THE SPECIAL
SENSES
Victoria Frawert
Anatomy
THE SENSES
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There are five general senses: Touch, sight, taste,
smell, and hearing. Equilibrium is considered a
special sense as well, found in the ear.
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Chemical Senses (Taste & Smell)
Chemoreceptors – Receptors for taste & smell that only
respond to chemicals.
 Excited by chemicals dissolved in saliva & airborn
chemicals dissolved in nasal membranes.
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Taste buds: located in oral cavity; 10,000; most in
tongue papillae; each taste bud has 40-100 epithelial
cells made of 3 major types.
Supporting Cells: separate and insulate
 Receptor Cells: deal with taste
 Basal cells: like stem cells, they give rise to new cells
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Taste Sensations
Sweet at tip of tongue
 Salty & sour on the sides
 Bitter in the back
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Physiology of Taste
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Activation
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To be tasted, first must be dissolved in saliva, diffuse into the pore
and make contact with gustatory hairs which trigger
neurotransmitters to elicit action potentials in these fibers.
Adapt rapidly 3-5 seconds & completely in 1-5 minutes
Taste Transduction
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Process in which stimulus energy is converted into a nerve impulse
due to influx of different ions
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Gustatory Pathway
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Taste is carried in two cranial nervers
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Facial: anterior 2/3rds of tongue
Glossopharyngeal: posterior 1/3rd
Taste triggers reflexes in digestion such as increasing saliva & gastric
juice
Influence of other sensations on taste
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Taste is 80% smell, when olfactory receptors are blocked food
becomes bland
Thermoreceptors, mechanoreceptors, nociceptors, temperature and
texture can enhance or detract
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Olfactory & Sense of Smell
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Structure
Detects chemicals in solution
 Olfactory Epithelium:
 Located on roof of nasal cavity
 Contain olfactory receptor cells with columnar
supporting cells
 Covered by mucous to trap airborn molecules
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Physiology
In order to smell the substance must be in a gaseous state
 Must be water soluble to dissolve in olfactory epithelium
 Bind to protein receptors which open ion channels that send
action potentials to olfactory bulb
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Pathway
Send impulses from bulb down tract
 Thalmus  Frontal Lobe or Hypothalmus to interpret and
elicit emotional responses to odor
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Imablances include anosmias (without smells) from
head injuries; unicinate fits (olfactory hallucinations)
EYE & VISION
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Accessory Structures
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Eyebrows
Shade the eyes
 Prevent perspiration into eye
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Eyelids
Palpabrae protects eye
 Levator palpebrae superioris raises eyelid
 Eyelashes trigger blinking
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Conjunctiva
Mucous membrane over eyelids and anterior surface of
eyeball (white part)
 Vascular, when irritated eyes are blood shot
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Lacrimal Apparatus
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Eye muscles
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Consist of gland and ducts that drain
excess secretions into nasal cavity
Secretes saline solution (tears)
Contains mucous, antibodies, and
lysosomes to clean eye & destroy
bacteria
Movement is controlled by 6 muscles
Four Rectus muscles: Superior, Inferior,
Lateral, Medial
Two Oblique muscles: Superior, Inferior
Nerve Innervation: abducens, trochlear,
oculomotor
Lens : Divides eye into anterior and
posterior segments
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Transparent, flexible structure that can
change shape to allow focus of light on
retina
Avascular
Becomes less elastic through life causing
focus impairment
Cataract – cloudy lens due to thickening of
lens or diabetes
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Structure of the Eyeball
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Divided into 3 tunics
Fibrous – dense avascular tissue
 Sclera: white part that protects, shapes, and provides
attachment for eye muscles
 Cornea: buldges anteriorly and allows light into eye
 Vascular
 Choroid – highly vascular & provides nutrition
 Ciliary Body – encircles lense and keeps it in place
 Iris – contains pupil and changes in shape due to light
 Sensory – contains the retina, which are photoreceptors of
rods & cones
 Optic Disc (blind spot) – Where optic nerve exits eye
 Rods – dim light
 Cones – bright light and color
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Filled with humors to maintain shape
Vitreous humor – in posterior
 Aqueous humor – in anterior (if undrained causes
glaucoma)
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Physiology
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Wavelength & Color
Eyes respond to visible light spectrum
 Progresses from red to violet
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Refraction & lenses
Light travels in straight lines and blocked by
nontrasnparent objects
 Light reflects or bounces off a surface
 Reflection accounts for most of light reaching our eyes; as
light changes mediums it can bend or refract.
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Focus
Your lens refracts the light to your focal point which
projects on your retina
 Images are upside down & reversed
 Myopia – nearsighted
 Hyperopia – farsighted
 Astigmatism – unequal curvature of lens leading to blur
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Photoreception
 Photoreceptors are modified neurons
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Rods
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Outer segment connected to inner, inner connects to cell body
which has synaptic endings.
Sensitive to low light, best at night
Cones
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Require high light, provides color
EAR: HEARING & BALANCE
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Structure – three areas: Outer, middle, & inner
ear
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Outer Ear
Auricle or Pinna: ear composed of elastic cartilage & skin to
direct sound waves to external auditory canal
 External auditory meatus: Short curved tube from auricle
to eardrum
 Lined with skin, sebaceous glands, & ceruminous glands
(secrete earwax)
 Tympanic membrane ( ear drum ) boundary between outer
& middle ear
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Middle Ear (tympanic cavity)
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Small air filled mucus lined cavity
Between eardrum & bony wall with two openings oval (vestibular) & round
(cochlear) window
Contains pharyngotympanic (auditory tube) running from middle ear to
nasopharynx & helps equalize pressure
Otitis Media – middle ear inflammation
Inner Ear
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Behind eye socket & contains receptor information
2 Major divisions
 Bony (osseous ) labyrinth
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Vestibule – contains saccule and utricle which have equilibrium receptors that
respond to gravity & changes of head position
Cochlea – contains the organ of corti which is the sensory organ for hearing
Semicircular Canals – respond to movement of head
Membranous Labyrinth
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Series of sacs and ducts containing endolymph fluid to help conduct sound
vibrations.
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Sound & Mechanisms of Hearing
Sound – a disturbance of pressure
 Frequency – measurement of offurrences of a repeated
event per unit of time
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Distance between two crests is a wavelength
Frequency is expressed in hertz
Range for humans is 20-20,000 Hz
Amplitude or height of wave is related to intensity
Loudness is measured in decibles
 We can hear from .1 dB to over 120 dB
 Threshold for pain is 130 dB
 Hearing loss occurs with exposure to 90 dB
 Noisy restaurant is 70 dB, normal talking is 50 dB
 A rock concert is 120 dB. You do the math.
Transmission
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Sound waves move through the air, membranes, bones,
fluids to reach receptor cells in the organ of corti.
Vibrations excite hair cells which send messages to cochlear
nerve and brings the impulses to the brain for processing
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Imbalances of Hearing
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Deafness – any hearing loss
Conduction deafness
 When something hampers sound conduction to fluids of
inner ear
 Ruptures, perforated eardrum can cause problems
 Sensorinerual
 Damage to neural structures of cochlear hair cells
 Can be partial or complete & generally there is gradual
loss of hearing throughout life
 Cells can be damaged to extremely loud noises or
prolonged exposure
 Can be fixed with cochlear implants
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Tinnitus
Ringing of ear
 Symptom of pathology and not disease
 1st symptom of cochlear nerve degeneration
 Can be from inflammation or medication or trauma
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Meniere’s Syndrom
Affects semicircular & cochlear canals
 Causes vertigo, nausea, vomitting
 Standing erect is near impossible
 Caused by excess fluid, rupture or infection
 Mild cases can be cleared with anti motion drugs,
sometimes surgery
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Equilibrium & Orientation
Responds to head movement without awareness
 Receptors of inner ear are divided into two parts
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Static
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Sensory receptors for static are the maculae
Found in saccules and utricle
Monitor position of head in space, control posture
Dynamic
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Receptor for dynamic are the crista ampullaris
Excited by head movement but major stimuli are rotatory
These areas are at work when twirling or feeling ill on a boat