1. Gross Anatomy and Functions of Skeletal Muscles
Chapter 9
Gross Anatomy and Functions of Skeletal Muscles
Skeletal Muscle
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2. General Principles
The less movable end of a muscle attachment is the origin; the more movable end is the insertion
An agonist causes a certain movement and an antagonist acts in opposition to the agonist
Synergists are muscles that function together to produce movement
Prime movers are mainly responsible for a movement
Fixators stabilize the action of prime movers

3. Fig. 9.1

4. Nomenclature Muscles are named according to their: Location Size
Pectoralis (chest)
Gluteus (buttock)
Brachial (arm)
Size
Maximus (large)
Minimus (small)
Major (larger of two muscles)
Minor (smaller of two muscles)
Longus (long)
Brevis (short)
Origin and insertion
Shape
Deltoid (triangular)
Quadratus (quadrate - rectangular)
Teres (round)
Orientation of fasciculi
Rectus (straight)
Oblique (at an angle)
Number of heads
Biceps (two)
Triceps (three)
Function
Abductor (away form midline)
Adductor (towards midline)
Masseter (a chewer)

5. Movements Accomplished by Muscles
Pull (P): muscle contraction applied to applied to levers (force)
Lever: a rigid shaft capable of turning about a hinge, or pivot point, called a fulcrum (F)
Effort: force applied to a lever
Weight (W) – resistance moved by the effort
Joints function as fulcrums
Bones function as levers
Muscles provide the pull to move the levers

6. Movements Accomplished by Muscles
Class I Lever: the fulcrum is between the pull and the weight
Class II Lever: the weight is between the fulcrum and the pull
Class III Lever: the pull is applied between the fulcrum and the weight
Most common type in the body

7. Fig. 9.2

8. Movements Accomplished by Muscles
Class I Lever: the fulcrum is between the pull and the weight

9. Movements Accomplished by Muscles
Class II Lever: the weight is between the fulcrum and the pull

10. Movements Accomplished by Muscles
Class III Lever: the pull is applied between the fulcrum and the weight
Most common type in the body

11. General Overview of the Superficial Body Musculature
Fig. 9.3a

12. General Overview of the Superficial Body Musculature
Fig. 9.3b

13. Head and Neck Muscles Involved in Facial expression
Mastication (chewing)
Movement of the tongue
Movement of the head and neck

14. Facial Expression Muscles
Cutaneous muscles
Origins of facial muscles are on skull bones or fascia
Insertions are into the skin, causing movement of the facial skin, lips, and eyelids
Animals have cutaneous muscles all over the trunk that allow skin to twitch
Humans have cutaneous muscles primarily on the face and neck
Table 9.1 summarizes the muscles of facial expression

15. Tab. 9.1

16. Tab. 9.1(Contd.)

17. Fig. 9.4a

18. Fig. 9.4b

19. Fig. 9.5

20. Muscles of Mastication
Mainly deal with the movement of the mandible
Temporalis and masseter muscles elevate the mandible
Gravity opens the jaw
Digastric muscle depresses the mandible
Pterygoid muscles move the mandible from side to side

21. Fig. 9.6

22. Tab. 9.2

23. Fig. 9.7

24. Tab. 9.3

25. Muscles that Move the Tongue
Important in mastication and speech
Two types of muscles
Intrinsic muscles
Change the shape of the tongue
Found entirely within the tongue
Extrinsic muscles
Move the tongue
Found outside of the tongue but are attached to it

26. Fig. 9.8

27. Tab. 9.4

28. Muscles that Move the Head and Neck
Neck muscles cause flexion, extension, rotation, and lateral flexion of the head and neck
Head extension is accomplished by the splenius capitis and trapezius muscles
Major head flexor is the sternocleidomastoid
Lateral head movements are accomplished by the sternocleidomastoid and scalene muscles

29. Fig. 9.9

30. Tab. 9.5