; converts vibrations into electrical signals. Hearing

Vestibulocochlear Nerve (CN VIII)

Carries auditory & balance information from inner ear to brain

Vestibule

Detects linear acceleration & head position for balance. Static Equilibrium

Semicircular Canals

Detect rotational movement; maintain balance. Dynamic Equilibrium

Pharyngotympanic (Eustachian) Tube

Equalizes pressure between middle ear and throat

What are olfactory receptors for?

They detect smells.

What part of the ear could have been damaged if you heard an extremely loud explosion?

The hair cells in the cochlea or the eardrum.

Sclera

Outer layer of the eyeball; provides structure & protection

Cornea

Transparent front part; focuses light & protects eye

Choroid

Middle layer; provides nutrients and oxygen to retina

Retina

Inner layer; contains photosensitive cells (rods & cones) and detects light

Rods

Peripheral retina; detect dim light & black-and-white vision

Cones

Central retina (fovea); detect bright light & color vision

Pupil

Controls light entering the eye

Iris

Controls pupil size; gives eye color

Ciliary Body

Changes lens shape for focusing (accommodation); produces aqueous humor

Lens

Focuses light for near and far vision

Aqueous Humor

Fills anterior chamber; nourishes cornea & lens; maintains intraocular pressure

Vitreous Humor

Fills posterior chamber; maintains eye shape

Optic Nerve

Sends visual information from retina to brain

Optic Disc

Where the optic nerve exits the eyeball; no photoreceptors here

Blind Spot

Area at optic disc with no photoreceptors; light not detected

Visual Cortex

Located in occipital lobe; processes visual information from retina

Lacrimal Gland

Produces tears

Lacrimal Canaliculi

Drains tears from eye surface

Lacrimal Sac

Collects tears from canaliculi

Nasolacrimal Duct

Drains tears into nasal cavity

Cranial Nerves Controlling Eye Movement

Oculomotor (III): moves most eye muscles, controls pupil constriction & lens shape; Trochlear (IV): moves superior oblique muscle; Abducens (VI): moves lateral rectus muscle

What separates the aqueous humor in the anterior segment from the vitreous humor in the posterior segment of the eye?

The lens separates the aqueous humor in the anterior segment from the vitreous humor in the posterior segment.

Myopia

Nearsightedness; distant objects appear blurry because the eyeball is too long or lens too strong

Hyperopia

Farsightedness; near objects appear blurry because the eyeball is too short or lens too weak

Astigmatism

Blurred vision caused by irregular shape of the cornea or lens

Presbyopia

Age-related loss of lens flexibility; difficulty focusing on close objects