The Muscular System

1. The Muscular System Chapter 8

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 and separates 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 (aka: one muscle cell) • 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. Muscles are made of 2 main proteins: • thick filaments =myosin. • thin filaments =actin.

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

13. 2 main regions: • I band (light region)- composed of thin actin filaments directly attached to structures called Z lines. • A band (dark region)- composed of thick myosin filaments overlapping thin actin filaments.

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

15. Sarcomere Unit myosin actin actin

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

17. Muscle Microfilaments • Thick filaments • Composed of myosin - protein • Each myosin molecule has tail and a double head Thin filaments • Like two strands of pearls twisted together • Pearls are actin – protein • Other proteins in grooves in filament • Troponin & tropomyosin

18. Sliding-Filament Model • Myosin heads attach to actin filaments by ATP & Calcium • Myosin heads tilt toward the sarcomere center, pulling actin with them (shortening the sarcomere). • When the nerve impulse stops, Calcium leaves the binding sites and the muscle relaxes (lengthens)

19. Sliding-Filament Model Sarcomere shortens because the actin filaments are pulled inward, toward the sarcomere center

21. Contraction Requires Energy • Muscle cells require huge amounts of ATP energy to power contraction • The cells have only a very small store of ATP • Three pathways supply ATP to power muscle contraction • Creatine Phosphate – supplies energy for the first few seconds of intense activity (donates phosphate groups) • Aerobic Respiration – requires oxygen, yields 36 ATP • Anaerobic Respiration – no oxygen needed (2 ATP produced) but results in lactic acid = MUSCLE CRAMPS!!!

22. Nervous System Controls Contraction • Signals from nervous system travel along spinal cord, down a motor neuron • Endings of motor neuron synapse on a muscle cell at a neuromuscular junction

23. Motor Unit • One neuron and all the muscle cells that form junctions with its endings • When a motor neuron is stimulated, all the muscle cells it supplies are activated to contract simultaneously = “all or none response” • Each muscle consists of many motor units

24. All-or-None Response • Each muscle fiber has a threshold stimulus • The minimal strength required to cause a contraction • A muscle fiber exposed to a stimulus of threshold strength (or above) responds to its fullest extent • All-or-None • Different muscle fibers have different thresholds

25. 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

26. 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

27. 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

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

29. 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.

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

31. 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

32. 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

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

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

35. Forearm • Brachioradialis – helps with forearm flexion

36. 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

37. 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

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

39. Thigh • Tensor fascia latae– 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

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

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

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