Taste, Smell, Sight, Hearing(we’re just going to focus on

“Sight & Hearing”)

• Photoreceptors – visual receptor cells

• Adult eye = ~ 1 in. diameter

• Accessory structures – protect the eye or aid in its functioning– Eyebrows– Eyelids– Conjunctiva– Lacrimal apparatus– Extrinsic Eye muscles

Eyebrows & Eyelids• Eyebrows

– Shade eyes from sunlight– Prevent perspiration from

entering eyes

• Eyelids (palpabrae) – Blinking occurs every 3-7

secs to prevent dehydration of eyes

– Eyelashes are richly innervated, so anything that touches them, including a puff of air, triggers reflex blinking

Conjunctiva• Transparent mucous

membrane that lines eyelids & reflects over surface of eyeball

• Lubricate eye & to prevent invasion to posterior portion of eye

• Conjunctivitis is an inflammation of the conjunctiva – Pinkeye is a type of

conjunctivitis caused by bacteria or virus

Lacrimal Apparatus

• Consists of the lacrimal gland & lacrimal ducts

• Lacrimal gland releases fluid that is spread over eye when blinking– Contains mucus,

antibodies & lysozyme (a bacteria-destroying enzyme)

Don’t need to know this!

Don’t need to know this!

Structure of the Eyeball• Made up of three layers called tunics

– Fibrous (1)– Vascular (2)– Sensory (3)

• Fibrous tunic is the outermost coat of the eye (1)– Divided into 2 major

regions: sclera & cornea• Sclera (tough connective tissue) -

“whites of the eye” – Functions to protect & shape

eyeball– Sturdy anchoring for extrinsic

eye muscles

3

More on the Eye• Cornea - anterior 6th of fibrous tunic

– Covered on both sides by simple squamous epithelium

– Lined with pain fibers (which is why contacts can be so tough to adjust to)

• When cornea is touched, reflex blinking & increased lacrimal fluid secretion occur

• FUN FACT:– Since cornea has no blood supply it is the only tissue that

can be transplanted with very little fear of rejection (does not have contact with immune system)

Iris• Most anterior part of

vascular tunic (middle layer) (2)– Between cornea &

lens• Round central opening

(pupil) allows light to enter eye

• Made of smooth muscle fibers that contract & dilate depending on light stimulus

3

Iris• Though it seems to appear in many colors (Iris

means “rainbow”), it actually only contains brown pigment– When an iris contains a lot of pigment, the eyes

appear brown or black

– If the amount of pigment is small, the short wavelengths of light are scattered from the unpigmented parts of the iris & eyes appear blue, green, or gray

– Why, then, do newborn babies often appear to have gray or blue eyes?

The Sensory Tunic (Retina & Lens)• Deepest layer • Contains the lens (hard disc) which

allows an image that is upside down & backwards

• Has pigmented cells that absorb light

• Stores Vitamin A, which is needed by photoreceptor cells– Contains millions of

photoreceptors• Rods & cones• Rods - more numerous & are our

dim-light & peripheral receptors (more sensitive to light)

• Cones - bright light & provide high-acuity color vision

• The optic disc (located where the optic nerve leaves the posterior portion of the eye) is called the “blind spot” because it contains no photoreceptors

Lens

Internal Chambers

• Filled with aqueous humor which is produced in posterior chamber & drains from anterior chamber

• If drainage is blocked, pressure within eye may increase & cause compression of retina and optic nerve condition called glaucoma

• Exam to diagnose is simple…a puff of air at the sclera will produce a measurable amount of deformation

• Divided into 3 major regions:– Inner ear– Middle ear– Outer ear

•

LABEL & COLOR-CODE YOUR WKSTOuter Ear Middle Ear Inner Ear

Outer Ear• Consists of the auricle &

the external auditory canal– Auricle

• helix (rigid portion) • lobule (no cartilage)• Functions to direct sound waves into

external auditory canal

– External auditory canal • Short (~2.5 cm) & curved • Extends to the tympanic membrane

(“eardrum”)

Middle Ear• Small, air-filled

cavity within the temporal bone

• Eustachian tube links middle ear to superior-most part of the throat– Normally this is

closed, but yawning & swallowing opens this tube briefly to equalize pressure

• Contains the 3 smallest bones in the body: the ossicles– Malleus – secured to the

tympanic membrane– Incus– Stapes – connects to the

inner ear (via the oval window)

• Tensor tympani muscle attaches auditory tube (Eustachian tube) to malleus– This muscle helps prevent

damage to inner ear under extremely loud conditions

Middle Ear

Inner Ear• Located deep

within the temporal bone & posterior to the eye socket

• Made up of the vestibule, semicircular canals & cochlea

Vestibule• Central egg-shaped cavity that medially

borders the middle ear• Contains perilymph

(similar to CSF)• Houses equilibrium

censors called maculae that respond to pull of gravity & report changes of head position

Semicircular Canals• Made up of an

anterior, posterior, & lateral canals

• Have receptors to help with equilibrium

Cochlea• About 1/2 size of a pea• Contains 3 hollow

cavities• Cochlear duct contains

spiral organ of Corti – receptor organ for hearing

• Cochlear nerve runs from the spiral organ of Corti to the brain

Hair Cells in the

Spiral Organ of Corti

• Roughly 16,000 hearing receptor cells called cochlear hair cells line the spiral organ of Corti

• Sounds set up vibrations in air that beat against the ear drum

• This pushes the ossicles that press fluid in the inner ear against membranes

• This pressure on the membranes pulls on tiny hair cells that stimulate nearby neurons that give rise to impulses that travels to the brain, where they are interpreted

Deafness• 2 types:

– Conduction– Sensorineural

• Conduction deafness – occurs when something interferes with conduction of sound vibrations to the fluids of the inner ear

• Sensorineural deafness – results from damage to neural structures at any point in the hearing pathway– This typically results from the gradual loss of

hearing receptor cells:• Throughout life• Single explosively loud noise• Prolonged exposure to high-intensity sounds,

which cause these cells to stiffen

http://www.nbclearn.com/portal/site/learn/science-of-nhl-hockey