1. Sliding Filament Theory
Muscle Contractions
Sliding Filament Theory

2. Goal:
I will be able to explain the Sliding Filament Theory.

3. Skeletal Muscle

4. Similar to Fig. 3.4 on page 36

5. Sliding Filament Theory
muscle contraction

6. Muscle Fibers
Muscle fibers contain cylindrical bundles called myofibrils which extend from one end of the muscle to the other.
Each myofibril is composed of thick and thin filaments arranged in a repeating pattern.
One unit of repeating pattern in known as a sarcomere.

7. The thick filaments are composed almost entirely of a contractile protein myosin.
The thin filaments contain the contractile protein actin as well as two other proteins – troponin and tropomyosin.

8. Sliding Filament Theory
A message is released from the central nervous system.
The message travels from neuron to neuron until it reaches the specific motor unit.
Acetylcholine (ACh) is released from the axon terminal of the motor unit.
The ACh causes the release of Ca2+ into the cytoplasm of the muscle fiber.

9. The calcium ions attach to troponin sites on the actin molecule which causes the molecule to shift.
The myosin binding sites, which are normally guarded by tropomyosin, are exposed allowing myosin to bond with actin.
The bonding is known as a cross-bridge and allows for an overlap of the filaments and thus a contraction.
This entire process does require energy in the form of ATP.

10. Work
Find the diagram of the structure of a skeletal muscle. Identify and colour the sarcomere, actin, myosin, and cross bridges.
Complete the Muscle Contraction and Sliding Filament Theory sheet from yesterday.
Explain at the molecular level how you are able to brush your teeth. Use scientific terms in your answer.