sarcomere stucture by nehemia kindole

1. Introduction to the Sarcomere
The sarcomere is the contractile unit of muscle. This means it is the part of muscle that does the
actual contracting. There are several terms that you will need to know. They are thick filament
(myosin), thin filament (actin), Z line, I band, A band, H zone, and M line.
Diagram of the Sarcomere
SOURCE: HTTP://WWW.UNM.EDU/~LKRAVITZ/MEDIA2/SARCOMERE.JPG
Sarcomere under microscope
Important Terms Defined
Thin Filaments: The smaller filaments in the sarcomere. They are made out of the protein
actin.

2. Thick Filaments: The larger filaments in the sarcomere. They are made out of the protein
myosin
Sarcomere: The unit of muscle that contracts.
Z-line: Found at the end of each sarcomere. They define where one sarcomere begins and
another ends. The thin filaments connect to the Z-line.
M-Line: Found at the middle of each sarcomere. This is also the middle of the thick filament.
This part of the sacomere only contains thick filaments.
I band: The I band is a zone around the Z-lines. This includes part of two separate sarcomeres.
The I band only has thin filaments. The I band gets smaller when the muscle contracts.
H band: The H band is a zone around the M-line. It only includes thick filaments. The H band
gets smaller when the muslce contracts.
A band: The A band is a zone that includes the length of the sarcomere where thick filaments
are. This does not change size. It can include only thick or thick and thin filaments.