Nasal polyps grow in inflamed tissue of the nasal mucosa. The mucosa is a very wet layer that helps protect the inside of your nose and sinuses and humidifies the air you breathe. During an infection or allergy-induced irritation, the nasal mucosa becomes swollen and red, and it may produce fluid that drips out. With prolonged irritation, the mucosa may form a polyp.
Muscle action can be classified as being either voluntary or involuntary. Cardiac and smooth muscles contract without conscious thought and are termed involuntary, whereas the skeletal muscles contract upon command. Skeletal muscles in turn can be divided into fast and slow twitch fibers.
This shortening is called a muscle contraction. There are three types of muscle cells in the human body: 1  Skeletal muscle: Drives voluntary movement.  Cardiac muscle: Cells of the heart that pump blood.