1. Types of Myofilaments

2. Thick Filaments (Myosin)‏
Called the “Motor Protein” part of the muscle fiber that moves
ATPase enzymes will split ATP to get energy for movement
Extend the entire length of the A band of a muscle bundle (dark)‏
Contains studded ends called cross- bridges which are used to attach and link to actin (light bands)‏

4. Thin Filaments (Actin)‏
Composed of the protein actin
Anchored to the Z-disc
These filaments overlap the thick (myosin) filaments in an area called the H-zone
During contraction the Myosin pulls the actin threads towards the middle of the sarcomere
Cause the muscle to shorten and bulge during a contraction
Immobile protein

6. Sarcoplasmic Recticulum (SR)‏
Fluid filled system of sacs found in the space around the muscle fibers
Encircles each myofibril
Like smooth endoplasmic recticulum
Stores Calcium ions
Release of the calcium ions is the trigger for a muscle contraction