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Notes: Special Senses Chapter 8 Anatomy of the EYE 3 External Eye Structures • External & Accessory structures include: • Eyelids • Conjunctiva • Lacrimal apparatus • Extrinsic eye muscles Tendon of levator palpebrae superioris Orbicularis oculi Eyelid Eyelash Cornea Conjunctiva 4 Eyelids •Protects the anterior of the eyes •Eyelashes project from the border of each eyelid •Tarsal glands on the edges of the eyelids produce an oily secretion that lubricates the eye Conjunctiva • This is a delicate membrane that lines the eyelids and covers a portion of the eyeball • Function: secrete mucus to help lubricate the eyeball and keep it moist. 6 Conjunctiva • Conjunctivitis is due to inflammation of the conjunctiva. It results in reddened irritated eyes • Pink Eye is the infection form that is caused by bacteria or viruses and is highly contagious. 7 Lacrimal Apparatus • Produce a saline solution, which washes and lubricates the eyeball. • Tears are an increase in lacrimal secretions • Makes your nose run because it drains into nasal cavity. Lacrimal gland Superior and inferior canaliculi Lacrimal sac Nasolacrimal duct 8 Extrinsic Eye Muscles Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. • These are attached to the outer surface of the eye • Are responsible for allowing the eye to follow a moving object. Medial Superior rectus rectus Superior oblique Lateral rectus (cut) Inferior rectus Inferior oblique 9 Internal Eye Structures • The eyeball is a hollow sphere. • Its wall is made of 3 layers or tunics • The inside is filled with fluids called humors. • The lens is the main focusing apparatus and divides the eye into 2 chambers 10 Structure of the Eye • Wall has three (3) layers: • Outer fibrous tunic • Middle vascular tunic • Inner sensory tunic Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Lateral rectus Retina Ciliary body Suspensory ligaments Choroid coat Sclera Vitreous humor Iris Lens Fovea centralis Pupil Cornea Aqueous humor Anterior cavity Anterior chamber Posterior chamber Optic nerve Optic disc Posterior cavity Medial rectus 11 Outer Fibrous Tunic • Consists of the sclera and the cornea. •The sclera is a thick, glistening white connective tissue. •Found on the posterior of the eye. •It is known as the “white of the eye”. Outer Fibrous Tunic •The Cornea is located on the anterior of the eye •This part is clear and it is where light enters •It is the most exposed part of the eye and vulnerable to damage, but it is quick to heal. Middle Vascular Tunic • Choroid • Posterior Portion • Provides blood supply • Contains dark pigments to absorb extra light 14 Middle Vascular Tunic • Ciliary body • Anterior portion • Pigmented • Holds lens • Moves lens for focusing Ciliary muscle fibers contracted Suspensory ligaments relaxed Lens thick (a) Ciliary muscle fibers relaxed Suspensory ligaments taut Lens thin (b) Middle Vascular Tunic Sympathetic motor nerve fiber In dim light • Iris • Anterior portion • Pigmented • Controls light intensity by adjusting size of pupil •Pupil •The rounded opening in the iris Radially arranged Smooth muscle fibers of the iris Parasympathetic ganglion Circularly arranged smooth muscle fibers of the iris Pupil In normal light Parasympathetic motor nerve fiber In bright light Inner Sensory Tunic • Includes the RETINA that has two layers • The pigmented layer absorbs extra light. The cells of the retina also remove dead or damaged receptor cells. They also help to store vitamin A that is needed for vision. Inner Sensory Tunic • The neural layer of the retina has photoreceptors that respond to light. – RODS- allow us to see in dim light and are responsible for our peripheral vision – CONES- allow us to see the details of our world in color and under bright light conditions. 18 Rods & Cones in Retina 19 Inner Sensory Tunic • Blind Spot: – This is the spot where the optic nerve leaves the eyeball. There are no photoreceptors here so when light passes over this optic disc the object dissappears. 20 Inner Sensory Tunic • Fovea Centralis– A tiny pit that contains only cones. It is the area of greatest visual acuity or your point of sharpest vision. – Center of the retina 21 Inner Sensory Tunic • Lens– Is a flexible biconvex crystal-like structure. – Held in place by a ligament from the ciliary body. – It divides the eye into two chambers • Anterior segment contains a clear watery fluid called aqueous humor. • Posterior segment is filled with a gel-like vitreous humor. • Both help to provide pressure in the eye. 22 Aqueous & Vitreous Humor Aqueous Humor Vitreous humor Lens Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cornea Anterior chamber Iris Posterior chamber Ciliary process Suspensory ligaments Ciliary muscles Conjunctiva Vitreous humor Lens Sclera 24 Lens • LENS • biconvex: convex on both sides • can change shape to focus Lens • AQUEOUS HUMOR • liquid between cornea and iris • maintains shape of cornea • produced by the ciliary body • VITREOUS HUMOR • clear, jelly-like liquid inside the eyeball • helps maintain spherical shape of eye • Presbyopia • ciliary muscles lose power and the person becomes farsighted – convex reading glasses help this • Colorblindness • genetic disorder – person missing cones • most colorblind people are red-green colorblind • Glaucoma • aqueous humor does not drain • results in pain and can lead to blindness as pressure inside eyeball damages retina 28 • Cataracts • lens becomes cloudy – usually with age • Cataract Vision Anatomy of the EAR 31 External Ear (3 parts) • Auricle (or pinna)– Is what most people call the ear. – shell-shaped structure that collects and directs sound waves into the auditory canal. External or Outer Ear • External Acoustic Meatus (aka the auditory canal) – Passage to eardrum – Short, narrow chamber which secretes earwax to trap foreign bodies and repel insects. External or Outer Ear • Tympanic Membrane, or eardrum – Sound waves hit the eardrum causing it to vibrate. – It separates the external ear from the middle ear. Middle Ear • Is an Air-filled space in temporal bone •Is connected to the throat by the eustachian tube. •This equalizes pressure in the ear. •In infants it is very horizontal so that is why they should not lay down and drink •Sore throats in children also cause middle ear infections and may need to be surgically fixed with a tube. Middle Ear •Has the 3 smallest bones in the body called ossicles: • Vibrate in response to tympanic membrane •Hammer, anvil and stirrup • Oval window • Opening in wall of tympanic cavity • Stirrup vibrates against it to move fluids in inner ear Inner Ear Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. •Made of a bony labyrinth that is divided into 3 parts: • Cochlea • Functions in hearing • Semicircular canals • Functions in equilibrium • Vestibule • Functions in equilibrium Bony labyrinth Perilymph Membranous labyrinth Endolymph Bony labyrinth (contains perilymph) Membranous labyrinth (contains endolymph) Semicircular canals Utricle Saccule Vestibular nerve Cochlear nerve Scala vestibuli (cut) Scala tympani (cut) Cochlear duct (cut) containing endolymph Ampullae Oval Vestibule Round Maculae window window (a) Cochlea 37 Hearing 38 Mechanism of Hearing • Sound waves reach the cochlea through vibrations of the eardrum, ossicles, and oval window • This sets the fluid in the inner ear into motion • Hair cells in the spiral organ of Corti are stimulated and transmit impulses to the cochlear nerve. 39 Animation: Effect of Sound Waves on Cochlear Structures Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer. 40 Equilibrium 41 Sense of Equilibrium • Static equilibrium • Receptors called maculae are responsible for our static equilibrium • Senses position of head when body is not moving 42 Sense of Equilibrium • Dynamic Equilibrium – balance and movement • Semicircular canals • Senses rotation and movement of head and body Ear Disorders • Deafness - hearing loss of any kind • 2 types 1. Conduction Deafness • something interferes with sound waves entering the ear • EX: earwax, ruptured eardrum, infection 2. Sensorineural Deafness • damage to receptor cells in organ of Corti, cochlear nerve, or neurons Ear Disorders • Motion Sickness • impulses from ear nerves do not agree with visual input • can result in dizziness, nausea, loss of balance NOTES: Chemical Senses 46 CHEMORECEPTORS •Chemoreceptors: •The receptors for taste and smell are classified as chemoreceptors because they respond to chemicals dissolved in liquids 47 Sense of Smell 48 Sense of Smell • Olfactory organs •Are located in a postage stamped sized area in the roof of the nasal cavity. •Contain olfactory receptors and supporting epithelial cells The NoseSmelling & Tasting • 2 nasal chambers called nostrils – Separated by nasal septum – Receptors use cilia to capture smell • Nose also helps with taste • External nose is part bone and part cartilage Olfactory Receptors Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Nerve fibers within the olfactory bulb Olfactory Olfactory tract bulb Cribriform plate Olfactory area of nasal cavity Superior nasal concha Nasal cavity Cilia (a) Olfactory Columnar Cribriform receptor cells epithelial cells plate (b) 51 Olfactory Nerve Pathways • Once olfactory receptors are stimulated, nerve impulses travel through • Olfactory nerves olfactory bulbs olfactory tracts limbic system (for emotions) and olfactory cortex (for interpretation) 52 Smells and Emotion • Olfactory impressions are long-lasting and very much a part of our memories and emotions. • There are hospital smells, school smells, baby smells, travel smells. • Smells may remind you of specific people or events. 53 Olfactory Stimulation •Olfactory receptors are extremely sensitive and can by activated by just a few molecules. •Olfactory receptors undergo sensory adaptation rapidly • Sense of smell drops by 50% within a second after stimulation LAB: SMELL • • • • Pick a partner and spread out Get a beaker, 4 packs of cotton swabs, and 2 oils. Follow Directions on lab sheet. Throw away used cotton swabs. Place beakers and oils back on cart. • Turn in lab on front table. • Pick up a review sheet and begin working on it. 55 Sense of Taste 56 Sense of Taste • Taste buds • Organs of taste • Located on papillae of tongue, roof of mouth, linings of cheeks and walls of pharynx • Papillae are small peg-like projections on the dorsal surface of the tongue. •Get replaced every 7-10 days Sense of Taste • Taste receptors • Taste cells – modified epithelial cells that function as receptors • Taste hairs –microvilli that protrude from taste cells; sensitive parts of taste cells Taste Receptors Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Papillae Taste buds Epithelium of tongue Taste cell (a) Taste hair Supporting cell Taste pore (b) Connective tissue Sensory nerve fibers 59 Taste Nerve Pathways • Sensory impulses from taste receptors travel along: • Cranial nerves to… • Medulla oblongata to… • Thalamus to… • Gustatory cortex (for interpretation) 60 Taste Sensations • Five primary taste sensations • Sweet – stimulated by carbohydrates • Sour – stimulated by acids • Salty – stimulated by salts • Bitter – stimulated by many organic compounds •Umami- (means delicious in japan) detects beef taste or proteins