BIOL 105--Lab 12—Eye 1

The Eye and Vision•Most of eye protected by cushion of fat and bony orbit•Accessory Structures protect eye and aid eye function

– Eyebrows, Eyelids, Conjunctiva, Lacrimal apparatus

– Extrinsic eye muscles

Lab 11-12--BIO 105EYE-EAR

BIOL 105--Lab 12—Eye 2

Conjunctiva: Transparent mucous membrane– Produces lubricating mucous secretion– Covers white of eyes but not cornea

Lacrimal Apparatus• Lacrimal glands secrete tears and drain them

via ducts into nasolacrimal duct•Lacrimal gland in orbit above lateral end of eye•Tears are dilute saline solution containing mucus, antibodies, and lysozyme (an antibacterial enzyme)

– Blinking spreads tears toward medial commissure

BIOL 105--Lab 12—Eye 3

Structure of Eye:•Outermost layer; dense avascular connective tissue

– Two areas: sclera and cornea

1. Sclera--Opaque region• Protects, shapes eyeball; anchors extrinsic eye

muscles• Continuous with dura mater of brain posteriorly

2. Cornea--Transparent anterior area• Bends light as it enters eye; 2/3 of focusing takes place

at the cornea, 1/3 at the lens

• Pain receptors contribute to blinking and tearing reflexes

• Corneal transplants typically are not rejected by immune system because cornea has no blood vessels

BIOL 105--Lab 12—Eye 4

Choroid---Middle pigmented layer

•Contains: choroid, ciliary body, and iris

1. Choroid • Supplies blood to all layers of eyeball• Black pigment absorbs light to prevent it scattering

within eye which makes focusing difficult

2. Ciliary body

• Ring of smooth muscle surrounding lens

• Ciliary muscles relax and contract to control lens shape to allow lens to focus

• Capillaries of ciliary processes secrete fluid • Suspensory ligaments holds lens in position

BIOL 105--Lab 12—Eye 5

3. Iris-anterior to ciliary body• Colored part of eye• Pupil—central opening that regulates light

entering eye– Close vision and bright light —pupils constrict– Distant vision and dim light —pupils dilate

BIOL 105--Lab 12—Eye 6

Lens•Biconvex, transparent, flexible, and avascular•Changes shape to precisely focus light on retina

– filled with transparent protein – becomes more dense, convex, less elastic with age

• Cataracts (clouding of lens) consequence of aging, diabetes mellitus, heavy smoking, frequent exposure to intense sunlight

BIOL 105--Lab 12—Eye 7

Innermost Layer: Retina•Delicate multi-layered membrane; •Inner Neural layer •Composed of 3 types of neurons

–Photoreceptors, bipolar cells, ganglion cells

BIOL 105--Lab 12—Eye 8

– Light passes to the rear of the retina, through the ganglion cell and bipolar cell layers, in order to stimulate the rods and cones

– As light stimulates the photoreceptors, there is a change in their membrane potential which stimulates the bipolar cells ganglion cells

– Ganglion cell axons exit eye as optic nerve• Axons of the ganglion cells of the eye exit as the optic

nerve, • at the optic chiasma, fibers from the medial side of

each eye cross over to the opposite side• Fibers from the lateral portions of each retinal field do

not cross

BIOL 105--Lab 12—Eye 9

The Retina

•Optic disc (blind spot)– Lacks photoreceptors– Optic nerve leaves eye

•Photoreceptors (quarter-billion) of two types– Rods-black and white vision– Cones-color vision

BIOL 105--Lab 12—Eye 10

• Rods– Dim light, peripheral vision, motion receptors– More numerous, more sensitive to light than cones

(that is why dim light can stimulate the rods)• Not sensitive to visual detail because many rods connect to

one neuron

BIOL 105--Lab 12—Eye 11

• Cones– Receptors for color vision which function better in

bright light (daytime vision)• Fewer cones connect to one neuron so they produce a

sharper visual image

– Macula lutea• Fovea centralis

– best vision

BIOL 105--Lab 12—Eye 12

Internal Chambers and Fluids

• Anterior area contains Aqueous humor

• continuously formed

• Supplies nutrients and oxygen mainly to lens and cornea but also to retina, and removes wastes

• Helps maintain shape and pressure of eye

•Glaucoma: blocked drainage of aqueous humor increases pressure and causes compression of retina and optic nerve blindness

BIOL 105--Lab 12—Eye 13

• Posterior area contains vitreous humor that– Transmits light– Supports posterior surface of lens – Holds neural layer of retina firmly against pigmented

layer– Contributes to intraocular pressure and maintains

shape of eye

BIOL 105--Lab 12—Eye 14

• Vision:–Eye shape: normal allows focusing at fovea

• Myopia: nearsighted; lens slightly longer, eyeball is too long or the cornea has too much curvature.

• Hyperopia: farsighted; lens shorter, eyeball is too short, cornea or lens is abnormally shaped

• Astigmatism: irregularities in cornea or lens

BIOL 105--Lab 12—Eye 15

LABWORK

1. Dissect sheep eye

2. Using eye models and charts, locate the following: sclera, choroid, cornea, retina, iris, pupil, ciliary body, lens, aqueous humor, vitreous body, optic disk, optic nerve.

3. Perform eye tests for visual acuity, astigmatism, and other tests in your lab book, time permitting.

BIOL 105--Lab 12—Eye 16

The Ear: Hearing and Equilibrium (Balance)•Three major areas of ear

1. External (outer) ear – hearing only

2. Middle ear (tympanic cavity) – hearing only

3. Internal (inner) ear – hearing and equilibrium• Receptors for hearing and balance respond to

separate stimuli

BIOL 105--Lab 12—Eye 17

External Ear•Auricle (pinna)

– Funnels sound waves into auditory canal– Sound is form of energy transmitted in waves;

different sounds have different wavelengths•External acoustic meatus (auditory canal)

– Short tube lined with skin and ceruminous glands

– Transmits sound waves to eardrum

BIOL 105--Lab 12—Eye 18

• Tympanic membrane (eardrum)– Boundary between external and middle ears– Connective tissue membrane that vibrates in

response to sound– Transfers sound energy to bones of middle

ear

Middle Ear – Small, air-filled, mucosa-lined cavity in

temporal bone– Eardrum at lateral border and medially is bony wall containing oval

(vestibular) and round (cochlear) windows

BIOL 105--Lab 12—Eye 19

• Eustachian or Pharyngotympanic (auditory) tube—connects middle ear to nasopharynx– Equalizes pressure in middle ear cavity with

external air pressure

BIOL 105--Lab 12—Eye 20

Ear Ossicles•Three small bones in tympanic cavity: the malleus (hammer), incus (anvil), and stapes (stirrup)

– Suspended by ligaments and joined by synovial joints

– Transmit vibratory motion of eardrum to oval window

– Tensor tympani and stapedius muscles contract reflexively in response to loud sounds to prevent damage to hearing receptors

BIOL 105--Lab 12—Eye 21

Inner Ear (has sound and equilibrium receptors)• Bony labyrinth --filled with perilymph

– Three regions: vestibule, semicircular canals, and cochlea

• Membranous labyrinth -filled with endolymph

– Series of membranous sacs and ducts

BIOL 105--Lab 12—Eye 22

• Vestibular apparatus – Equilibrium receptors in semicircular canals

and vestibule– Vestibular receptors monitor static equilibrium– Semicircular canal receptors monitor dynamic

equilibrium

BIOL 105--Lab 12—Eye 23

Vestibule•Central cavity of bony labyrinth•Contains two membranous sacs

1. Saccule: continuous with cochlear duct2. Utricle: continuous with semicircular canals

•Sacs responsible for static or linear equilibrium– Maculae contain equilibrium receptor regions – Responds to gravity and changes in position of head

BIOL 105--Lab 12—Eye 24

Maculae•Sensory receptors for static equilibrium •One in each saccule wall and one in each utricle wall•Monitor the position of head in space, necessary for control of posture•Respond to linear acceleration forces, but not rotation•Contain supporting cells and hair cells (stereocilia and kinocilia) embedded in the otolith membrane studded with otoliths (tiny CaCO3 stones)

– Hair cells synapse with vestibular nerve fibers– Keeps brain informed of changing position of head

BIOL 105--Lab 12—Eye 25

Semicircular Canals•Three canals (anterior, lateral, and posterior) lie in three planes of space

–Membranous ducts line canals and communicate with utricle

–Receptors respond to angular (rotational) movements of head

BIOL 105--Lab 12—Eye 26

The Cochlea--hearing•spiral, conical, bony chamber; size of split pea

– Extends from vestibule– Coils around bony pillar – Contains cochlear duct, which contains Organ

of Corti (spiral organ)

BIOL 105--Lab 12—Eye 27

• The cochlea contains the organ of Corti, the receptor organ for hearing.

• As the stapes vibrates against the oval window, it transmits pressure waves of sound through the fluid of the cochlea, sending the organ of Corti in the cochlear duct into motion.

• Cochlea consists of tiny hair cells that translate the fluid vibration of sounds from its surrounding ducts into electrical impulses that are carried to the brain by sensory nerves.

BIOL 105--Lab 12—Eye 28

Pathway for Hearing•Sound waves enter the ear canal eardrum vibrates• Vibrations pass through 3 middle ear bones • Motion causes fluid to move in the inner ear.• Moving fluid causes thousands of hair-like cells to bend which convert the vibrations into nerve impulses•Nerve impulses are CARRIED to the brain by the auditory nerve•Brain converts impulses into what we "hear" as sound.

BIOL 105--Lab 12—Eye 29

Auditory Processing

• Pitch perceived by impulses from specific hair cells in different positions along basilar membrane

• Loudness detected by increased numbers of action potentials that result when hair cells experience larger deflections

• Localization of sound depends on relative intensity and relative timing of sound waves reaching both ears

BIOL 105--Lab 12—Eye 30

The Ear:

1. Find the following structures in your lab book and the human ear models:

Pinna, pharyngotympanic (auditory) tube, Tympanic membrane (eardrum), malleus, Incus, Stapes, Cochlea, Vestibule, Semicircular canals, Auditory

canal, Round/oval windows, Vestibulocochlear nerve.

2. View slide of the cochlea and note the three fluid-filled chambers and the organ of Corti.

3. Perform hearing/balance tests in lab book.