taste, smell, sight, hearing (we’re just going to focus on “sight & hearing”)
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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
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