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The Special Senses
Chapter 17
Objective
• Describe the structure of vertebrate sensory organs and relate structure to function in vertebrate sensory systems.
The 5 Special Senses
1. Olfaction
2. Gustation
3. Vision
4. Equilibrium
5. Hearing
Vision - Eye Anatomy
• Cornea – clear protective layer of eye (also refracts light)
• Iris – colored muscle of eye which protects retina by changing pupil size
• Pupil – allows light into eye
• Aqueous humor – watery fluid filled substance that gives the front of eye its shape
• Lens – refracts light onto retina
• Vitreous humor – jelly like fluid that gives eye it’s shape
Eye Anatomy • Retina – back part of eye that contains rods & cones for detecting
light
• Fovea centralis – contains cones for color vision
• Optic nerve – impulses sent via this nerve to the occipital lobe of the brain
• Blind spot – part of the retina where the optic nerve attaches (lacks rods & cones)
• Sclera – White part of external eye (Outermost protective layer)
• Choroid – middle layer in eye with blood vessels
LASIK
Eyelashes
Sclera
(covered by
conjunctiva)
Site where
conjunctiva
merges with
cornea
Lateral
commissure
Iris
Medial
commissure
Lacrimal
caruncle
Eyelid
Eyelid
Eyebrow
Pupil
Palpebral
fissure
(a) Surface anatomy of the right eye
Problems of Refraction
• Myopia (nearsightedness)—focal point is in front of the retina, e.g. in a longer than normal eyeball • Corrected with a concave lens
• Hyperopia (farsightedness)—focal point is behind the retina, e.g. in a shorter than normal eyeball • Corrected with a convex lens
• Astigmatism—caused by unequal curvatures in different parts of the cornea or lens • Corrected with cylindrically ground lenses, corneal
implants, or laser procedures
Figure 15.14 (1 of 3)
Focal
plane
Focal point is on retina.
Emmetropic eye (normal)
Figure 15.14 (2 of 3)
Concave lens moves focal
point further back.
Eyeball
too long
Uncorrected
Focal point is in front of retina.
Corrected
Myopic eye (nearsighted)
Figure 15.14 (3 of 3)
Eyeball
too short
Uncorrected
Focal point is behind retina.
Corrected
Convex lens moves focal
point forward.
Hyperopic eye (farsighted)
Cataracts
Diabetic retinopathy
Glaucoma
Macular degeneration
Olfactory Organs
• Sensory organs of smell
• Organs have 2 layers:
• Olfactory epithelium
• Lamina propria
• Contains olfactory glands – secretions absorb water, form a thick, pigmented mucus
Special Senses of the Ear
• Special senses of equilibrium and hearing are provided by the inner ear
• Equilibrium
• Position of the head in
space
• Hearing
• Detect and determine
sound waves
Anatomy of the Ear
• 3 regions:
• External ear
• Detects sound waves towards middle ear
• Middle ear
• Collects sound waves
• Inner ear
• Contains sensory
organs
External Ear
• Fleshy and cartilagenous auricle (pinna)
• Provides directional sensitivity
• Ends at the tympanic membrane
• Ear drum
• Thin, semitransparent sheet
• Delicate
• Protected by cerumen
Middle Ear
• Air-filled chamber
• Auditory tube permits equalization on both sides of the tympanic membrane
• 3 tiny bones: • Malleus
• Hammer
• Incus • Anvil
• Stapes • Stirrup
Inner Ear
• Labyrinth of dense bones • 3 subdivisions:
• Vestibule • Saccule • Utricle
• Sensations of gravity and linear acceleration
• Cochlea • Snail shell • Sense of hearing
Equlibrium
• Hair cells receive signals
• Provide info about the direction and strength of stimuli
Hearing
• Receptors can detect frequency and intensity of sounds
• Intensity is measured in decibels (dB) • Normal conversation 60-70dB
• Telephone dial tone 80dB
• Sustained exposure resulting in hearing loss: 90dB
• Rock concert 115dB
• Loudest recommended with protection: 140dB
• Gun blast 140dB
Olfactory Discrimination
• Olfactory system can distinguish thousands of chemical stimuli
• Olfactory
receptors
decline with
age
Gustatory Receptors
• Taste receptors
• Aka taste buds
• An adult has ~3000 taste buds
• 3 types of projections:
• Filiform
• Fungiform
• Circumvallate
Filiform Papillae
• Provide friction
• Help the tongue move around the mouth
• Do not contain taste buds
Fungiform Papillae
• Each contains about 5 taste buds
Circumvallate Papillae
• Contain ~100 taste buds each
• Form a V near the posterior region of the tongue
Aging and Taste
• 10,000 taste buds when born
• # declines dramatically by age 50
• ** olfactory stimuli has a powerful effect on mood & behavior
• ** if we cannot smell the food, we believe it is more bland
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