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Chapter 14 Seeing and Hearing © 2009 Delmar, Cengage Learning Senses –General and Special • General – Visceral sensations • Hunger, thirst – Touch • Touch / tactile, pressure – Temperature • Hot/cold – Pain • Receptors inside and surface of body – Proprioception • Sense of body movement and position © 2009 Delmar, Cengage Learning Special Senses • • • • • • (Touch) Smell Taste Vision Hearing Equilibrium • More complex than General senses, • Sensory structures located in the head © 2009 Delmar, Cengage Learning 1. Smell • Olfactory Sense • “chemical” sense • Dogs – Average of 220 million receptors – Humans: 5 million © 2009 Delmar, Cengage Learning How do they smell • Two patches of olfactory epithelial cells Located up high in both nasal passages • Odor molecules dissolve in the mucus nerve impulses are generated that travel to the brain • Cranial Nerve I: called Olfactory nerve © 2009 Delmar, Cengage Learning © 2009 Delmar, Cengage Learning Best Smellers • • • • • • • • • Pointers Coonhounds English Springer Spaniel Belgian Malinois Labrador Retreivers German Shepherd – 225 million scent receptors Beagle Basset Hound Blood Hound – 300 million scent receptors! © 2009 Delmar, Cengage Learning 2. Taste • Gustatory Sense • “chemical” sense • Taste sensations vary from species to species Humans taste: sweet sour salty and bitter Cats do not “taste” sweet (“tasting” refers to responding to a particular taste sensation) © 2009 Delmar, Cengage Learning Taste Buds • Tiny rounded structures made up of gustatory sensory cells sensory receptors (modified dendrites of neurons) • Found in elevated papillae around the tongue • Substance dissolve in saliva, nerve impulses are generated that travel to the brain • Cranial Nerve IX (glossopharyngeal nerve) © 2009 Delmar, Cengage Learning 3. Equilibrium • Mechanical sense • Balance • Equilibrium works by keeping track of the position and movement of the head • Equilibrium receptors are located in portions of the inner ear (vestibule and semicircular canals) © 2009 Delmar, Cengage Learning 4. Hearing • Auditory Sense • “mechanical” sense • Vibrations of air molecules are converted into nerve impulses that are interpreted by the brain External Ear Middle Ear Inner Ear © 2009 Delmar, Cengage Learning Functions of the Ear • The ear is the sensory organ that enables hearing and helps to maintain balance. • The combining forms for ear are audit/o, aud/i, and ot/o. © 2009 Delmar, Cengage Learning Outer Ear Structures • Pinna – catches and then transmits sound waves – Pinn/i is the combining form. – Aur/i and aur/o also mean external ear. • External auditory canal – tube that transmits sound from the pinna to the tympanic membrane – Glands secrete cerumen here. © 2009 Delmar, Cengage Learning Middle Ear Structures • Auditory ossicles – malleus, incus, and stapes © 2009 Delmar, Cengage Learning Middle Ear Structures • Tympanic membrane – “eardrum” – Transmits sound waves to the ossicles – Tympan/o and myring/o mean eardrum. © 2009 Delmar, Cengage Learning Middle Ear Structures • Eustachian tube – equalizes air and middle ear pressure • Tympanic bulla – osseous chamber that houses the middle ear © 2009 Delmar, Cengage Learning Inner Ear Structures • Bony labyrinth – vestibule • balance and equilibrium – semicircular canals • three canals that regulate equilibrium – cochlea • organ of hearing © 2009 Delmar, Cengage Learning Pathological conditions • Vestibular Disease / Old Dog Vestibular Syndrome – – – – Equilibrium Vestibular Cranial Nerve Possible inner ear infection Ideopathic © 2009 Delmar, Cengage Learning Deafness and “white” hair Vibrations occur and the hair cells in the Cochlea move. The mechanical energy is converted by the hair cells of the cochlea into electrical impulses through the cochlear nerve to the brain. In order for the hair to convert the mechanical energy the cell must contain pigment. Lack of pigment in the inner ear is difficult to predict…but too much white in Certain dogs seems to be correlated to the amount of white found in the hair cells. © 2009 Delmar, Cengage Learning Functions of the Eye • The ocular system is responsible for vision. • The combining forms for the eye or sight are opt/i, opt/o, optic/o, ocul/o, and ophthalm/o. © 2009 Delmar, Cengage Learning Structures of the Eye • The accessory structures of the eye: – Orbit • Bony cavity of the skull that contains the eyeball – eye muscles • 7 major muscles attach to each eye for movement – eyelids or palpebrae • Palpebral reflex (result of Trigeminal Nerve and CN VII) – Also depth of anesthesia – https://www.youtube.com/watch?v=4_zdjL51qoU • Belphar/o is the combining form. © 2009 Delmar, Cengage Learning Structures of the Eye – eyelashes • Hairlike structures called cilia • Protect the eye from foreign material – conjunctiva • Mucous membrane that lines the underside of the eyelid • Forms protective covering when the eyelids are closed • Nictitating membrane=third eyelid. – lacrimal apparatus • Lacrim/o and dacry/o are the combining forms. © 2009 Delmar, Cengage Learning Structures of the Eye – lacrimal apparatus • Lacrim/o and dacry/o are the combining forms. • Lacrimal glands produce and secrete tears • Lacrimal canaliculi or lacrimal duct collects tears and drains them into the lacrimal sac • Lacrimal sac collects tears at the upper portion of the tear duct • Nasolacrimal duct is the passageway that drains tears into the nose. © 2009 Delmar, Cengage Learning Structures of the Eye • Outer covering of the eyeball: – Sclera • White of the eye • Fibrous outer layer that maintains shape of the eye • Surrounds most of the eyeball – Cornea • The transparent anterior portion of the sclera is called the cornea. © 2009 Delmar, Cengage Learning Sclera and Cornea © 2009 Delmar, Cengage Learning – Middle Structures of the Eye • Iris – Colored portion of the eye – Pigmented muscular diaphragm controls amount of light – Located right behind the cornea • Pupil – Hole in the center of the iris through which light passes » Constricts or dilates • Lens – Layers of connective tissue fibers © 2009 Delmar, Cengage Learning • Choroid – – – – Main portion of the middle layer Blood vessels Dark pigmentation (caudal portion of the eye) Tapetum Lucidum » Very reflective “mother of pearl” blues and greens » Aids night vision due to reflective nature » Pigs and humans do not have a tapetum lucidum © 2009 Delmar, Cengage Learning Structures of the Eye – Inner layer • • • • Retina Nervous tissue layer that receives images Converts light rays into nerve impulses Photoreceptors “rods and cones” – Rods – light – Cones - color and detail • Send messages via the optic nerve © 2009 Delmar, Cengage Learning Structures of the Eye © 2009 Delmar, Cengage Learning Eye Chambers • The eye is divided into parts: – Anterior segment contains watery fluid called aqueous humor. • anterior chamber • posterior chamber – Vitreous chamber contains vitreous humor. • Gel like mass © 2009 Delmar, Cengage Learning Patological Conditions • • • • • • • Lenticular sclerosis Cataracts Glaucoma Eye Enucleation Eye Entropion Tear Production Scratches on the Cornea © 2009 Delmar, Cengage Learning Lenticular Sclerosis • • • • Age associated Hardening of the lens Pupil appears cloudy and gray Very little loss of vision © 2009 Delmar, Cengage Learning Cataracts • • • • • Protein and cellular debris clump together Old age – gradual Sudden – diabetes White Surgical removal of lens • https://www.youtube.com/watch?v=4JFmPU50kZY © 2009 Delmar, Cengage Learning Glaucoma • • • • • Intraocular pressure Very painful Irreversible blindness Different reasons One reason is breed predisposition © 2009 Delmar, Cengage Learning • Intracular pressure should be between 12 and 25 mm Hg • Can be measured with a tonometer or tonopen • Usually surgically remove the eye – eye enucleation © 2009 Delmar, Cengage Learning Eye Entropion • An inversion (turned inward) of the eyelid • Causes irritation of the cornea and sclera © 2009 Delmar, Cengage Learning Tear Production • “Dry Eye” Lack of tears allows the normally transparent cornea to become thickened and opaque, leading to blindness. Corneal ulcers and bacterial conjunctivitis are other disorders occurring as a result of dry eye. • Schirmer Tear Test © 2009 Delmar, Cengage Learning Corneal Scratches / Ulceration • If superficial “scratch” – 1st layer – epithelium • Deeper ulceration – 2nd / 3rd layers – the liquid inside the eyeball leaks out, the eye collapses and irreparable damage occurs. © 2009 Delmar, Cengage Learning • Flourescein Stain adheres to ulceration © 2009 Delmar, Cengage Learning Medical Terms for the Ocular System • Additional terms for ocular system tests, pathology, and procedures can be found in the text. • Review StudyWARE to make sure you understand these terms. © 2009 Delmar, Cengage Learning
