Anterior Muscles of the Chest, Back, and Abdomen

What is this muscle?

rectus abdominis

rectus abdominis origin

pubic crest and pubic symphysis

rectus abdominis insertion

cartilage of ribs 5-7 and xiphoid process

rectus abdominis action

Flexes vertebral column, especially lumbar portion, and compresses abdomen to aid in defecation, urination, forced exhalation, and childbirth. RMA: Flexes pelvis on the vertebral column.

rectus abdominis innervation

thoracic spinal nerves T7-T12

What is this muscle?

external abdominal oblique

external abdominal oblique origin

ribs 5-12

external abdominal oblique insertion

iliac crest and linea alba

external abdominal oblique action

Acting together (bilaterally), compress abdomen and flex vertebral column; acting singly (unilaterally), laterally flex vertebral column, especially lumbar portion, and rotate vertebral column

external abdominal oblique innervation

thoracic spinal nerves T7-T12 and the iliohypogastric nerve

What muscle is this?

internal abdominal oblique

internal abdominal oblique origin

iliac crest, inguinal ligament, and linea alba

internal abdominal oblique insertion

cartilage of ribs 7-10 and thoracolumbar fascia

internal abdominal oblique action

Acting together, compress abdomen and flex vertebral column; acting singly, laterally flex vertebral column, especially lumbar portion, and rotate vertebral column.

internal abdominal oblique innervation

thoracic spinal nerves T8-T12 the iliohypogastric nerve, and ilioinguinal nerve

What muscle is this?

transversus abdominis

transversus abdominis origin

iliac crest, inguinal ligament, lumbar fascia, and cartilages of ribs 5-10

transversus abdominis insertion

xiphoid process, linea alba, and pubis

transversus abdominis action

compresses abdomen

transversus abdominis innervation

thoracic spinal nerves T8-T12, iliohypogastric nerve, and ilioinguinal nerve

What muscle is this?

Diaphragm

diaphragm origin

xiphoid process of sternum, costal cartilages and adjacent portions of ribs 7-12, lumbar vertebrae and their intervertebral discs

diaphragm insertion

central tendon

diaphragm action

Contraction of diaphragm causes it to flatten and increases vertical dimension of thoracic cavity, resulting in inhalation; relaxation of diaphragm causes it to move superiorly and decreases vertical dimension of thoracic cavity, resulting in exhalation.

diaphragm innervation

phrenic nerve, which contains axons from cervical spinal nerves

What muscle is this?

external intercostals

external intercostals origin

inferior border of rib above

external intercostals insertion

superior border of rib below

external intercostals action

Contraction elevates ribs and increases anteroposterior and lateral dimensions of thoracic cavity, resulting in inhalation; relaxation depresses ribs and decreases anteroposterior and lateral dimensions of thoracic cavity, resulting in exhalation.

external intercostals innervation

thoracic spinal nerves T2-T12

What is this muscle?

internal intercostals

internal intercostals origin

superior border of rib below

internal intercostals insertion

inferior border of rib above

internal intercostals action

Contraction draws adjacent ribs together to further decrease anteroposterior and lateral dimensions of thoracic cavity during forced exhalation.

internal intercostals innervation

thoracic spinal nerves T2-T12

What muscle is this?

sternocleidomastoid

sternocleidomastoid origin

Sternal head: manubrium of sternum; clavicular head: medial third of clavicle

sternocleidomastoid insertion

mastoid process of temporal bone and lateral half of superior nuchal line of occipital bone

sternocleidomastoid action

Acting together (bilaterally), flex cervical portion of vertebral column, extend head at atlanto-occipital joints; acting singly (unilaterally), laterally flex neck and head to same side and rotate head to side opposite contracting muscle. Laterally rotate and flex head to opposite side of contracting muscle. Posterior fibers of muscle can assist in extension of head. RMA: Elevate sternum during forced inhalation.

sternocleidomastoid innervation

accessory (XI) nerve, C2, C3

What muscle is this?

pectoralis major

pectoralis major origin

Clavicle (clavicular head), sternum, and costal cartilages of ribs 2-6 and sometimes ribs 1-7 (sternocostal head).

pectoralis major insertion

Greater tubercle and lateral lip of intertubercular sulcus of humerus.

pectoralis major action

As a whole, adducts and medially rotates arm at shoulder joint; clavicular head flexes arm, and sternocostal head flexes the extended arm to side of trunk.

pectoralis major innervation

Medial and lateral pectoral nerves.

What muscle is this?

pectoralis minor

pectoralis minor origin

ribs 2-5, 3-5, or 2-4

pectoralis minor insertion

Coracoid process of scapula.

pectoralis minor action

Abducts scapula and rotates it downward. RMA: Elevates ribs 3-5 during forced inhalation when scapula is fixed.

pectoralis minor innervation

Medial and lateral pectoral nerve.

What muscle is this?

platysma

platysma origin

Fascia over deltoid and pectoralis major muscles.

platysma insertion

Mandible, blends with muscles around angle of mouth, and skin of lower face.

platysma action

Draws outer part of lower lip inferiorly and posteriorly as in pouting; depresses mandible.

platysma innervation

Facial (VII) nerve.

What muscle is this?

serratus anterior

serratus anterior origin

Ribs 1-8 or 1-9.

serratus anterior insertion

Vertebral border and inferior angle of scapula.

serratus anterior action

Abducts scapula and rotates it upward. RMA: Elevates ribs when scapula is stabilized. Known as "boxer's muscle" because it is important in horizontal arm movements such as punching and pushing.

serratus anterior innervation

Long thoracic nerve.

What muscle is this?

scalenus anterior

scalenus anterior origin

Transverse processes of C3-C6.

scalenus anterior insertion

Rib 1.

scalenus anterior action

Acting together, right and left scalenus anterior and scalenus medius muscles elevate first ribs during deep inhalation.

scalenus anterior innervation

Cervical spinal nerves.

What muscle is this?

scalenus medius

scalenus medius origin

Transverse processes of C2-C7.

scalenus medius insertion

Rib 1

scalenus medius action

elevate first ribs during deep inhalation. RMA: Flex cervical vertebrae; acting singly, laterally flex and slightly rotate cervical vertebrae.

scalenus medius innervation

Cervical spinal nerves.

What muscle is this?

scalenus posterior

scalenus posterior origin

Transverse processes of C4-C6.

scalenus posterior insertion

Rib 2.

scalenus posterior action

Acting together, right and left scalenus posterior elevate second ribs during deep inhalation. RMA: Flex cervical vertebrae; acting singly, laterally flex and slightly rotate cervical vertebrae.

scalenus posterior innervation

Cervical spinal nerves.

What muscle is this?

Sternal head

What muscle is this?

Clavicular head