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 ■ 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

■ 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

■ 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