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Sense Organs

Sense Organs

The eyes:

The eyes are the sense organs of sight. There are two located in bony orbital cavities of the skull embedded in the fatty connective tissue. The eye ball is rounded or ball like structure having the diameter about 2.5cms. The eye ball contains the three important layers.

  1. Sclera
  2. Choroid
  3. Retina

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Horizontal section of eye ball

  1. Sclera: The sclera is the outer most layer of dense fibrous tissue. It protects the eyes on the posterior side of the sclera. It is perforated by optic nerve. The thickness of the sclera is not uniform on the anterior side it is 0.6mm thick and 0.3mm on the point of the insertion of rectus muscles and 0.1mm thick at the posterior pole. Externally it is covered by EPISCLERA.

Cornea: This is the clear transparent position present on the anterior side of the eye. The layer vascular and contains 5 layers:

i) Epithelium: This is squamous non keratinized epithelium (5-6 layers of cells). This is highly sensitive and has maximum regenerative power.

ii) Bowman: Membrane and acellular

iii) Stroma: if forms 90% of cornea thickness.

iv) Descent membrane: It is about 3-12 microns.

v) Endothelium: It is single layer of simple cuboidal cells and hexagonal cells.

  1. Choroid: This is a spongy brown membrane. It has four layers.

i) Epicordial layer

ii) chorio capillaries

iii) Vessel layers

iv) Bruch membrane

Ciliary muscle/body: This muscle the thicket part anteriorly adjustment of lens.

Iris: This is the part present in the middle of the cornea and it contains the radial and muscular muscles. It gives the different colons to the eyes due to the pigments.

Lens: The lens is crystalline structure biconcave and covered by the lens capsule. The lens is muscular and gets the nutrition from the aqueous human filled in the aqueous chamber. It is Elastic and transparent and held in position by the ciliary muscles.

  1. Retina: This is the inner most layer of the eye the retina is two layered. It is pigment cell absorbs the light and present scattering in the eye. The retina contains millions of the photo receptor cells on posterior wall of retina. There is present the blind spot which doesn’t contain the rod and cone cells so no image is formed on this point.

The rod cells helps to see in the darkness and the cone cells help to see in the brightness and also helps to see different color.

There is present the most sensitive point on the retina which is just opposite to the center of the pupil on the retina on the point most clear image is formed.

Blood supply: The outer 3rd part of the retina is supplied by the vessels in the choroid. The inner two third is supplied by central artery and central vein of the retina the fundus of the eye is only the place in the body where small blood vessels can be absorbed directly in a living person.

Histology of retina: The cells of retina can be divided in three types:

  1. Photoreceptor cells: They contain the rod and cone cells. The rod cells provide the black and white vision in darkness and the cone cells provide the color in brightness. The human retina contains about 120 million rod cells and 6 million cone cells.
  2. Neural cells: These cells contain the bi-polar cells, ganglion cells, horizontal cells and amacrine cells. Bi-polar cells are present in the complete retina. The axons of ganglion cells become the nerve fiber layer within retina than becomes optic nerve fibers to brain.
  3. Supporting cells: These cells are present between axon cells and optic nerve within retina the retina is approximately 0.5 mm thick and lies the back of eye.

Histology of cornea: The cornea is bulginfront position of the eye. It is non-vascular, transparent, microscopically it contain five layers.

1. Corneal epithelium

2. Anterior propria

3. Substania propria

4. Posterior limiting membrane

5. Corneal endothelium

Focusing of light on retina: As the light passes from the air into the eye it moves through the cornea aqueous humor lens vitreous humor and then to retina. The light rays binding takes place after entering as it enters the cornea and entering and living the lens. The lens is highly elastic and the five following of the image is done on the retina.

  1. Focusing for distant object: For the distant vision no change in the shape is needed by the lens. The light rays travel parallel from the distant object and is focused on the retina during the distant vision the ciliary muscles are completely relaxed and the lens becomes thin. The light from distant object over 6 meter approaches as parallel rays and in the normal eye need not be adjusted for proper focusing on retina.
  2. Focusing for closed vision: The light from the objects lens than 6m away diverges as it approaches the eye for the nearer objects eyes want an active adjustment. Therefore three processes occur simultaneously.

1. Accommodation of lens

2. Construction (Contraction) of pupil

3. Conversion of eyeball

The image formed on the retina is inverted, which is taken by the 2nd optic nerve to the brain. In the brain it is corrected and the real image of the object is formed on the retina.

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Lens is flattened for distal vision

The clinical part and applied aspects:

  1. Decryocystities: This is the inflammation of lacrimal sac is called as the decryocystitis. In this condition fluid drainage takes place in nose.
  2. Ptosis: Paralysis of levator palpibrae leads to ptosis. In this case there is a dropping of upper eye lid.
  3. Squint: This is the unilateral paralysis of an extra ocular muscle. It produces the double vision.
  4. Arcus seniculus: Due to aging there is fatty degeneration along the periphery of cornea. It becomes visible as a white ring.
  5. Refractive error: This is the defect in image formation in the eye.
  6. Myopia (short vision): The myopia occurs when the distant objects are not founded on the retina but before the retina. The people can see the nearer objects but not the distant objects also called as near sightedness. It can be corrected by concave lens.
  7. Hypermetropia/Hyperopia: This is called as for sightedness in this case the image is formed behind the retina. The person can see the distant objects but not the nearer. The problem can be corrected by convex lens.
  8. Detached retina: A detached retina occurs when the retina is pulled away from its normal position. In the back of the eye when the detachment takes place the vision is blurred. It is a serious problem and can cause blindness if not treated

Symptoms: 1. flashing lights 2. Grey curtain across the field of vision.

Causes: The vitreous humor gets away from retina with older age when it pulls hard to tear the retina causes the retinal attachment.

Treatment: 1. the retinal holes are treated by laser treatment 2. By surgical

  1. Cataract: The cataract is the clouding of the eyes of natural lens. The cataracts are the most common cause of loss of vision and blindness. It can also cause injury in the lens.

Type of cataracts:

Sub scapular: it takes place at the back of lens, chances in more diabetic patients.

Nuclear cataract: It occurs in the nucleus of the lens with aging.

Cortical cataract: This is whitish structure which starts at periphery to the center of the lens.

Secondary cataract: This can occur after surgery.

Congenital cataract: Some babies are born with contract but do not affect vision. The lenses are removed.

Radiation cataract: It can develop to certain type of radiation.

  1. Glaucoma: This is an optic nerve disease which causes the glaucoma. It starts with loss of sight, if untreated cause the blindness.

Lacrimal gland:

The lacrimal gland is also called as the tear gland. There are two tear glands situated one on each eye. The lacrimal glands are connected to the eye by the lacrimal duct towards the caruncle side. These is present the lacrimal canal which is connected to the lacrimal sac which forms the nasolacrimal duct in the nose.

Lacrimal Gland Anatomy and Drainage System #Anatomy #Ophthalmology ...

Functions: The lacrimal gland perform the fallowing important function.

  1. The lacrimal gland secrets a clear watery slightly salty secretion in the eyes. It helps the eyes to keep moist and present from the dryness.
  2. The secretion of the lacrimal gland is function as the cleaning agent for the eyes.
  3. The secretion of lacrimal gland prevents the eyes from the tissue damage. If the tissues of the eye come in contact with the watery secretion they clean the eyes and protect the eye.
  4. The secretion of lacrimal gland prevents the eyes from the harmful microorganism by giving a coating to them.
  5. The lacrimal glands are also related with the emotions. When a person is emotionally disturbed in the form of the tears it clears the emotion by giving relief to the person.
  6. The lacrimal gland gives the nourishment to the cornea

The focusing muscles present in the eye rotate 1000, 000/day.

Meibomian gland: These are also called as the tarsal glands. These are emended in tarsal plates of the eyelids they secrete the oily secretion which help in the lubrication of eye lids with the eye lashes the maximum ciliary gland are present.

Vitreous humor: Present in posterior side of lens in vitreous chamber. It is sticky fluid and provides nutrition to retina.

Pupil: Pupil is small aperture present in iris to function contraction and relaxations of lens radial and circulation muscle helps in contraction and relaxation. Pupil helps in dilation.

Tongue- Sense organs of taste

The Tongue:

The tongue is muscular organ of sense present in the lower part of buccal cavity.

It contains 3 parts

  1. Tip
  2. Body
  3. Root

The anterior part is free. The posterior part root is fixed part. The tongue contains the filly form papillae towards the tip and detect the sweet taste just above this the salty taste can be felt.

The body contains fungi form papillae which detects the sour taste towards the root side there are present the vallate papillae which is responsible for the bitter taste the papillae are very small projections on the surface of the tongue.

Tongue – Papillae – Taste buds – chemo receptor cells/ gustatory cells.


The tongue contains following layer:

  1. Mucus membrane: It contains the epithelial and connective tissue which contain lamina propria. In the anterior portion of 2/3rd of the tongue there are present upward projections which are called as papillae. There are present three types of papillae, filiform, fungiform and vallate.
  2. Lamina propria: This is papillae very thin and is made up of sense connective tissue with elastic fibers blood vessels nerves and scattered lymphatic cells.
  3. Core of tongue: It contains the bundles of muscle fibers with connective tissue and scattered mucus and serous lingual glands.

Structure of taste buds: The taste buds are bell shape structure narrow at the end and border at the middle which are present within epitheliums of the buccal cavity open by the taste pores. These are present about 10,000 taste buds on the surface of the tongue each taste bud contains about 60-70 gustatory cell which are the chemoreceptor cells which gives the taste sensation. The taste bud made up of the types of cells.

  1. Gustatory cells: These are slender rod shaped cells with a central nucleus. Free surface of these cells provides hair like structure in the lumen of taste bud.
  2. Supporting cells: These cells are spindle shaped the base of each taste bud is penetrated by the afferent gustatory fibers. All the papillae except the filiform contain the taste buds. The taste buds are present at the following sites.

1. Anterior 2/3 of tongue calorically

2. Interior surface of the soft palate

3. posterior surface of epiglottis

4. posterior wall of oropharynx

The sweet taste is mainly due to the organic substance of diverse nature such as sugar, dextrin’s, glycerol and saccharides. The salty taste is mainly from some cations like sodium of inorganic salt. The sour taste is due to the hydrogen ion produced by the acids.

The bitter taste is by much organic substance like quinine, morphine, coffin nicotine and urea.

The taste of chili black pepper and hot sauces is not a true sensation it is mainly a burning sensation which is produced by the stimulation or pain receptors of the tongue by specific chemical substances present in the food.

The Skin-

the skin is the sense organ of touch


Structure of skin: The skin is the largest organ of our body skin is the sense organ of touch. It gives the different sensation like touch hotness, coldness and felling the pain etc.

The skin contains two parts:

1. Outer layer epidermis

2. Inner layer dermis

  1. Epidermis: This is the outer layer made up of epithelium and contains the following layers:

a) Stratum corneum: It contains the scale like cells which are regularly replace and the cells contain the protein keratin.

b) Stratum granulosum: This layer contains the scale like cell which are spindle in shape and contains the granules and cytoplasm.

c) Stratum germination: This layer contains the cube like cells the skin cells multiply in thin layers.

  1. Dermis: The dermis is also called as the true skin. This is tough and elastic and it is made up of collagen fibers and elastic fibers. The collagen fibers bind the water but with the age thin decrease and the wrinkles appear in the deeper layer there is areolar tissue and the fats.

a) Blood vessels: The arterioles from a fine network of capillaries which gland, sebaceous gland, hair follicle. There is no blood supply in epidermis.

b) Lymph vessels: The dermis is supplied by the network of lymph vessels.

c) Sensory nerve endings: The nerves sensitive to touch temperature change in temperature are widely distributed in the dermis.

d) Sweat glands: These glands are present in the complete skin but maximum in the palms of the hand and sole of the feet. They are made up of epithelial cells. The bodies are in the coiled form some open in the hair follicle. The sweat glands are stimulated in sympathetic nervous system about 500ml of sweat formed in 24 hours. The sweat mainly contains the water and minerals waste products.

e) Sebaceous gland: It contains epithelial cells. They secrete the only secretion sebum which gives the softness to the skin. It given shining to the hair. On the skin this is water profane and the skin protective. It keeps the skin oily. It is present in the complete body part except the palms of the hand and sides of the feet. These are grown by the lower epidural cells in the dermis and the base of the hair root and outside the hair follicles there is present the hair papilla. The part of the hair above the skin is called shaft and the rest is called as root. The color of the hair is due to pigment melanin. The white hair is the result of the replacement of melanin by tiny air bubbles.

Functions of skin:

  1. Regulation of body temperature: The skin maintains the body temperature by heat production and heat loss heat production by body activates and heat loss by conduction evaporation and radiation.
  2. Excretion: The skin help in the excretion of some extra material like water, sodium, chlorides, lactic acid, urea, amino acid in the sweat.
  3. Protection: The skins function as the outer protection layer to the body. It gives protection to various important internal part of body.
  4. Absorption: The skin helps in the absorption for many oil ointments, chemicals which are useful to body.
  5. Color of the body: Due to the presence of the pigment melanin the skin give different color to the body.
  6. As special sense organs: The skin gives the feeling of hotness, coldness and pain etc.
  7. Storage function: The skin helps in the storage of water and fats.
  8. Sebum secretions: The skin secrets the oily secretion sebum by the sebaceous gland which protects the skin from the dryness.
  9. Vitamin D synthesis: In the presence of sunlight the skin manufacture vitamin D which is very beneficial for body.
  10. Facial expression: The facial skin gives the various expressions like happiness, sorrow, pain, fear, anxiety, excitement etc.

The Nose:

The nose is a sense organ of smell. The nose can be divided into two parts.

  1. Internal nose
  2. External nose

External position: It contains the bone cartilage and the nostrils. The nostrils are separated by the septum. The inner walls of nose are covered by the nasal mucosa this is called as the olfactory epithelium. It covers a very small portion of the external portion near the septum about 5cms in the nasal cavity. The olfactory receptor cells contain the tree types of the cells:

  1. Olfactory receptor cells
  2. Supporting cells
  3. Basal cells

The olfactory receptor cells function as a chemoreceptor cells become they are stimulated by particular chemical substances.

Internal position: This is also called as nasal cavity. The nasal cavity contains four sinuses.

  1. Maxillary
  2. Frontal
  3. Ethmoidal
  4. Sphenoid

Sinuses: The nasal sinuses are air filled spaces present in the bones of the skull.

Nose and Sinuses - Ear, Nose, and Throat Disorders - MSD Manual ...

Air sinuses (maxillary): There are two in number and the largest sinuses present in maxillary. This air capacity is about 15cc. the medial wall formed the base of pyramid. The roof is very thin and is formed by the floor of the orbit. The blood supply is by the inform orbital facial and greater palliative artery. The verve supply is by the infra orbital nerve.

Frontal sinuses: There are also 2 in number and present in frontal bone. This is also like the pyramid which the apex pointing upwards and base is formed by the floor. The air capacity is about 7cc in adults. The anterior wall is formed by outer part of the frontal bone. The posterior wall is thin and separates the sinus from the cranial cavity formed by the inner plate of frontal bone. The floor is formed by the inner bone separating the sinus from the orbit. The medial wall forms the septum between the 2 frontal sinuses. The blood supply is by supra orbital nerve.

Ethmoidal sinuses: There are two group of ethmoidal sinuses having approximately 15-20 ethmoidal cells on both sides the ethmoidal sinuses open in middle meatus (aperture).

Sphenoid sinuses: There are two sphenoid sinuses in the sphenoid bone and they are separated in two unequal sinuses by a septum. They open in the spheno-ethmoidal recess above the superior turbinate. It is related with the 2nd, 3rd, 4th, 5th and 6th cranial nerves.

The ear:

(Sense organ of hearing)

  • The ear is the sense organ of hearing
  • It contain 3 parts- externally and internally part and middle
  • The ear contains both the receptor for hearing and equilibrium
external structure of ear

External ear: contains the immovable pinna which is made up of cartilage, auditory canal and the ear sends it to the auditory canal and the ear drum. The canal is about 2.5cm in length. This is not the straight tube, slightly curved at the end of this tube. There is present the vibrating tympanic membrane (ear drum).

Middle ear: Is an ear filled cavity on the other side of ear drum inside the cranial bone. Cavity is connected with pharynx through the Eustachian tube. It maintains the air balance pressure between two sides of the ear drum so that the ear drum can vibrate freely when the sound wave strikes on it.

The middle ear contains 3 bones.

  1. Malleus
  2. Incus
  3. Stapes which are called an auditory ossicles

Internal ear: This is also called as labyrinth. It is present deep in the temporal bone.

The internal ear has two important divisions:

  1. Bony labyrinth
  2. Membranous labyrinth

There are three regions:

  1. Vestibule
  2. Cochlea
  3. Semi- circular canal

There is hollow space in bony Ladysmith within the bony labyrinth. The membranous labyrinth with perilymph fluid which is similar to CSF. The membranous labyrinth is filled with end lymph. These 2 fluids conduct the sound waves which are involved in hearing.

Vestibule: Is a central egg shape cavity of the bony labyrinth. It is present posterior to cochlea, anterior to semi-circular canal. It is lateral wall there is present the round window. These are 2 membranous labyrinth racs. The secular and utricle. The saccule and utricle gives responds to pull of gravity and change of head position. Semicircular canals are present posterior and lateral to the vestibule and are just like 2/3 of circle. These are anterior posterior and lateral semicircular canal which helps in equilibrium.

Cochlea: This is a snail like structure in a cochlea there is present the organ of hearing which is called as the spinal organ of corti, it contains the hair cells. It is about 4cm long. This is the deeply embedded in the temporal bone. The hair cell due to their movement generates the electrical signal which stimulates the auditory nerve. The organ of cost performs two important functions.

  1. It converts the mechanical energy into electrical energy.
  2. It sends the original sound to the brain.
  3. The organ of costs sends the signal of round to CNS.

The physiology of having taken place as following.

  1. Conducting apparatus: The sound waves are collected by the pinna and send to the ear drum through the auditory canal and strike the ear drum as a result of this the ear drum starts vibrating when the ear drum vibrates the three small bones attached with this the malleus + incus + stapes also vibrates from this part the sound waves enter in the cochlea.

Ext ear + ear drum + acicular chain

  1. Perceiving apparatus: From the stapes the sound waves enter in cochlea which is filled with perilymph. The perilymph sends the vibrations to hair cells which are stimulated the nerve impulses. The nerve impulses are conducted by the nerve fibers to the brain and ultimately the sound reaches the brain this is called physiology of hearing.

Clinical aspects of ear:

  1. Deafness: Any hearing loss is called as deafness

a) Conduction deafness: This is the max blocking the auditory canal perforated ear drum middle ear inflammation (otitis media)

b) Oto sclerosis: This is the age related problem due to the over growth of bony tissue fusion with the stapes bone.

c) Sensor neural deafness: This is due to the damage in the neural structure. This can be due to the loud noise and degeneration of cochlear nerve.

  1. Tinnitus: This is the ringing sound in the ears without any sound produced due to cochlea nerve degeneration.

The inflammation in middle ear takes place this is due to side effects of some of the medicines.

  1. Otitis media: This is the medical term for the middle ear inflammation

a)Acute otitis media

b) Otitis media with effusion

The first symptom is the ear pain, later is very common without any symptoms. The otitis media is most common in children up to 10 years.


1. URI (upper respiratory infection)

2. Fever

3. Cough

4. Ear pain

5. Nasal discharge etc.