Axial Muscles

Scalenus anterior

Origin: Transverse and costal processes of C3–C6;

Insertion: Superior surface of first rib;

Action: Elevates ribs and/or flexes neck; one side bends neck and rotates to opposite side.

Scalenus medius

Origin: Transverse and costal processes of atlas (C1) and C3–C7;

Insertion: Superior surface of first rib;

Action: Elevates ribs and/or flexes neck; one side bends neck and rotates same side.

Scalenus posterior

Origin: Transverse and costal processes of C4–C6;

Insertion: Superior surface of second rib;

Action: Elevates ribs and/or flexes neck; one side bends neck and rotates same side.

External intercostals

Origin: Inferior border of each rib;

Insertion: Superior border of next rib;

Action: Elevate ribs.

Internal intercostals

Origin: Superior border of each rib;

Insertion: Inferior border of next rib;

Action: Depress ribs.

Transversus thoracis

Origin: Posterior surface of sternum;

Insertion: Cartilages of ribs;

Action: Depress ribs.

Serratus posterior superior

Origin: Spinous processes C7–T3 & ligamentum nuchae;

Insertion: Superior borders of ribs 2–5;

Action: Elevates ribs, enlarges thoracic cavity.

Serratus posterior inferior

Origin: Spinous processes of T11–L2 or L3;

Insertion: Inferior borders of ribs 9–12;

Action: Pull ribs inferiorly; opposes diaphragm.

External oblique

Origin: External and inferior borders of ribs 5–12;

Insertion: External oblique aponeurosis to linea alba & iliac crest;

Action: Compress abdomen; depress ribs; flex, laterally flex, or rotate vertebral column opposite side.

Internal oblique

Origin: Thoracolumbar fascia, inguinal ligament, iliac crest;

Insertion: Inferior surfaces ribs 9–12, costal cartilages 8–10, linea alba, pubis;

Action: Compress abdomen; flex, laterally flex, rotate vertebral column same side.

Transversus abdominis

Origin: Cartilages of ribs 7–12, iliac crest, thoracolumbar fascia;

Insertion: Linea alba & pubis;

Action: Compress abdomen.

Diaphragm

Origin: Xiphoid process, ribs 7–12, lumbar vertebrae;

Insertion: Central tendon sheet;

Action: Expands thoracic cavity, compresses abdominopelvic cavity.

Rectus abdominis

Origin: Superior surface of pubis around symphysis;

Insertion: Inferior surfaces of ribs 5–7 & xiphoid process;

Action: Depresses ribs, flexes vertebral column, compresses abdomen.

Splenius capitis

Origin: Spinous processes & ligamentum nuchae of inferior cervical/upper thoracic vertebrae;

Insertion: Mastoid process & occipital bone;

Action: Together extend neck; alone rotate/laterally flex to same side.

Splenius cervicis

Origin: Spinous processes of T3–T6;

Insertion: Transverse processes of cervical vertebrae C1–C3;

Action: Extend neck.

Spinalis cervicis

Origin: Inferior portion ligamentum nuchae and C7 spinous process;

Insertion: Spinous process of C2–C4;

Action: Extends neck.

Spinalis thoracis

Origin: Spinous processes of T11–T12 and L1–L2;

Insertion: Spinous processes of superior thoracic vertebrae;

Action: Extends vertebral column.

Longissimus capitis

Origin: Transverse processes of inferior cervical/superior thoracic vertebrae;

Insertion: Mastoid process;

Action: Extend neck; rotate/lateral flex same side.

Longissimus cervicis

Origin: Transverse processes of middle/superior cervical vertebrae;

Insertion: Transverse processes superior thoracic vertebrae;

Action: Extend neck; alone rotate/lateral flex.

Longissimus thoracis

Origin: Broad tendon from thoracic/lumbar processes and iliac crest;

Insertion: Transverse processes superior lumbar/thoracic vertebrae and ribs;

Action: Extend vertebral column; lateral flex.

Iliocostalis cervicis

Origin: Superior borders ribs 3–6;

Insertion: Transverse processes of C4–C6;

Action: Extend or laterally flex neck; elevate ribs.

Iliocostalis thoracis

Origin: Superior borders ribs 6–12;

Insertion: Superior ribs & C7;

Action: Stabilizes thoracic vertebrae.

Iliocostalis lumborum

Origin: Iliac crest, sacral crests, lumbar spinous processes;

Insertion: Inferior surfaces ribs 6–12;

Action: Extends vertebral column, depresses ribs.

Semispinalis capitis

Origin: Transverse processes lower cervical and upper thoracic vertebrae;

Insertion: Occipital bone;

Action: Extend neck, flex to opposite side.

Semispinalis cervicis

Origin: Transverse processes T1–T5;

Insertion: Spinous processes C2–C5;

Action: Extend vertebral column, rotate opposite side.

Semispinalis thoracis

Origin: Transverse processes T6–T10;

Insertion: Spinous processes C6–T4;

Action: Extend vertebral column, rotate opposite side.

Multifidus

Origin: Sacrum & transverse processes of each vertebra;

Insertion: Spinous process of superior vertebra;

Action: Extend & rotate vertebral column.

Rotatores

Origin: Transverse processes of vertebrae;

Insertion: Spinous process of adjacent superior vertebra;

Action: Extend vertebral column, rotate opposite side.

Interspinales

Origin: Spinous processes of vertebrae;

Insertion: Spinous processes next superior vertebra;

Action: Extend vertebral column.

Intertransversarii

Origin: Transverse processes;

Insertion: Transverse processes next superior vertebra;

Action: Lateral flexion vertebral column.

Longus capitis

Origin: Transverse processes C4–C6;

Insertion: Base of occiput;

Action: Flex neck.

Longus colli

Origin: Cervical/upper thoracic anterior surfaces;

Insertion: Transverse processes cervical vertebrae;

Action: Flex/rotate neck; limit hyperextension.

Quadratus lumborum

Origin: Iliac crest & iliolumbar ligament;

Insertion: Last rib, transverse processes lumbar vertebrae;

Action: Depress ribs; lateral flexion; stabilize diaphragm.

Digastric (anterior belly)

Origin: Inferior mandible;

Insertion: Hyoid bone;

Action: Depresses mandible or elevates larynx.

Digastric (posterior belly)

Origin: Mastoid region;

Insertion: Hyoid bone;

Action: Same as above.

Geniohyoid

Origin: Medial mandible;

Insertion: Hyoid;

Action: Depresses mandible, elevates larynx, retracts hyoid.

Mylohyoid

Origin: Mylohyoid line mandible;

Insertion: Median raphe to hyoid;

Action: Elevates floor of mouth; elevates hyoid; depresses mandible.

Omohyoid

Origin: Superior scapula;

Insertion: Hyoid;

Action: Depresses hyoid & larynx.

Sternohyoid

Origin: Clavicle & manubrium;

Insertion: Hyoid;

Action: Depresses hyoid & larynx.

Sternothyroid

Origin: Posterior manubrium & first costal cartilage;

Insertion: Thyroid cartilage;

Action: Depresses hyoid & larynx.

Stylohyoid

Origin: Styloid process;

Insertion: Hyoid;

Action: Elevates larynx.

Thyrohyoid

Origin: Thyroid cartilage;

Insertion: Hyoid;

Action: Elevates larynx, depresses hyoid.

Sternocleidomastoid

Origin: Clavicle & manubrium;

Insertion: Mastoid region;

Action: Together flex neck; alone rotates head to opposite side.