12 special senses

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



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.



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.


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.


Physiology of Olfaction

Odorant molecule binds to olfactory hairIt causes transduction Propagation of impulse along axon of

olfactory receptorIn some cases odorant binds to G-Protein

in Plasma membrane of olfactory receptor activates enzyme adenylate cyclaseProduction of cAMP Influx of Na+

Generation of impulse & propagation of impulse


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


Olfactory TractSome 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


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



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.


• 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.


Physiology of GustationTestant Dissolved in Saliva

Gustatory hair

Transduction

Receptor Potential

Exocytosis of Synaptic vesicles

Liberation of Neurotransmitter

Trigger nerve impulse


SWEET, BITTER, UMAMI TESTANTS

• Binds to receptors on plasma membrane linked to G-proteins

Activates several different chemicals (secondary messengers)

Release of Neurotransmitter


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


Gustatory PathwayTaste Buds Taste Buds Taste buds inIn Ant.2/3 in post. 1/3 throat, epiglottis

Facial Glossopharyngeal VagusNerve(VII) Nerve(IX) Nerve(X)

Medulla Oblongata

Limbic System Thalamus& Hypothalamus Primary Gustatory Area (Parietal lobe)


EYE : SENSE OF VISION (SIGHT)

Vision: important to human survival

More than half sensory receptorsLarger part of cerebral cortex


Anatomy of Eye BallWall of Eyeball

Fibrous Vascular Retina

layer layer Neuronal layer

-Cornea -Choroid

-Sclera -Ciliary body

-Iris



Interior of Eye ball

Aqueous Vitreous Lens

Humour body


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


Canal of Schlemm:

• An opening at junction of sclera & cornea

• It drains aqueous humour from anterior chamber


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


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



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



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



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



-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.


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


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.


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


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


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 collapsingGLAUCOMA:Condition in which there is increased

intraocular pressure due to defective drainage of aqueous humour through canal of Schlemm.


Accessory structures of EyeEyelids, Eyelashes, Eyebrows, Lacrimal

Apparatus & Extrinsic eye MusclesSuperior rectusrotates eyeball upwardsInferior rectus rotates eyeball downwardsLateral rectusrotates eyeball outwardsMedial rectusrotates eyeball inwardsSuperior obliquerotates eyeball so that

cornea turns in downwards & outwards direction

Inferior obliquecornea turns upward & outward direction


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)


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)


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



EAR:SENSE OF SOUND (HEARING)

Ear- an engineering marvel,contains receptors for Hearing &

EquilibriumTransmits 1000 times faster

than photoreceptors


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



External EarAURICLE (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


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


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.



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



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


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



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


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.


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.



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



PHYSIOLOGY OF HEARING1. The auricle because of it shape

concentrates sound waves and direct them along auditory canal

2. Soundwaves stike eardrumproduces 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


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


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 potentialgeneration of nerve imp[ulse



AUDITORY PATHWAYFirst order sensory neuron (cochlear

branch) Cochlear nuvlei in medulla oblongataOlivery nuclei in ponsInferior colicullus of midbrain Geniculate nucleus of Thalamus Primary Auditory Area in superior temporal gyrus of Cerebral cortex

12 special senses

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