GLOSSARY

The A band is the dark, central region of the sarcomere whose length equals the full length of the thick myosin filaments; at both ends it overlaps with actin filaments.
The letter A comes from anisotropic, because this region transmits light unevenly in a polarising microscope and appears dark.

Parts

• Overlap zone: the two ends of the A band where both myosin and actin are present; the site of cross-bridge formation and force production.
• H zone: the lighter central part containing only myosin.
• M line: in the middle of the H zone.

Behaviour During Contraction