More women than men are affected. There may be a genetic predisposition to rheumatoid arthritis. Joint replacement may in some cases restore function. Tendons attach many skeletal muscles across joints, allowing muscle contraction to move the bones across the joint. Images from W.H. Freeman and Sinauer Associates, used by permission.
Muscles have both electrical and chemical activity.
Image from W.H. Freeman and Sinauer Associates, used by permission. Skeletal Muscle Structure Muscle fibers are multinucleated, with the nuclei located just under the plasma membrane. Most of the cell is occupied by striated, thread-like myofibrils . Within each myofibril there are dense Z lines . Each sarcomere has thick and thin filaments.