Muscles of the Body

1. Muscles of the Body Chapter 11

2. Interactions of Skeletal Muscles • The arrangement of body muscles permits them to work either together or in opposition to achieve a movement • As muscle contract they can only pull on the skeleton; they can never push • If you are pushing an object it is the contraction of some group of muscles in the body that will accomplish it • Generally muscles are grouped to “undo” an action done by another group • Quadriceps / Hamstrings

3. Working out with Muscles • Muscle contraction causes shortening, not lengthening of a muscle • Concentric / shortening against resistance • Eccentric / lengthening against resistance • Typically as a muscle contracts it moves its insertion toward its origin • Lat. bar pull down / Latissimus dorsi • However, some muscles can contract and move its origin toward its insertion • Pull ups / Latissiums dorsi

4. Functional Muscle Groups • Muscles can be classified into four functional groups • Prime movers • Antagonists • Synergists • Fixators

5. Prime Movers Origin of Biceps Brachii Coracoid Process • A muscle that provides the major force for producing a specific movement is called a prime mover or agonist • The biceps brachii is the prime mover of elbow flexion

6. Antagonist • Muscles that oppose a particular movement are called antagonist • When a prime mover is active, the antagonist muscles are often stretched and may be in a relaxed state • Antagonists also regulate the action of prime mover

7. Synergist • Synergists aid agonists by promoting the same movement and by reducing extraneous movements that may be produced when the prime mover acts • In two joint muscles synergists stabilize a joint as the muscle acts on the other Synergist can also restrict rotary movement at a joint so the muscle’s full effort be applied to the desired movement

8. Fixator • When a synergist immobilize a muscle’s origin they are called fixators • Their action serves to stabilize the bone upon which a prime mover acts • Serratus anterior holds the scapula against the thorax while a prime mover acts upon the arm

9. Naming Skeletal Muscles • Location of the muscle • Intercostal, Temporalis • Shape of the muscle • Deltoid; Trapezius • Relative size of the muscle • Maximus; medius; minimus; brevis; longus • Direction of muscle fibers • Rectus (straight) fibers run parallel to line of pull • Transverse; fibers run perpendicular to line • Oblique; fibers are oblique to the line

10. Naming of Muscles • Number of origins • Biceps; triceps; quadriceps • Location of muscle origin and/or insertion • Sterno (sternum); cleido (clavicle); mastoid (mastoid process of temporal bone) • Action of the muscle • Flexor; extensor; adductor, supinator

11. Arrangement of Fascicles • Arrangement of fascicles within a muscle vary • Arrangements result in differing shapes and capabilities • Common forms are • Parallel • fusiform • Pennate • Uni-, bi-, multi- • Convergent • Circular or sphincteral

13. Parallel Arrangement of Fascicles • In parallel arrange- ment the long axis of the fascicles run parallel to the long axis of the muscle • Form long straplike muscles that have greatest potential for shortening • Act over a long excursion • Not very powerful

14. Pennate Arrangement of Fascicles • Pennate fascicles are short and they attach obliquely to a central tendon • Occur as pennate, bipennate and multipennate forms • Pennate muscles with the highest concentration of fibers, shorten little, but are very powerful A) Pennate / Ext. digitorum longus B) Bipennate / Rectus Femoris C) Multipennate / Deltoid

15. Convergent Arrangement of Fascicle • A convergent muscle has a broad origin and its fascicles converge toward a single tendon • Muscle has a broad triangular shape • Muscle can act upon the joint from a variety of positions • Pectoralis major

16. Circular Arrangement of Fascicles • Fascicular pattern is arranged in concentric rings • Muscles with this arrangement surround external body openings which they close by contracting • This type of muscles are called sphincters which literally means squeezers

17. Lever Systems • The operation of most skeletal muscles involves the use of levers and lever systems • Lever • A rigid bar that moves on a fixed point • Fulcrum • A fixed point of leverage • Effort • The forced applied to move a resistance • Load • The resistance to me moved

18. Lever Systems • In the human body . . . • Levers • The bones of the skeleton • Fulcrums • The joints of the body • Effort • Applied by the muscles of the body • Load • Bone, overlying tissue, and other objects to which your body applies force

19. Lever Systems • A lever allows a given effort to move a heavier load or to move a load farther or faster that it otherwise could • A small difference in the site of a muscle’s insertion can translate into large differences in the amount of force must generate to move a given load

20. Mechanical Advantage • A small effort applied over a relatively long distance can be used to move a large load over a small distance • Such a lever operates at a mechanical advantage and is commonly called a power lever because it can lift heavy loads

21. Mechanical Disadvantage • When the load is far from the fulcrum and the force is applied near the fulcrum, the force exerted by the muscle must be greater than the load moved • These levers are useful because they allow the load to move rapidly through a large distance and are called speed levers

22. Lever Systems • Regardless of type, all levers follow the same basic principle: • Effort farther than load from fulcrum = mechanical advantage • Effort nearer than load to fulcrum = mechanical disadvantage • Depending on the relative position of the three elements (effort, fulcrum, load) a lever is classified as either a first, second, or third class lever

23. First Class Levers • In first class levers the effort is applied at one end of the lever and the load is at the other end with the fulcrum in between them (LFE) • Extension/flexion of the head, other exist but usually operate at a mechanical disadvantage

24. Second Class Levers • In second class levers the effort is applied at one end, the fulcrum is at the other, with the load somewhere in between (FLE) • Plantar flexion of the foot

25. Third Class Levers • In third class levers, the effort is applied at a point between the load and the fulcrum (LEF) • These levers operate with great speed and always at a mechanical disadvantage • Most levers of the body are third class levers which permit an insertion close to the joint and allow rapid movement with little shortening of the muscle

26. Which Lever is it? • Fulcrum in the middle? 1st Class • Load in the middle? 2nd Class • Effort in the middle? 3rd Class

27. Lever Summary • Difference in the positioning of the three elements modify muscle activity with respect to • Speed on contraction • Range of movement • Weight of the load that can be lifted • Speed levers act at a mechanical disadvantage • Force is lost, but speed is gained • Power levers act at a mechanical advantage • Force is gained, but speed is lost

28. Major Skeletal Muscles • There are over 600 muscles in the body • Approximately 125 are presented in text • There will be 55 assigned to you to learn • As you learn these muscles try to relate to its attachments and position and what joint(s) it acts across • The best way to learn muscle actions is to act them out in your body

31. Muscle of Head: Facial Expression Table 10.1

32. Muscles of Head: Facial Expression • Promote facial expression and non-verbal expression • Highly variable in shape and strength • Unusual in that they insert into skin or other muscles and not bone • Innervated by Cranial nerve VII (facial)

33. Muscles of Head: Mastication

34. Muscles of Head: Mastication • Four pairs of muscles are involved with mastication • Chewing and biting • Masseter • Temporalis • Grinding movements • Pterygoid • Buccinator • Trigeminal and Facial nerves

35. Muscles of Head: Tongue Movement Table 10.2

36. Muscles of Head: Tongue Movement • The extrinsic muscles of the tongue serve to anchor and move the tongue • These muscles serve to protrude, depress, and retract the tongue • Innervated by the hypoglossal nerve

37. Muscle that Promote Swallowing Table 10.8

38. Muscles that Promote Swallowing • Lateral view of the constrictor muscles of the pharynx • These muscles are shown in their proper anatomical relationship

39. Muscles of Anterior Neck & Throat Table 10.3

40. Muscles of Anterior Neck & Throat • Most of these muscles are involved with the coordinated action of swallowing which have the following sequence • Widening the pharynx and closing the larynx • Closing the superior nasal cavity • Propulsion of food through the pharynx into the esophagus • Return of musculature to normal positioning

41. Muscles of Neck • Sternocleidomastoid is a head flexor • Scalenes contribute to lateral flexion of the neck • Splenius is a head extensor

42. Muscles of Neck • The head is moved by muscles originating from the axial skeleton which include • Sternocleidomastoid / head flexors • Scalenes / lateral head flexion • Splenius / head extension

43. Muscles of Vertebral Column

44. Muscle of the Vertebral Column • Trunk extension is effected by the deep muscles of the back • The erector spinae is the largest of the group and consists of three bands • Iliocostalis • Longissimus • Spinalis • Other muscles of the vertebral column include • Semispinalis / extends head • Quadratus lumborum / Lateral flexion

45. Muscle of the Thorax: Breathing

46. External Intercostals • O - Inferior border of rib above • I - Superior border of rib below • A - Pulls ribs upward to aid in respiration

47. Internal intercostals • O - Superior border of rib below • I - Inferior border of rib above • Draws ribs together; aids in expiration

48. Muscles of the Thorax: Breathing

49. Diaphragm • O - Inferior border of rib cage, costal cartilages of last 6 ribs, and lumber vertabrae • I - Central tendon • A - Inspiration

50. Muscles of the Abdominal Wall