Chapter 8 The Sensory System Chapter Objectives Upon completion of the chapter the participant will be able to: 1. Describe the structures involved with hearing. 2. Describe the structures involved with seeing. 3. Discuss the physiology of being able to see. 4. Discuss the physiology of being able to hear. 5. Analyze, define, spell and pronounce the medical terms common to the ear. 6. Analyze, define, spell and pronounce the medical terms common to the eye. 7. Successfully complete the review exercises at the end of the chapter. The Eye Our eyes are the receptor organs for the sense of sight and provide the window that lets in the light of the outside world. Light waves are transformed by the eye into nerve impulses that are sent to the occipital lobe of the brain. Here the waves are processed and we experience vision. It is the job of the eye to let light in, focus it, transform it into an impulse and send the impulse to the brain. Light enters the eye through the pupil (pupil/o, core/o) and then passes through the lens (phac/o, phak/o) found behind the pupil. The lens has the ability to adjust its shape in order to adjust to objects that are close at hand and those that are at a distance. As many people age their lens may become cloudy which will affect their ability to see. This condition is referred to as cataracts. The light from the lens then goes to the back of the eyeball where it strikes the retina (retin/o). It is the retina that transforms the image into a nerve impulse. The impulses travel along the optic nerve to the brain. Revised August 2003 -83-
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Chapter 8 The Sensory System
Chapter Objectives
Upon completion of the chapter the participant will be able to:
1. Describe the structures involved with hearing.2. Describe the structures involved with seeing.3. Discuss the physiology of being able to see.4. Discuss the physiology of being able to hear.5. Analyze, define, spell and pronounce the medical terms common to the ear.6. Analyze, define, spell and pronounce the medical terms common to the eye.7. Successfully complete the review exercises at the end of the chapter.
The Eye
Our eyes are the receptor organs for the sense of sight and provide the window that lets in the light of the outside world. Light waves are transformed by the eye into nerve impulses that are sent to the occipital lobe of the brain. Here the waves are processed and we experience vision.
It is the job of the eye to let light in, focus it, transform it into an impulse and send the impulse to the brain. Light enters the eye through the pupil (pupil/o, core/o) and then passes through the lens (phac/o, phak/o) found behind the pupil. The lens has the ability to adjust its shape in order to adjust to objects that are close at hand and those that are at a distance. As many people age their lens may become cloudy which will affect their ability to see. This condition is referred to as cataracts. The light from the lens then goes to the back of the eyeball where it strikes the retina (retin/o). It is the retina that transforms the image into a nerve impulse. The impulses travel along the optic nerve to the brain.
The eye consists of two parts: the inner eye and the outer eye.
Inner Eye
Consists of three layers: outer, middle and inner Outer layer consists of the cornea (corne/o, kerat/o) and the sclera (scler/o).
The cornea is the transparent anterior portion of the sclera that allows light into the eye and allows for focusing of the light on the back of the eye. The sclera is known as the “white of the eye” which maintains the shape of the eye and protects the delicate inner structures.
Middle layer is the vascular layer and is referred to as the uvea (uve/o) and consists of the choroid (choroid/o) the ciliary body (cycl/o) and iris (ir/o, irido/, irit/o, ir/i). The choroid is the inner lining of the sclera and has the blood vessels that nourish the eye. The ciliary body consists of muscles that change the shape of the lens so you are able to see things at various distances. This process is
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referred to as accommodation. The ciliary body is responsible to produce a liquid that bathes the anterior surface of the eye.
The iris is the circular colored part of the eye. The center of the iris is a circular opening called the pupil (pupill/o, core/o) that regulates the amount of light that can get into the eye. In bright light the pupil will constrict and in darkness it will dilates.
Inner layer consists of the retina. This is nerve tissue made up of rods and cones. They transform light into nerve impulses.
Outer Eye
The outer eye consists of the orbital cavity, ocular muscles, the eyelids (palpebr/o, blephar/o) the conjunctival membrane (conjunctiv/o) and the lacrimal apparatus (lacrim/o, dacry/o). The orbital cavity acts as a protective device for the eyeball. The six muscles allow the eye to move in all directions. The eyelid acts as a protection from dust and dirt entering the eye and the membrane lubricates as well as protects the eyeball. The lacrimal glands produce tears that continuously bathe the eye. The tears drain into the back of the nasal cavity that explains why your nose runs when you cry.
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Ciliary Body
Conjunctiva
Cornea
Anterior ChamberPath of Light
Blood Vessels
Optic Nerve
Vitreous
Sclera
Choroid
Iris
Pupil
Lens
Choroid
Retina
Word Parts for the Eye
aque/o water blephar/o, palpebr/o eyelid chrom/o color chori/o, choroid/o choroids conjunctiv/o conjunctiva core/o, pupill/o pupil corne/o, kerat/o cornea cycl/o ciliary body dacry/o, lacrim/o tear/lacrimal duct, tears dipl/o double irid/o, ir/o, ir/i, irit/o iris mi/o contraction, less, smaller mydri/o wide, dilation ocul/o, ophthalm/o, opt/o, optic/o, opt/i eye, vision, sight papill/o optic disc phac/o, phak/o lens phot/o light presby/o old age retin/o retina scler/o sclera ton/o tension uve/o uvea vitre/o glasslike, glassy, gel like -chalasis relaxation -opia, -opsia vision, visual condition -ptosis drooping, sagging -pexy put in place -tropia, -tropion turning
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Iris
ScleraPupil
Lacrimal Gland
Conjunctiv
Nasolacrimal
eso- inward exo- outward extra- on the outside intra- on the inside
Term Analysis and Definition (The Eye)
Word Part Term Term Analysis Definition
aque/o aqueous humor
aque = water-ous = pertaining tohumor = body fluid
Pertaining to the watery fluid found in the anterior chamber of the eye.
ton/o tonometry ton = tension-metry = process of measuring
Measurement of the intraocular pressure
uve/o uveitis uve = uvea-itis = inflammation
Inflammation of the uvea of the eye
vitre/o vitreous humor vitre = gel-like-ous = pertaining to
Pertaining to the gel-like substance in the posterior cavity of the eye
-chalasis blepharochalasis
blephar = eyelid-chalasis = relaxation
Relaxation of the eyelid
-tropia esotropia
exotropia
eso = inward-tropia = turning
exo = outward
Turning inward of the eyeball. Also referred to as “cross-eyes”
Turning outward of the eyeball
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Word Part Term Term Analysis Definition
-opia, -opsia
amblyopia
diplopia
presbyopia
hyperopia
myopia
ambly = dull, dim-opia = vision
di = double
presby = old age
hyper = above, excessive
my = to shut
Dimness of vision
Double vision
Impaired vision due to aging
Farsightedness ( the light rays go beyond the retina)
(Light rays focus in front of the retina) nearsightedness
-tropion ectropion
entropion
ec = out-tropion = turning
en = inward
Outward turning of the eyelid
Inward turning of the eyelid
Vocabulary Words:
Accommodation The process whereby the eyes make adjustments for seeing objects at various distances
Cararact An opacity of the crystalline lens or its capsule; most often occurs in adults past middle age.
Conjunctivitis Inflammation of the conjunctiva caused by allergy, trauma, chemical injury, bacterial, viral or infection. The type ‘pinkeye’ is infectious and contagious
Enucleation A process of removal of the eyeball from the orbit
Glaucoma A disease characterized by a increased intraocular pressure which results in atrophy of the optic nerve and blindness
Nystagmus An involuntary, constant, rhythmic movement of the eyeball
Snellen Chart A chart for testing visual acuity
Strabismus a squint
Abbreviations:
OP intraocular pressure
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OD oculus dexter (right eye)
OS oculus sinister (left eye)
PERLA pupil equal and reactive to light and accommodation
REM rapid eye movement
The Ear
The ear is the sensory organ that allows us to hear. It consists of the external ear, middle ear and inner ear. The ear is responsible for hearing and as well plays an important role in our balance. The word roots audi/o, and audit/o mean hearing.
The hearing process consists of detecting and transmitting sound waves for interpretation. Detecting involves receiving the sound stimulus and then it is transmitted though a nerve called the auditory nerve to the temporal lobe of the brain where it is interpreted.
External Ear
Composed of the auricle, external auditory meatus, and eardrum or the tympanic membrane.
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Cochlea
Stapes
Incus
Malleus
Auricle
SemicircularCanals
Eustachian tube
Tympanic Membrane
External ear Canal
Auricle (pinn/i, aur/o, aur/i) is also referred to as the pinna and is the external part of the ear that is attached to the head. It catches the sound waves and channels them into the external ear canal.
The canal that moves into the ear from the pinna is referred to as the external auditory canal. It is responsible to channel the sound waves toward the eardrum.
Middle Ear
The middle ear begins with the tympanic membrane (tympan/o, myring/o) or the eardrum as it is commonly referred to. When the sound waves reach the membrane they cause it to vibrate and the vibration causes the waves to travel into the middle ear.
In the middle ear are three small bones malleus, incus, and stapes. These bones are often referred to as the hammer, anvil and stirrup because of their shape. These bones begin vibrating when the sound waves hit them.
The air pressure that is found on either side of the eardrum must be kept equal. To do this there is a eustachian tube that connects the middle ear to the throat. If for some reason this tube becomes blocked a sense of pressure will build up in the middle ear and your ability to hear is affected.
The middle ear is surrounded by mastoid cells (mastoid/o) that are hollow spaces in the mastoid bone located directly behind the ear.
Inner Ear
If you think of a sponge you have a good idea of what the inner ear is like; a twisting series of canals and larger spaces. These canals and spaces are encased in bone that is referred to as the bony labyrinth (labyrinth/o).
This is the part of the ear that has the receptors needed for both hearing and your balance.
The bony labyrinth consists of the vestibule, semicircular canals and the cochlea. The vestibule and semicircular canals are important in maintaining your sense of balance. The cochlea is responsible for hearing.
Sound is transmitted into the cochlea through the oval window. In the cochlea is the organ of Corti that contains fine hair cells that move because of the sound waves. This movement stimulates the nerve cells that create the impulse that is transmitted to the brain.
Word Parts for the Ear
Roots
acoust/o, acous/o hearing, related to hearing audi/o, audit/o hearing, ear aur/o, aur/i,ot/o ear, hearing