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7
The Sensory
Systems
Lesson 7.1: The Eye
Lesson 7.2: The Ear
Lesson 7.3: Smell and Taste
Chapter 7: The Sensory Systems
Lesson 7.1
The Eye
External Structures of the Eye
• Tarsal glands
– located in the eyelids
– produce an oily secretion
• Ciliary glands
- modified sweat glands
- located between the eyelashes
• Conjunctiva
- membrane that covers the exposed eyeball and lines
the eyelid
- secretes a lubricating mucus
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External Structures of the Eye
• Lacrimal glands
-
above the lateral end of each eye
release tears through excretory ducts
tears contain lysozyme, an enzyme that attacks bacteria
tears drain into the lacrimal canaliculi located in the
medial corner of each eye, then to the nasolacrimal
duct, then to the nasal cavity
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External Structures of the Eye
• tarsal glands
• ciliary glands
• conjunctiva
• lacrimal glands
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Extrinsic Muscles
• 6 extrinsic eye muscles
• named by shape and location
– rectus – long muscle fibers
– oblique – muscles are at an angle
– location – inferior, superior, lateral, medial
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Extrinsic Muscles
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Internal Structures of the Eye
• eyeball is a hollow chamber filled with aqueous
and vitreous humor- fluids that help the eyeball
maintain shape
• 3 tissue layers form the wall of the eyeball
– sclera
– choroid
– retina
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3 Tissue Layers of the Eyeball
• Sclera
- outer layer of the eye
- consists of the white part of the eye and the cornea
- cornea contains no blood supply
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3 Tissue Layers of the Eyeball
•
Choroid
- middle layer of the eye
- contains rich supply of blood vessels
- includes the iris
o colored part of eye
o contains 2 sets of muscles which control the amount of light
admitted to the eye
 sphincter pupillae – contracts in the presence of bright light
or when the eye focuses on an object up close – pupil
grows smaller
 Dilator pupillae – contracts in the presence of dim light –or
when the eye focuses on a distant object – pupil grows
larger
- includes the pupil – opening through which light passes into the
- the interior of the eye
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3 Tissue Layers of the Eyeball
• Retina
- innermost layer of the eye
- contains 2 types of light-sensitive sensory neurons
o rods – activated in dim light
o cones – sensitive to bright light and provide color vision
- bipolar neurons provide connections between the retina
and rods and cones
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Internal Structures of the Eye
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Blind Spot
• area on the retina where the optic nerve joins the
eye – optic disc
• no rods and cones on the optic disc
• we do not perceive this blind spot because the
brain fills in this visual info from the other eye
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Lens
• located behind the iris
• transparent, flexible structure
• held in place by suspensory ligaments which
attach to the ciliary body
- ciliary body contracts to view objects within 20 ft which
changes the shape of the lens – after the age of 40, the
ability of the ciliary body to contract diminishes
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Vision
• optic nerve
- receive impulses from the rods and cones and transmits
the impulses to the brain
• optic chiasm
- location in the brain where the optic nerves cross
• optic tracts
- nerve fibers exiting the optic chiasm
- carry visual stimuli to the occipital lobe
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Vision Disorders
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Vision Disorders
• vision disorders
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Eye Diseases
• Conjunctivitis
– also known as pink eye
– contagious inflammation of the conjunctiva
• Cataracts
- Clouding of the transparent lens of the eye causing
blurred vision, poor night vision, and halos around light
• Glaucoma
- increased pressure within the eyeball
• macular degeneration
- progressive loss of central vision
- peripheral vision remains unaffected
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Eye Diseases
• diabetic retinopathy
- caused by long-term diabetes
- damage to the retina caused by swelling and leaking
of the vessels that supply blood to the retina
- leading cause of blindness in American adults
• vitreous floaters
- tiny chunks of the gel-like vitreous humor break off and
float in the aqueous humor
- irregular shaped specks drift within your field of vision
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Review and Assessment
Fill in the blanks with: choroid, cornea, cones, or
vitreous.
1. The pupil is part of the _______________ tissue
layer.
2. The two humors are aqueous and
_______________.
3. The retina contains the rods and
_______________.
4. The clear part of the sclera is the
_______________.
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Chapter 7: The Sensory Systems
Lesson 7.2
The Ear
Anatomy of the Ear
• external ear
– auricle
 Irregularly-shaped outer portion of ear
– auditory canal
 short, tube-like structure connected to the auricle
 walls are lined with skin that contain ceruminous glands
that produce cerumen (earwax)
– tympanic membrane
 eardrum
 soundwaves cause the eardrum to vibrate
 Separates the outer ear from the middle ear
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Anatomy of the Ear
• middle ear (tympanic cavity)
– ossicles – smallest bones in the body
• hammer, anvil, stirrup
• transmit and amplify sound waves
• tympanic membrane attaches to the hammer which
attaches to the anvil which attaches to the stirrup which
attaches to the oval membrane
– Eustachian tube
• connects the middle ear to the pharynx
• equalizes pressure on either side of the tympanic
membrane
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Anatomy of the Ear
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Anatomy of the Ear
• internal ear
-
semicircular canals
- bony labyrinth
 winding tunnels
 filled with clear fluid called perilymph
- membranous labyrinth
 inside the bony labyrinth
 filled with thicker fluid called endolymph
– cochlea
• cochlear nerve carries information about hearing
– vestibule
• vestibular nerve carries information about balance
-
vestibular and cochlear nerves join to form the vestibulocochlear
nerve
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Inner Ear
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Hearing
• Sound waves enter the ear,
– transmitted through the auditory canal - cause the tympanic
membrane to vibrate
• the hammer, anvil, and stirrup transmit and amplify the
vibrations to the membrane of the oval window causing the
fluid in the inner ear (endolymph) to be set into motion
• cochlear duct - the membranous labyrinth inside the
cochlea
• inside the cochlear duct is the organ of Corti which
contains hair cells which are specialized hearing receptors
• these hair cells are stimulated by the motion of the
endolymph
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Hearing
• stimulation of cilia cells stimulates the cochlear
branch of the vestibulocochlear nerve
• the cochlear nerve sends the impulse to the
auditory region of the brain in the temporal lobe
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Balance/Equilibrium
• hair cells in the semicircular canals are stimulated
by movement of endolymph in the canals
• vestibular nerve is stimulated and information on
body orientation is sent to the cerebellum
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Disorders and Infections of the Ear
• Deafness
• Tinnitus
- ringing in the ears
- hair cells in the organ of Corti are damaged
- often caused by repeated exposure to loud noise
• external otitis (swimmer’s ear)
- bacterial or fungal infection of the auditory canal caused
by immersion in contaminated water
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Disorders and Infections of the Ear
• otitis media (middle ear infection)
- caused by bacteria or virus
- common in infants and toddlers because their
Eustachian tubes are not fully developed
- treated with antibiotics or in chronic cases, tubes are
inserted in the tympanic membrane to relieve pressure
• labyrinthitis (inner ear infection)
- often affects the semicircular canals
- can cause vertigo (dizzines), nausea, and vomiting
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Review and Assessment
True or False?
1. External otitis is swimmer’s ear.
2. The ossicles are in the external ear.
3. Hair cells are responsible for equilibrium.
4. The cochlea is part of the inner ear.
5. Labyrinthitis is an inner ear infection.
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Chapter 7: The Sensory Systems
Lesson 7.3
Smell and Taste
Smell and Taste
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•
•
•
olfactory sense (sense of smell)
injuries and disease of the nose
gustatory sense (sense of taste)
disorders of the tongue
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Olfactory Sense
•
•
•
•
•
•
olfactory region
olfactory receptor cells
olfactory hairs
olfactory filaments
olfactory nerve
olfactory bulb
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Olfactory Sense
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Injuries and Disorders of the Nose
• rhinitis
– inflammation of nasal membrane
• septum problems
– deviated septum
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Gustatory Sense
•
•
•
•
•
•
taste buds
papillae
gustatory cells
gustatory hairs
taste pores
tastants
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Disorders of the Tongue
• infection
– severely bitten tongue during a traumatic accident
– tongue piercing
• injury
• abnormal growth
– hairy tongue
– burning mouth syndrome
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Review and Assessment
Match these words with 1–4 below: gustatory,
gustatory hairs, olfactory hairs, rhinitis.
1. inflammation of the nasal membrane
2. sense of taste
3. part of taste bud
4. part of sense of smell
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