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

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 3^rd 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 2^nd optic nerve to the brain. In the brain it is corrected and the real image of the object is formed on the retina.

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.

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.