special senses - Doctor Jade Main

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Transcript special senses - Doctor Jade Main

SPECIAL SENSES
Making Sense of The World
Sensation
• relationship
between physical
energies in the
environment &
psychological
experience of those
energies
• to perceive & detect
physical energies &
encode them into
neural signals
Basic Senses
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Sight
Hearing
Touch
Smell
Taste
also
Pain
Pressure
Temperature
Joint position
Muscle sense
Movement
SENSES
• systems that translate outside information
into activity in nervous system
• gather information by detecting energies
• environment contains many different
forms of energies
Receptors
• detect only the energies have receptor
for
• restricted awareness
• receptor cells transduce or change physical
energy into a signal brain can understand
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
Olfaction
• sense of smell
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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
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 Bowman’s glands
– produce secretions that bathe surface of olfactory receptors
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
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
OLFACTION
• dissolved chemicals interact with receptorsodorant 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
Olfactory Discrimination
• can recognize 2000-4000
chemical stimuli
• several primary smells for which
thousands of receptors are
needed
• 1) ethereal
2) camphoraceous
3) musky
4) floral
5) minty
6) pungent
7) putrid
• 1% of genes are needed to
make receptor proteins to
recognize smells
• no distinct receptor for each
detectable odor
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
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
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
Anatomy of Gustation
• gustatory receptors
– embedded in
specializations of
surrounding
epithelium called
papillae
• three types contain
taste buds
• vallate
• fungiform papillae
• folliate
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
Gustatory Transduction
• dissolved
chemicals contact
taste hairs
• bind to receptor
proteins on
gustatory cell
• causes series of
chemical
reactions
producingaction
potential
Gustatory Transduction
• different tastes involve different
receptor mechanisms
• salt receptorsdepolarize after Na
channels open
• sweet receptors depolarize after K
channels open
Gustatory Transduction
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
Vision
• primary sense in humans
• sensory organs-eyes
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
Lateral
Canthus
Medial
Canthus
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
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
ACCESSORY STRUCTURES-Lacrimal Apparatus
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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
Fibrous Tunic
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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
Vascular
Tunic-Uvea
• site of attachment for
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intrinsic eye muscles
provides route for
blood & lymph
regulates amount of
light entering eye
secretes & reabsorbs
aqueous humor
controls shape of lens
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Parts:
iris
cilliary body
choroid
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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
Cilliary Body
• thicken area at
periphery of eye
• iris is attached to it
• composed of cilliary
muscles
CHOROID
• separates
fibrous &
neural tunics
Neural Tunic-Retina
• light sensitive
• thin, pigmented outer
layer
• sheet of melanin
containing cells
• thick, inner layercontains light receptors
• begins visual pathway
• consists of three layers
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
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
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
RODS & CONES
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18X more rods than cones
approximately 125 million rods
6 million cones
arranged to produce best possible
combination of night & day vision
Cones
• color vision
• operate in bright
light
• Three types
• Blue
• Red
• Green
• experience of color
is due to
combination of
these three cones
Cones
• concentrated in
macula leutea
• center is fovea
centralis
• site of highest
visual acuity or
resolution
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
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
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
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
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
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
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
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
Errors of Refraction
• Hypermetropiafar-sightedness
–eyeball is too
short
• Astigmatism
–lens or cornea
not smoothly
spherical
Image Formation
• Final stageconstriction of
pupil
• pupil constricts
hole narrows
• due to the
circular muscles
of iris
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
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
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
PHOTOPIGMENTS
• one in rods
• one in each of 3 cones
• derivatives of rhodopsin or
visual purple
• consists of
• protein-opsin-bound to light
sensitive chromophoreretinal-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
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
Steps in Photoreception
• Step 1:
Isomerization
• Photon of light
absorbed
• Opsin is
activated
• cis formtrans
form
Step 2-Photoreception
• Bleaching
• trans retinal
separates from
opsin
• Photopigment
looks colorless
Step 3-Photoreception
Regeneration
Trans retinal
transforms back
to the cis form
Cis-retinal can bind
to opsin
Photopigment is
functional again
Color Deficiency
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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)
can’t color blend
Vision is said to be di- instead of tri-chromatic
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
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
• 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
The Ear
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
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
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
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
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
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longer waves produce lower frequencies & lower pitches
shorter wavelengths make higher frequencies & higher pitches
amplitude determines loudness
greater amplitude louder a sound
Sound
• measured in decibels
• 0 decibels=absolute
threshold
• 10 decibels indicates 10X
increase
• normal conversationaround 60 decibels
• passing train-about 100
• above 80 damages hair
cells
• uncomfortable at 120
• painful above 140
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
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
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
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
Transduction of Sound
Auditory Pathways
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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 3dimensional 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
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
Equilibrium
• vestibular sense
• sensation provided
by vestibular
complex
• Two types
• Static
• Dynamic
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
Vestibular Sense
Receptors
• Vestibular
apparatus
• Saccule
• Utricle
• Semicircular
ducts
Saccule & Utricle
• Otolithic organs
• walls contain
macula
• houses receptors for
equilibrium
• contains two types
of cells
• 1) hair cells-sensory
receptors 2)
supporting cells
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
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
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
Semicircular Ducts
• contain receptors which respond to rotational head movementsdynamic 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
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
Vestibular Sense & Equilibrium
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Hair cells of vestible & semicircular
ducts are monitored by sensory
neurons-vestibular ganglia
Branches form cranial nerve 8vestibulocochlear nerve
– innervates vestibular nuclei located
between pons & medulla
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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.