ASU BIO 201: Special Senses Eyes and Ears (Lab)

Conjunctiva

transparent mucus membrane that covers the inner surface of the eyelid and anterior surface of the eye, with the exception of the Cornea

Lacrimal apparatus

lacrimal gland produces tears; tears flow through lacrimal punctum, lacrimal canals, lacrimal sac, nasolacrimal duct; tears cleanse and lubricate the eye, deliver oxygen and nutrients to the conjunctiva, and prevent bacterial infection via lysozyme

Flow of tears

Lacrimal gland -> surface of eye -> lacrimal punctum -> lacrimal canals -> lacrimal sac -> nasolacrimal duct

Extrinsic muscles of the eye

Superior, Inferior, Medial, and Lateral rectus

Superior and Inferior Oblique

Superior rectus

elevates eye, innervated by oculomotor III

Inferior rectus of eye

depresses eye, innervated by oculomotor III

Medial rectus

moves eye medially, innervated by oculomotor III

Lateral rectus

moves eye laterally, innervated abducens VI

Superior oblique

depresses and turns eye laterally, innervated by trochlear VI

Inferior oblique

elevates and turns eye laterally, innervated by oculomotor III

Layers of the eye

fibrous, vascular, inner

fibrous layer

tunica fibrosa:

sclera, cornea

Sclera

white of the eye, formed from dense collagenous CT; shapes eye and anchors extrinsic muscles

Cornea

anterior transparent region that admits light that covers the pupil/iris

Vascular layer

tunica vasculosa:

choroid, ciliary body, iris, pupil

Choroid

highly vascular, deeply pigmented layer behind retina, helps absorb light and provide nutrients to retina

Ciliary body

thickened extension of choroid forming a muscular ring around the lens, and shapes the lens via suspensory ligaments. Supports iris and secretes aqueous humor

Iris

adjustable diaphragm that controls the diameter of the pupil

Pupil

opening created by the iris which allows light to pass into the eye

Inner layer

tunica interna:

retina, optic nerve

Retina

cup-shaped extension of the diencephalon; contains a pigmented and a neural (sensory) layer

Optic nerve

Cranial Nerve II which innervates the eye; joins the retina at the optic disc, crosses at the optic chiasm

Composition: sensory

Function: vision

Damage: blindness

Optic components

transparent components of the eye that admit light rays, bend lights, and focus them on the retina

posterior and anterior chamber, aqueous humor, lens, vitreous humor

Posterior chamber

lies between the iris and lens

Anterior chamber

lies between the cornea and the iris

Aqueous humor

clear fluid secreted by ciliary body; flows from posterior chamber through pupil to anterior chamber and replenishes throughout life

Lens

can be bent by the ciliary body to focus passing light

Vitreous humor

transparent jelly that lies in vitreous chamber behind the lens the holds the retina in place; is never replaced

Neural components

retina - pigmented layer and neural layer (optic nerve, fovea centralis, rods/cones)

Pigmented layer

absorbs light and prevents it from scattering; stores Vitamin A which is needed by photoreceptors

Fovea Centralis

produces finely detailed images on retina

Optic disc

Blind spot, visual filling

Photoreceptors

cells that absorb light and produce a chemical or electrical signal, rods and cones

Rods

responsible for night vision and produces images in shades of gray, most numerous photoreceptor, animals have higher density allowing for night vision

Cones

responsible for color vision and respond to bright light, provide higher detail, humans have high density

Color blindness

sex-linked recessive trait which results in a lack of various cone cells. Occurs in 8% of men and 0.5% of women

Visual pathway

cornea -> anterior chamber -> iris (pupil) -> posterior chamber -> lens -> vitreous humor -> retina -> optic nerve -> optic chiasm -> occipital lobe

optic nerves cross at the optic chiasm therefore the right occipital lobe monitors the left side of the visual field, while the left occipital lobe monitors the right side of the visual field

Anatomy of the ear

outer, middle, inner ear

Outer ear

funnels vibrations to the tympanic membrane (eardrum)

Auricle (pinna), external auditory canal

Auricle

Pinna, shell-shaped structure formed by elastic cartilage that funnels vibrations to the external auditory canal

External Auditory Canal

passage leading from the auricle, through the temporal bone, to the tympanic membrane

Middle Ear

found in tympanic cavity

Tympanic membrane, pharyngotympanic (auditory) tube, auditory ossicles, stapedius, tensor tympani

Tympanic membrane

"ear drum" that separates the external auditory canal form the tympanic cavity. Transfers vibrations to the auditory ossicles

Pharyngotympanic (auditory) tube

passageway to the nasopharynx and functions to equalize pressure between the middle and outer ear

Auditory ossicles

smallest bones in the human body; function to transfer vibrations from the tympanic membrane to the inner ear

malleus, incus, stapes

Malleus

"hammer" that is found between tympanic membrane and incus, connected to tensor tympani muscle

Incus

"anvil" found between malleus and stapes

Stapes

"stirrup" that is found between incus and oval window; connected to stapedius muscles

Stapedius

reduces motion of stapes to lessen effect on inner ear

Tensor Tympani

pulls malleus away from eardrum

Inner ear

housed in the temporal bone passageways called the bony labyrinth. The bony labyrinth houses the membraneous labyrinth

Perilymph, Endolymph, cochlea

Perilymph

cushioning fluid found between the bony and membranous labyrinth

Endolymph

fluid found within the membranous labyrinth

Cochlea

coiled, snail-shell-like organ for hearing that arises from the vestibule;

oval window, round window, scala vestibuli, scala media, scala tympani, vestibular membrane, tectorial membrane, basilar membrane, spiral organ of corti

Oval window

connected to stapes; transfers vibrations to cochlea

Round Window

found at the end of the cochlea acting as a pressure relief

Scala Vestibuli

filled with perilymph, begins near the oval window

Scala Media

Cochlear duct; filled with endolymph, contains spiral organ of corti

Scala Tympani

filled with perilymph, ends at the round window

Vestibular membrane

separates the scala vestibuli from the cochlear duct

Tectorial membrane

feather-shaped gelatinous substance that acts to open channels for depolarization; part of the spiral organ of corti

Basilar membrane

separates the cochlear duct from the Scala Tympani

Spiral Organ of Corti

structure that converts vibrations to neural impulses; stereocilia vibrate pressing up against the tectorial membrane in order to open channels allowing for depolarization

Vestibule

chamber that contains the organs of equilibrium

oval window, saccule, utricles, maculae

Saccule

portion of the vestibule that leads to the cochlea; contains maculae and is responsible for linear acceleration

Utricle

portion of the vestibule that leads to the semicircular canals; contains maculae and is responsible for linear acceleration

Maculae

equilibrium receptors found in the vestibule that respond to gravitational pull and changes in head position

-small crystals called otoliths add to the weight and inertia to enhance a sense of gravity and motion

Static Equilibrium

the body is stationary but the head is tilted; perceived by macula found in the saccule and utricle

Semicircular Canals

responsible for sense of equilibrium

made up of anterior, posterior, and lateral ducts which respond to angular movement of the head

Dynamic equilibrium

perception of motion or angular acceleration, perceived by the semicircular canals

ex) turning in a car

Vestibulocochlear Nerve

CN VIII

Formed from vestibular nerve and cochlear nerve

Composition: Sensory

Function: Hearing and balance

Damage: deafness and impaired balance

Step 1 of hearing

vibrations are captured by the auricle -> funneled by the external auditory canal -> hit tympanic membrane -> transfers vibrations through the auditory ossicles -> oval window

Step 2 of hearing

vibrations travel -> perilymph -> up scala vestibule -> vibrates the vestibular membrane -> vibration of scala vestibuli vibrates the endolymph -> causing movement of stereocilia against the tectorial membrane (depolarizing neural cells) -> vibrations travel through basilar membrane -> scala tympani -> out the round window