Major Muscles of the Upper Body

Different arrangements of fascicles

Arrangement of fascicles influences movement and power Skeletal muscles can shorten by about 1/3 of their resting length The more nearly parallel to the axis, the more they can shorten This results in a larger distance of movement The power depends on the total number of fibers Stocky muscles (like bipennate vs parallel) have more fibers, therefore more powerful even though shorten very little

Interactions of Skeletal Muscles Muscles can only pull, they can’t push Actions must be “undone” by a different muscle Muscles that produce opposite movements usually lie on opposite sides of a given joint

Interactions, continued Agonist: prime mover, major responsibility for producing a specific movement Antagonist: oppose or reverse a particular movement Usually contract a little to prevent overshooting the mark or slow the agonist’s action near the end Are being stretched or can remain relaxed when agonist works Antagonists for one movement can be agonists for another

Synergists help prime movers Add a little extra force to the same movement Or reduce undesirable extra movements (e.g. making a fist without flexing at wrist) Fixators: hold a bone firmly so agonist has a stable base on which to move a body part (e.g. fixing scapula when arm moves)

Naming skeletal muscles (examples) Location: brachialis is in arm (brachium = arm) Shape: deltoid is triangular (delta = triangle) Size: minimus (smallest), longus (long), brevis (short) Direction of fascicles and fibers: rectus (straight); transversus (right angle) and oblique (oblique) to midline Number of origins: biceps (“two heads”), triceps (“three heads”), quadriceps (“four heads”) Action: “flexor,” “extensor,” “adductor” or “abductor” appear in the name Combinations of the above, e.g. extensor carpi radialis longus

Muscles of the Head and Neck Scalp Muscle: epicranius frontal belly occipital belly gala aponeurotica Muscles of Facial Expression: insert on skin or another muscle Muscles of Mastication (chewing): all have insertions on the mandible Anterior Neck Muscles Posterior Neck Muscles

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Anterior

Anterior Chest Muscles

Posterior

Muscles moving the scapula posterior

Rotator cuff supraspinatus, infraspinatus, subscapularis, teres minor

Anterior Arm

Forearm extensors (posterior) Triceps brachii Anconeus helps

Deep muscles of back

Deep muscles of the thorax: breathing Intercostals Short: rib to rib Diaphragm prime mover of inspiration

Muscles of the abdominal wall

Muscles of the abdominal wall from the side