Principles of Human Anatomy and Physiology, 11e1 Chapter 17 The Special Senses Lecture Outline

Principles of Human Anatomy and Physiology, 11e2 Chapter 17 The Special Senses Smell, taste, vision, hearing and equilibrium Housed in complex sensory organs Ophthalmology is science of the eye Otolaryngology is science of the ear

Smell Smell is called olfaction We recognize over 10,000 distinct odors Smell and memory are linked in our brains Principles of Human Anatomy and Physiology, 11e3

Taste Taste is gustation Our taste buds help us distinguish different tastes Principles of Human Anatomy and Physiology, 11e4

Vision More than half of the sensory receptors in our body are in our eyes Your eyeball is 1 inch in diameter Principles of Human Anatomy and Physiology, 11e5

Hearing The ear changes sound vibrations into electrical signals that the brain interprets as sound The ear has 3 main parts: external, middle, and internal ears Principles of Human Anatomy and Physiology, 11e6

Equilibrium The ear is also important in our equilibrium Equilibrium helps us balance and maintain upright posture. Principles of Human Anatomy and Physiology, 11e7

8 Development of the Eyes The eyes begin to develop 22 days after fertilization, small grooves called optic grooves appear. Eyelids form 8 weeks after fertilization. Eyes remain closed until 26 weeks of development.

Principles of Human Anatomy and Physiology, 11e9 Development of the Ears The inner ear forms first, 22 days after fertilization. Middle ears come next, followed by the outer ear.

Principles of Human Anatomy and Physiology, 11e10 AGING AND THE SPECIAL SENSES Age related changes in the eyes –Presbyopia (can’t see close) –Cataracts (film on the lenses) –Weakening of the muscles that regulate the size of the pupil (trouble seeing in the dark and bright light) –Diseases such as age related macular disease, detached retina, and glaucoma (all cause vision loss) –Decrease in tear production (dry eyes) –Sharpness of vision as well as depth and color perception are reduced.

Principles of Human Anatomy and Physiology, 11e11 AGING AND THE SPECIAL SENSES After age 50 some individuals experience loss of olfactory and gustatory receptors (smell and taste) Age related changes in the ears –Presbycusis – hearing loss due to damaged or loss of hair cells in the organ of Corti –Tinnitus (ringing in the ears) becomes more common

Principles of Human Anatomy and Physiology, 11e12 DISORDERS: HOMEOSTATIC IMBALANCES A cataract is a loss of transparency of the lens that can lead to blindness. Glaucoma is abnormally high intraocular pressure, due to a buildup of aqueous humor inside the eyeball, which destroys neurons of the retina. It is the second most common cause of blindness (after cataracts), especially in the elderly.

Principles of Human Anatomy and Physiology, 11e13 DISORDERS: HOMEOSTATIC IMBALANCES Meniere’s syndrome is a malfunction of the inner ear that may cause deafness and loss of equilibrium. Otitis media is an acute infection of the middle ear, primarily by bacteria. It is characterized by pain, malaise, fever, and reddening and outward bulging of the eardrum, which may rupture unless prompt treatment is given. Children are more susceptible than adults.

Special Senses Project 1. Choose a sense and sign-up for a presentation date. 2. Create something to share for your sense. Examples from last year: Smell: perfume manufacturing; smell + memories; examples of the 10,000 smells Taste: food sampling; drawings of the tongue; the 5 different tastes Vision: color-blind tests; color wheels; eyeball anatomy Hearing: binural beats; music for developing fetuses; music for studying; affects of different decibels Equilibrium: balance testing, yoga poses for balance Principles of Human Anatomy and Physiology, 11e14

Principles of Human Anatomy and Physiology, 11e15 Olfaction Olfaction is the sense of smell. It is a chemical sense, because smell comes from the interaction of molecules with sensory neurons called olfactory receptors. The chemicals that cause smell are called odorants and can evoke strong emotional responses or memories We can recognize 10,000 different smells!

Principles of Human Anatomy and Physiology, 11e16 Diseases/Disorders Women have a keener sense of smell than men do, especially around the time of ovulation. Smoking impairs the sense of smell. Hyposmia is the reduced ability to smell, which occurs in 75% of people age 80 and older. –it can also be caused by head injury, disease, steroids, and antihistamines.

Principles of Human Anatomy and Physiology, 11e17 Gustation Gustation is the sense of taste. It is also a chemical sense. –To be detected, molecules must be dissolved. –Taste stimuli classes include sour, sweet, bitter, salty, and umami (savory). –Gustation is closely linked to olfaction, without the sense of smell, you cannot taste.

Principles of Human Anatomy and Physiology, 11e18 Gustatory Sensation: Taste 10,000 taste buds found on tongue, soft palate & larynx They are found on elevations called papillae. The number of taste buds declines with age.

Principles of Human Anatomy and Physiology, 11e19 Anatomy of Taste Buds An oval body consisting of 50 receptor cells surrounded by supporting cells A single gustatory hair projects upward through the taste pore

Principles of Human Anatomy and Physiology, 11e20 Physiology of Taste Mechanism –Dissolved substance (food) contacts gustatory hairs –Receptor potential results in neurotransmitter release –Nerve impulses are formed –These nerve impulses travel to the medulla oblongata, the hypothalamus, and the cerebral cortex, where they are interpreted.

Taste Diseases/Disorder Taste aversion is the link that forms between unpleasant tastes and refusal to eat certain foods. sweet foods evoke pleasure Bitter foods evoke disgust This was an evolutionary adaptation to avoid ingesting poisons People with cancer may develop taste aversions to most food due to radiation treatment and resulting nausea Principles of Human Anatomy and Physiology, 11e21

Principles of Human Anatomy and Physiology, 11e22 VISION More than half the sensory receptors in the human body are located in the eyes. A large part of the cerebral cortex is devoted to processing visual information.

Principles of Human Anatomy and Physiology, 11e23 Anatomy of the Eye Eyelids Eyelashes Eyebrows Lacrimal (tearing) apparatus Extrinsic Eye muscles

Principles of Human Anatomy and Physiology, 11e24 Eyelids The eyelids have several functions: –Shade the eyes during sleep –Protect the eyes from excessive light –Protection from foreign objects –Keep the eyes moist –Eyelids have glands that secrete both oil and sweat –The upper eyelid is more mobile

Principles of Human Anatomy and Physiology, 11e25 Eyelashes & Eyebrows Eyelashes & eyebrows help protect from foreign objects, perspiration & sunlight Sebaceous glands are found at base of eyelashes An infection of these glands can cause a sty Eyeball = 1 inch diameter

Principles of Human Anatomy and Physiology, 11e26 Lacrimal Apparatus About 1 ml of tears produced per day. Spread over eye by blinking. Contains bactericidal enzyme called lysozyme.

Principles of Human Anatomy and Physiology, 11e27 Extraocular Muscles There are 6 muscles that control eye movement

Principles of Human Anatomy and Physiology, 11e28 Tunics (Layers) of Eyeball The eye is constructed of three layers –Fibrous Tunic –Vascular Tunic –Nervous Tunic

Principles of Human Anatomy and Physiology, 11e29 Outer layer of the eyeball Transparent The cornea helps focus light 3 layers Transplants – common & successful –no blood vessels so no antibodies to cause rejection Nourished by tears & aqueous humor Makes up the “whites” of our eyes Fibrous Tunic -- Description of Cornea

Principles of Human Anatomy and Physiology, 11e30 Vascular Tunic – Middle Layer Contains the iris: the colored part of the eyeball. It is shaped like a flattened donut. The iris regulates light entering the pupil, which is the hole in the center of the iris (the black part).

Principles of Human Anatomy and Physiology, 11e31 Vascular Tunic -- Description of lens Also contains the lens, which focuses the light entering the eye

Principles of Human Anatomy and Physiology, 11e32 Nervous Tunic -- Retina Posterior 3/4 of eyeball Where the optic nerve enters the eye Location of the retina, which supplies blood to the eye View with Ophthalmoscope

Principles of Human Anatomy and Physiology, 11e33 Photoreceptors Photoreceptors are specialized cells that convert images (light rays) into nerve impulses Rods –specialized for black-and-white vision in dim light –permit us to see shapes and movement. –120 million rods Cones –specialized for color vision and sharpness of vision (high visual acuity) in bright light –There are blue, green and red cones that work together to interpret colors. –6 million cones

Principles of Human Anatomy and Physiology, 11e34 Cavities of the Interior of Eyeball Anterior cavity (anterior to lens) –filled with aqueous humor continually drained replaced every 90 minutes Posterior (Vitreous) cavity (posterior to lens) –filled with vitreous body (jellylike) –formed once during embryonic life –Clears debris from the inner eye

Principles of Human Anatomy and Physiology, 11e35 Diseases/Disorders 1. Glaucoma –Increased pressure in the eye –problem with drainage of aqueous humor –may produce degeneration of the retina and blindness 2. Presbyopia -as you age, you lenses lose elasticity and you can no longer read print up close, bifocal glasses can correct this.

Principles of Human Anatomy and Physiology, 11e36 Refraction Abnormalities Myopia is nearsightedness (you can’t see things far away) Hyperopia is farsightedness (you can’t see things near) Astigmatism is a refraction abnormality due to an irregular curvature of either the cornea or lens.

Principles of Human Anatomy and Physiology, 11e37 Physiology of Vision Vision transduction is the process that takes what the eyes see and changing it into something that the brain can read. The first step is that light is absorbed by photopigments in the photoreceptors (rods and cones)

Principles of Human Anatomy and Physiology, 11e38 Photoreceptors The health of your photoreceptors depends on Vitamin A and carotene, found in: –Carrots –Spinach –Broccoli –Yellow squash –liver

Principles of Human Anatomy and Physiology, 11e39 Application: Color Blindness & Night Blindness Color blindness (sex-linked, more common in men) –inability to distinguish between certain colors –absence of certain cone photopigments –red-green color blind person can not tell red from green Night blindness (nyctalopia) –difficulty seeing in low light –possibly due to deficiency of vitamin A

Principles of Human Anatomy and Physiology, 11e40 Brain Pathways of Vision

Principles of Human Anatomy and Physiology, 11e41 Processing of Image Data in the Brain Visual information in optic nerve travels to –hypothalamus to establish sleep patterns based upon circadian rhythms of light and darkness –midbrain for controlling pupil size & coordination of head and eye movements –occipital lobe for vision

Principles of Human Anatomy and Physiology, 11e42 HEARING AND EQUILIBRIUM The external (outer) ear collects sound waves. The middle ear (tympanic cavity) is a small, air-filled cavity in the temporal bone that contains auditory ossicles (middle ear bones, the malleus, incus, and stapes), the oval window, and the round window The internal (inner) ear is also called the labyrinth because of its complicated series of canals

Principles of Human Anatomy and Physiology, 11e43 Anatomy of the Ear Region

Principles of Human Anatomy and Physiology, 11e44 External Ear The external (outer) ear collects sound waves and passes them inwards Structures 1. auricle or pinna elastic cartilage covered with skin 2. external auditory canal curved 1” tube of cartilage & bone leading into temporal bone ceruminous glands produce cerumen = ear wax 3. tympanic membrane or eardrum –Thin, semi-transparent partition between the external canal and the middle ear

Principles of Human Anatomy and Physiology, 11e45 Middle Ear Cavity

Principles of Human Anatomy and Physiology, 11e46 Middle Ear Cavity Air filled cavity in the temporal bone 3 ear ossicles (bones) connected by synovial joints –malleus attached to eardrum, incus & stapes attached by foot plate to membrane of oval window Auditory tube leads to nasopharynx –helps to equalize pressure on both sides of eardrum (such as when yawning or swallowing) –“ear popping”

Principles of Human Anatomy and Physiology, 11e47 Muscles of the Ear Stapedius muscle inserts onto stapes –prevents very large vibrations of stapes from loud noises Tensor tympani attaches to malleus –limits movements of malleus & stiffens eardrum to prevent damage

Principles of Human Anatomy and Physiology, 11e48 Inner Ear - Bony Labyrinth The bony labyrinth is a series of cavities and canals in the temporal bone. It is divided into 3 main areas: –Semicircular canals –Vestibule –cochlea

Principles of Human Anatomy and Physiology, 11e49 Semicircular Canals Projecting upward and posteriorly from the vestibule are the three bony semicircular canals. One end of each canal enlarges into a swelling called the ampulla. The portions of the membranous labyrinth that lie inside the semicircular canals are called the semicircular ducts (membranous semicircular canals).

Vestibule The vestibule is the oval central portion of the bony labyrinth. It contains receptors for equilibrium Principles of Human Anatomy and Physiology, 11e50

Principles of Human Anatomy and Physiology, 11e51 Cochlea The cochlea contains receptors for hearing. It is shaped like a snail. It makes 3 turns around a small bony core called the modiolus. It is attached to the Organ of Corti, which has tiny hairs that bend when sound waves reach them.

Principles of Human Anatomy and Physiology, 11e52 Physiology of Hearing - Overview Auricle (outer ear) collects sound waves Eardrum vibrates –slow vibration in response to low-pitched sounds –rapid vibration in response to high-pitched sounds Ossicles (ear bones) then begin to vibrate. The oval window begins to vibrate. Fluid pressure waves move through the cochlea Small hairs in the inner ear begin to move, and these attach to sensory neurons that generate nerve impulses which travel to the brain (nerve VIII to the midbrain, thalamus, and cerebral cortex where it is interpreted).

Principles of Human Anatomy and Physiology, 11e53 Deafness Nerve deafness –possibly nerve damage (CN VIII), but usually damage to hair cells from antibiotics, high pitched sounds, anticancer drugs, etc. –person may fail to notice loss until they have difficulty hearing frequencies of speech Conduction deafness –perforated eardrum –vibrations are not “conducted” to hair cells

Principles of Human Anatomy and Physiology, 11e54 Physiology of Equilibrium (Balance) Static equilibrium –maintain the position of the body (head) relative to the force of gravity Dynamic equilibrium –maintain body position (head) during sudden movement of any type--rotation, deceleration or acceleration

Principles of Human Anatomy and Physiology, 11e55 Otolithic Organs: Saccule and Utricle Two organs control static equilibrium: –Saccule: in the inner ear –Utricle: in the inner ear, larger –They both contain hair cells and sensory receptors that detect how our body is moving

Principles of Human Anatomy and Physiology, 11e56 Membranous Semicircular Ducts The three semicircular ducts maintain dynamic equilibrium. –anterior, posterior & horizontal ducts detect different movements (combined 3-D sensitivity) The cristae (hair cells) in the semicircular ducts are the primary sense organs of dynamic equilibrium. When the hairs bend, nerve impulses are sent to the brain

Principles of Human Anatomy and Physiology, 11e57 Equilibrium Pathways in the CNS Nerve VIII (the vestibulocochlear nerve) sends signals to -the medulla -the pons -the cerebellum The cerebellum coordinates these signals and helps correct balance.