Muscles

1. Muscles

2. Skeletal muscle Cross- Section Longitudinal

3. Smooth Muscle longitudinal Cross- Section

4. Muscle Tissue Components • tendon - connects skeletal muscle to bone • epimysium - fibrous connective tissue around belly of skeletal muscle • fasiculi - bundles of muscle fibers • perimysium - connective tissue surrounding fasiculi • endomysium - connective tissue surrounding the individual muscle fibers (muscle cell)

5. Muscle components • muscle fiber - single muscle cell (threadlike in shape) • sarcolemma - membrane surrounding the muscle fiber • sarcoplasm - specialized cytoplasm of muscle fiber containing multiple nuclei and mitochondria • myofibrils - "rod-like" structures running through the muscle fibers that contain actin and myosin make muscle appear striated

6. Muscle types • Myosins are protein motors. Upon interaction with actin filaments, they utilize energy from ATP hydrolysis to generate mechanical force. • Muscles are typed based upon the types of myosin protein fibers present • there are different forms of the muscle myosins • TYPE I (Slow Twitch)                    • Type IIa/IIx (Fast Twitch)

7. Muscle types • Are determined both genetically & functionally based upon how fast they can produce a contractile twitch  • every muscle composed of varying % composition of two types

9. Distribution of slow/fast twitch fibers

10. MUSCLES CONTRACT!!! • Muscles can not push, they may only CONTRACT (pull) • A muscle contraction is called a muscle TWITCH

11. The sarcomere • basic repeat unit of striated muscle, delimited by Z-lines

12. sarcomere • SARCOMERE REGIONS • I   band - "clear zone" around Z-line  • A  band - "dark region" in center of sarcomere • M  line - mid point of the sarcomere • H  zone - "clear zone" in the center of sarcomere around M line

13. Sliding Filament Theory • A  band remains constant in its size dimensions • H  Zone becomes denser • I  band varies in length becoming shorter & disappearing

14. 4 parts of a Muscle twitch    • 1) latent period – • 5 msec time between application of Action Potential & initiation of contraction   • 2) contraction – (slow twitch) • 40 msec muscle shortens & does its work  • 3) relaxation – • 50 msec muscle elongates & returns to original position  • 4) refractory period – • 2 msec time of recovery between stimulations of muscle 

15. Muscle contraction cycle • Step 1 • Arrival of the action potential • Action potential causes AcH to be released. • ACH binds to receptors on sarcolemma • Receptors open, causing Na+ to flood in changing membrane potential.

16. Muscle contraction #2

17. Muscle contraction #3 • Step 3 • Release of Calcium

18. Muscle Contraction #4 • Step 4: • calcium changes tropomyosin shape • Exposes myosin binding sites on actin

19. Muscle contraction #5 • #5 • ATP binds to cross bridge • Myosin head changes shape releases from actin • ATP hydrolyzes • Head is in high energy configuration • Head binds to actin • ADP+P are released from myosin • Head moves actin towards center

20. Types of contractions

21. DOMS • Occurs usually at the beginning of a new training program. • Characterized by stiffness, soreness • More often occur after activities with eccentric contractions. • causing damage to the muscle cell membrane, which sets off an inflammatory response. • This inflammatory response leads to the formation of metabolic waste products, • These chemicals stimulate pain nerves and attract neutrophils (a type of white blood cell) to the site of injury. • There, neutrophils generate free radicals (molecules with unshared electrons), which also damage the cell membrane. • Swelling is also common, and can lead to pain.

22. Effect of exercise on muscle • Eccentric contractions produce muscle hypertrophy • Eccentric contractions put your muscle fibers under a great deal of tension causing microtears and severe DOMS. • if you can induce muscle fiber injury, satellite cells are activated. • Satellite cells are myogenic stem cells which regenerate muscle. • Satellite cells proliferate (undergo mitosis) and give rise to new immature muscle cells. • These new cells fuse with an existing muscle fiber causing that fiber to get bigger (i.e., hypertrophy)

23. Maintaining muscle over time • Muscle strength in people increases until the early 20’s • It remains fairly stable until about 50 in untrained people • Loss of maximal strength is due to atrophy of type II fibers. • People of any age can show strength gains through regular strength training

24. Strength training benefits for women • Enhanced bone modeling to increase bone strength and reduce the risk of osteoporosis • Stronger connective tissues to increase joint stability and help prevent injury • Increased functional strength for sports and daily activity • Increased lean body mass and decreased nonfunctional body fat • Higher metabolic rate because of an increase in muscle and a decrease in fat • Improved self-esteem and confidence • Some factors may reduce these benefits including • including the exclusive use of weight training machines, training with loads that are too light, and not progressing in resistance or intensity.