Fluid filled sacs in the knee are specifically called Bursa or Bursae. Bursae is plural for Bursa.
A bursa is a closed fluid filled sac that function as a gliding surface to reduce friction between tissues of the body. Knee bursitis occurs when there is irritation or inflammation in one one of the knee bursa. The procedure of removing fluid-filled sac is called bursectomy. When the bursa become infected with bacteria, this condition is called septic bursitis.
Answer:
Sarcomere
Explanation:
A myofibril or muscle fiber under an electron microscope shows alternate light band and dark bands. These bands give the skeletal muscle and cardiac muscle a striated appearance. The light band is called the I- band or isotropic band, and the dark band is known as A- band or anisotropic band. In the center of the I-band Z-line is present. It is discovered from a German term Zwischenscheibe (between the disc). The portion of myofibril between one Z-line to the next Z-line is called sarcomere.
