1. Muscular System
Chapter 8

2. Introduction All movements require muscles
They are specialized cells that use chemical energy to contract
They provide muscle tone, propel body fluids and food, generate the heartbeat and distribute heat
Three types: skeletal, smooth and cardiac
We will just talk about skeletal this chapter

3. http://t1. gstatic. com/images

4. Structure of a Skeletal Muscle
It is composed of skeletal muscle tissue, nervous tissue, blood, and connective tissue
Muscles > Fascicles > Muscle fiber (cells) > Myofibrils > Thick and thin filaments

5. Structure of Skeletal muscle: Connective tissue coverings
A muscle is covered by layers of fibrous connective tissue called a fascia
It may project longer than the muscle and form a tendon by connecting to the bone
Sometimes they form aponeuroses which are sheets that connect to adjacent muscles

6. http://www. guwsmedical

7. All parts of a skeletal muscle are enclosed in layers of connective tissue which form a network
Epimyseum > perimyseum > fasicles > endomyseum
All of those are connective tissues

9. Structure of Skeletal Muscle: Skeletal Muscle Fibers
SMF is a single cell that contracts in response to stimulation and then relaxes when stimulation ends (may extend full length of muscle)
The sacroplasm (cytoplasm) contains many threadlike myofibrils that lie parallel to one another

10. SMF & Myofibril

11. These alternating bands cause the striations
Myofibrils aid in muscle contraction and contain 2 types of protein filaments:
Myosin- thick muscle filaments
Actin- thin muscle filaments
These alternating bands cause the striations

12. 2 main parts to striations:
I bands are composed of actin (thin/light) directly attached to z lines
A bands are composed of myosin (thick/dark) that overlap the thin filaments
In the center of the A band is the H zone which is a central region that has the M line inside
The segment of a myofibril that extends from one z line to the next is called a sacromere

14. Sacroplasmic reticulum – Membranous network of channels and tubules (similar to ER)
Transverse tubules – Membranous channel that extends inward from a muscle fiber membrane and passes through the fiber
These two structures activate muscle contraction when fiber is stimulated

16. Neuromuscular Junction
Each SMF connects to an axon from a nerve cell, called a motor neuron
Muscle fiber contracts only when stimulated by neuron
Neuromuscular junction – connection between the motor neuron and muscle fiber

17. http://www. biologycorner

18. The muscle fiber forms a motor end plate
The end of the motor neuron has many vesicles that contain chemicals called neurotransmitter (acetocholine)
A nerve impulse travels to the neuron which releases some of the neurotransmitters into the gap which stimulates the muscle fiber to contract

20. Motor Units
One motor neuron may connect to many muscle fibers because they are branched
When one impulse is sent it stimulates all of the muscle fibers that the motor neuron is connected to
A motor neuron and the muscle fibers that is controls make up a motor unit

21. Motor Unit Muscle contraction animation

22. Contraction video