1. Special Senses Chapter 8

2. Special Senses  The four special senses are smell, taste, sight, and hearing

3. Eye and Vision  Eye ball is approx 1in diameter.  Protected by fat and the orbit of the skull  Anteriorly protected by the eyelids, lined in eyelashes.  A membrane, conjunctiva, lines the eyelids and covers part of the outer surface of the eye. Can get infected with bacteria or virus, conjunctivitis aka pink eye  Both the eyelid and conjunctiva produces mucus to cover, lubricate, and protect the eye.

5. Eye and Vision  Lacrimal apparatus consists of the lacrimal gland and the various ducts.  The lacrimal gland produces salty tears filled with antibodies and enzymes used to lubricate and disinfect the surface of the eye.  This liquid is emptied into the nose through a duct.

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7. Eye Muscles  There are six muscles attached to the eye, you need to know four and their movements.  Lateral Rectus – moves eye laterally  Medial Rectus – moves eye medially  Superior Rectus – Elevates eye  Inferior Rectus – lowers eye

9. Eye: Internal Structure  Hollow sphere, made up of three layers called tunics, filled with liquid called humors.  The outside tunic of the eye is called the Sclera. White connective tissue, makes up the “whites” of the eyes.  The central anterior portion is modified to be crystal clear, called the cornea

11. Eye: Internal Structure  The second tunic/layer is called the vascular tunic. Has three sections.  Choroid – posterior, lots of blood vessels  Ciliary Body – smooth muscle that holds the lens in place  Iris – most anterior, pigmented, smooth muscle that contracts and relaxes to allow different amounts of light in. Reflex action

13. Eye: Internal Anatomy  The innermost tunic is the retina.  It covers the posterior area of the eye up to the ciliary body.  Contains rods and cones called photoreceptors that respond to light.  Light stimulus starts a neuron chain going through the optic nerve and out to the brain.  The area of the retina that the optic nerve connects to is called our blind spot.

15. Rods Vs. Cones  Rods see grey tones in dim light, usually found on the edge of the retina, used for peripheral vision  Cones see color. Found most abundant in the center of the retina and become less dense toward the edge.  Color blindness results from a malfunction or lack of certain cones genetically. Sex linked.

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20. Lens  Light entering the pupil has to be focused on the retina, this is the job of the lens.  The lens and ciliary body split the eye into anterior (aqueous humor) and posterior (vitreous humor).  Cataract – clouding of the lens  Glaucoma – condition where aqueous humor pressure builds and could cause blindness.

22. Focusing light  The eye is set up to focus light that is 20ft away.  When an object gets closer or further away, the ciliary body (smooth muscle) changes the shape of the lens to refocus light from a different distance.

23. I Need Glasses  Emmetropia – perfect focus  Myopia – nearsighted, light focuses before the retina, concave lens corrects  Hyperopia – farsighted, light focuses after the retina. Convex lens corrects.  Astigmatism – misshapen eye, light is not focused at a point, but scattered.

24. Taste and Smell  Called Chemoreceptors – responds to chemicals.  Olfactory, smell, receptors occupy a postage stamp size area at the top of our nasal cavity.  Olfactory pathways are tied into the limbic system of our brains, smells are very much a part of our memories.

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26. Taste  Taste buds are specific receptors of chemicals in the mouth.  Most reside on the tongue.  Dorsal tongue is covered in Papillae allowing for more surface area.  Five basic taste sensations. Sweet, sour, bitter, salty, and umami.

27. Taste  Sweet – need for carbs  Sour – vitamin C  Bitter – defense from spoiled foods  Salty – need for minerals  Umami – intake of proteins.  Spicy foods excite pain receptors in the mouth. Fact – humans are the only animal to eat spicy foods by choice.

28. Ear Anatomy  The Ear is in charge of hearing as well as balance.  Ear is divided into three major areas: external, middle, and inner.

29. Outer Ear  Composed of the Pinna (shell shaped structure) and the external acoustic meatus (ear canal)  Ear Canal is 1” by ¼” and is carved out of the temporal bone.  Lined with glands that secrete wax for protection.  Outer ear ends at the Eardrum (tympanic Membrane)

30. Middle Ear  AKA tympanic Cavity – air filled cavity in the temporal bone.  Sound collected by the outer ear vibrates the tympanic membrane.  The ossicles (bones of the ear) vibrate in turn, sending vibration to the inner ear.  In order, Malleus (hammer), Incus (anvil, and stapes (stirrup).

31. Middle Ear  Eustachian tube connects middle ear to throat.  Usually closed, opens during yawns and swallowing.  Equalizes pressure on both sides of the eardrum.  Infection can spread from back of throat to middle ear.

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33. Inner Ear  Inner ear is in charge of turning vibration into electrochemical signal.  Also in charge of balance.

34. Inner Ear: Hearing  The cochlea is the bony labyrinth where vibration turns to neuron impulse.  The snail shaped cochlea is filled with perilymph, plasmalike fluid, and also lined with hair cells.  As the stepes of the middle ear vibrates, this liquid is disturbed in the cochlea. This disturbance stimulates the hair cells which start a nerve impulse to the brain.  The amount and location of the disturbed hair cells distinguishes tune and volume. Further down the cochlea, the deeper the sound.

37. Inner Ear: Balance  Above the cochlea is the vestibule and the semicircular canals. These both help with balance.

38. Inner Ear: Balance  Both the vestibule and semicircular canals have hair cells that are covered in a gel.  When the head changes position, the gel is pulled based on gravity. This pulls the hairs, starting a neuron pathway to the brain.  Vestibule controls static equilibrium under water with your eyes closed.  Semicircular canals control dynamic equilibrium. Dizziness and sea sickness.

39. Defects in Hearing  Hearing lose can be caused by a number of problems. Ear wax build up, fusion of the ossicles, etc.  Most hearing lose is caused by exposure to excessively loud noise/music. 120-150 decibels  Talking is ~60db, city traffic is ~80.  Hair cells in the cochlea are knocked over and do not recover. Ringing in the ear, tinnitus.

40. Tears  When tears overflow the eyelids these ducts empty a lot of liquid into the nasal area causing the sniffles.  Tears are caused by irritants or emotional situations.  Clears off dust or irritants  Emotional tears are not well understood but seem to help lower stress.