ANATOMY OF THE
EYE & EAR
Exercise 21, 22
THE EYE
ANATOMY OF THE EYE
■ Sophiticated systems that includes the work of:
■ Retina receptors
■ Pupil dilation and contraction
■ 6 oculomotor muscles
■ 12 cranial nerves
EXTERNAL EYE
■ Only about 17% of the eye is visible
■ About 2.5 cm in diameter
■ Accessories / external features of
the eye:
–
Palpebrae - eyelids; evenly distribute
tears across the surface of the eye to
keep it moist
–
Eyelashes
–
Palpebral fissure – cleft between
upper/lower eyelid
–
Lacrimal caruncle – contains
sebaceous/sweat glands
–
Lateral / medial canthus – 2 points
where the upper/lower eyelid meet
–
Conjunctiva – thin mucous membrane
that covers the eye / lubricates eye
and contains vessels
Eye Glands / Ducts
■
Ciliary glands – modified sweat glands to lubricate the eyeball
■
Tarsal glands – secrete an oily lubricant to prevent eyelids from sticking together
■
Lacrimal glands – contains 12 excretory larcrimal ducts that secrete tears and lacrimal fluid
■
Lacrimal Apparatus
–
Lacrimal fluid contains lysozyme  fluid moves across eyeball surface and enters two openings in
medial canthus  superior / inferior lacrimal puncta  lacrimal canals  lacrimal sac  nasolacrimal
tract drains the tears into the nasal cavity
Eye Muscles – come back to haunt us
INTERNAL EYE
■
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–
–
Fibrous tunic – dense connective outer layer tissue
Sclera – white part of the tunic that covers the eye
Corneal lambus – the border between sclera and cornea; contain canal of Schlemm,
Cornea – NOT covered by sclera, transparent tissue where light enters the eye
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–
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–
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Vascular tunic (uvea)
Iris (anterior)
Lens (posterior to iris) – focuses light
Ciliary body – where iris attaches
Pupil
Choroid (posterior) – melanin that absorbs light and prevents against reflection
■
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Neural tunic (aka retina)
Pigemented part (outer layer)
Neural part – contains light-sensitive photoreceptors
Aqueous humor – maintains intraocular eyepressue and supplies nutritents to lens/ cornea
Vitreous body – holds retina against choroid and prevents collapse
How does the pupil change size?
■ Pupillary sphincter
muscles / pupillary
dilator muscles
■ Parasympathetic vs
Sympathetic innervation
Cellular Organization of the Retina
■ Neural part of the retina contains the photoreceptors
■ And 2 types of sensory neurons  bipolar cells and ganglion cells
■ Photoreceptors
– Rods – motion detection
– Cones – visual acuity
■ Light  pigemented area  neural part  photoreceptors  bipolar cells  ganglion
cells axons converge at optic disc
■ Amacrine cells – communication between bipolar and ganglion cells
■ Horizontal cells – inhibit or facilitate communication b/w photoreceptors and bipolar cells
■ Macula lutea – contains many cones
– Fovea (center of ML) – sharpest vision at this point / no rods here
Diseases of the Eye
■ Glaucoma
■ Diabetic Retinopathy
■ Conjunctivitis
■ Macular Degeneration
■ Sty
Marijuana and Glaucoma
■ THC causes the blood vessels in the eye to decrease
■ Therefore, reduced IOP levels
THE EAR
Anatomy of the Ear
■ External – direct sound waves
■ Middle – direct sound waves
■ Outer – balance and hearing
External Ear
■ Pinna, auricle – funnels sound waves into external acoustic meatus  tympanic
membrane (eardrum)
■ Ceruminous glands – prevent dust and debris from entering the middle ear
Middle Ear
■ AKA tympanic cavity
■ Connected to the back of the upper throat by the auditory tube
■ Sound vibrations  malleus  incus and stapes  pushes on the oval window
(inner ear)  stimulate auditory receptors
■ Tiny muscles – tensor typani and stapedius
– Smallest skeletal muscles on the human body
Inner Ear – Regions
■ Cochlea – receptors for
hearing
■ Vestibule – receptive to
static equilibrium
■ Semicircular canals –
receptors for “dynamic
equilibrium” (when body
moves)
– Contain semicircular ducts
that have a swollen
ampulla that houses the
balance receptors called
cristae
Inner Ear – Regions
■ Vestibule
■ Contain utricle and saccule
■ Maintain maculae
■ Receptors that maintain
static EQ
■ Suspended in a gel matrix
which also contains
statoconia (calcium
carbonate crystals)
■ Gel + Statoconia = otolith
Inner Ear – Regions
■ Cochlea
■ 3 ducts in a spiral
formation – chochlear duct
– Contains hair cells that are
sensitive to vibrations
– Contains sensory receptor,
organ of Corti
■
Inner hair cells / outter hair
cells
■ Vestibular duct and
tympanic duct - filled with
perilymph
■ Basilar membrane – where
hair cells occur