Sense Organ System

Receptors for the special senses -vision, smell, taste, hearing and equilibrium are housed in complex sensory organs such as eyes, nose, tongue, ears and skin.

Vision
More than half of the sensory receptors in the human body are located in the eye and large part of the cerebral cortex is devoted to processing visual information.

Structure of the eye

the accessory structures of the eye are the eye lids, eye lashes, eyebrows, the lacrimal (tearing) apparatus and extrisic eye muscles.

Eyelids: The upper and lower eyelids, or palpebrae, shade the eyes during sleep, protect the eyes from excessive light and foreign objects, and spread lubricating secretion over the eyeballs. The upper eyelid is more movable than the lower and contains in its superior region the levator palpebrae superiors muscle. The space between the upper and lower eyelids that exposes the eyeball is the palpebral fissure.

Eyelashes and eyebrows: The eyelashes, which project from the border from each eyelid and the eyebrows, which arch transversely above the upper eyelid, help protect from foreign objects, perspiration, and the direct rays of the sun. Sebaceous glands at the base of the hair follicles of the eyelashes called sebaceous ciliary glands, release a lubricating fluid into the follicles. Infection of these glands called as sty.

The Lacrimal Apparatus: The lacrimal apparatus is a group of structures that produces and drains lacrimal fluid or tears. The lacrimal glands, each about the size and shape of an almond secrete lacrimal fluid, which drains into 6-12 excretory lacrimal ducts that empty tears onto the surface of the conjunctiva of the upper lid. From here the tears passes medially over the anterior surface of the eyeball to enter to small openings called lacrimal puncta. Tears then passes into two ducts, the lacrimal canals, which lead into the lacrimal sac and then into the nasolacrimal duct. This ducts carries the lacrimal fluid into the nasal cavity just inferior to the inferior nasal concha.