Muscles of the Body

1. 11 Muscles of the Body

2. Muscles of the Body • Skeletal muscles • Produce movements • Blinking of eye, standing on tiptoe, swallowing food, etc. • General principles of leverage • Muscles act with or against each other • Criteria used in naming muscles

3. Arrangement of Fascicles in Muscles • Skeletal muscles—consist of fascicles • Fascicles—arranged in different patterns • Fascicle arrangement—tells about action of a muscle

4. Arrangement of Fascicles in Muscles • Types of fascicle arrangement • Parallel—fascicles run parallel to the long axis of the muscle • Strap-like—sternocleidomastoid • Fusiform—biceps brachii

5. Arrangement of Fascicles in Muscles • Types of fascicle arrangement • Convergent • Origin of the muscle is broad • Fascicles converge toward the tendon of insertion • Example—pectoralis major

6. Arrangement of Fascicles in Muscles • Types of fascicle arrangement • Pennate • Unipennate—fascicles insert into one side of the tendon • Bipennate—fascicles insert into the tendon from both sides • Multipennate—fascicles insert into one large tendon from all sides

7. Arrangement of Fascicles in Muscles • Circular • Fascicles are arranged in concentric rings • Surround external body openings • Sphincter—general name for a circular muscle • Examples • Orbicularis oris and orbicularis oculi

8. Arrangement of Fascicles in Muscles (a) (e) (b) (a) Circular (orbicularis oris) (c) (b) Convergent (pectoralis major) (d) (f) (g) (c) Fusiform (biceps brachii) (d) Parallel (sartorius) (e) Multipennate (deltoid) (f) Bipennate (rectus femoris) (g) Unipennate (extensor digitorum longus) Figure 11.1

9. Lever Systems: Bone-Muscle Relationships • Movement of skeletal muscles involves leverage • Lever—a rigid bar that moves • Fulcrum—a fixed point • Effort—applied force • Load—resistance

10. Lever Systems Effort x length of effort arm = load x length of load arm (force x distance) = (resistance x distance) Effort 10 kg Effort 0.25 cm 25 cm Fulcrum Load 1000 kg 10 x 25 = 1000 x 0.25 250 = 250 Load Fulcrum (a) Mechanical advantage with a power lever Figure 11.2a

11. Lever Systems Effort 100 kg Effort Load 25 cm 50 cm Fulcrum Fulcrum 50 kg 100 x 25 = 50 x 50 2500 = 2500 Load (b) Mechanical disadvantage with a speed lever Figure 11.2b

12. Lever Systems: Bone-Muscle Relationships • Bones—act as levers • Joints—act as fulcrums • Muscle contraction—provides effort • Applies force where muscle attaches to bone • Load—bone, overlying tissue, and anything lifted

13. Lever Systems: Bone-Muscle Relationships • Levers allow a given effort to • Move a heavier load • Move a load farther • Mechanical advantage • Moves a large load over small distances • Mechanical disadvantage • Allows a load to be moved over a large distance

14. Lever Systems: Bone-Muscle Relationships • First-class lever • Effort applied at one end • Load is at the opposite end • Fulcrum is located between load and effort

15. (a) First-class lever Arrangement of the elements is load-fulcrum-effort. (a) First-class lever Arrangement of the elements is load-fulcrum-effort. Load Effort L Fulcrum Fulcrum Load Load Effort L In the body: A first-class lever system raises your head off your chest. The posterior neck muscles provide the effort; the atlanto-occipital joint is the fulcrum; and the weight to be lifted is the facial skeleton. Effort Fulcrum Example: scissors Lever Systems: Bone-Muscle Relationships • Examples—seesaws, scissors, and lifting your head off your chest Figure 11.3a

16. Lever Systems: Bone-Muscle Relationships • Second-class lever • Effort applied at one end • Fulcrum is at the opposite end • Load is between the effort and fulcrum • Examples—wheelbarrow or standing on tiptoe • An uncommon type of lever in the body • Work at a mechanical advantage

17. (b) Second-class lever (b) Second-class lever Arrangement of the elements is fulcrum-load-effort. Arrangement of the elements is fulcrum-load-effort. Load Effort L Fulcrum Effort Load Load L Fulcrum In the body: Second-class leverage is exerted when you stand on tip-toe. The effort is exerted by the calf muscles pulling upward on the heel; the joints of the ball of the foot are the fulcrum; and the weight of the body is the load. Effort Fulcrum Example: wheelbarrow Lever Systems: Bone-Muscle Relationships Figure 11.3b

18. (c) Third-class lever (c) Third-class lever Arrangement of the elements is load-effort-fulcrum. Arrangement of the elements is load-effort-fulcrum. Load Effort Effort L Fulcrum Load Load L Fulcrum In the body: Flexing the forearm by the biceps brachii muscle exemplifies third-class leverage. The effort is exerted on the proximal radius of the forearm; the fulcrum is the elbow joint; and the load is the hand and distal end of the forearm. Fulcrum Effort Example: tweezers or forceps Lever Systems: Bone-Muscle Relationships • Third-class lever • Effort is applied between the load and the fulcrum • Work speedily • Always at a mechanical disadvantage Figure 11.3c

19. Lever Systems: Bone-Muscle Relationships • Most skeletal muscles are third-class levers • Example—biceps brachii • Fulcrum—the elbow joint • Force—exerted on the proximal region of the radius • Load—the distal part of the forearm

20. Muscle Actions and Interactions • A muscle cannot reverse the movement it produces • Another muscle must undo the action • Muscles with opposite actions lie on opposite sides of a joint

21. Muscle Actions and Interactions • Prime mover (agonist) • Has major responsibility for a certain movement • Antagonist • Opposes or reverses a movement • Synergist—helps the prime mover • By adding extra force • By reducing undesirable movements • Fixator • A type of synergist that holds a bone firmly in place

22. (a) A muscle that crosses on the anterior side of a joint produces flexion* (b) A muscle that crosses on the posterior side of a joint produces extension* Example: Latissimus dorsi (posterior view) Example: Pectoralis major (anterior view) *These generalities do not apply to the knee and ankle because the lower limb is rotated during development. The muscles that cross these joints posteriorly produce flexion, and those that cross anteriorly produce extension. *These generalities do not apply to the knee and ankle because the lower limb is rotated during development. The muscles that cross these joints posteriorly produce flexion, and those that cross anteriorly produce extension. Muscle Actions and Interactions Figure 11.5a, b

23. (c) A muscle that crosses on the lateral side of a joint produces abduction (d) A muscle that crosses on the medial side of a joint produces adduction Example: Medial deltoid (anterolateral view) Example: Teres major (posterolateral view) Muscle Actions and Interactions Figure 11.5c, d

24. Muscle Compartments of the Limbs • Dense fibrous connective tissue divides limb muscles into compartments • Muscles in opposing compartments are • Agonist and antagonist pairs • Each compartment is innervated by a single nerve

25. Muscle Compartments of the Thigh • Posterior compartment muscles • Extend the hip and flex the knee • Innervation is the tibial branch of the sciatic nerve • Anterior compartment muscles • Flex the hip and extend the knee • Innervation is the femoral nerve • Medial compartment • Adduct the thigh • Innervation is the obturator nerve

26. Hamstrings Adductors (a) Vastus lateralis Femur Posterior compartment of thigh (flexes leg and extends thigh); innervation: tibial nerve (portion of sciatic nerve) Vastus intermedius Rectus femoris Vastus medialis Posterior compartment muscles Anterior compartment muscles Medial compartment (adducts thigh); innervation: obturator nerve Anterior compartment (extends leg); innervated by femoral nerve Medial compartment muscles of thigh and lateral compartment muscles of leg (a) Muscles of the thigh Muscle Compartments of the Thigh and Leg Figure 11.7a

27. Naming the Skeletal Muscles • Location • Example—the brachialis is located on the arm • Shape • Example—the deltoid is triangular • Relative size • Maximus, minimus, and longus indicate size • Example—gluteus maximus and gluteus minimus

28. Naming the Skeletal Muscles • Direction of fascicles and muscle fibers • Name tells direction in which fibers run • Example—rectus abdominis and transversus abdominis • Location of attachments—name reveals point of origin and insertion • Example—brachioradialis

29. Naming the Skeletal Muscles • Number of origins • Two, three, or four origins • Indicated by the words biceps, triceps, and quadriceps • Action • The action is part of the muscle’s name • Indicates type of muscle movement • Flexor, extensor, adductor, or abductor