Muscles

1. Muscles

2. The Muscular System Functions • Body Movement • Maintenance of Position • Respiration / organ volume • Production of Body Heat (Thermogensis) • Movement of substances (construction of organ and vessels) • Heart Beat

3. Characteristics of Skeletal Muscle • Contractility • A muscle’s ability to shorten and generate force to do useful work at the expense of cellular energy. • Excitability • Muscles need to be stimulated before contracting • Extensibility • The way muscles can be stretched without damage • Elasticity • Muscle’s return to their original length and shape after contracting • Conductivity – conducts action / potential along plasma membrane

4. Skeletal muscle picture • Striated, multinucleated and voluntary

5. Skeletal Muscle • Each skeletal muscle fiber is a single cell containing numerous myofibrils • Myofibrils are composed of actin and myosin myofilaments • Myofibrils are joined end to end to form sarcomeres • Muscle fibers are organized into fasciculi and fasciculi are organized into muscles by associated connected tissue. Myofibrils Myofilaments Sacomere

6. Connective tissue components • Endomysium – separating individual muscle fibers • Perimysium – surround borders of 10 – 100 fibers (fascicles) • Epimysium – outlines the whole muscle • Deep fascia – dense irregular tissue, holds muscles together, separating into functional groups.

7. Smooth Muscles Smooth muscle is nonstriated (striped), uninucleated, and involuntary. Visceral organs (alimentary canal)

8. Cardiac Muscle *Cardiac: striated, uninucleated, branches, interculated discs, involuntary Both Cardiac and Smooth muscle are under involuntary control and is influenced by hormones, such as epinephrine.

9. Innervation of a Motor Unit and Muscle Fiber

10. Neuroelectrical factors • Potassium ions (K+) are greater inside the muscle cell than outside, whereas sodium ions (Na+) are greater outside than inside • The inside of cell is negatively charged electrically, whereas outside is positively charged • (Neuromuscular junction) Nerve impulse reaching the neuromuscular junction causes and axon ending to release the neurotransmitter acetylcholine.

11. Neuronelectical factor con’t • This makes cell membrane permeable to Na+. They rush in creating an electrical potential. K+ begins to move out to restore resting potential (Not as Na+ comes in) • This causes muscles to generate its own impulse called the action potential • The sarcoplasm reticulum then release Ca++ into the fluids surrounding myofibrils. • Ca++ stops the action of the inhibitor substance troponin and tropomysin (which keep actin and myosin apart), causing contractile process to occur

12. Chemical factors • Ca++ combines loosely with myosin to form activated myosin. • Activated myosin reacts with ATP, attached to the myosin, and releases energy from the ATP to form actomyosin • Myosin filaments have cross bridges that now connect with the actin and pull the actin filaments in among the myosin filament • A sliding process occurs: The width of the A bands remain constant, but Z lines move closer. By now the sodium – potassium pump has kicked in to restore the resting potential. Ca++ gets reabsorbed and contraction ceases

13. Energy sources: ATP • Glycolysis: glucose to pyruvic acid, net gain of 8 ATP if O2 present, if no O2 then lactic acid (burn in muscles) forms with net gain of 2 ATP • Krebs’ citric acid cycle: pyruvic to CO2+H2O+30 ATP (28 ATP + 2 GTP) • Phosphocreatine in muscle cells: used in sprinting • Free fatty acid: fatty acids + H2O + ATP

14. Muscle Terms • Twitch • A sudden uncontrollable muscle spasm • Threshold • A very small detectable sensation • All-or-none response • A muscle will respond to stimulation completely or not at all • Lag phase • The interval of time between stimulus and contractions

15. Muscle Terms (Cont.) • Contraction phase • Tension rises to a peak • Relaxation phase • The phase of decreased tension after all or none • Tetanus • Calcium ions cause spasmodic / sustained contractions • Recruitment • Patterns and corresponding change of muscle patterns, increase number of motor units activated

16. Muscle Anatomy Terms • Tendon • Tough fibers that connect muscle to bony structures; wide flat sheet called aponeurosis • Origin • The head of the muscle, where it is located, stationary bone • Head • Explains where the muscle begins • Insertion • Muscle’s relationship with other muscles, moveable bone • Belly • The fleshy part of the contracting muscle • Resistance – force opposes movement • Effort – force exerted to achieve movement

17. Anatomy of Skeletal Muscle • A single skeletal muscle, such as the triceps muscle, is attached at its origin to a large area of bone; in this case, the humerus. At its other end, the insertion, it tapers into a glistening white tendon which, in this case, is attached to the ulna, one of the bones of the lower arm.

19. Terms • Prime mover • Muscle that contracts (pulls) mainly by itself • Antagonist • A muscle that works opposite of another, relaxing muscle • Synergists • Muscles working together REMEMBER: muscles only pull

20. Naming skeletal muscles • A. Direction of muscle fiber to midline • B. Location – structure near muscle is found • C. Relative SIZE of muscle • D. NUMBER of origins (tendons) • E. SHAPE of Muscles • F. Origin and insertion sites • G. Action – same as in joints. 2 new are Sphincter – decrease size of opening, Tensor – make body more rigid

21. Isometric / Isotonic Muscle Contraction • Isotonic contractions • Tension on a muscle stays the same but the muscle shortens so things can be lifted, joints moves • Isometric contractions • This is when the muscle does not shorten when contracting. This can happen when pushing on a wall or something else that will not move. TONE • This is a constant state of partial contraction maintained in a muscle

22. Muscle disorder • Symptoms: Paralysis, weakness, degeneration or atrophy, pain, spasms • Causes: Muscular tissue, Vascular system feeding muscle cells, nervous system connections, connective tissue surrounding cell bundles (fascicles)

23. Types of disorders • Fibromyalgia – muscle pain • Myasthenia gravis- muscle tiring / weakness, acetylcholine receptor destruction • Muscular dystrophy- inherited, males, muscles degenerate • Hernia – myocele – muscle breaks through sheath, Inguinal – bowel through abdominal muscle • Myoclonus – spasm / twitching of muscle, singultus – hiccup (myoclonus of diaphragm) • Botox – paralyze the muscle that causes wrinkles.