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