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