SPECIAL SENSES

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SPECIAL SENSES

• Making Sense of The World

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Sensation

• relationship between physical energies in the
  environment psychological experience of those
  energies
• to perceive detect physical energies encode
  them into neural signals

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Basic Senses

• Sight
• Hearing
• Touch
• Smell
• Taste
• also
• Pain
• Pressure
• Temperature
• Joint position
• Muscle sense
• Movement

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SENSES

• systems that translate outside information into
  activity in nervous system
• gather information by detecting energies
• environment contains many different forms of
  energies

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Receptors

• detect only the energies have receptor for
• restricted awareness
• receptor cells transduce or change physical
  energy into a signal brain can understand

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Transduction

• conversion of physical energies into language of
  brain
• receptor cells convert physical energies into
  neural impulses which travel to cerebral cortex
  to be decoded
• all sense signals except smell go to relay
  station-thalamus
• from there to primary sensory areas in
  cerebrum-different for each sense
• here they are modified and sent on to higher
  regions of brain

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Olfaction

• sense of smell
• chemical sense
• air borne chemicals detected
• oldest sense
• all organisms have some type of chemical sense
• major senses in most animals
• help locate food, recognize trails territories
  identify kin find receptive mates
• social insects send receive intricate chemical
  signals which tell them where to go and how to
  behave
• social behavior of most animals is controlled by
  chemical signals
• olfactory receptor area in German Shepherd-72X
  bigger than in humans

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Olfactory System

• humans are able to distinguish 10,000 smells
• detected in paired olfactory organs in nasal
  cavity by specialized receptor cells found in
  olfactory epithelium-olfactory receptor neurons

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Olfactory System

• olfactory organs posses 2 layers
• olfactory epithelium
• lamina propria
• olfactory epithelium covers inferior cribifrom
  plate, superior perpendicular plate superior
  nasal conchae of ethmoid bone
• covered by mucus which contains olfactory
  receptors
• lamina propria-comprised of areolar tissue, blood
  vessels, nerves olfactory or Bowmans glands
• produce secretions that bathe surface of
  olfactory receptors

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Olfactory System

• 10 100 million olfactory receptors
• modified bipolar neurons
• have terminal enlargements or knobs which project
  above epithelial surface
• from each 8-20 olfactory cilia extend into mucus
• contain smell receptors
• cilia project from knob lie parallel to
  epithelia surface
• exposes considerable surface area to dissolved
  compounds
• at other end of receptor cell, axons project to
  olfactory bulb
• 10-100 axons form into bundles, penetrate
  cribriform plate? terminate in olfactory bulb
• stem cells allow neurons to regenerate

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Olfaction

• refers to breathing in chemicals
• Inhale?take in chemicals or odorants
• chemicals that stimulate olfactory receptors
• must be small enough to be volatile to vaporize,
  reach the nose dissolve in mucus to stimulate
  olfactory receptors
• at olfactory organs?water lipid soluble
  materials diffuse into mucus

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OLFACTION

• dissolved chemicals interact with receptors-
  odorant binding proteins
• 4 odorant molecules will activate an olfactory
  receptor?activates adenylate cyclase?converts
  ATP?cAMP?opens Na channels in membrane ?local
  depolarization?depolarization large enough
  ?action potential in axon? conveyed to CNS

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Olfactory Pathways

• axons of receptors extend through olfactory
  foramina in cribiform plate to form? right left
  olfactory nerves
• terminate in brain in the olfactory bulbs?axons
  of bulbs extend posteriorly?form olfactory tract?
  projects to primary olfactory cortex located at
  inferior medial surface of the temporal lobe
• projects to hypothalamus amygdala
• parts of limbic system
• amygdale associate experiences with
  smells?producing emotion
• projections are sent to thalamus and to frontal
  cortex-recognition

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Olfactory Discrimination

• can recognize 2000-4000 chemical stimuli
• several primary smells for which thousands of
  receptors are needed
• 1) ethereal2) camphoraceous3) musky4)
  floral5) minty6) pungent7) putrid
• 1 of genes are needed to make receptor proteins
  to recognize smells
• no distinct receptor for each detectable odor

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Gustation

• chemical sense
• chemicals are taken into the body dissolved in
  oral cavity
• drives appetite
• protects from poisons
• bitter sour tastes produce aversive, avoidance
  reactions
• most poisons are bitter
• off food goes sour or has an acidic taste

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Taste Discrimination

• 5 primary sensations
• Sweet
• Salty
• Sour
• Bitter
• Umami
• MSG
• taste of beef, chicken broth parmesan cheese
• taste combined with smell gives flavor
• when nose is blocked foods seem bland or
  tasteless

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Anatomy of Gustation

• receptor-taste bud
• 10,000
• tongue, soft palate, pharynx epiglottis
• survives about 10 days
• Consists of
• taste receptors or gustatory cells
• basal or stem cells
• supporting cells

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Anatomy of Gustation

• Supporting cells
• surrounds about 50 gustatory receptors cells in
  each taste bud
• one single long micovillus (gustatory hair)
  projects from each gustatory receptor cell to
  surface through taste pore
• Basal cells
• stem cells
• found in periphery of taste buds

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Anatomy of Gustation

• gustatory receptors
• embedded in specializations of surrounding
  epithelium called papillae
• three types contain taste buds
• vallate
• fungiform papillae
• folliate

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PapillaeTypes

• Vallate or circumvallate papillae
• have 100 taste buds
• back of tongue
• Fungiform papillae
• possess 5 taste buds
• over entire tongue
• Folliate
• lateral margins
• taste buds degenerate in early childhoog
• Filiform papillae
• no taste buds
• Tactile receptors
• provide friction sensations

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Gustatory Transduction

• dissolved chemicals contact taste hairs
• bind to receptor proteins on gustatory cell
• causes series of chemical reactions
  producing?action potential

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Gustatory Transduction

• different tastes involve different receptor
  mechanisms
• salt receptors?depolarize after Na channels open
• sweet receptors depolarize after K channels open

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Gustatory Transduction
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Gustatory Pathways

• Taste is monitored by cranial nerves VII-facial
• picks up sensation from anterior 2/3rds of
  tongue
• IX-glossopharyngeal
• covers posterior 1/3rd of tongue
• X-vagus
• receives information from epiglottis
• axons from these nerves synapse on nucleus
  solitarius in medulla oblongata
• axons of postsynaptic neurons enter medial
  lemniscus synapse in thalamus
• then project to gustatory cortex? conscious
  perception
• here information is correlated with other sensory
  data such as texture, peppery, hot

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Vision

• primary sense in humans
• sensory organs-eyes

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Accessory Eye Structures

• Eyelids or palpebrae
• continuations of skin
• blink continually to keep surfaces lubricated
  things out of eyes
• Palpebral fissure
• gap separating free margins of upper lower
  eyelids
• Medial Lateral canthus
• where eyelids are connected
• Eyelashes
• keep foreign materials out

Medial Canthus
Lateral Canthus
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Accessory Eye Structures

• Tarsal glands
• sebaceous glands associated with eyelashes at
  inner margin
• secrete lipids to keep eyelids from sticking
  together
• Lacrimal Caruncle
• medial canthus
• makes a thick, gritty secretion often found in
  eyes after sleeping

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ACCESSORY STRUCTURES

• Palpebral conjunctiva
• epithelium covers inner surface of eye
• Ocular conjunctiva
• covers anterior surface
• extends to edges of cornea
• transparent part of outer fibrous layer

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ACCESSORY STRUCTURES-Lacrimal Apparatus

• produces, distributes removes tears
• tears reduce friction, remove debris, prevent
  bacterial infections provide nutrients and O2
  to eye
• consists of
• lacrimal gland
• lacrimal canaliculi
• lacrimal sac
• nasolacrimal duct
• lacrimal gland produces key ingredients and most
  of volume
• tears accumulate at medial canthus or lacrimal
  lake
• lacrimal puncta drains lake?empties into lacrimal
  caniliculi?lacrimal sac?nasolacrimal duct?
  nasolacrimal canal?nasal cavity

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THE EYE

• irregular spheroid
• three layers or tunics
• outer fibrous tunic
• intermediate vascular tunic
• inner neural tunic
• two hollow cavities
• posterior, vitreous chamber
• contains gelatinous vitreous body
• helps stabilize shape of eye
• anterior chamber
• filled with aqueous humor
• functions to retain shape of eyeball

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Fibrous Tunic

• sclera cornea
• Functions
• mechanical support
• physical protection
• attachment site-extrinsic eye muscles
• housing of focusing structures
• Sclera
• white of eye
• site for insertion of 6 extrinsic eye muscles
• contains blood vessels nerves
• Cornea-continuous with sclera
• cornea lens comprise-refractive system
• focuses light on retina
• where photosensitive pigments are found

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Vascular Tunic-Uvea

• site of attachment for intrinsic eye muscles
• provides route for blood lymph
• regulates amount of light entering eye
• secretes reabsorbs aqueous humor
• controls shape of lens
• Parts
• iris
• cilliary body
• choroid

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THE IRIS

• consists of pigment cells 2 layers of smooth
  muscle
• contraction of muscle produces change in diameter
  of pupil
• central opening in iris
• controlled by ANS
• bright light causes constriction via consensual
  light reflex
• parasympathic pathway
• dim light causes dilatation via pupillary reflex
• sympathetic pathway

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Cilliary Body

• thicken area at periphery of eye
• iris is attached to it
• composed of cilliary muscles

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CHOROID

• separates fibrous neural tunics

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Neural Tunic-Retina

• light sensitive
• thin, pigmented outer layer
• sheet of melanin containing cells
• thick, inner layer-contains light receptors
• begins visual pathway
• consists of three layers

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Retina Layers

• Photoreceptor layer
• Bipolar cell layer
• Ganglion cell layer

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The Retina

• Third layer
• light energy converted into neural activity
• contains specialized photoreceptor cells-rods
  cone
• transduce light wavelengths into information the
  brain understands
• Second layer
• bipolar cells
• magnifies image
• First layer
• ganglion cells
• further adjust image
• axons form optic nerve

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Retina

• if eyes simply transferred stimuli from retina to
  brain?images would be blurry
• images are sharpened by sending information from
  photoreceptor cells back through first 2 layers
  of retina
• Bipolar cells connect photoreceptors to retinal
  ganglion cells
• axons from ganglion cells form optic nerve

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Third Layer

• light energy is converted into neural activity
• contains specialized photoreceptor cells-rods
  cones
• rods cannot see color
• more sensitive than cones
• sensitive enough to respond to a single photon of
  light
• basic unit of light
• create coarse, gray image
• adequate for seeing in poor or dim light
• can make out shapes fairly well
• colors are completely absent
• no color vision in dim light

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RODS CONES

• 18X more rods than cones
• approximately 125 million rods
• 6 million cones
• arranged to produce best possible combination of
  night day vision

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Cones

• color vision
• operate in bright light
• Three types
• Blue
• Red
• Green
• experience of color is due to combination of
  these three cones

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Cones

• concentrated in macula leutea
• center is fovea centralis
• site of highest visual acuity or resolution

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THE LENS

• transparent structure located behind pupil in
  cavity of eyeball
• consists of concentric layers of cells, filled
  with crystallins
• transparent proteins responsible for clarity of
  lens for focusing

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Focusing

• requires the cornea lens
• light is refracted or bent as it passes from one
  medium to another with different density
• greatest amount of refraction occurs as light
  passes from air to cornea
• more refraction occurs as light passes from
  aqueous humor to lens
• lens provides extra refraction needed to focus
  light from object to focal point
• specific point of interaction in retina
• distance between center of lens focal point is
  focal length or distance

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PhotoPathway

• Horizontal cells extend across outer part of
  retina at level of synapses between photoreceptor
  bipolar cells
• Amacrine cells found where ganglion cells synapse
  with bipolar cells
• Light energy must pass through both ganglion
  bipolar cells to get to photoreceptor cells where
  light energy is converted into neural signals
  which activates bipolar cells
• One cone converges on one bipolar cell
• preserves precise information, provides high
  acuity and fine detail
• 1000 or more rods funnel information onto one
  bipolar cell
• increases original illumination activates
  ganglion cells

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OPTIC NERVE

• Axons from 1 X 106 ganglion cells converge on
  optic disc
• circular region medial to fovea
• origin of optic nerve
• penetrates wall of eye at area known as blind
  spot
• no photoreceptors
• forms optic nerve which partially crosses at
  optic chiasm
• continues on to thalamus
• from there to other areas of cortex all at the
  same time

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Refraction

• light rays reflected by object enter eye through
  cornea
• light proceeds through pupil
• size controlled by iris
• behind pupil?lens focuses light rays into an
  inverted image onto retina at back of eye

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Refraction

• lens focuses image on photoreceptors by changing
  shape
• accommmoation
• shape of lens is determined by tone of ciliary
  muscles
• shape determined by tone of cilliary muscles

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Accommodation

• cilliary muscles relax for far vision
• zonular fibers are pulled taut ?lens is under
  tension flat
• cilliary muscle contract for near vision
• releases zonular fibers from tension?lens
  assumes a natural, rounder more refractive
  state
• rounder shape increases refractive power of lens

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Errors of Refraction

• Presbyopia
• lens thickens?becomes harder? won't accommodate
• seen in almost all people over the age of 40
• Myopia-near sightedness
• eyeball is too long

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Errors of Refraction

• Hypermetropia-far-sightedness
• eyeball is too short
• Astigmatism
• lens or cornea not smoothly spherical

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Image Formation

• Final stage- constriction of pupil
• pupil constricts ?hole narrows
• due to the circular muscles of iris

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Photoreception

• Photoreceptors detect photons of light
• basic unit of visible light
• light is radiant energy or electromagnetic
  radiation
• comes in waves
• referred to by wavelengths
• wavelengths eyes detect are found in visible part
  of spectrum
• can detect these because possess receptors
  excited by wavelengths between 400-700nm

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LIGHT

• 2 physical characteristics of light determine
  sensory experience of it
• Wavelength
• distance of one wave peak to next
• each wavelength is sensed as a color
• Amplitude
• indicates amount of energy
• determines intensity of light
• large amplitude makes for bright color
• small amplitude makes dull color

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Photoreceptors

• have outer segment containing discs
• shape of outer segment provides name of
  photoreceptor
• Rods
• each disc is independent entity
• outer segment forms elongate cylinder
• Cones
• discs are infoldings of cell membrane
• outer segment tapers to tip
• outer segment is connected to inner by narrow
  stalk
• outer segments of both contain photopigment
• absorbs light

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PHOTOPIGMENTS

• one in rods
• one in each of 3 cones
• derivatives of rhodopsin or visual purple
• consists of
• protein-opsin-bound to light sensitive
  chromophore-retinal-made from vitamin A
• Retinal-common to all photopigments
• attaches to different opsins in cones
• opsin determines wavelength of light that can be
  absorbed by retinal

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Photoreception

• photon strikes part of rhodopsin molecule
• absorbed by visual pigment
• retinal has 2 possible configurations
• cis trans forms
• normally retinal is in cis form
• once light is absorbed?cis form?trans
  form?triggers chain of enzymatic steps

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Steps in Photoreception

• Step 1 Isomerization
• Photon of light absorbed
• Opsin is activated
• cis form?trans form

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Step 2-Photoreception

• Bleaching
• trans retinal separates from opsin
• Photopigment looks colorless

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Step 3-Photoreception

• Regeneration
• Trans retinal transforms back to the cis form
• Cis-retinal can bind to opsin
• Photopigment is functional again

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Color Deficiency

• Humans can discriminate 7X106 colors
• some have difficulty with color perception
• color deficient
• 1 out of 50 individuals
• gene responsible is sex-linked
• deficiency seen more in males than in females
• 8 of males 0.05
• color deficient usually lacks either red or green
  opsin
• have difficulty distinguishing red from green
  (both appear the same)
• cant color blend
• Vision is said to be di- instead of tri-chromatic

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Depth Perception

• have binocular vision
• when looking at an object a representation comes
  from both retinas
• foveas are about 5-7.5 cm apart
• visual fields for each eye slightly different
• occipital cortex receives both of these images
  fuses them into one picture
• fusing confers perception of depth
• Convergence

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Visual Processing

• axons from all ganglion cells?optic disc
• optic nerves reach diencephalon incompletely
  cross over at optic chiasm
• From there ½ the fibers? lateral geniculate
  nucleus on same side of brain
• ½ the fibers continue to opposite lateral
  geniculate nucleus
• From there image proceeds to occipital cortex via
  projection fibers

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The Ear

• three anatomical areas
• External
• collects sound waves directs them toward middle
  ear
• Middle
• consists of a chamber in temporal bone
• Inner
• contains sensory organs for hearing equilibrium

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External Ear

• composed of pinna
• cartilaginous auricle
• surrounds
• external auditory canal
• channels sound waves through auditory canal to
• eardrum or tympanic membrane
• thin, semi transparent membrane separates
  external from middle ear
• ceruminous glands
• secrete cerumen
• waxy substance
• needed for protection
• helps keep foreign objects out of ear
• helps slow infections

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Middle Ear

• filled with air
• communicates with nasopharynx through auditory or
  eustachian tube
• equalization of pressures
• contains auditory ossicles
• 3 tiny bones
• malleus
• incus
• stapes
• malleus attaches to tympanic membrane
• stapes is bound to oval window
• opening in middle ear going to inner ear
• incus lies between malleus stapes

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Inner Ear

• labyrinth
• contains receptors for hearing equilibrium
• Outer bony labyrinth encloses an inner-membranous
  labyrinth
• bony labyrinth consists of vestibule, cochlea
  semicircular canals
• filled with perilymph
• fluid in membranous part is endolymph
• vestible comprised of membranous sacs saccule
  utricle
• house receptors for gravity linear acceleration
  perception
• semicircular canals
• receptors in canals provide information on head
  location
• vestibule semicircular canals make up
  vestibular complex

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Hearing Receptors

• receptors for hearing are in cochlea
• spiral shaped bony chamber
• divided into thee channels
• cochlear duct, scala vestibuli scala tympani
• the vestibular membrane separates the cochlear
  duct from the scala vestibuli
• the basilar membrane separates cochlear duct form
  scala tympani
• Resting on basilar membrane is spiral organ or
  organ or Corti

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Hearing Receptors

• sensory receptors are hair cells
• on basilar membrane
• 16 X 106 hair cells found in two groups
• one-inner group arranged in a row
• outer group arranged in three rows
• free surface of each hair cell contains 40-80
  stereocilia
• similar to long microvilli
• tectorial membrane covers the hair cells

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Audition

• detection of sound
• stimulus is sound waves
• from compression rarefaction of air-or
  alternating air pressure
• distance between pressure peaks is wavelength
• frequency determines pitch
• measured in terms of cycles or waves per second
  called hertz-Hz
• humans detect sounds in frequency range from 20
  to 20,000Hz
• longer waves produce lower frequencies lower
  pitches
• shorter wavelengths make higher frequencies
  higher pitches
• amplitude determines loudness
• greater amplitude? louder a sound

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Sound

• measured in decibels
• 0 decibelsabsolute threshold
• 10 decibels indicates 10X increase
• normal conversation- around 60 decibels
• passing train-about 100
• above 80 damages hair cells
• uncomfortable at 120
• painful above 140

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Transduction of Sound

• when we speak vocal cords vibrate? molecules of
  air move?bump into one another producing waves of
  compressed, expanded air
• ears detect these waves transduce them into
  nerve impulses?brain decodes as sound
• sound waves enter via external ear?continue on
  to tympanic membrane
• air molecules under pressure cause tympanic
  membrane to vibrate

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Transduction of Sound

• movement of tympanic membrane displaces
  auditory ossicles
• first malleus vibrates
• handle of malleus strikes incus causing it to
  vibrate
• vibrating incus moves stapes
• vibrates oval window
• total force transferred to oval window
• because window is much smaller? force per unit
  area increases 15-20X.
• vibrations of oval window produce pressure waves
  that vibrate perilymph in vestibular duct
• these waves distort basilar membrane on way to
  round window of tympanic duct
• location of maximum distortion varies with
  frequency

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Frequency Coding

• basilar membrane is narrow and stiff at window
  end
• wide and flexible at apical end
• topographical difference results in different
  regions vibrating at different frequencies
• end near stapes (window end) vibrates at high
  frequencies
• apical end vibrates at low frequencies

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Transduction of Sound

• pressure waves continue into endolymph inside
  cochlear duct
• pressure waves in endolymph cause basilar
  membrane to vibrate which moves the hair cells of
  spiral organ against tectorial membrane
• leads to bending of stereocillia generation of
  nerve impulse

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Transduction of Sound
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Auditory Pathways

• bending of hair cells opens potassium channels
• Produces depolarizing potential
• opens calcium channels
• causes neurotransmitter vesicles (probably
  glutamate) release
• generates nerve impulse
• impulses pass along axons of forming cochlear
  branch of vestibulocochlear nerve (VIII)
• axons synapse with neurons in cochlear nucleus in
  medulla
• some axons cross over ascend in lateral
  meniscus terminate in inferior colliculi in
  midbrain
• other axons form cochlear nuclei
• end in superior olivary nucleus in pons

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Localization of Sounds

• requires binaural fusion
• brain compares information received from each ear
• ears are about 6 inches apart
• makes for intensity differences time lags to
  brain
• very small but allow for stereophonic or
  3-dimensional hearing
• auditory system can detect minute differences
• time difference of 0.000027 seconds is all that
  is needed to be able to identify direction from
  which 2 sounds are coming
• localization is quite accurate unless sound is
  located directly ahead, behind, overhead or
  beneath ears-equidistant from both

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Hair Cells

• 16,000 hair cells
• extremely vulnerable
• overexposure to loud noises, disease, heredity or
  aging most humans will lose 40 of hearing by age
  65
• once destroyed hair cells cannot regenerate

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Equilibrium

• vestibular sense
• sensation provided by vestibular complex
• Two types
• Static
• Dynamic

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Static Dynamic Equilibrium

• Static
• maintenance of position of body (mainly head)
  relative to force of gravity
• know where head is when it is tilted
• Dynamic
• maintenance of body position (mainly head) in
  response to sudden movements, such as rotational
  deceleration or acceleration
• know where head is if it moves quickly

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Vestibular Sense Receptors

• Vestibular apparatus
• Saccule
• Utricle
• Semicircular ducts

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Saccule Utricle

• Otolithic organs
• walls contain macula
• houses receptors for equilibrium
• contains two types of cells
• 1) hair cells-sensory receptors 2) supporting
  cells

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Saccule Utricle

• hair cells of utricle saccule have 40-80
  stereocillia of grduated height one kinocillium
• Longer than longest stereocilia
• steorcillia are connected by tip inks
• Together sterocilia and kinocillium are-hair
  bundle

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Saccule Utricle

• supporting cells secrete a gelatin like
  glycoprotein layer called otolithic membrane
• rests on hair cells
• layer of dense calcium carbonate crystals called
  otoliths extend over surface of otolithic
  membrane

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Equilibrium

• when head is upright? statoconia sit on top of
  macula
• weight presses down
• when head is tilted?statoconia shift to
  side?distorting hair cells
• sends information to CNS that head is no longer
  level

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Semicircular Ducts

• contain receptors which respond to rotational
  head movements-dynamic equilibrium
• anterior, posterior lateral semicircular ducts
  are continuous with utricle
• each semicircular duct has an ampulla-expanded
  region containing hair cells
• hair cells attached to wall of ampulla form
  crista
• each crista consists of hair and supporting cells
• covering the cells is a gelatinous structure-
  cupula

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Vestibular Sense

• when head is rotated?endolymph moves?pushes
  cupula ?distorts processes of receptor
• gluid movement in one direction?stimulates hair
  cells
• movement in other direction?inhibits hair cells

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Vestibular Sense Equilibrium

• Hair cells of vestible semicircular ducts are
  monitored by sensory neurons-vestibular ganglia
• Branches form cranial nerve 8- vestibulocochlear
  nerve
• innervates vestibular nuclei located between pons
  medulla
• nuclei send information to cranial nerves III,
  IV, VI and XI-involved with eye, head and neck
  movements
• information is then sent down vestibulospinal
  tracts of spinal cord ? adjusts peripheral
  muscle tone complements reflexive movements of
  head neck
• nuclei also connect with cerebellum to coordinate
  movement
• one spins very fast stops abruptly, liquid
  cannot return to normal?feel dizzy
• Neural connections are also made with
  ANS?digestive system part?nausea.