第 5 单元 - 第 4 课

The eye is a complex sensory organ that enables vision in humans. It consists of several parts working together to capture and process visual information. The front part of the eye includes the transparent cornea and the colored iris, which controls the amount of light entering the eye through the pupil. Behind the iris is the crystalline lens, which focuses light onto the retina at the back of the eye. The retina contains specialized cells called photoreceptors that convert light into electrical signals, which are then sent to the brain via the optic nerve. The eye also has structures such as the sclera, the white outer layer, and the conjunctiva, a thin membrane covering the front of the eye.

The nose is a prominent facial feature located in the center of the face, above the mouth, and between the eyes. It serves as a passage for air during breathing and is responsible for the sense of smell. The nose consists of external and internal structures, including the nostrils, nasal cavity, nasal septum, and nasal cartilage. It plays a vital role in the respiratory system by filtering, warming, and humidifying the air we breathe. The shape and size of the nose can vary greatly among individuals and are influenced by genetics and ethnic background. Apart from its functional role, the nose also contributes to facial aesthetics and expressions, making it an important aspect of overall facial appearance.

The mouth is an essential anatomical feature of the human body involved in various functions. It serves as the primary entrance for food and drink, allowing us to consume and ingest nutrients necessary for sustenance. The mouth houses several structures, including the lips, teeth, tongue, and palate. The teeth aid in chewing and breaking down food, while the tongue assists in manipulating the food and initiating the process of swallowing. Additionally, the mouth plays a crucial role in speech and communication, allowing us to articulate sounds and form words.