Sense Organs.pdf

HUMAN ANATOMY AND PHYSIOLOGY NOTES
RAMDAS BHAT
KARAVALI COLLEGE OF PHARMACY 1
CHAPTER NO:6
SENSE ORGANS
Prepared by,
RAMDAS BHAT
Asst. Professor
Karavali college of Pharmacy
Mangalore
7795772463
Ramdas21@gmail.com

RAMDAS BHAT
INTEGUMENTARY SYSTEM:
This system is divided into:
1. Skin
2. Hair
3. Glands
4. Nails
5. Nerve endings
SKIN
• Skin is an organ because it consists of different tissues that are joined to perform a specific
function.
• Largest organ of the body in surface area and weight.
• Dermatology is the medical specialty concerning the diagnosing and treatment of skin
disorders.
Anatomy (structure)
• Epidermis (thinner outer layer of skin)
• Dermis (thicker connective tissue layer)
• Hypodermis (subcutaneous layer or Sub-Q)
• Muscle and bone
Physiology (function)
1. Protection:
• Physical barrier that protects underlying tissues from injury, UV light and bacterial invasion.
• Mechanical barrier is part nonspecific immunity (skin, tears and saliva).
SENSE ORGANS

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2. Regulation of body temperature:
• High temperature or strenuous exercise; sweat is evaporated from the skin surface to cool
it down.
• Vasodilation (increases blood flow) and vasoconstriction (decrease in blood flow) regulates
body temperature.
3. Sensation:
• Nerve endings and receptor cells that detect stimuli to temp., pain, pressure and touch.
4. Excretion:
• sweat removes water and small amounts of salt, uric acid and ammonia from the body
surface
5. Blood reservoir:
• Dermis houses an extensive network of blood vessels carrying 8-10% of total blood flow in
a resting adult.
6. Synthesis of Vitamin D (cholecalciferol):
• UV rays in sunlight stimulate the production of Vit. D.
• Enzymes in the kidney and liver modify and convert to final form; calcitriol (most active
form of Vit. D.)
• Calcitriol aids in absorption of calcium from foods and is considered a hormone.
EPIDERMIS:
They are Keratinized stratified squamous epithelium with four distinct cell types and five
distinct layers.

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5 layers of the epidermis:
1. Stratum corneum (horny layer):
• layer has many rows of dead cells filled with keratin
• continuously shed and replaced (desquamation)
• effective barrier against light, heat and bacteria
• 20-30 cell layers thick
• dandruff and flakes
• 40 lbs. of skin flakes in a lifetime (dust mites!)
2. Stratum lucidum
• seen in thick skin of the palms and soles of feet.
• 3-5 rows of clear flat dead cells
• it contains keratohyalin granules(precursor) for production of keratin.
3. Stratum granulosum
• 3-5 rows of flattened cells
• nuclei of cells flatten out
• organelles disintegrate cells eventually die
• keratohyalin granules (darkly stained) accumulate
4. Stratum spinosum: “spiny layer”
• 8-10 rows of polyhedral (many sided) cells
• appearance of prickly spines
• melanin granules and Langerhans’ cell predominate
5. Stratum basale: deepest epidermal layer
• attached to dermis
• single layer of cells
• mostly columnar keratinocytes
• with rapid mitotic division
• stratum germinativum
• contain merkel cells and melanocytes
• 10-25%

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Cells in the epidermis:
1. Keratinocytes
2. Melanocytes
3. Merkel cells
4. Langerhans cells
1. Keratinocytes: most abundant
• produce keratin (fibrous protein)
• protective; waterproofing the skin
• continuous mitosis
• form in the deepest layer called the Stratum Basal cells push their way up to the surface
where they are dead cells filled with keratin; will slough off. Regenerates every 25-45 days.
2. Melanocytes:
• cells produce brownish/black pigment called melanin. (8% of epidermal cells)
• produced in stratum basale
• the melanocytes have branching processes (dendrites)
• Melanin accumulates in the Melanosomes (Granules) and transported along the dendrites
of the melanocytes to the keratinocytes.
• Melanin accumulates at the superficial aspect of the Keratinocytes.
3. Merkel cells:
• stratum basale
• epidermis of hairless skin
• attach to keratinocytes by desmosomes
• make contact with a sensory neuron ending called a Merkel disc (touch).
4. Langerhans’ cells:
• star-shaped cells arising from bone marrow that migrate to epidermis.
• epidermal dendritic cells (macrophages)
• interact with a WBC called a T- helper cell
• easily damaged by UV light.

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DERMIS:
• flexible and strong connective tissue
• elastic, reticular and collagen fibers
• cells: fibroblasts, macrophages (WBC), mast cells (histamine).
• nerves, blood and lymphatic vessels
• oil and sweat glands originate
• two layers: papillary and reticular
Papillary layer:
• loose connective tissue with nipple like surface projection called dermal papillae
• capillaries
• contain pain receptors
• contain touch receptors (Meissner’s corpuscles)
• dermal ridges- epidermal ridges- pattern called fingerprints.
Reticular layer:
• dense irregular connective tissue.
• collagen fibers offer strength
• holds water
• dermal tearing causes stretch marks.
Hair (pili)
• main function is protection
• normal hair loss in adult 70-100 hairs/day

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Arrector Pilli muscle:
• Involuntary smooth muscle
• Helps hair to stand
• Produces goose bumps
Hair root:
• Lower part of hair
• Attached to dermis
Hair shaft:
• Upper part of hair
• Contains medulla (central portion), cortex layer (middle portion) and Cuticle region
Functions of Hair:
• UV protection
• Insulating property
• Sensory detection
• Prevent entry of foreign matters (eye lashes, nostrils).
Glands:
Two types of glands exist in the integument.
1. Sebaceous glands (oil glands)
2. Sudoriferous glands (sweat glands)
1. Sebaceous glands: (holocrine glands)
• connected to hair follicle
• not found on palms and soles of feet
• secretes sebum (fats, cholesterol and proteins)
• keep hair from drying out, keeps skin moist
• whiteheads, blackheads and acne
2. Sudoriferous glands: exocrine glands
millions located throughout the skin and are of two types:
A) Eccrine: more common (merocrine)
• originate in subcutaneous layer
• duct empties on skin surface
• more prominent palms and soles of feet
• sweat is watery (99% H20)
• sweating regulated by sympathetic nervous system
B) Apocrine: axillary (under arm) and pubic region
• duct empties onto hair follicle
• viscous fluid
• causes body odour when bacteria break it down.

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3. Ceruminous glands: located in ear only
• modified apocrine glands
• produces cerumen (ear wax): brown sticky substance that prevents foreign material from
entering.
Receptors of skin
1. Cutaneous receptors:
Nociceptors/Pain receptors:
• found in joints, periosteum of bone and skin
• Pain due to touching of any object is felt through this
• It plays important role in the withdrawal reflex
• Pain originating in viscera is felt on body surfaces
Thermoreceptors:
• Free nerve endings in skin, muscle, liver, and hypothalamus
• Cold receptors respond to temps <50
• Warm receptors respond to temps >113
• Both are structurally identical.
2. Mechanoreceptors:
• Membrane distortion opens mechanically regulated ion channels to create impulses.
There are 3 classes:
• Tactile – respond to touch
• Baroreceptors – respond to pressure
• Proprioceptors – respond to changes in body position.

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Tactile receptors:
• May be simple or complex, superficial or deep, fine (provide detailed information) or
crude (provide little information)
• Merkel’s disc – fine touch and pressure
• Pacinian – deep pressure
• Meissner’s – fine touch and pressure in select areas
• Ruffini – pressure or distortion in deep dermal layers.
Baroreceptors:
• stretch receptors that monitor changes in organ pressure in distensible organs
• rapidly adapting
• Generate an AP from their dendrites when organs are stretched or change position
• They monitor BP, respiration, digestion, and urinary control
Proprioceptors:
• They are present in the joints.
• They are sense of motion or muscle sense.
• They will detect the pressure caused by movements.
• They play an important role in the stretching reflex.
3. Chemoreceptors:
• Only respond to dissolved chemicals
• Rapidly adapting:
• found in olfaction, taste & the CNS at:
• Medulla – receptors are sensitive to pH/CO2 changes in CSF– trigger respiratory
adjustments
• Aortic/Carotid bodies – sensitive to changes in pH/CO2/O2 blood levels – trigger
adjustments in respiration and cardiovascular activity.

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Nails:
• Protect the fingers and toes
• Made of the dead cell containing keratin
• Nail consist of
a) Nail body: visible portion of nail and covers
nail bed,
b) Lanula: a pale crescent at the base of nail,
c) Sides of nail: contain lateral groove
surrounded by lateral nail folds
TONGUE
• Tongue consists of receptor for perception of taste.
• Receptors are called as Taste buds.
• Taste buds can detect types of taste
• Salty, sweet, bitter and sour
• It can detect a sensation called UMAMI from taste receptor. It mainly detects meaty taste.
It gets activated in the presence of Glutamate.
• Taste buds at tip detect sweet
• Back can detect the bitter
• Sides can detect salty and sour.
• Taste buds are present on surface of papillae's
• 4 papillae can be found

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• Fungiform: mushroom shaped. Found near tip of tongue. 5 taste buds it contains.
• Filiform: has no taste buds but has tactile receptors. Spiny elevations. Increase friction
b/w tongue and food.
• Foliate: they are present on lateral margins(sides) of tongue.
• Circumvallate: V shaped row back of tongue. It has 100-300 taste buds.
STRUCTURE OF TASTE BUD:
• Around 10000 taste buds are present in humans on tongue but some are found on
pharynx, epiglottis
• It decreases with age
• It consists of following features.
• Supporting cells: they will surround the Gustatory receptor cells in the taste bud.
• Gustatory receptors cells: a single microvillus (GUSTATORY HAIR) will project from each
receptor cells to outside layer through the taste pore.
• Basal cells: these are stem cells that are present at the periphery of the taste bud nearer
to connective tissue layer. Produces supporting cells and Receptor cell

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Taste pathway:
• The Gustatory receptor cell will form synapse with the first order neurons which form the
first part of the mechanism.
• The chemicals substances for food that stimulate the receptor are call as the Tastants.
• The Tastants will be dissolved in saliva that comes in contact with the gustatory hairs
causes the signal transduction to the receptor cell through the gustatory hair,
• The potential will cause the exocytosis of the synaptic vesicles from gustatory receptors.
• The neurotransmitter released from the Gustatory cell will causes the signal transduction
to first order neurons causes the triggering of nerve impulses in 1st order neurons.
• Potential will be different for different Tastants.
• Na+ from salty food will move inside the gustatory receptor cell through Na+ channel.
• Na+ inside the cell will cause the depolarisation and vesicle release.
• H+ in case of sour Tastants.
• Other Tastants like sweet, bitter and umami cannot enter receptor cells.
• Instead, they will bind to the receptor present in plasma membrane of receptor cell.
• The receptors are linked to G-protein coupled receptor.
• Activation of the G-protein will now activate various chemical messengers called as the
secondary messengers.
• Secondary messengers will cause the depolarization and release Neuro transmitter.
• 1st order neurons are the cranial nerves.
• Sensory fibers from taste buds present in anterior 2/3rd of the tongue will run to VII
nerves.
• Taste fibers from posterior 1/3rd will run to IX nerves.
• Those from pharynx and epiglottis will run to X nerves.
• All the 3 nerves run into medulla of brain and synapses with solitary nucleus of M.O and
in the form of 2nd order neurons are carried to thalamus where they synapse with V nerve.
• The V nerve in the form of the 3rd order neurons is carried to the post central gyrus.

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NOSE
Olfaction:
• Smell or olfaction is a physiological activity carried out by the nose
• Smell around us is present in the form of the vapours
• The smell goes inside the nasal septum.
• The smell then enters into the mucous membrane having multiple sense receptors which
carries impulses to brain.
• The receptors are called as the olfactory receptors.
• And the smelling process is called as Olfaction.
• Olfactory membrane contains the epithelium containing
1. Olfactory receptors
2. Supporting cells
3. Basal cells

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1. OLFACTORY RECEPTORS:
• These are the 1st order neurons ad are bipolar neurons
• Neurons consist of the dendrite containing cilia (olfactory hairs) that will catch the volatile
components(odorants)
• While the axons will pass on to the cribriform bony plate and then projects itself into
olfactory bulb
• The receptors respond to the vapours and produce potential.
2. SUPPORTING CELLS:
• These are present around the olfactory receptors
• These are columnar epithelium that lines olfactory mucous membrane
• They provide physical support, nourishment and electrical insulation for the receptors,
• They also will detoxify the chemical substances that come in contact with the epithelium
3. BASAL CELLS:
• These are the stem cells present at the posterior end of the olfactory epithelium
• They undergo division to form the olfactory receptors and supporting cells.
• Olfactory epithelium produces the mucous.

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OLFACTORY PATHWAYS:
• When the odorants come in contact with the olfactory receptors (1st order neurons) they
will get dissolved in the thin layer of mucous that are spread over olfactory epithelium
• The substances then penetrate through membrane then into the Cilia of the receptor
cells.
• All the odoriferous substance combines and generate potential inside the receptor cell.
• These potentials are now taken to the olfactory bulb through the 2nd order neurons
• The olfactory bulb then carries impulses through the 3rd order neurons to various centres
• They are taken to the Frontal cortex of the cerebrum perception of the smell is done
• To the hypothalamus and amygdala that senses the emotional aspects of the smell
• To the hippocampus where the memory of the odour is presented
SMELLING DISORDERS INCLUDE:
• Anosmia: total loss of sense of smell
• Dyssomnia: distorted sense of smell
• Hypersomnia: increased sensitivity to smell
• Presbyosmia: loss of smell from normal aging
Rhinitis
• A nasal disorder that is most common during childhood and adolescence
• Generally caused by allergens
• Signs and symptoms may include:
a) Nasal congestion

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b) Itchy runny nose and eyes
c) Postnasal drip
Sinusitis
• Infection occurs when an obstruction or growth blocks the paranasal sinus.
• Patients experience thick nasal discharge, sinus and facial pressure, headache, and fever.
EAR
Ear is made up of:
a) Outer ear
b) Middle ear
c) Inner ear
• Ear also functions as sense of equilibrium
OUTER EAR/EXTERNAL EAR:
• 2 parts
a) Auricle (Pinna)
• Funnel-like structure
• Helps collect sound waves traveling
through the air and directs them into the
external acoustic meatus.
b) External Acoustic Meatus (External Auditory Canal)
• S-shaped tube of 2.5cm length.
• It is a long tube running from the
PINNA to the TYMPANIC MEMBRANE
• It is 2.5cm in length and also it moves
medially inside
• It carries sound waves from auricle to
the tympanic membrane

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MIDDLE EAR:
• It conveys impulses to the oval window.
• Middle ear is called as the tympanic cavity,
• Middle ear is small and filled with air cavity in the temporal bone lined with epithelium
• It contains oval window and round window
• 3 ligaments attached bones can be seen in the middle ear
• They are called as ear ossicles.
• They are a) The malleus or the hammer b) The incus or the anvil and c) The stapes or the
stirrup.
a) Tympanic membrane/ Ear Drum
• Semi-transparent membrane made of connective tissue and is covered by a thin layer of
skin on its outer surface and a mucosa membrane in the inside
• Has an oval margin and cone-shape with the cone apex pointing inward.
b) Ear ossicles:
• They are of 3 types
a) Malleus: their handle will be attached to the ear drum the head will be articulating with
Incus
b) Incus: they are middle bone in series and articulates with Stapes
c) Stapes: the foot plate of stapes will fit to oval window.
• Lower to oval window there are round window. They are enclosed by secondary tympanic
membrane.
• The middle ear is filled with air and it also contains a tube which connects middle ear to
pharynx this tube is called as EUSTACHIAN TUBE it helps in maintaining the air in both
ears.

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INNER EAR:
• It is also called as LABYRINTH
• It has 2 parts a) bony labyrinth (outer part) and the b) membranous labyrinth (inner part).
• Internal ear contains 3 parts a) semi-circular canals b) the vestibule c) the cochlea.
• The receptors for equilibrium are situated in semicircular canal
• The receptor for audition is present in Cochlea.
• The fluid present in the bony part is called as Perilymph
• Fluid in the membrane part is called as Endolymph.
• Central part of the labyrinth is called as the Vestibule
• The vestibule is connected to 3 semicircular canals in posterior side where as the
anteriorly it is connected to the Cochlea.
• 3 types of semicircular canals are present
a) Anterior semicircular canal
b) Posterior semicircular canal
c) Lateral semicircular canal
Each of them is arranged right angles to each other.
• The vestibule consists of the 2 sacs
a) Utricle
b) Saccule

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• At one end of the canal an enlargement is seen called as the ampulla
Cochlea:
• It is present anterior to the vestibule
• It looks like a snail shell
• It makes 3 turns around the central bony core called as MODIOLUS
• The receptor cells for audition sensation lies in cochlea
• Cochlea is divided into Cochlear duct and Cochlear spiral (bony part)
• On one side of cochlear duct it contains BASILAR MEMBRANE, ORGAN OF CORTI is
attached to it
• The sensory receptors of ear are present in Organ of Corti and are called as HAIR CELLS.
• The hair cells will convert the pressurized waves of sound into the potential.
• On other side it contains TECTORIAL MEMBRANE

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• On the either side of the tubules there are compartment filled with fluid
• They are
a) Scala vestibule
b) Scala tympani
c) Scala Media
• Scala vestibule: they are present on the sides of the cochlear duct and ends at oval window
• Scala tympani: they are present below the cochlear duct they will end up at the round
window.

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• Scala tympani and Scala Vestibule will communicate at apex through an opening called as
HELICOTREMA.
• THE ORGAN OF CORTI is the site where the Auditory hairs are present.
• The organ of the corti is present in the basilar membrane
• Organ of corti consist of the Supporting cells and the Specialized cells that converts
pressurized sound waves into the potential these cells are called as HAIR CELLS.
• 2 types of hair cells can be seen Inner hair cells and Outer hair cells
• The hair cells have a cilium on their surface called as STEREOCILIA.

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• Above the steriocilia tectorial membrane is seen when the mechanical disturbance due to
the sound waves between the tectorial and basilar membrane happens the STEREO CILIA
are displayed.
MECHANIM OF AUDITION:
• Pinna will receive the sound impulses from all direction and passes to the external
auditory meatus
• Then the sound waves hit the Tympanic membrane
• Tympanic membrane will now vibrate with higher frequency
• Tympanic membrane now cause the displacement of the ear ossicles and the Stapes will
push the oval window inside with the foot of stapes.
• This causes the pressurized waves to pass on to the Cochlea,
• Vibration of the Basilar membrane of the cochlea happens due to the pressurized waves
movement inside the Labyrinth membrane with higher frequency and the movement of
the endolymph inside the membrane.
• The basilar membrane contains the ORGAN OF CORTI containing the hair cells.
• Once the basilar membrane undergoes the motion the hair cells will now project on to
the Tectorial membrane this causes one directional bending of the Hair cell.
• The bending of the hair cell will cause the generation of the potential inside the Hair cell
• Hair cell will undergo depolarization and finally vesicular degranulation of the
neurotransmitter in the hair cells.
• The hair cells are innervated with the Auditory VIII nerve.
• The neurotransmitter then setup the stimulus to VIII nerve
• VIII nerve then move onto the Vestibulo Cochlear region, then on to the thalamus and
finally taken to the primary auditory cortex present in temporal lobe.

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MECHANISM OF EQUILIBRIUM
• The equilibrium done by ear is of 2 types
• Dynamic equilibrium: maintains the body position in response to the sudden movements
as rotation, acceleration and deceleration
• Static equilibrium: maintains the body position relative to the force of gravity.
• The receptors region for the equilibrium is the Vestibular apparatus containing utricle,
saccule and semicircular canal
• Semicircular canal does not show auditory functions but are closely attached to cochlea
• They provide the information for maintaining the body and postural balance in the space
• Walls of Utricle and Saccule contains the thickened region called as maculae
• Maculae will help in maintaining the STATIC EQUILIBRIUM and DYNAMIC EQUILIBRIUM
• For static equilibrium it will send the sensory impulses about the position of the head in
the space for maintain the body posture and balance.
• For dynamic equilibrium it will send sensory impulses about the acceleration and
deceleration of the body
• The maculae contain 2 cells a) supporting cells and b) receptor cells
• The sensory impulses from the receptor cells will move on to the nerve fibres then into
the Vestibular tract.
• Some axons of the nerve fibres then enter the brain stem ie. medulla and pons
• Remaining axons will move onto the cerebellum
• And this is how Cerebellum will maintain the equilibrium of the body both the static and
dynamic.

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DISEASES:
Labyrinthitis
• Feeling of vertigo or loss of balance after an ear infection or upper respiratory infection
• Other symptoms may include:
• Ringing in the ears
• Loss of hearing
• Vomiting
• Endolymphatic rupture creates increased pressure in the cochlear duct
• Damages organ of Corti and semicircular canal
• Patients will likely experience:
• Severe vertigo
• Tinnitus
• Sensorineural hearing loss
Otitis Externa and Media
• Infection resulting from bacterial growth in the ear canal
• Externa: outer ear
• Media: middle ear
• More common in children than adults
• Signs and symptoms may include:
a) Edema and erythema
b) Diminished hearing acuity
c) Inflamed, bulging tympanic membrane

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EYE
• EYE is a complex sensory organ
• They are located in an orbital cavity
• They are supplied with C-2(optic) nerves.
• Spherical in shape
• The space b/w the orbital cavity and eye is filled with the adipose tissue.
Structure of eye:
• The eye has 3 layers
• Outer fibrous layer containing sclera and cornea
• Middle vascular layer containing choroid, ciliary body and iris
• Inner nervous tissue containing Retina.
• Inner part of eye contains lens, Aq. Fluid, Vitreous body.

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EYE BALL:
• EYE ball contains a) Fibrous tunic, b) Vascular tunic, c) Retina
a) Fibrous tunic:
• It contains the anterior cornea and sclera
❖ Cornea:
• Transparent coat covering Iris
• Curved in shape and focus light on retina
• Outer layer: non keratinised epithelium
• Middle: collagen fibers and fibroblast.
• Inner: simple squamous epithelium
❖ Sclera:
• White part of eye
• Made of dense connective tissue made of collagen fibers and fibroblast.
• They give shape to eyeball.
b) Vascular tunic:
• It is middle layer of eyeball
• It has 4 parts:
a) Choroid
b) Ciliary body
c) Iris
d) Pupil
❖ Choroid:
• Provides nutrients to posterior surface of retina

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❖ Ciliary body:
• Circular bands of smooth muscles
• Alters shape of eye when nearer and far image
❖ Iris:
• Coloured part of eye
• Placed between cornea and lens attached to ciliary body
• Contains circular and radial muscle.
• They regulate the amt. of light entering the vitreous body through the pupil.
❖ Pupil:
• Pupil is the central aperture of the iris
• It has 2 types of muscles Sphincter pupillae and dilator pupillae
• These muscles will determine the size of pupil.
• ANS will regulate the diameter of pupil
• In the presence of the bright light Para. Symp neurons will stimulate the circular muscle
of the iris to contract. Causing myosis (decrease in size) of pupil
• Dim light Symp neurons causes increase size of pupil (Mydriasis)
c) Retina:
• Inner coat of eye ball
• Present posterior to eye ball
• It is the place of beginning of the visual activity
• Optic disc is a place from which the optic nerve will arise from eye ball
• Pigmented layer is melanin containing epithelial cells.
• Melanin will absorb the light and prevent the reflection and scattering of light within
eyeball
• Macula lutea- yellow spot, area of high cone
• Fovea centralis- in center of macula lutea, contains only cones, area of greatest visual
acuity.

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Neural layer:
• It has 3 layers
1. Photoreceptor
2. Bipolar cells
3. Ganglionic cell layer
• Photoreceptors: they are of 2 types
a) rods or rhodopsin(120million): has low threshold allowing to see in dim light
b) cons or iodopsin(6million): has higher threshold to produce coloured image
• Loss of rods: night blindness
• Loss of cons: permanent blindness

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Lens:
• Behind the pupil and the iris there is a lens
• Lens is present in the cavity of the eye.
• Proteins called as the crystallins are arranged layer by layer and hence it is transparent and
lacks the blood flow
• The images from lens will falls on retina
• Hence helping in clear vision.
Interiors of eyeball:
• The lens divides the eye into 2 cavities.
• Vitreous cavity and aqueous cavity
• The chambers of the anterior eye ball contain a fluid called as the Aqueous humor that
surround the lens and cornea
• The pressure in eye is called as the intraocular pressure 16mm hg)
• It maintains the shape of the eye ball
• It also prevents eye ball from collapse
• The Vitreous cavity is present posterior to the lens filled by Vitreous humor that keep lens
clean and provide nutrition to eye
• IOP is exerted by Aq. Humor prominently and Vit. Humor partly.

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PHYSIOLOGY OF IMAGE FORMATION:
• The process happening is like a camera
• Here the various components will focus the object on the light sensitive film called as
retina
• Ensuring the correct amount of light entering the eye.
• The process of image formation involves 3 major steps
1. Refraction of light rays:
• As the light enters the eye it will strike anterior and posterior part of cornea.
• Both the surface causes the refraction, convergence and focusing the light on retina.
• The refraction of light will happen and images will be formed inverted and upside down
and right to left reversal.
2. Accommodation:
• Increase in curvature of the lens
when a nearer image is seen is
called as the Accommodation
• If the object is closer to eyes
there will be minimum distance
between the eye and object
• Object can now be clearly
focused on to retina with
maximum accommodation
3. Constriction of pupil:
• Circular muscles fibres of the iris play an important role in clear image formation in retina
• Accommodation involves the contraction of the circular muscles and involving the
constriction of pupil.

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4. Convergence:
• When an object is seen by an eye both eyes will look object
• This is called as the binocular vision
• Convergence refers to both eyes looking at an object so that that clearer image is focused
on to the eye
• Nearer the object greater the degree of convergence so that the image can be focused.
5. Optic nerve:
• They originate from retina
• They converge together and form optic nerve in the optic disc region.
• They then move backward onto the choroid and sclera and medially onto the Orbital
cavity.
• Then pass on to the sphenoid bone and backward and medially where they meet with
nerves of the other eye at Optic Chiasma.
6. Optic Chiasma:
• They are found in the front and above the pituitary gland in sphenoid bone.
• The optic nerves from retina of the both eyes will pass on to the opposite sides. These
sensory neurons are carried to the cerebral hemispheres.

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Visual Accessory Organs
• Eyelids
• Eye lashes and eye brows
• extrinsic eye muscles
❑ Eyelids:
• Upper and lower eyelids protect the eye from
excess sunlight and foreign bodies.
• It spreads lacrimal secretions around eyeball
and lubricates them.
❑ Eye lashes and eyebrows:
• They prevent eyeballs from sweat, direct sunlight.
❑ Extrinsic eye muscles:
• 6 muscles can be seen
• They are
a) Superior rectus muscle
b) Inferior rectus muscle
c) Lateral rectus muscle
d) Medial rectus muscle
e) Superior oblique muscle
f) Inferior oblique muscle
• All the muscles are innervated
with 3 types of Cranial nerves.
They are C-III, C-IV, C-VI
Lacrimal apparatus:
• Each eye contains a 1 lacrimal gland and its ducts, 2 lacrimal canaliculi one lacrimal sac
and one naso lacrimal duct.
❑ Tears:
• TEARS are produced from
lacrimal gland
• Produced under ANS
stimulation
❖ Functions are:
• Keeps eye ball moist
• Nourishes cornea
• Washes away irritants
• Lysozymes are present which kills microorganism.

RAMDAS BHAT
DISEASES/DISSORDERS OF EYE:
Blepharoptosis (Ptosis):
• Occurs when eyelid partially or entirely covers the eye as a result of a weakened muscle
Blindness:
• Absence of vision or the need for assistive devices and
• assistance from others to accomplish daily activities due to inability to see.
Blepharitis:
• Inflammation of the eyelid margins stemming from seborrheic, allergic, or bacterial origin.
Monochromatism (Colour Blindness):
• Inability to sharply perceive visual colours
Daltonism:
• Unable to distinguish greens from reds
Achromatic Vision:
• Cannot distinguish any colour; perceives only white, Gray, and black.
Cataract:
• Lens in the eye becomes progressively cloudy losing its normal transparency
• Alters perception of images due to interference of light transmission to retina.
Conjunctivitis, Acute:
• Inflammation of mucous membrane lining the eyelids and covering the front part of the
eyeball
• Also called “Pinkeye
Diabetic Retinopathy:
• Condition that occurs as a consequence of an 8 to 10-year duration of diabetes mellitus
in which the capillaries of retina experience scarring
Causes:
• Abnormal dilation and constriction of vessels
• Haemorrhages in capillaries
Glaucoma:
• Ocular disorders identified as a group due to the increase in intraocular pressure
❖ Acute closed-angle glaucoma
• Mouth of drainage system is narrow and closes completely
• Allowing no flow of aqueous humor

RAMDAS BHAT
❖ Chronic open-angle glaucoma
• Primary disorder
• Breakdown in drainage system of the circulation of aqueous humor.
Hyperopia:
• Refractive error in which the lens of the eye cannot focus on an image accurately
• Results in blurred vision due to light rays focused behind the retina because eyeball is
shorter than normal
• Also called farsightedness
Myopia:
• Refractive error in which the lens of the eye cannot focus on an image accurately
• Resulting in blurred distant vision due to light rays focused in front of retina because
eyeball is longer than normal
• Also known as near-sightedness.
Nyctalopia (Night Blindness):
• Inadequate vision at night or in faint lighting following reduction in synthesis of rhodopsin
Compound in rods of retina that enables the eye to adjust to low-density light

Sense Organs.pdf

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Sense Organs.pdf