Chapter 6 – Muscular System

1. Chapter 6 – Muscular System Anatomy and Physiology Mrs. Harborth

2. Muscle Types • ALL muscle cells are elongated – Muscle fibers • Contractility depends on myofilaments • “myo” – muscle; “sarco” – flesh • Three types: • Skeletal: striated, voluntary. Endoysium, perimysium, epimysium, tendons, aponeuroses. • Smooth: no striations, involuntary. Found in hollow visceral organs. Usually two layers. • Cardiac: striated, involuntary. Found in heart. Spiral or figure 8 bundles. Intercalated discs.

4. Muscle Functions • Movement – skeletal muscle (s.m.) contractions move the body in whole or in part. • Posture – continued partial contraction of s.m. makes it possible to sit, stand, and maintain a stable position while walking, running, etc. • Stabilizing joints – muscle tendons reinforce and stabilize joints that have poorly fitting articulating surfaces. • Heat Production – muscle cells produce heat via catabolism; S.M. contractions are one of the most important parts of maintaining temperature homeostasis

5. Microscopic Anatomy of Skeletal Muscle • Multinucleate • Sarcolemma – plasma membrane • Myofibrils – long ribbonlike organelles. Push nuclei to the side. • Light (I) and Dark (A) bands – alternate along the myofibrils, giving striped appearance. I band has Z disc (darker), A band has H zone (lighter). • Sarcomere – contractile units lined up end-to-end along myofibrils. Made up of myofilaments. • Myofilaments – thick and thin filaments • Sarcoplasmicreticulum – specialized smooth ER. Stores calcium and releases it on demand for contractions.

6. Myofilaments • Myosinfilaments: “thick filaments”, made of myosin protein and ATPase. Extend entire length of dark A band. Midparts are smooth, but ends are studded with myosin “heads” or cross bridges. • Actinfilaments: “thin filaments”, made of actin protein and regulatory proteins that allow/prevent myosin head binding to actin. Anchored to the Z disc. Do not extend to middle of relaxed sarcomere, forms H zone (bare zone).

8. Neuromuscular Junction • Irritability: the ability to receive and respond to a stimulus • Contractility: ability to shorten when an adequate stimulus is received • Motor unit: one neuron and all the s.m. cells it stimulates • Neuromuscularjunctions: axon reaches muscle and branches into axonal terminals, which form junctions with sarcolemma of different muscle cell. • Synapticcleft: gap between neurons and muscle cells (they never touch). Filled with interstitial fluid.

9. Neuromuscular junctions

10. Nerve Stimulus and Action Potential • Acetylcholine (ACh) – neurotransmitter that stimulates s.m.Diffuses across synaptic cleft and attaches to receptors on sarcolemma. • If enough Ach is released, sarcolemma becomes temporarily permeable to sodium ions. • Na+ rushes into muscle cell, making cell positive, upsets electrical conditions, thus setting up an action potential. • Action potential is unstoppable, travels entire surface of sarcolemma, conducting electrical impulse from one end of cell to other, making a contraction.

11. Sliding Filament Theory

12. Animations • Action Potential • http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter10/animation__action_potentials_and_muscle_contraction.html • Myofilament Contraction • http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter10/animation__myofilament_contraction.html • Sarcomere Contraction • http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter10/animation__sarcomere_contraction.html

13. Graded Response • A muscle CELL is “all or nothing”, but whole muscles have graded response. • Graded response can be produced by 1) changing frequency of stimulation or 2) changing # of cells stimulated • 1) Increased stimulation • Muscles are stimulated back to back, so can’t relax between stimuations. Contractions get stronger and smoother (complete or fused tetanus) • 2) Increased # of cells stimulated • Few or hundreds of cells stimulated. Changes strength of contraction (soothing hand –vs- slap)

14. Energy for Contractions • Muscles only have 4-6 seconds worth of ATP stored • Three ways to get more • Direct phosphorylation of ADP by creatine phosphate (CP gives phosphate to ADP, making ATP). Only about 20 seconds worth of CP in cells • Aerobic respiration (95% of ATP used comes from this. Glucose is broken down in mitochondria to make 36 ATP. Slow reaction and requires oxygen) • Anaerobic respiration (glycolysis occurs in cytoplasm, glucose broken down into pyruvic acid and 2 ATPs. Pyruvic acid can continue into Aerobic respiration if O2 is present, but if intense muscle work then it’s made into lactic acid. 2.5x as fast as Aerobic but few ATPs. About 30-60 sec of strenuous muscle activity)

15. Fatigue and Oxygen Debt • Muscle fatigue – when muscles are stimulated but cannot contract anymore. Caused by oxygen debt. • Oxygen debt – when low amounts of O2 are present, lactic acid builds up and ATP levels run low. Oxygen debt is “paid back” after workout (breathing hard) so muscles can get rid of accumulated lactic acid and make more ATP

16. Types of Muscle Contractions • Isotonic – Myofilaments are successful in sliding movements, the muscle shortens, and movement occurs. Ex: bending knee, rotating arm, smiling • Isometric – myosin myofilaments are “skidding their wheels” and tension keeps increasing. They’re trying to slide, but trying to move an object that is immovable.

17. Muscle Tone and Exercise • Even when you’re relaxed some of your muscle fibers are stimulated, keeping muscles firm and healthy. This is muscle tone. • Aerobic (endurance) exercise • Resistance (isometric) exercise

18. Types of Body Movements • S.M.’s are all attached at an origin (immovable or less movable bone) and an insertion (movable bone) • Flexion – brings 2 bones closer together • Extension – increases angle between two bones • Rotation – movement of bone around its longitudinal axis • Abduction – moving a limb away from midline • Adduction – moving a limb toward the midline • Circumduction – in leg or arm; distal end rotates, proximal end stationary (cone) • Dorsiflexion and plantar flexion – standing on heels; pointing toes • Inversion and eversion – turn sole medially; turn sole laterally • Supination and pronation – palm facing anteriorly (radius and ulna parallel); palm faces posteriorly (bones form x) • Opposition – touch thumb to tip of each finger on same hand

19. Origin –vs- Insertion

21. Types of Muscles • Prime mover – muscle with major responsibility for movement • Antagonists – muscles that oppose or reverse movements • Synergists – help prime moversby producing same movement or reducing undesirable movements (ex: making fist without moving wrist) • Fixators – specialized synergists. Hold bone still or stabilize origin

22. Naming Skeletal Muscles • Direction of muscle fibers – rectus (straight), oblique (slanted) • Relative size of muscle – maximus (largest), minimus (smallest), longus (long) • Location of the muscle – name of bone on which muscle is associated • Number of origins – biceps (2), triceps (3), quadriceps (4) • Location of the muscle’s origin and insertion – named for attachment sites • Shape of the muscle – ex: deltoid “triangular” • Action of the muscle – flexor, extensor, adductor

23. Head and Neck Muscles • Facial • Frontalis • Orbicularis Oculi • Zygomaticus • Orbicularis Oris • Buccinator • Chewing • Masseter • Temporalis • Neck • Platysma • Sternocleidomastoid

24. Trunk Muscles • Pectoralis major • Intercostal muscles • Abdominal muscles • Rectus abdominis • External oblique • Internal oblique • Transverse abdominis • Posterior muscles • Trapezius • Latissimusdorsi • Erector spinae • Deltoid

25. Muscles of Arm/Leg • Upper Limb: • Biceps brachii • Brachialis • Brachioradialis • Triceps Brachii • Lower Limb: • Gluteus maximus • Gluteus medius • Iliopsoas • Adductor muscles • Hamstring group (biceps femoris, semimembranosus, semitendinosus) • Sartorius • Quadriceps group (rectus femoris and 3 vastus muscles)

26. Leg Continued • Tibialis anterior • Extensor digitorumlongus • Fibularis muscles • Gastrocnemius • Soleus