The Muscular System

1. The Muscular System

2. *The sole function of muscle tissue is to contract or shorten. As it contracts it -causes movement -maintains posture -stabilizes joints -and generates heat.

3. Muscle Types • Skeletal muscle (voluntary) • muscle attached to the skeleton • cells are long, striated, and multinucleate • Connective tissue coverings (endomysium, perimysium, and epimysium) enclose and protect the muscle fibers and increase the strength of skeletal muscles. • Smooth muscle (involuntary) • cells are uninucleate, spindle-shaped, and arranged in opposing layers in the walls of hollow organs. • Cardiac muscle (involuntary) • cells are striated, branching and fit closely together arranged in spiral bundles in the heart.

4. Skeletal Muscle

5. Connective Tissue Wrappings *endomysium: forms a sheath around a fiber *perimysium: coarse membrane that surrounds several sheathed fibers *fascicle: bundle of fibers covered in perimysium *epimysium: tough overcoat that surrounds several fascicles that make a muscle

6. Attachment • Skeletal muscles attach to bone using tendons or aponeuroses. • Tendons: stong, cord-like structures • Can cross bony projections • Used to stabilize joints • Aponeuroses: sheet-like structures that attach muscle indirectly

7. Microscopic Anatomy sarcolema- plasma membrane that serves as the “muscle husk” myofibrils- long ribbon-like organelles which nearly fill the cytoplasm. Alternating light (I) and dark (A) bands give the striped appearance. Midsection of the light band is the Z disc Midsection of the dark band is the H zone

8. Microscopic Anatomy, Cont. sarcomere- unit of a myofibrile that stretches from one Z to the next Z. Myofilaments- threadlike protein structures within the sarcomere Myosin- thick fibers that split ATP to generate power. Heads or cross bridges link filaments during contraction. Actin- thin fibers that are anchored to the Z disc

9. Microscopic Physiology • During contraction: • Myosin heads pull on actin filaments. • Actin filaments slide toward the center of the sarcomere. • Light zones disappear.

10. Skeletal Muscle Activity

11. Special functional properties: • Irritability • Ability to receive and respond to stimuli • Contractility • Ability to forcibly shorten

12. Nerves and muscles: • Motor unit: one neuron and all muscle it stimulates. • Neuromuscular junction: where nerve fiber ends (axon terminals)at skeletal muscle. • Synaptic cleft: gap between axon terminals and sarcolema.

13. How it works: • Nerve impulse to axon • Chemical release of neurotransmitter. • ACh crosses synaptic cleft and attaches to receptors. • Muscle becomes permeable to Na+. • Inward rush of Na generates electrical impulse, Action Potential. • AP travels over muscle causing contraction.

14. Energy for Muscle Contractions • Direct phosphorolation of ADP by creatine phosphate. • ATP transfer of phosphate group from CP to ADP ATP • Lasts about 20 seconds. (makes 1 ATP) • Aerobic Respiration • C6H12O6 CO2 + H2O + energy (ATP) • Yields 36 ATP. • Requires oxygen.

15. Energy for Muscle Contractions, Cont. • Anaerobic Glycolysis and lactic acid formation. • Glucose pyruvic acid + 2 ATP • Without oxygen, pyruvic acid converts to lactic acid. • Fast process. Good for 30-60 seconds of energy. • Lactic acid accumulation causes muscle fatigue and soreness.

16. Skeletal Muscle Movements Types and Names

17. Attachment of skeletal muscles • Origin • Attachment to the immovable or less movable bone • Insertion • attachment to the movable bone **When a muscle contracts, the insertion moves toward the origin.

18. Example: During contraction of the biceps, the insertion moves toward the origin.

19. Flexion • Movement that decreases the angle of a joint. • Bringing two bones closer together • Extension • Increases the distance or angle between two bones. • If extension is >180 degrees, it is called hyperextension.

20. Rotation • Movement of a bone around its longitudinal axis. • Lateral: away from midline • Medial: toward midline

21. Abduction • away from central axis of the body • Adduction • closer to central axis of the body

22. Circumduction • Common in ball and socket joints • Proximal end of limb is stationary while distal end moves in a circle.

23. Special Movements Special movements of the foot. Up and down movements at the ankle.

24. Special Movements, cont. Movements of the radius around the ulna. Movement of the thumb.

25. Types of Skeletal Muscles

26. Vocabulary • Prime mover • Muscle that has the major responsibility for causing a movement. • Antagonist • Muscles that oppose or reverse a movement • Synergyst • Help prime movers • Fixator • Special synergists • Stabilize the origin of the prime mover

27. Developmental Aspects Homeostatic Imbalance

28. Development • In the fetus, muscles are laid down in segments and then segments are invaded by nerves. • Occurs very early in the pregnancy.

29. Homeostatic Imbalance • Muscular Dystrophy • Congenital muscle-destroying disease • Duchenne: usually diagnosed between age 2-6 • Normal child begins to fall, lose coordination. • Wheel chair by age 12 • Generally do not live beyond teens • Myastenia gravis • Happens in adults • Shortage of acetylcholine receptors at neuromuscular junctions results in generalized muscle weakness.

30. Homeostatic Imbalance, cont. • Nerve Damage • Destruction of nerve supply to muscle causes the muscle to lose tone and become paralyzed. • Over time, the muscle with become soft and atrophy.