8.8 Major Skeletal Muscles

What muscle names tell us  Relative size  Shape  Location  Action  Number of attachments  Direction of fibers

Examples  Zygomaticus – originates at the zygomatic bone  Gluteus maximus – originates in the gluteal region and is a large muscle  Tibialis anterior – originates on the anterior surface of the tibia

Muscles of Facial Expression

Epicranus  Origin – occipital bone  Insertion – skin and muscles around eye  Action – raises eyebrow

Orbicularis oculi  Origin – maxillary and frontal bones  Insertion – skin around eye  Action – closes eye

Orbicularis oris  Origin – muscles near the mouth  Insertion – skin of lips  Action – closes and protrudes lips

Buccinator  Origin – outer surfaces of maxilla and mandible  Insertion – orbicularis oris  Action – compresses cheeks inward

Zygomaticus  Origin – zygomatic bone  Insertion – orbicularis oris  Action – raises corner of mouth

Platysma  Origin – fascia in upper chest  Insertion – lower border of mandible  Action – draws angle of mouth downward

Muscles of Mastication

Masseter  Origin – lower border of zygomatic arch  Insertion – lateral surface of mandible  Action – closes jaw

Temporalis  Origin – temporal bone  Insertion – coronoid process and lateral surface of mandible  Action – closes jaw

Muscles that move the head

Sternocleidomastoid  Origin – anterior surface of sternum and upper surface of clavicle  Insertion – mastoid process of temporal bone  Action – pulls head to one side, pulls head toward chest, or raises sternum

Splenius capitis  Origin – spinous processes of lower cervical and upper thoracic vertebrae  Insertion – mastoid process of temporal bone  Action – rotates head, bends head to one side, or brings head into an upright position.

Semispinalis capitis  Origin – processes of lower cervical and upper thoracic vertebrae  Insertion – occipital bone  Action – extends head, bends head to one side, or rotates head.

Muscles that move the pectoral girdle  Closely associated with those that move the arm.  Many of these move the scapula up and down, back and forth.

Muscles that move the pectoral girdle

Trapezius  Origin – occipital bone and spines of cervical and thoracic vertebrae  Insertion – clavicle; spine and acromion process of scapula  Action – rotate scapula and raises arm, raises scapula, pulls scapula medially or pulls scapula and shoulder downward.

Rhomboideus major  Origin – spines of upper thoracic vertebrae  Insertion – medial border of scapula  Action – raises and adducts scapula

Levator scapula  Origin – transverse process of cervical vertebrae  Insertion – medial margin of scapula  Action – elevates scapula

Serratus anterior  Origin – outer surface of upper ribs  Insertion – ventral surface of scapula  Action – pulls scapula anteriorly and downward

Pectoralis minor  Origin – sternal ends of upper ribs  Insertion – coracoid process of scapula  Action – pulls scapula anteriorly and downward or raises ribs

Muscles that move the arm  Arm is freely movable.  Muscles are grouped by their primary action.  Flexion – flexors  Extension – extensors  Abduction – abductors  Rotation - rotators

Flexors  Coracobrachialis  Pectoralis major

Coracobrachialis

Extensors  Teres major  Latissimus dorsi

Abductors  Supraspinatus  Deltoid

Rotators  Subscapularis  Infraspinatus  Teres minor

Muscles that move the forearm  Most forearm movement is accomplished by muscles that connect the radius or ulna to the humerus or pectoral girdle.  Again, we have flexors, extensors and rotators.

Flexors  Biceps brachii  Brachialis  Brachioradialis

Extensor  Triceps brachii

Rotators  Supinator  Pronator teres  Pronator quadratus

Muscles that move the hand  Flexors  Anterior side  Flexor carpi radialis  Flexor carpi ulnaris  Palmaris longus  Flexor digitorum profundus  Extensors  Posterior side  Extensor carpi radialis longus  Extensor carpi radialis brevis  Extensor carpi ulnaris  Extensor digitorum

Muscles of the abdominal wall  External oblique  Internal oblique  Transversus abdominis  Rectus abdominis

Muscles of the pelvic outlet  Pelvic diaphragm  Levator ani  Urogenital diaphragm  Superficial transversus perinei  Bulbospongiosus  Ischiocavernosus

Muscles that move the thigh Anterior group  Psoas major  Iliacus Posterior group  Gluteus maximus  Gluteus medius  Gluteus minimus  Tensor fasciae latae

Muscles that move the leg Flex the knee  Biceps femoris  Semitendinosus  Semimembranosus  Sartorius Extend the knee  Quadriceps femoris group, consisting of:  Rectus femoris  Vastus lateralis  Vastus medialis  Vastus intermedius

Muscles that move the foot Dorsal flexors  Tibialis anterior  Fibularis  Extensor digitorum Plantar flexors  Gastrocnemius  Soleus  Flexor digitorum longus