The Muscular System

1. The Muscular System

2. Muscle Attachment Sites • Muscle exerts force on tendons, which in turn pull on bones or other structures. • When a muscle contracts, it pulls one of the articulating bones toward the other.

3. Muscle Attachment Sites: Origin & Insertion • Origin – the site of a muscle’s attachment to the more stationary bone. • Insertion – the site of a muscle’s attachment to the more movable bone. • Often, the origin is proximal to the insertion. • Belly – the fleshy part of the muscle between the tendons of the origin and insertion.

4. Tenosynovitis • Commonly known as tendinitis. • Painful inflammation of the tendons, tendon sheaths, and synovial membranes of the joints. • Trauma, strain, excessive exercise, chronic, repetitive motions can all cause tenosynovitis.

5. Lever Systems & Leverage • A lever is a rigid structure that can move around a fixed point called a fulcrum. • Two forces act upon a lever: • Effort – causes movement. • Load (resistance) – opposes movement.

6. Lever Systems & Leverage • Levers produce trade-offs between effort and the speed and range of motion. • Mechanical advantage (leverage) – a smaller effort can move a heavier load – the effort must move a greater distance. • Mechanical disadvantage – a larger effort moves a lighter load – the effort must move a shorter distance and slower than the load.

8. Types of Levers • First-class levers. • The fulcrum is between the effort and the load. • Scissors and seesaws are examples. • It can produce either a mechanical advantage or disadvantage depending upon whether the effort or load is placed closer to the fulcrum. • If an effort is placed farther from the fulcrum than the load, a heavy load can be moved, but not fast or far. • If an effort is placed closer to the fulcrum than the load, only a lighter load can be moved, but it moves far and fast. • Raising the head at the atlanto-occipital joint.

9. Types of Levers • Second-class levers. • The load is between the fulcrum and the effort. • An example is a wheelbarrow. • Always produces a mechanical advantage because the load is always closer to the fulcrum than the effort. • None present in the human body.

10. Types of Levers • Third-class levers. • The effort is between the fulcrum and the load. • An example is a forceps. • Always produces a mechanical disadvantage because the effort is always closer to the fulcrum than the load. • This arrangement favors speed and range of motion over force.

12. Effects of Fascicle Arrangement • Within a fascicle, all muscles are parallel to one another. • The fascicles may form patterns with respect to the tendon: • Parallel. • Fusiform (cigar shaped). • Circular. • Triangular. • Pennate (feather shaped).

13. Effects of Fascicle Arrangement • Fascicular arrangement affects a muscle’s power and range of motion. • The longer the muscles in a fiber, the greater the range of motion they can produce. • The power of a muscle depends upon it’s cross-sectional area (a short muscle fiber can contract as powerfully as a long one).

14. Coordination Within Muscle Groups • Movements are typically the result of several skeletal muscles acting as a group. • Most skeletal muscles are arranged in opposing (antagonistic) pairs at joints: • Flexors – extensors, abductors – adductors, etc. • One muscle is called the prime mover (agonist) which contracts to cause an action and the other muscle is called the antagonist which stretches and yields to the effects of the prime mover.

15. Coordination Within Muscle Groups • Synergists work with agonists to stabilize intermediate joints and assist the prime mover. • Fixators stabilize the origin of the prime mover so that the prime mover can operate more efficiently. • In limbs, a compartment is a group of skeletal muscles, and their associated blood vessels and nerves, that have a common function. • I.E. In the upper limbs with have flexor compartments and extensor compartments.

16. Benefits of Stretching • Improved physical performance – greater R.O.M. • Decreased risk of injury – decreases the resistance in tissues. • Reduced muscle soreness. • Improved posture – stretching helps realign soft tissues. • Muscles should be stretched at a point of slight discomfort (not pain) for 15-30 seconds.

19. Muscles of Facial Expression • Scalp muscles • Occipitofrontalis • Frontal belly • Occipital belly

20. Muscles of Facial Expression • Mouth muscles • Orbicularis oris • Zygomaticus major • Zygomaticus minor • Levator labii superioris • Depressor labii inferioris • Depressor anguli oris • Buccinator

21. Muscles of Facial Expression • Neck muscle • Platysma • Orbit and eyebrow muscles • Orbicularis Oculi • Corrugator Supercilii • Levator palpebrae superioris

22. Frontalis • Origin – Epicranial aponeurosis • Insertion – skin above the eye • Action – draws skin anteriorly, raises eyebrows, and wrinkles skin of the forehead

23. Occipitalis • Origin – occipital bone and mastoid process of the temporal bone • Insertion – epicranial aponeurosis • Action – draws scalp posteriorly

24. Orbicularis Oris • Origin – surrounding the opening of the mouth • Insertion – skin at the corner of the mouth • Action – closes and protrudes lips, compresses lips against the teeth, and shapes lips during speech

25. Buccinator • Origin – maxilla and mandible • Insertion – orbicularis oris • Action – draws the angle of the mouth laterally and inferiorly as in opening the mouth

26. Platysma • Origin – fascia over deltoid and pectoralis major muscles • Insertion – mandible, muscles around the angle of the mouth and the skin of the lower face • Action – draws the outer part of the lower lip inferiorly and posteriorly as in pouting and depresses the mandible

27. Orbicularis Oculi • Origin – medial wall of orbit • Insertion – circular path around orbit • Action – closes eye

30. Bell’s Palsy (Facial Paralysis) • Unilateral paralysis of the muscles of facial expression. • Due to damage or disease of the facial nerve (cranial nerve VII). • The causes is unknown; However, inflammation of the facial nerve or infection by herpes simplex are suggested causes.

31. Bell’s Palsy (Facial Paralysis) • The person cannot wrinkle the forehead, close the eye, or pucker the lips on the affected side. • Difficulty in swallowing and drooling often occur. • 80% recover within a few weeks to a few months; However, for some the paralysis is permanent.

32. Muscles That Move the Eyeballs – Extrinsic Eye Muscles • Superior Rectus • Inferior Rectus • Lateral Rectus • Medial Rectus • Superior oblique • Inferior oblique

34. Strabismus • A condition in which the eyes are not properly aligned. • A lesion of the oculomotor nerve (cranial nerve III) or the abducens nerve (cranial nerve VI).

35. Muscles That Move the Mandible • Masseter • Temporalis • Medial Pterygoid • Lateral Pterygoid

36. Masseter • Origin – maxilla and zygomatic arch • Insertion – angle and ramus of mandible • Action – elevates mandible and retracts mandible (closes mouth)

37. Temporalis • Origin – temporal bone • Insertion – coronoid process and ramus of mandible • Action – elevates and protracts mandible and moves mandible from side to side

40. Muscle That Move The Tongue • Genioglossus • Styloglossus • Palatoglossus • Hyoglossus

42. Muscles of the Anterior Neck • Suprahyoid muscles • Digastric • Stylohyoid • Mylohyoid • Geniohyoid

43. Muscles of the Anterior Neck • Infrahyoid muscles • Omohyoid • Sternohyoid • Sternothyroid • Thyrohyoid

45. Muscles That Move the Head • Sternocleidomastoid • Semispinalis Capitis • Splenius Capitus • Longissimus Capitis

46. Sternocleidomastoid • Origin – sternum and clavicle • Insertion – mastoid process of the temporal bone • Action – • Acting together (bilaterally), they flex the cervical portion of the vertebral column, extend the head, and elevate the sternum during forced inhalation • Acting singly (unilaterally), laterally flexes head towards and rotates head away from the side of the contracting muscle

48. Muscles That Act on the Abdominal Wall • Rectus Abdominus • External oblique • Internal oblique • Transversus Abdominus • Quadratus Lumborum

49. Rectus Abdominus • Origin – pubic crest and pubic symphisis. • Insertion – cartilage of the 5th to 7th ribs and xiphoid process. • Action – flexes vertebral column, compresses the abdomen to aid in defecation, urination, forced exhalation and childbirth.

50. External Oblique • Origin – inferior eight ribs. • Insertion – iliac crest and linea alba. • Action –. • Acting together (bilaterally) they compress the abdomen and flex the vertebral column. • Acting singly (unilaterally), laterally flexes the vertebral column and rotates the vertebral column.