Special Senses Eye and Ear

Eye and Vision

Quick Facts about the Eye 70% of all sensory receptors are in the eye Approx. 1 inch in diameter Uses light to gather information about environment

External Eye Eyelid Eyelashes Medial canthus Lateral canthus

Accessory Structures of the Eye Tarsal glands (within eyelids) Conjuctiva Lacrimal apparatus Lacrimal glands  Lacrimal canals and lacrimal sac  Nasolacrimal duct  nasal cavity Lacrimal secretions are made up of a dilute salt solution and lysozyme (antibiotic)

Internal Eye Anatomy

Eye Overview Made of tunics and humors Tunics: layers surrounding the eye and it’s parts Humors: fluid areas within the tunics to give eye pressure and keep it’s shape

Tunics Sclera: outermost tunic Thick, white covering Anterior portion modified into cornea (window where light can enter the eye) No blood vessels

Tunics Vascular tunic: middle tunic Iris Pupil Supplies blood to eye 2 parts: Choroid (posterior) Ciliary body (anterior) attaches lens using ciliary zonule Iris Pupil

Tunics Sensory tunic: innermost tunic Retina: contains photoreceptors Rods: black, white and shades of gray in dim light, peripheral vision Cones: color receptors Signals sent from retina to optic nerve to brain

Lens Biconvex structure Behind cornea, iris, pupil Bends to focus on objects Humors: fluid filled areas in eye Anterior: aqueous humor Fluid gives anterior portion shape Constantly replaced to bring nutrients to areas without blood supply Posterior: vitreous humor Constant pressure to give eye shape (intraocular pressure)

How does the eye work? Light is refracted by each layer it moves through Humors, lens, cornea Image is shown on retina (upside-down) and sent to brain Brain flips the image and uses other cues to make sense of image

Problems within the Eye Conjuctivitis Nearsightedness – distant objects are blurry Farsightedness – close objects are blurry Astigmatism Glaucoma

The Ear, Hearing, and Balance

Overview of the Ear 3 parts: outer, middle, inner Mechanoreceptor: respond to physical forces (sound vibrations, movement of the head)

Outer Ear Pinna or auricle – external ear Surrounds auditory canal into ear canal External acoustic meatus (external auditory canal) – skin lined canal between outside of the head and the eardrum Glands in skin (ceruminous canals) secrete cerumen to protect ear

Middle Ear Tympanic membrane Tympanic cavity Ossicles (hammer/malleus, anvil/incus, stirrup/stapes) Oval window Round window Pharyngotympanic tube – connects ear and throat and will open and close to keep pressure within ear the same as external pressure

Inner Ear Made up of bony chambers called the osseous (bony) labyrinth 3 divisions: Cochlea Vestibule Semicircular canals Filled with fluid called perilymph Within labyrinth are membranes (membranous labyrinth) Filled with endolymph

Hearing Organ of Corti Within the cochlea Contain hair cells to detect vibrations which cause cochlear fluid to move Send sound signals along cochlear nerve to the temporal lobe (auditory cortex) Two ears help us determine where sounds are coming from Over-stimulation of cochlear nerve allows us to “tune out” certain sounds

Hearing Video http://www.youtube.com/watch?v=ahCbGjasm_E

Equilibrium and Balance Vestibular Apparatus: equilibrium detectors in the vestibule and semicircular canals Static equilibrium – detects up and down Maculae: otolithic membrane with a gel-like material with otoliths (calcium salt stones) detect movement of head Dynamic equilibrium – movement in all directions Crista ampularis – tuft of hair cells with cupula (gel cap) Movement bends hairs and cupula All send signals to brain through vestibular nerve to cerebellum