Gross Anatomy and Functions of Skeletal Muscles Chapter 9 Gross Anatomy and Functions of Skeletal Muscles Skeletal Muscle Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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

Fig. 9.1

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)

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

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

Fig. 9.2

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

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

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

General Overview of the Superficial Body Musculature Fig. 9.3a

General Overview of the Superficial Body Musculature Fig. 9.3b

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

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

Tab. 9.1

Tab. 9.1(Contd.)

Fig. 9.4a

Fig. 9.4b

Fig. 9.5

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

Fig. 9.6

Tab. 9.2

Fig. 9.7

Tab. 9.3

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

Fig. 9.8

Tab. 9.4

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

Fig. 9.9

Tab. 9.5