1. Objectives 32.2 The Muscular System
-Describe the structure and function of each of the three types of muscle tissue.
-Describe the mechanism of muscle contraction.
-Describe the interaction of muscles, bones, and tendons to produce movement.

2. Muscle Tissue There are three different types of muscle tissue:
1.Skeletal
2.Smooth
3.Cardiac.

3. Skeletal Muscles
Skeletal muscles are usually attached to bones, as they aid in the movement of the skeleton.
Skeletal muscle movements are voluntary and has a striated (or striped) appearance under a microscope.

4. Smooth Muscles
Smooth muscle cells don’t have striations and therefore look “smooth” under the microscope.
Smooth muscles’ movements are involuntary; such as moving food through the digestive tract, flow of blood through the circulatory system and decreasing pupil size in bright light.

5. Cardiac Muscle Cardiac muscle is found in the heart.
It is striated like skeletal muscle, however, it is involuntary like smooth muscle.

6. Muscle Fiber Structure
Skeletal muscle fibers are filled with tightly-packed filament bundles called myofibrils.
Each myofibril contains:
thick filaments of a protein called myosin
thin filaments of a protein called actin.

7. Muscle Fiber Structure
The actin filaments are bound together in areas called Z lines.
Two Z lines and the filaments between them make up a unit called a sarcomere.

8. Control of Muscle Contraction
The point of contact between a motor neuron and a skeletal muscle cell is called a neuromuscular junction.
The motor neuron releases a neurotransmitter called acetylcholine (Ach) which causes a muscle fiber to contract.

9. Control of Muscle Contraction
When you lift something light, such as a sheet of paper, your brain stimulates only a few cells to contract.
As you exert maximum effort, like a weight lifter, almost all the muscle cells in your arm are stimulated to contract.

10. Muscle to Bone Skeletal muscles are joined to bones by tendons.
Tendons pull on the bones and make them work like levers.

11. How Muscles and Bones Interact
Most skeletal muscles work in opposing pairs—when one muscle contracts, the other relaxes; such as occurs with the biceps and triceps muscle.

12. Red Muscle Fibers
There are two principal types of skeletal muscle fibers—red and white.
Red muscle, or slow twitch muscle, contains many mitochondria.
Red muscle is useful for endurance activities like long-distance running.

13. White Muscle Fibers
White muscle, or fast-twitch muscle, contracts more rapidly and generates more force than red muscle, but its cells contain few mitochondria and tire quickly.
White fibers are useful for activities that require great strength or quick bursts of speed like sprinting.