Special Senses

1
Special Senses

• Monday November 29, 2004

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What well cover

• Tactile mechanoreceptors
• Olfaction
• Equilibrium and hearing
• Vision/Eye

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Tactile mechanoreceptors

• Meissners corpuscles very well developed
  anchored w/n dermis
• Eyelids, lips, fingertips, nipples, external
  genitalia
• Light touch, movement, vibration
• Ruffini corpuscles in dermis pressure and skin
  distortion
• Pacinian corpuscle concentric layers heavy
  pressure (pulsation or vibration)
• Dermis fingers, breasts, external genitalia

Meissner
Pacinian
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Olfaction
Fig 18.6

• Neuroepithelium (olfactory epi) covers inf
  surface of cribriform plate and sup nasal septum
  and conchae (turbulent air to epi) lipid-soluble
  molecules diffuse into mucus covering this
  epithelium
• Olfactory receptors highly modified neurons
  w/cilia bind lipid molecules and depolarizes (AP
  may occur)
• Axons bundle (CN I) and go through cribriform
  plate to synapse on neurons w/n olfactory bulbs
  to olfactory tract to the hypothalamus

5
Olfaction

• Normal inhalation 2
• Sniff repeatedly intensifies receptor stimulation
• Few molecules can activate receptor
• Inhibition along olfactory pathway can prevent
  stimulation to reach cerebral cortex
• Distinction b/n thousands of stimuli
• 50 different primary stimuli
• Different sensitivities, not different types of
  receptors
• Interpretation based on pattern of receptor
  activity

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Equilibrium Hearing

• External ear pinna surrounds external auditory
  meatus collect and direct sound waves to
  tympanic membrane
• Middle ear w/n petrous portion
• Auditory ossicles amplify sound waves, conduct
  them to inner ear and change them to mechanical
  movements
• Malleus sound vibrations from tympanic membrane
  to
• Incus middle bone and connects malleus to
• Stapes covers oval window of the cochlea
  mechanical to fluid vibration w/n cochlea
• Eustachian tube to nasopharynx equalize pressure
  in middle ear w/external atmospheric pressure

Fig 18.9
Fig 18.10
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Inner Ear
Fig 18.11

• Sensory organs for equilibrium and hearing
• Membranous labyrinth filled with endolymph (high
  K, low Na)
• Surrounded by perilymph inside bony labyrinth
  subdivided into
• Vestibule
• Semicircular canals
• Cochlea Hearing

Equilibrium
Fig 18.12 b
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Strucutures

• Sensory receptors hair cells
• Supporting cells around
• Stereocilia
• One true kinocilium

Fig 18.12
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Equilibrium

• Semicircular canals (3)
• Surround semicircular duct w/ ampulla sensory
  receptors/hair cells stereocilia
• Cristae ampullaris angular acceleration of head
• Kinocilia and stereocilia w/n galatinous cupula
• When head moves endolymph pushes cupula and
  distorts the cilia
• Opposite direction inhibits

Fig 18.13
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Vestibule

• Within maculae
• Utriclulus and sacculus gravity and linear
  acceleration
• Hair embedded in gelatin, covered by calcium
  carbonate crystals called otoliths
• Head at rest otoliths sitting on maculae pushing
  cilia down
• Head tilted gravity pulls otolighs to one side
  distorting cilia head not level

Fig 18.14
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Hearing

• Cochlea cochlear duct b/n perilymph filled
  chambers? continuous in spiral
• Vestibular duct and tympanic duct start at oval
  window end at round window
• Organ of Corti contain hair cells (NO kinocilia)
  to tell us what we hear
• Sits on basilar membrane separating cochlear duct
  from tympanic duct
• Stereocilia contact tectorial membrane firmly
  attached to cochlear duct
• So sound heard when basilar membrane vibrates
  hair cells

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Fig 18.16
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How do we hear?

• Stapes conducts mechanical vibration to oval
  window pressure waves in perilymph of vestibular
  duct
• Changes mechanical to fluid vibration
• Since cochlea is sheathed in bone, fluid can only
  relieve pressure at round window
• Pressure waves distort cochlear duct and organ of
  Corti vibrating hair cells
• High frequencies affect hair cells near oval
  window
• Low frequencies affect hair cells farther along

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Fig 18.20
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Accessory structures of eye
Fig 18.18

• Eyelids windshield wipers
• Visible surface supported by tarsal plate CT
• Orbicularis oculi and lev palpebrae sup mm insert
• Epithelium (mucus membrane) on inner eyelid and
  on eye conjunctiva
• Lacrimal gland watery, alkaline, lysozyme
• Tears remove debris, prevent infection, reduce
  friction
• To lacrimal lake through the lacrimal puncta into
  the lacrimal canaliculi (in lacrimal bone)
• On to lacrimal sac (in groove of lacrimal bone)
  into nasolacrimal duct to inf meatus

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The Eye

• Sclera dense fibrous CT thin at ant
• All 6 extra-ocular mm insert
• Cornea avascular stratified squamous
• Then many layers of collagen fibers to simple
  squamous as ant chamber
• Choroid MANY blood vessels to outer part of
  retina melanocytes intrinsic eye mm
• Regulate amt of light in, secrete aqueous humor,
  control lens shape

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Fig 18.20
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The Eye

• Iris blood vessels pigment cells intrinsic eye
  mm change central diameter ?pupil
• Diameter smaller sphincter pupillae m (circle)
• Parasympathetic
• Diameter enlargement dilator pupillae m (radial)
• Sympathetic
• Ciliary body iris attaches to
• Ciliary m to zonular fibers of lens

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Fig 18.23
Fig 18.20
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Fig 18.20
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Retina

• Outer pigmented layer and
• Inner neural retina (visual receptors)
• Outermost layer of cells photoreceptors (rods
  and cones)
• Rods light sensitive pale moon light periphery
  of retina none in macula lutea
• Cones color sharper clearer images posterior
  retinal surface highest concentration found in
  center of macula lutea fovea (sharpest vision)
• Both synapse w/bipolar cells which synapse on
  ganglion cells (only ones to create AP to brain)
• Horizontal cells inhibit or facilitate
  communication b/n photoreceptors and bipolar
  cells
• Optic disc where CN II, aa and vv are found
  blind spot

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Fig 18.22
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Chambers

• Anterior aqueous humor
• b/n cornea and pupil
• Posterior aqueous humor
• b/n pupil and lens
• Vitreous vitreous body
• b/n lens and optic disc maintain shape of eye

Fig 18.21
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Fig 18.20 b
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Lens

• Focus visual images onto retinal photoreceptors
  by changing its shape
• Dense, fibrous (elastic) capsule covers
• Contract to make lens spherical w/no outside
  force
• Interdigitate w/zonular fibers
• At rest tension of zonular fibers overpowers
  capsule and flattens lens far-sighted
• Ciliary mm contract reducing tension in zonular
  fibers and the lens becomes spherical near
  sighted

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Fig 18.23