The Anatomy and Physiology of Vision and Olfaction

Prof.Sunil Chavan Prin.K.M.Kundnani Pharmacy
Polytechnic
OLFACTION:SENSE OF SMELL
• Olfactory Apparatus:
• Superior part of nasal cavity, inferior
surface of cribiform plate of ethmoid bone
is lined with Olfactory Epithelium
Olfactory Epithelium
Olfactory supporting Basal Olfactory
Receptors Cells Cells Glands

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Olfactory Receptors:
• These are first order neurons of Olfactory
Pathway
• Each Olfactory receptor is a bipolar
neuron
• Knob shaped dendrites have olfactory
hairs, cilia, these causes transduction.
• Axons project through cribiform plate &
end in Olfactory bulb
• Olfactory receptors respond to chemical
stimulation of an odorant molecule by
producing nerve impulse.

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Supporting Cells:
• These are columnar epithelium cells of
mucus lining of nose.
• Provide physical support, nourishment &
electrical insulation for olfactory receptors.
Basal Cells:
• These are stem cells, located between
bases of supporting cells.
• These continually undergo cell division to
produce new olfactory receptors.

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Olfactory Gland (Bowman’s):
• These are present within connective
tissue that support olfactory epithelium.
• These produce mucus that is carried to
surface to epithelium.
• Secretion moisten surface & dissolves
odorants, so that transduction can occur.

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Physiology of Olfaction
Odorant molecule binds to olfactory hair
It causes transduction
Propagation of impulse along axon of
olfactory receptor
In some cases odorant binds to G-Protein
in Plasma membrane of olfactory receptor
activates enzyme adenylate cyclase
Production of cAMP Influx of Na+
Generation of impulse & propagation of
impulse

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Olfactory Pathway
• On each side of nose, bundles of axons of
olfactory receptors extend through 20 olfactory
foramina in cribiform plate
• These bundles collectively form Right & Left
Olfactory Nerve (I).
• These nerve terminate in olfactory bulb. Here
axons of receptors form synapses with dendrites
of second order neurons in olfactory
pathway.
• Axons of olfactory bulb extend posteriorly
& form olfactory Tract

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Olfactory Tract
Some axons project to primary olfactory
area conscious awareness of smell
begins
Other axons projected to Limbic system &
Hypothalamus Responsible for
emotional & memory evoked responses to
odors

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GUSTATION:SENSE OF
TASTE
• Taste-Chemical sense
• Five primary tastes: Sour, Bitter, Sweet, Salty, &
U….
• Anatomy of Taste Buds & Papillae
• Vallate: Circular, large, 8-12, form inverted V
shape. Each papilla has 100-300 taste buds.
• Fungiform: Mushroom shapr, entire surface,
each papilla has about 5 taste buds.
• Foliate: Located in small trenches on lateral
margins. These degenerate in early childhood

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Taste Buds: Receptors for
sensation of taste
• About 10,000 TB in young adult
• Most of them on tongue, some of them on
soft palate, pharynx & epiglottis.
• No. of TB declines with age.
• Oval body-consist of 3 kinds of epithelial
cells: Supporting cell, Gustatory receptor
cell Basal cell
• Supporting cell: Surround about 50
gustatory receptor cells in each taste bud.

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• Gustatory Receptor Cell: Each cell
projects single long microvillus-Gustatory
hair.
• Basal Cell; Present at periphery, produce
supporting cells Gustatory receptor
cell. Each has 10 days life span.
• At the base gustatory receptor cell
synapses with dendrites of first-order
neuron. This neuron forms the first part of
gustatory pathway.

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Physiology of Gustation
Testant Dissolved in Saliva
Gustatory hair
Transduction
Receptor Potential
Exocytosis of Synaptic vesicles
Liberation of Neurotransmitter
Trigger nerve impulse

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SWEET, BITTER, UMAMI TESTANTS
• Binds to receptors on plasma membrane
linked to G-proteins
Activates several different chemicals
(secondary
messengers)
Release of Neurotransmitter

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Salty food: Na +
from testants
Na+
Gustatory receptor Cell
Accumulation of Na+
inside
Opening of Ca2+
channels
Influx of Ca2+
Exocytosis of Synaptic Vesicles
Sour Food: H+
from testants

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Gustatory Pathway
Taste Buds Taste Buds Taste buds in
In Ant.2/3 in post. 1/3 throat, epiglottis
Facial Glossopharyngeal Vagus
Nerve(VII) Nerve(IX) Nerve(X)
Medulla Oblongata
Limbic System Thalamus
& Hypothalamus
Primary Gustatory Area
(Parietal lobe)

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EYE : SENSE OF VISION (SIGHT)
Vision: important to human
survival
More than half sensory receptors
Larger part of cerebral cortex

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Anatomy of Eye Ball
Wall of Eyeball
Fibrous Vascular Retina
layer layer Neuronal layer
-Cornea -Choroid
-Sclera -Ciliary body
-Iris

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Interior of Eye ball
Aqueous Vitreous Lens
Humour body

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Fibrous Layer:
• Outer coat of eyeball
• Consist of anterior cornea, posterior sclera
CORNEA:
-Transparent epithelial coat, covers iris
-Curved shape helps focus light into retina
SCLERA (white of eye):
-Layer of dense connective tissue, mostly collagen
fibers & fibroblasts
-Covers eyeball except cornea
-Gives shape to eyeball, make it more rigid,
protects inner parts

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Canal of Schlemm:
• An opening at junction of sclera & cornea
• It drains aqueous humour from anterior
chamber

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Vascular Layer:
• Middle layer of the eyeball
• Three parts: Choroid, Ciliary body, Iris
CHOROID:
-Posterior portion of meddle layer
-Lines most of internal surface of sclera
-Rich in blood vessels, provides nutrients to retina
-Contains melanocytes, produces melanin
-Melanin absorbs stray light rays, prevent
reflection & scattering of light within eyeball
Sharp & clear image

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CILIARY BODY:
-Anterior portion of choroid
-Consists of Ciliary Processes & Ciliary Muscle
Ciliary processes are folds on internal side,
contain blood capillaries, secrete aqueous
humour
Suspensory Ligaments (Zonular fibers):
-Extends from Processes to lens
Ciliary muscle- circular band of smooth muscle.
Its contraction/relaxation Tightness of zonular
fibers alters shape of lens

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IRIS:
-Coloured portion of eyeball
-Suspended between Cornea & Lens
-Melanocytes, Circular & Radial smooth
muscle fibers
Amount of melanin Colour of eye
-Regulate amount of light entering
through pupil

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Retina:
-Innermost layer of eyeball
-Lines about ¾ of eyeball
Thickest at the back, thins out interiorly,
ends just behind ciliary body
-Consists of Pigmented layer & Neural layer
Pigmented Layer:
-Made up of melanocytes
-Melanin helps to absorb stray light

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NEURAL LAYER:
Three distinct layers of retinal neurons:
Photoreceptor Layer, Bipolar layer &
Ganglion Cell Layer
-Separated by two zones: Outer & Inner
Synaptic layer
PHOTORECEPTORS:
Specialized cells, begin process of
conversion of light rays to nerve impulse

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-Cells: two types;
ROD- outer segment is cylindrical
CONE- outer segment cone shaped
-Each retina has about 6 million cones &
120 million rods
-Rods allow us to see in dim light
-Cones produce colour vision
Axons of ganglion cells extend posteriorly
exit at a site called OPTIC DISC (Blind
Spot) as Optic Nerve.

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INTERIOR OF EYEBALL
LENS:
-Highly elastic circular biconvex transparent
body
-Located behind pupil & iris, enclosed in
connective tissue capsule
-Held in position by zonular fibers, attached to
ciliary processes
-Consists of protein Crystallins
-Lens help focus image on retina by refraction,
facilitates clear vision
-Vary its refracting power by changing its
thickness

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LENS DIVIDES interior of eyeball into two
cavities: Anterior Cavity & Vitreous
Chamber
ANTERIOR CAVITY: Consists of two
chambers:
Anterior Chamber- between cornea & Iris
Posterior Chamber-behind Iris & infront of
lens & zonular fibers
Both chamber are filled with aqueous
humour-watery fluid nourishes lens &
cornea.

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Aqueous humour filters out of blood
capillaries in ciliary processes & enters
posterior chamber
-Flows forward between iris & lens, through
pupil into anterior chamber
-From ant. Chamber it drains into Canal of
Schlemm, and then into blood.
-it is completely replaced about every 90
minutes

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VITREOUS CHAMBER:
-lies between lens & retina
-Contains viscous substance:Vitreous Body
-Formed during embryonic development not
replaced thereafter.
-It contains 99% water, mucoprotein, salts
and phagocytic cells
-It prevents collapsing of eye walls
-It keeps this part clear for unobstructed
vision

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INTRA-OCULAR PRESSURE:
-Produced mainly by Aq. Humour & partly by
Vitreous body
-normal 16 mm Hg (15 – 20 mm Hg)
-maintains shape of Eyeball & prevents it
from collapsing
GLAUCOMA:
Condition in which there is increased
intraocular pressure due to defective
drainage of aqueous humour through
canal of Schlemm.

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Accessory structures of Eye
Eyelids, Eyelashes, Eyebrows, Lacrimal
Apparatus & Extrinsic eye Muscles
Superior rectusrotates eyeball upwards
Inferior rectus rotates eyeball downwards
Lateral rectusrotates eyeball outwards
Medial rectusrotates eyeball inwards
Superior obliquerotates eyeball so that
cornea turns in downwards & outwards
direction
Inferior obliquecornea turns upward &
outward direction

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PHYSIOLOGY OF VISION
• ISOMERIZATION OF RETINAL:
Retinal in photoreceptor cells present in cis- form
in darkness. This absorbs light (photon) and
converts into trans- form
• RELEASE OF NEUROTRANSMITTER:
Isomerization activates enzyme that breaks down
cyclic Guanosine Monophosphate (cGMP)
closure of cGMP gated Na+ channels Na+
influx Membrane potential more negative
affects release of Glutamate
(Hyperpolarisation)

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DIM LIGHT-small & brief receptor potential
that partially turnoff glutamate release
BRIGHT LIGHT-larger & longer receptor
potential that completely shut down
glutamate release
Excites bipolar cell & subsequently
stimulates ganglion cells to generate
nerve impulse in their axons
Axons of all retinal ganglion cells exit
eyeball at Optic disc and form Optic Nerve
(II)

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Visual Pathway
• At the optic chaism axons from temporal half of
each retina do not cross, continue directly to
thalamus on same side
• Axons from nasal half of each retina cross optic
chaism and continue to opposite thalamus
• Each optic tract consists of crossed & uncrossed axons
• Branches of axon project to midbrain that
govern constriction of pupils in response to light
& co-ordination of head & Eye movements
• Axons of thalamic neurons project to primary
visual area in occipital lobe of cortex image is
perceived

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EAR:SENSE OF SOUND
(HEARING)
Ear- an engineering marvel,
contains receptors for Hearing &
Equilibrium
Transmits 1000 times faster
than photoreceptors

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ANATOMY OF EAR
External Ear Middle Ear Internal ear
-Auricle (tympanic cavity) (Labyrinth)
-Auditory canal -Auditory Ossicles -Bony
(acoustic 1.Malleus
-Membranous
meatus) 2.Incus
3.Stapes
-Eustachian Tube

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External Ear
AURICLE (Pinna):
• Expanded portion from side of head
• Composed of fibroelastic cartilage
• Deeply grooved & ridged
• Prominent outer ridge-Helix
• Soft inferior portion-Lobule, composed of
fibrous & adipose tissue, richly supplied
with blood capillaries

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EXTERNAL AUDITORY CANAL
(ACOUSTIC MEATUS):
• Slightly curved tube, about 2.5cm long,
lies in temporal bone, extended from
auricle to tympanic membrane
• Lined with hairy skin, continues with auricle
• Contains numerous specialized sweat glands-
Ceruminus glands, secret earwax, sticky
material containing lysozome & immunoglobins
• Prevent foreign material like dust, insects,
microbes reaching eardrum.
Function:Collection of sound waves &
channel them inward  eardrum

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TYMPANIC MEMBRANE/EARDRUM
• Thin partition between auditory canal &
tympanic cavity
• Oval shaped, slightly broader edge
upwards
• Composed of three layers of tissues-
-outer covering of hairless skin
-middle layer of fibrous tissue
-inner lining of mucus membrane
FUNCTION: production of vibrations, as
sound waves strike it.

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Middle Ear/Tympanic Cavity
• Small, irregular, air-filled cavity in temporal bone
• Cavity & its contents are lined with either simple
squamous or cuboidal epithelium
• Extend till oval window & round window of
internal ear
AUDITORY OSSICLES:
• Three very small bones extend across cavity-
Malleus, Incus, Stapes
• Attached to cavity by ligaments
• Connected by synovial joints

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MALLEUS:
• Handle is in contact with eardrum
• Head forms joint with incus
INCUS:
• Body articulates with malleus, long
process with stapes, stabilized by short
process
STAPES:
• Head articulates with incus, base or
footplate fits into oval window

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EUSTACHIAN TUBE (AUDITORY)
• About 4 cm long tube, connects middle
ear with nasopharynx, lined with ciliated
epithelium
• Normally closed, opens during swallowing,
yawning, sneezing
• Balanced pressure allows eardrum
vibrates freely as sound waves strike it
FUNCTION: Transmission of vibrations till
oval window, work as piston, its action add
force

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Inner Ear (Labyrinth)
• Contains the organs of hearing and
balance.
• Described in two parts, the bony labyrinth
and the membranous labyrinth.
BONY LABYRINTH:
• This is a cavity within the temporal bone
lined with periosteum.
• The bony labyrinth consists of:
1 vestibule , 1 cochlea , 3 semicircular
canals

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VESTIBULE:
• Expanded part nearest the middle ear
• Contains the oval and round windows in
its
lateral wall.
COCHLEA:
• Has a broad base where it is continuous with the
vestibule and a narrow apex, and it spirals round
a central bony column.
THE SEMICIRCULAR CANALS:
• These are three tubes arranged so that one is
situated in each of the three planes of space.
They are continuous with the vestibule.

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MEMBARNOUS LABYRINTH
• Contains endolymph
• It comprises of: vestibule, cochlea & 3
semicircular canals
COCHLEA: contains three compartments:
-the scala vestibuli
-the scala media, or cochlear duct
-the scala tympani.

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Cochlear duct:
• It is triangular in shape
• On the base of triangle there are
supporting cells and specialised cochlear
hair cells containing auditory receptors.
• These cells for Spiral organ (of Corti) that
responds to vibrations
• Auditory receptors are dendrites of
efferent nerves that form cohlear nevre,
part of 8th
cranial nerve

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PHYSIOLOGY OF HEARING
1. The auricle because of it shape
concentrates sound waves and direct
them along auditory canal
2. Soundwaves stike eardrumproduces
vibrations
3. Transmission of vibrations across middle
ear via auditory ossicles
4. As stapes moves back & froth it pushes
membrane of oval window in & out

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5. Movement of oval window sets up fluid
pressure waves in the perilymph of
cochlea. It pushes perilymph of scala
vestibuli
6. Transmission of pressure from scala
vestibuli to scala tympani to roun window
7. Pressure in scala vestibuli & scala
tympani transmits pressure waves in
endolymph inside cochlear duct

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8. Pressure waves in endolymph causes
basilar membrane to vibrate, it moves
hair cells of spiral organ against tectorial
membrane, bending of hair cells of spiral
organ against tectorial membrane
9. Bending of hair cell Stereocilia produces
receptor potentialgeneration of nerve
imp[ulse

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AUDITORY PATHWAY
First order sensory neuron (cochlear
branch) Cochlear nuvlei in medulla
oblongataOlivery nuclei in
ponsInferior colicullus of midbrain
Geniculate nucleus of Thalamus
Primary Auditory Area in superior
temporal gyrus of Cerebral cortex

The Anatomy and Physiology of Vision and Olfaction

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The Anatomy and Physiology of Vision and Olfaction