Special Senses Unit 6.7 (6 th Edition) Chapter 7.7 (7 th Edition) 1
Learning Objectives Identify the five special senses. Identify the four general senses. Trace the pathway of light rays as they pass through the eye and how sight works. Identify the major parts (anatomy) of the eye. Distinguish between the major eye abnormalities. Identify the major parts (anatomy) of the ear. Trace path of sound waves as pass through ear. Explain how the ear helps maintain balance. Identify major diseases affecting the ear. Distinguish between the four main tastes. Explain the role of the nose in our sense of smell. 2
Fun Facts About the Special Senses Color blindness affects about 1 in 30 people and is more common in men than women. Our sense of smell can tell the difference between approximately 6,000 smells! As you grow older, your sense of smell gets worse. A bloodhound can smell at least 1000 times better than humans. If saliva cannot dissolve something, you cannot taste it. 2/3 of the human population has less than perfect vision. Everyone has a unique smell, except for identical twins. 3
Special Senses vs. General Senses 5 Special Senses senses that have specific organs devoted to them Sight (eye) Hearing (ear) Taste (tongue) Smell (nose) Balance (ear) 4 General Senses senses that do nothave a specialized organ but comes from all over the body (skin and internal organs) Touch Pain Heat Cold 4
How Does Sight Work? Light rays enter the eye through the cornea and then pupil. The convex lens behind the eye focuses the light to form an image on the screen at the back of the eye (retina). This image is upside down. Signals from photoreceptors travel along nerve fibers. The optic nerve carries impulses to brain (occipital lobe). Brain interprets impulses as vision, or sight. 5
Eye Anatomy *Know the highlighted terms* 6
Eye Protection & Layers Protection enclosed in bony socket of skull eyelids & eyelashes keep out dirt and germs lacrimal glands produce tears which moisten and cleanse eye conjunctiva is a mucous membrane that lines the eyelids Three Eye Layers sclera (white) tough outermost layer & maintains eye shape cornea transparent part of sclera & allows light to enter eye choroid coat middle layer of eye interlaced with blood vessels that nourish eye retina innermost layer of eye has many nerve cells that transmit impulses to optic nerve cones nerve cells sensitive to color and used when light rods nerve cells used for vision when it is dark 7
Eye Anatomy & Physiology Iris colored portion of eye located behind cornea pupil is opening (black) in iris center contains 2 muscles that control pupil size regulates how much light enters the eye Lens circular structure behind the pupil refracts (bends) light rays so that they focus on retina Aqueous Humor clear, watery fluid that fills space between cornea & iris helps maintain forward curvature of eye & refracts light Vitreous Humor jellylike substance that fills area behind lens helps maintain eye shape and also refracts light 8
Eye Diseases and Abnormalities Amblyopia (Lazy Eye) occurs in early childhood poor vision in one eye causes dominance in the good eye if condition not treated by 8-9 years old, blindness may occur Astigmatism abnormal shape/curvature of cornea (football instead of sphere) causes blurred vision Cataract normally clear lens becomes cloudy or opaque typically the result of aging or trauma Conjunctivitis (Pink Eye) very contagious inflammation of conjunctiva usually caused by virus or bacterium Glaucoma increased pressure in eye caused by excess of aqueous humor common after age 40 and is leading cause of blindness 9
Impaired Vision 10
The Ear and Hearing The Ear transmits impulses from sound waves to auditory nerve impulses carried to brain for interpretation as hearing Three Main Ear Sections Outer Ear pinna (auricle) visible part of the ear that leads to auditory canal glands in this canal produce cerumen(ear wax) that protects ear sound waves travel through canal to tympanic membrane (eardrum) eardrum vibrates when waves hit it & transmits waves to middle ear Middle Ear small cavity in temporal bone that contains three small bones ossicles- malleus, incus, and stapes bones connect and transmit sound waves from eardrum to inner ear Inner Ear most complex part of ear contains cochlea containing delicate, hair like cells that are receptors organ of Corti transmits impulses from sound waves to auditory nerve impulses carried to temporal lobe where interpreted as hearing 11
Ear Anatomy 12
The Ear and Balance Semicircular Canals Located in inner ear Contain liquid and delicate hair-like cells that bend when liquid moves with head and body movements Impulses sent from these canals to cerebellum of brain help to maintain our sense of balance and equilibrium 13
Ear Diseases and Abnormalities Conductive Hearing Loss occurs when sound waves are not conducted to the inner ear possible causes include wax plug, foreign body obstruction, an infection, or ruptured eardrum surgery and hearing aids are common form treatments Sensory Hearing Loss (Deafness) occurs when there is damage to inner ear or auditory nerve cochlear implants can improve severe hearing loss Meniere s Disease collection of fluid in labyrinth of inner ear and degeneration of hair cells symptoms - severe dizziness, ringing in the ears, nausea, loss of balance Otitis Externa inflammation of external auditory canal (Swimmer s Ear) caused by pathogenic organism (virus or bacteria) Otitis Media inflammation or infection of middle ear caused by virus or bacterium and frequently follows sore throat 14
The Tongue and Taste The Tongue mass of muscle tissue with projections called papillae papillae contain taste buds that are stimulated by flavor Four Main Tastes Sweet (tip of tongue) Salty (tip of tongue) Sour (sides of tongue) Bitter (back of tongue) Taste is influenced by smell 15
The Nose and Smell The nose is the organ of smell olfactory receptors are located in upper part of nasal cavity impulses from receptors are carried to brain by the olfactory nerve the sense of smell is more sensitive than taste human nose can detect over 6,000 different smells smell and taste are closely linked if you have a cold, your sense of smell and taste are impaired 16