Anatomy and Physiology: Special Senses – The EYES
A person’s sense of sight is very important to humans. Vision is arguably the most used of the 5 senses and is one of the primary means that we use to gather information from our surroundings. The human eye is the organ which gives us the sense of sight, allowing us to observe and learn more about the surrounding world than we do with any of the other four senses.
People use their eyes in almost every activity they perform, whether reading, working, watching television, writing a letter, driving a car, and in countless other ways. Most people probably would agree that sight is the sense they value more than all the rest. The eyes are at work from the moment a person is wake up to the moment he or she closes them to go to sleep.
This special organ takes in tons of information about the world around you — shapes, colors, movements, and more. Then they send the information to your brain for processing so the brain knows what’s going on outside of your body.
Anatomy of the Eye
External and Accessory Structures
The adult eye is a sphere-shaped organ that measures about 1 inch or 2.5 cm in diameter. However, only one sixth (1/6) of the eye’s surface can normally be seen and the rest is enclosed and protected by a cushion of fat and the walls of the bony orbit.
The accessory structures of the eye are the following:
- Extrinsic eye muscles. The extrinsic muscles of the eye come from the bones of the orbit and are movable due to broad tendons in the eye’s tough outer surface. There are six extrinsic eye muscles that function to MOVE the eye in various directions:
- Superior rectus muscle – rotates the eye upward and toward the midline
- Inferior rectus muscle – rotates the eye downward and toward the midline
- Medial rectus – rotates the eye toward the midline
- Lateral rectus – rotates the eye away from the midline
- Superior oblique – rotates the eye downward and away from the midline
- Inferior oblique – rotates the eye upward and away from the midline
- Eyelids. The eyelids protect the eyes anteriorly which meet at the medial and the lateral corners of the eye. From the border of each eyelid are the EYELASHES. The eyelashes help filter out foreign matter, including dust and debris, and prevent it from getting into the eye. Eyelid edges associate with modified sebaceous glands make up the TARSAL GLANDs. These glands produce an oily secretion that lubricates the eye. Between the eyelashes, modified sweat glands called ciliary glands are found.