1. MUSCULAR SYSTEM Part 3: Muscle Structure & Contraction

2. OBJECTIVES  Describe the structure of skeletal muscle  Name the major parts of skeletal muscle fiber and describe the major functions of each  Describe the neural control of skeletal muscle fiber contraction  Identify the major events in muscle fiber contraction  Describe how muscle may become fatigued and oxygen debt

3. MUSCLE IN GENERAL  Is made up of hundreds to thousands of single, _______________ muscle cells  A large amount of connective tissue, blood vessels and nerves are also present  Muscle cells are soft and easy to injure  Connective tissue covers and supports each muscle fiber and reinforces the muscle as a whole

4. LAYERS OF CONNECTIVE TISSUE IN MUSCLE  There are 3 major layers of connective tissue …_________________

5. MUSCLE TISSUE  The health of a muscle depends on a __________________________________________  Each skeletal muscle fiber has a nerve ending that controls its activity  Active muscles use a lot of energy and need a continuous supply of oxygen and nutrients  Muscles produce large amounts of metabolic waste that must be removed through veins

6. SKELETAL MUSCLE COMPONENTS  It is made up of elongated cells called muscle fibers  Each muscle cell has a special membrane called the ________________  Skeletal muscle fibers are grouped into dense bundles called _____________  Between each fiber is the endomysium  These fascicles are bound together by connective tissue called the perimysium  The fascicles & perimysium are wrapped in the epimysium or deep fascia

7. Fascicle

8. MICROSCOPIC STRUCTURE  A skeletal muscle fiber contains bundles of threadlike structures called myofibrils  Each myofibril is made up of two types of protein filaments: thick ones and thin ones  Thick filaments are made of the protein _________  Thin filaments are made of the protein _____________

9. MICROSCOPIC STRUCTURE  Myosin and actin filaments are arranged to form an overlapping pattern, giving striated muscle tissue its striped appearance  Thin actin filaments are anchored at their endpoints to a structure called the __________  The region from one Z line to the next is called a ________________

11. THE STRUCTURE OF CONTRACTION  The sarcomere is the functional unit of muscle contraction  As a muscle contracts, myosin filaments and actin filaments “slide” past each other, _____________ the sarcomere  Myosin filaments have extensions shaped like oval “heads,” called ________________  Actin filaments look like a twisted strand of beads

12. THE STRUCTURE OF CONTRACTION 1.When a ___________stimulates a muscle to contract, the myosin filaments’ heads attach to points between the beads of the actin filaments 2.The myosin heads then bend inward, pulling the actin with them 3.The myosin heads then let go, bend back into their original position, attach to a new point on the actin filament, and pull again 4.The __________ shortening of sarcomeres along the length of a muscle fiber causes the whole fiber, and thus the muscle, to contract

13. REQUIREMENTS OF MUSCLE CONTRACTION

14. REQUIREMENTS OF MUSCLE RELAXATION

15. WHY THE NEED FOR ATP?  Muscle cells must have ______________________________________________  Without ATP, _____________________________________________  Muscle contraction is an ____________________: either the fibers contract or they remain relaxed

16. QUESTION?  How, then, are you able to contract your muscles tightly enough to lift a dumbbell or gently enough to lift a pen?

18. SIMPLE MUSCLE CONTRACTION ANIMATION SLIDING FILAMENT THEORY

19. MUSCLE CONTRACTION STEPS IN-DEPTH 1.An action potential arrives at the sarcolemma of the muscle fiber 2.Acetylcholine is released, depolarizing the sarcolemma so that Na+ ions flood into the fiber 3.Action potential is then transmitted via T- tubules to sarcoplasmic reticulum (SR) …The sarcoplasmic reticulum is a special type of smooth endoplasmic reticulum found only in smooth and striated muscle 4.Ca++ ions are released from the SR into the sarcoplasm (cytoplasm of muscle cells)

20. MUSCLE CONTRACTION STEPS IN-DEPTH 5.Ca++ ions are bound by troponin 6.ATP binds to myosin heads 7.Tropomyosin (actin binding protein) shift from actin binding site 8.Actin-myosin crossbridge formation 9.Repeated formation & breaking of crossbridges resulting in sliding of filaments and sarcomere shortening

21. MUSCLE RELAXATION STEPS IN-DEPTH 1.Acetylcholine is destroyed by the enzyme cholinesterase making the membrane no longer permeable to sodium ions 2.Sarcolemma & T-tubules are repolarized 3.Ca 2+ transported (active, ATP used) back into the sarcoplasmic reticulum. 4.Low concentration of Ca 2+ ]in the sarcoplasm causes Ca 2+ to leave troponin

22. MUSCLE RELAXATION STEPS IN-DEPTH 5.Actin-myosin crossbridge formation is terminated 6.Return of tropomyosin to actin binding site 2+ 7.Mg 2+ complex formed with ATP 8.Passive sliding of filaments returns the sarcomeres to the resting state