The Muscular System

1. The Muscular System Chapters 9 & 10

2. Overview Functions: • movement • maintain posture • stabilize joints • generate heat

3. 3 Types 1) Skeletal 2) Cardiac 3)Smooth • Striated - striated - not striated • voluntary - involuntary - involuntary

4. Gross Anatomy • made of muscle fibers, blood vessels, nerve fibers and connective tissue

5. CT wrappings surrounding muscle fibers • endomysium – fine layer CT that surrounds each fiber • perimysium – collagenic sheath that surrounds each fascicle (bundle of muscle fibers)

6. epimysium –CT that binds several fascicles together to surround the entire muscle • deep fascia – coarser sheet of CT that binds muscles into functional groups

7. Nerve and Blood Supply • each muscle contains an artery and one or more veins

8. Attachments • origin – attachment to immovable, or less movable, bone • insertion – attached to movable bone • in muscles of the limbs, origin typically lies proximal to the insertion

9. Microscopic Anatomy of a Skeletal Muscle Fiber • sarcolemma = plasma membrane • sarcoplasm = cytoplasm • sarcoplasmic reticulum = endoplasmic reticulum • width = 10-100um • length = up to 30 cm (12 in)

10. Myofibrils • there are hundreds to thousands in each muscle fiber, depending on its size • account for 80% of volume and organelles are squeezed around them

11. striations formed from where actin and myosin overlap or don’t overlap

12. Sarcomere • functional unit of muscle • portion of myofibril between two Z discs

13. Muscle Metabolism • energy stored in ATP • comes from cellular respiration, hydrolysis of creatine phosphate and lactic acid fermentation

14. Contraction of Motor Units • a motor unit consists of a single motor neuron and all of the muscle cells it stimulates • recruitment = when more motor units need to be stimulated for increased strength

15. the advantage of having only a few muscle cells per motor unit is to allow precise movements • small motor units, containing fewer cells, provide precise movements • muscles of the eye • large motor units, containing many cells, provide gross movements • movement of thigh

16. muscle tone is achieved by random, asynchronous motor unit contractions that provide a constant state of low-level tension • without stimulation, muscle loses tone

17. The Sliding Filament Theory • involves 5 molecules plus Ca+ ions • actin • myosin • tropomyosin • troponin • ATP

18. The Theory • The contraction of a muscle cell occurs as the thin filament slides past the thick filament. • During contraction the sarcomere shortens and the thin and thick filaments overlap to a great degree

19. Thick filaments • made of myosin filaments • myosin head = cross bridge Thin filaments • made of actin, tropomyosin & troponin • tropomyosin covers actin binding sites in a unstimulated muscle

21. during the contraction of an entire muscle, the cross bridges stagger their binding

22. Smooth Muscle • Diameter 3-6 um • Length 100-500 um • Lack neuromuscular junctions found in skeletal muscle, but have varicosities that release neurotransmitters into a wide synaptic cleft in the general area of smooth muscle cells • Have actin and myosin filaments, but no sarcomeres

23. intermediate filaments are interlaced through the cell much like the threads in a pair of "fish-net" stockings • because smooth muscle is not as organized as skeletal muscle, shortening occurs in all directions

24. Cardiac Muscle • Has myofibrils that are organized into sarcomeres, but the myofibrils have irregular thickness

25. Major Skeletal Muscles of the Body • There are over 600 skeletal muscles! • You will only be held responsible for the names and locations of the 32 shown in the following slides.

26. Head • Temporalis – closes jaw, elevates mandible; maintains posture of mandible at rest • Masseter – elevates mandible • Frontalis – raises eyebrows and wrinkles forehead skin horizontally

27. Head • Orbicularis oris – closes lips; purses and protrudes lips • Orbicularis oculi – produces blinking, squinting and draws eyebrows downward • Zygomaticus – raises lateral corners of the mouth upward

28. Neck • Sternocleidomastoid - prime mover of active head flexion; acting alone, each muscle rotates head towards side and tilts or laterally flexes head to its own side

29. Shoulder • Trapezius – stabilizes, raises, retracts and rotates scapula • Deltoid – prime mover of arm abduction

30. Arm • Triceps brachii – powerful forearm extensor • Biceps brachii – flexes elbow joint and supinates forearm (movements usually happen at same time)

31. Forearm • Brachioradialis – helps with forearm flexion

32. Thorax • Pectoralis major – prime mover of arm flexion • Intercostals – elevate and depress ribs to aid in breathing • Latissimus dorsi –prime mover of arm extension; medially rotates arm at shoulder

33. Abdomen • Rectus abdominis – flex and rotate lumbar region of vertebral column • External oblique – aid rectus abdominus in flexing vertebral column; help with trunk rotation and lateral flexion • Transverse abdominis – compress abdominal contents

34. Gluteal Region • Gluteus maximus – major extensor of thigh; laterally rotates thigh • Gluteus medius – abducts and medially rotates thigh; steadies pelvis

35. Thigh • Tensor fascia lata – flexes and abducts thigh; rotates thigh medially • Sartorius – flexes and laterally rotates thigh; flexes knee • Gracilis – adducts thigh, flexes and medially rotates leg, especially during walking

36. Thigh • Rectus femoris – extends knee and flexes thigh at hip • Vastus lateralis – extends knee • Vastus medialis – extends knee; inferior fibers stabilize patella

37. Thigh • Biceps femoris – extends thigh and flexes knee • Semitendinosus – extends thigh at hip; flexes knee • Adductor muscles – adduct and laterally rotate the thighs

38. Leg • Tibialis anterior – prime mover of dorsiflexion; inverts foot • Gastrocnemius – plantar flexes foot when knee is extended • Fibularis longus – plantar flexes foot

39. Other Fun Facts

40. Other Fun Facts • Calcaneal tendon = tendon of gastrocnemius = achilles tendon = achilles heel

44. It takes 17 muscles to smile and 43 to frown