SENSE ORGANS

                                      SENSE ORGANS

Definition of sense organ

1.  A sense organ is defined as a group of specialized cells, tissues or receptors which is able to receive, perceive or detect stimulus and transmit information, impulse or message to the central nervous system.
   
   1. Sense organs are the bodily structure that receives a stimulus and is affected in such a manner as to initiate excitation of associated sensory nerve fibers which convey specific impulses to the central nervous system where they are interpreted as corresponding sensations

   1.                         TYPES OF SENSE ORGANS 

There are five senses: sight, hearing, taste, smell and touch. There are organs connected with these sense that take in information that is sent to the brain so that the body can act on it.


                                    THE ORGAN OF SIGHT (THE HUMAN EYE)

The eye is the organ of sight found in all vertebrates. The mammalian eye is almost spherical in shape.It has a complex structure consisting of a transparent lens that focuses light on the retina. The retina is covered with two basic types of light-sensitive cells-rods and cones. The cone cells are sensitive to color and are located in the part of the retina called the fovea, where the light is focused by the lens. The rod cells are not sensitive to color, but have greater sensitivity to light than the cone cells. These cells are located around the fovea and are responsible for peripheral vision and night vision. The eye is connected to the brain through the optic nerve. The point of this connection is called the "blind spot" because it is insensitive to light. Experiments have shown that the back of the brain maps the visual input from the eyes.

                VERTICAL SECTION OF THE HUMAN EYE

1.Cornea

The transparent window at the front of the eye which is covered in a thin layer of tears.

2. Aqueous humor

On the other side of the cornea is more moisture. This clear, watery fluid is the aqueous humor. It circulates throughout the front part of the eye and keeps a constant pressure within the eye.

3. Pupil and iris

The pupil is the circular opening in the colored part of the eye which is the iris. The iris dilates or opens and contracts to let in more or less light.

4. Lens

Resembles the lens of a camera and focuses the light, changing shape as it takes in light reflected from objects near and far.

5. Vitreous humour 

A clear jelly that the focused light passes through to the retina.THE SENSE ORGAN

6. Retina

The inner lining at the back of the eye. It contains blood vessels which bring nutrients to the nerve cells. The macula is at the very center of the retina and contains the fovea. The photoreceptors of the retina are the rods and cones. The cones perceive color and finer elements. The retinal pigment epithelium, choroid and sclera are three more layers. The photoreceptors send light and images to a large nerve called the optic nerve. This carries the information to the occipital lobe of the brain where they are interpreted.

7. Yellow spot(Fovea centralis)

This is the most sensitve part of the retina. From it, the fullest visual information is sent to the brain

8. Blind spot 

the blind spot is also found on the retina. it is the point where the cells are not sensitve to light.

9. Ciliary muscle 

In front of the eye, the choroid layer forms the ciliary muscle. Attached to the ciliary muscle is the suspensory ligaments which hold the lens in place.

10. conjuctiva

This is a thin tough transparent membrane which lines inside of the eyelids and covers the cornea protectively