Eye and Ear

Sense organs (eye and ear)

Sense organs are group of highly specialized sensory receptor cells to receive stimuli from changes environment and transform into electrochemical impulses.

There are mainly two types of sense organs based on their position.

1. Exteroreceptors: Found outside or body surface which receive external stimuli e.g. heat light pain pressure etc.

2.       Interoreceptor: Found inside on the walls of internal organs which receive internal stimuli such as PH oxygen              tension, osmotic pressure etc.                                                                                                                                                 

                       

Other types of sense organs are:

1.       Proprioreceptors: Found in the joints tendons joints which responsive to movements of muscles.

2.       Nocireceptors; Found in muscle which responsive to injury in the body.

3.       Telereceptor: Responsive to distance and sound. E.g. ear and eye.

4.       Melanoreceptors: responsive to tactile and vibration.

5.       Thermo receptors: responsive to temp changes.

6.       Chemoreceptor: responsive to taste and smell.

7.       Photoreceptor: responsive to the intensity of light.

8.       Phonoreceptor: responsive to the hearing.

9.       Olfactoreceptor: responsive to the smell.

Eye (Organ of sight)

It is a photoreceptor organ. Human eye is about spherical in shape fitted in the skull. There are six sets of muscles attached on surface of eye ball to rotate in the different directions.

These are:

1.        Superior rectal muscle.                       

2.        Inferior rectal muscle.

3.        Medical rectal muscle.

4.        Lateral rectal muscle.

5.        Superior oblique muscle.

6.        Inferior oblique muscle.

                                                       

Muscles of eye lid protect the eye from injury dust and germs due to their regular blinking. Eye lashes filter the air also.

Glands

1. Meiobomian gland- These lie in eye lids. These produce oily secretion to lubricate eye lids & eye lashes.
2. Lachrymal gland or tear gland- These are present in socket or orbit on superior and present in socket or eye ball. The glands produce alkaline tear which keep eye moist and clean. It has lysosome to kill the bacteria.

There are three coats or tunics to form eye ball.

1.       Outer fibrous coat: It consist of three parts

                                                               i.      Sclerotic: It is an outermost layer made up of fibrous connective tissues. It is white-opaque. It covers 5/6 part of the eye ball..

                                                             ii.      Cornea; it is the front part of eye. It slightly bulges out. It has no blood supply. This part of eye absorbs oxygen. It refracts light to focus on retina.

                                                           iii.      Conjunctiva:  it is thin transparent layer that cover the cornea made up of single layer of stratified squamous epithelium. It protects the cornea (conjunction).

2.       Middle vascular and pigmented coat: it is also consists of three parts.

                                                               i.      Choroid: it lies just below the sclera. It is thick, vascular, pigmented, connective tissue. The pigmented cell absorbs light. It provides nutrition and darkens the eye ball.

                                                             ii.      Ciliary part or ciliary body: these are extended from choroids. There are two sets of ciliary muscle and suspensory ligament. Its functions are to change the shape of lens due to contraction and relaxation of ciliary muscles holding the lens in right position.

                                                           iii.      Iris: it is circular muscular opaque diaphragm hangs in front of lens. It form small opening called pupil. In dim light the pupil becomes larger and in bright light pupil becomes smaller. It determines the color of eye due to its colored pigments.

3.       Retina or inner layer:  it is light sensitive membrane that’s lines the interior of the eyes. The retina consist of two       layers. The outer layer is pigmented, which prevents the backs reflection of light. The inner layer contains nerve       cells, blood vessel and two types of the light sensitive cells (rods and cones). Light passing through the lens        stimulates rods and cones which generate nerve impulses that are transmitted through bipolar and ganglionic cells to               optic nerve and finally to brain where the visual image is formed.

Lens: it is large flexible transparent biconvex fibrous crystalline tissue. Lenses focus the image of an object onto the          retina. The separates the eye balls into chambers.    

1. Aqueous chamber: it is smaller chamber between cornea and lens. it is filled with clear aqueous humor containing amino acids, glucose, ascorbic acids and respectively gases. It nourishes and supports the lens and also refract light rays to focus on retina.
2. Vitreous chamber: It is the chamber between lens and retina. It is filled with jelly like vitreous humour that contains 99% water, salts, and some mucoprotiens. Ti support retina and lens, give shape to eye ball and refracts light.

Q. Write difference between rods and cones.

Image formation(working of eye)

There dioptric apparatus (cornea, aqueous humour lens and vitreous humour) help to focus the image of an object on the retain (fovea centralis). Rays came from object fall on cornea; passes from pupil refracted conversed on retina. Its control the intensity and amount of light. Lens expands and contract for sharp focusing. This adjustment by all apparatus is called accomodation. Image formed on the retina is inverted. Which stimulate rods and cones and actual vision occurs due to chemical changes on the cells. The image is picked up by optic nerve as impulses and reached to brain. Brain interprets image in upright position and sightness occur.

Accommodation is brought about by changing the convexity (thickness) of lens. Cornea arches ciliary muscles push the lens to make lens more convex to see the near object and just opposite phenomenon occur to see the object.

Defect of eyes

1.        Hypermetropia (far slightness)-Can see far object clear but not near object. Image forms behind the retina. Convex lens needs to correct the defect.

2.        Myopia (long slightness)-can see near object clear but not far object. Image forms in front of retina. Concave lens needs to correct the defect.

3.        Astigmatism- the defect is caused when the cornea is not spherical. It is corrected by lens having different radii of curvature called cylindrical lens.

4.        Cataract- it is due to the lens becoming opaque and light does not pass. It is corrected by surgical removal of opaque lens and transplantation of new one. Biconvex glasses are also used.

5.        Glaucoma-It is due to tension and increase in intra-ocular presence of fluid cause press blood vessels and nerve fibers and loss of vision.

6.        Presbyopia-It is a defect in accommodation occurring in advancing age, mainly difficult to see near object. It is correct by using convex lens.

7.        Conjunctivitis-Infection or inflammation of conjunctiva.

Ear( stoacousting organ)

                It is a organ of hearing and equilibrium. The ears are situated on the lateral side of head. Ears are formed by three parts:

1.External ear: It is formed by pinna and auditory tube (meatus).

a. Pinna: It is composed of cartilage and skin. Ear muscles are (auricular muscle) non functional                                                                                                                                                                                                  In man pinna are immovable.

b. External auditory tube(meatus): It is 2.5cm long. It is supported by cartilage and bore. It outer hairy part prevent entry of dust particles. The tube is supplied with wax gland( ceruminous gland). The secretion lubricates ear drum (tympanum) and stick foreign bodies entering into internal ear.

2. Middle ear

Middle ear is filled chamber called tympanic cavity which is connected to pharynx by an Eustachian tube balance air pressure with external ear this part of ear.

                Tympanum or ears drum capable of vibrating. It lies end of auditory meatus. It separate external and middle ears.

                Tympanic cavity consist of three bony ossciles  called Malleus, Inais and stapes. Ossciles Transmitte sound waves from external ear to internal ear and also amplify the sound.

                The middle ear is connected with internal ear by two small openings

i)                     Fenestra ovalis(oval)

ii)                   Fenestra rotunda(round)

3.Internal ear: it is also called membranous labyrinth. It float in perilymph of auditory capsule. It consist of three parts 

i.Vestibule : It is a central sac. It can be divided into central utricle (larger) and lower sacule. Sensory spot or macula present in both utricle and sacule. Macula consist of otolith(small crystal of caco₃). Otolith concern in balance in body.

ii.Semicular cannals: There are anterior, posterior and lateral semicircular cannals. Anterior and posterior cannals      open at one end to ftpm common cris. End of each cannal has one ampulla, There are sensory spots cristaine of each        ampulla. Each crista consists of two kinds of cells- sensory and supporting cells.The sensory cell bear long sensory            hair.

iii.Cochela: it is the main hearing organ. It is spirally coiled tube about 20-32mm long. It is arised from saccule part      of vestibule. Internally it consists of three fluid filled chain bars or channels. These are- upper scala vestibules    which is filled with perikymph. Middle scala media. It is filled with endolymph.lower scala tympani. It is filled with             perilymph. The middle scala media is concern with hearing of sound. Ther are about 2400 receptors hair cells and                 tectorial membrane combinely called organ of corti. Function of these devices is recive, condution and determines                 the patterns.

Functions of ears

Ears receive the sound and maintain the equilibrium of the body.

a.Hearing (recive sound): sound wave strike tympanumic membrane and it vibrates. The vibrations pass throughossicles to internal ear by fenestion ovails, the vibrations cause movement of perilymph an endolymph.Organ of certipercive      the vibrations. It changes into nerve impulses. These nerve impulse are talen away from the cells by the nerve fibres of auditory nerve to brain. Hence sound is heard.normally hearing frequency of sound of man is 20hz to 20khz. The ear is most sensitive between 2-3khz

b.Equillibrium: it is two types.

                i. Dynamic equilibrium:  Cristea found in the ampulae of semi-circular cannal are responsible to detect           rotational movements of the body. The three cannals contains three cristae which detect the difference            postion and direction. The endolymph stimulates the sensory hair-cells of cristae to produce nerve impulses                 when it moves. The impulses send to brain by auditory.

                ii. Static equilibrium: It is concerned with stable equilibrium and linear acceleration of body. Maculae of       vestibule contain receptor cells the cells posses sensory hairs in a gelateneous mass and caco₃. The mass      and caco₃ responds right angle pull of gravity to earth surface. So that head movement influences the mass           to detect the direction.