Anatomy of the eye & ear

THE EYE

ANATOMY OF THE EYE Sophisticated 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)

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