Muscles of the Body: Lever Systems and Fascicle Arrangements

1. PART 1 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. 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

4. Lever Systems Figure 11.1a

5. Lever Systems Figure 11.1b

6. 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

7. 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

8. 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

9. Lever Systems: Bone-Muscle Relationships • Examples – seesaws, scissors, and lifting your head off your chest Figure 11.2a

10. 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

11. Lever Systems: Bone-Muscle Relationships Figure 11.2b

12. 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 11.2c

13. 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

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

15. 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

16. 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

17. 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

18. 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

19. Arrangement of Fascicles in Muscles Figure 11.3

20. Organization Scheme Based on Embryonic Development • Overview based upon • Embryonic origin • General function • Muscles develop from mesoderm • Myotomes • Somitomeres • The first seven myotomes of the head • Splanchnic mesoderm

21. Development and Basic Organization of the Muscles Figure 11.4a, b

22. Organization Scheme Based on Embryonic Development • Muscles organized into four groups • Musculature of the visceral organs • Pharyngeal arch muscles • Axial muscles • Limb muscles

23. Organization Scheme Based on Embryonic Development • Musculature of the visceral organs • Includes – smooth and cardiac muscle • Develops from splanchnic mesoderm • Pharyngeal arch muscles • Includes • Skeletal muscles of the pharynx • Muscles of the head and neck • Develop from the fourth to seventh somitomeres

24. Pharyngeal Arch Muscles Figure 11.4c

25. Axial Muscles • Lie anterior and posterior to the body axis • Muscles of the • Thorax, abdomen, and pelvis • Many muscles of the • Neck and some of the head • Function to move the trunk and maintain posture

26. Axial Muscles • Develop from myotomes and some somitomeres • Dorsal regions of myotomes – deep muscles of the back • Ventral regions of myotomes – muscles of the trunk and neck • Respiratory muscles • Anterior abdominal wall muscles • Muscles of the pelvic floor

27. Axial Muscles Figure 11.4d

28. Limb Muscles • Limb muscles arise from lateral parts of nearby myotomes • Extensors • Muscle mass dorsal to limb bones • Flexors • Muscle mass ventral to limb bones

29. Limb Muscles Figure 11.4e

30. Interactions of Skeletal Muscles in the Body • 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

31. Muscles Classified into Several Functional Groups • 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

32. 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

33. Muscle Compartments of Arm and Forearm • The upper limb has anterior and posterior compartments • Anterior arm compartment muscles • Flex the shoulder or arm • Innervation is the musculocutaneous nerve • Anterior forearm compartment muscles • Flex the wrist and digits • Innervation is the median or ulnar nerve

34. Muscle Compartments of the Arm and Forearm Figure 11.5a

35. Muscle Compartments of the Arm and Forearm Figure 11.5b

36. 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

37. Compartments of the Leg • Posterior compartment muscles • Contains digital and plantar flexors • Innervation is the tibial nerve • Anterior compartment muscles • Contains digital extensors and dorsiflexors • Innervation is the deep fibular nerve • Lateral compartment muscles • Plantar flex and evert the foot • Innervation is the superficial fibular nerve

38. Muscle Compartments of the Thigh and Leg Figure 11.6a

39. Muscle Compartments of the Thigh and Leg Figure 11.6b

40. 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

41. 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

42. 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