Muscles of the Axial Skeleton on Head and Neck

• Depression of lower lip (pout)

• Origin: Mandible

• Insertion: muscles of lower lip

• Innervation: Facial nerve (CN VII)

Depressor labii inferioris m.

• Action: Elevation of upper lip (sneer)

• Origin: Maxilla, Zygomatic bone

• Insertion: muscles of upper lip

• Innervation: Facial nerve (CN VII)

Levator labii superioris m.

• Action: Depression of hyoid bone

• Origin: Scapula (superior border)

• Insertion: Hyoid bone

• Innervation: Ventral rami of C1-3 spinal nerves (ansa cervicalis)

Omohyoid m.

• Action: Closes eyelids (blink/wink)

• Origin: Frontal bone, Maxilla

• Insertion: lateral side of orbit

• Innervation: Facial nerve (CN VII)

Obicularis oculi m.

• Action: Closes lips, Protrudes lips (pucker)

• Origin: Skin around mouth, Mandible (midline), Maxilla (midline)

• Insertion:, Lips, Interdigitation with fibers from opposite side

• Innervation: Facial nerve (CN VII)

Obicularis oris m.

• Action: Unilateral: rotation of head so face turns to opposite side, Bilateral: flexion of neck & extension of head

• Origin: Clavicle (medial), Sternum (manubrium)

• Insertion: Mastoid process of temporal bone, Lateral one-half of superior nuchal line of occipital bone

• Innervation: Accessory nerve (CN XI)

Sternocleidomastoid m. (frontal view)

• Action: Depression of hyoid bone

• Origin: Sternum (manubrium), Clavicle (medial end)

• Insertion: Hyoid bone

• Innervation: Ventral rami of C1-3 spinal nerves (ansa cervicalis)

Sternphyoid m.

• Action: Depression of larynx

• Origin: Sternum (manubrium)

• Insertion: Thyroid cartilage of larynx

• Innervation: Ventral rami of C1-3 spinal nerves (ansa cervicalis)

Sternothyroid m.

• Action: Elevation of larynx, Depression of hyoid bone

• Origin: Thyroid cartilage of larynx

• Insertion: Hyoid bone

• Innervation: Ventral ramus of C1 spinal nerve
  

Thyrohyoid m. (frontal view)

• Action: Elevation of corner of mouth (smile)

• Origin: Zygomatic bone

• Insertion: Blends with muscles at angle of mouth

• Innervation: Facial nerve (CN VII)

Zygomaticus major m.

• Action: Compression of cheek (e.g., inflating a balloon; playing a wind musical instrument)

• Origin: Pterygomandibular raphe, Maxilla (lateral aspect), Mandible (lateral body)

• Insertion: Blends with muscles at angle of mouth

• Innervation: Facial nerve (CN VII)

Buccinator m.

• Action: Depression of mandible (opens mouth), Elevation of hyoid bone

• Origin: Anterior belly: mandible (inner aspect of body near midline), Posterior belly: temporal bone (mastoid process)

• Insertion: Hyoid bone

• Innervation: Anterior belly: trigeminal nerve (mandibular division - CN V3), Posterior belly: facial nerve (CN VII)

Digastric m.

Geniohyoid m.

• Action: Elevation of hyoid bone

• Origin: Mandible (mental tubercle)

• Insertion: Hyoid bone

• Innervation: C1 spinal nerve (ventral ramus)

• Action: Elevation of mandible (e.g., closing mouth), Protraction of mandible

• Origin: Zygomatic arch

• Insertion: Mandible (external surface of angle and ramus)

• Innervation: Trigeminal nerve (mandibular division - CN V3)

Masseter m.

• Action: Elevation of floor of mouth

• Origin: Mandible (inner aspect of body)

• Insertion: Hyoid bone (posterior fibers), Midline fibrous raphe (anterior fibers)

• Innervation: Trigeminal nerve (mandibular division - CN V3)

Mylohyoid m.

• Action: Elevation of eyebrows, Creases skin of forehead, Moves scalp backward and forward

• Origin: Occipitalis: occipital bone (superior nuchal line), Frontalis: skin of eyebrow and forehead (blends with orbicularis oculi muscle)

• Insertion: Epicranial aponeurosis

• Innervation: Facial nerve (CN VII)

Occipitofrontalis m.

• Action: Depression of hyoid bone

• Origin: Scapula (superior border)

• Insertion: Hyoid bone

• Innervation: Ventral rami of C1-3 spinal nerves (ansa cervicalis)

Omohyoid m. (lateral view)

• Action: Unilateral: rotation of head so face turns to opposite side, Bilateral: flexion of neck, extension of head

• Origin: Clavicle (medial), Sternum (manubrium)

• Insertion: Mastoid process of temporal bone, Lateral one-half of superior nuchal line of occipital bone

• Innervation: Accessory nerve (CN XI)

Sternocleidomastoid m.

• Action: Depression of hyoid bone

Origin: Sternum (manubrium), Clavicle (medial end)

• Insertion: Hyoid bone

• Innervation: Ventral rami of C1-3 spinal nerves (ansa cervicalis)

Sternohyoid m. (lateral view)

• Action: Depression of larynx

• Origin: Sternum (manubrium)

• Insertion: Thyroid cartilage of larynx

• Innervation: Ventral rami of C1-3 spinal nerves (ansa cervicalis)

Sternothyroid m.

• Action: Elevation of hyoid bone

• Origin: Styloid process of temporal bone

• Insertion: Hyoid bone

• Innervation: Facial nerve (CN VII)

Stylohyoid m.

• Action: Elevation of mandible (e.g., closing mouth), Retraction of mandible

• Origin: Temporal fossa (formed by parts of frontal, parietal, sphenoid (greater wing), and temporal bones)

• Insertion: Mandible (coronoid process and ramus)

• Innervation: Trigeminal nerve (mandibular division - CN V3)

Temporalis m.

• Action: Elevation of larynx, Depression of hyoid bone

• Origin: Thyroid cartilage of larynx

• Insertion: Hyoid bone

• Innervation: Ventral ramus of C1 spinal nerve

Thyrohyoid m.

• Action: Superior fibers: elevation of scapula; superior rotation of scapula (glenoid cavity directed superiorly), Middle fibers: retraction (adduction) of scapula, Inferior fibers: depression of scapula

• Origin: Occipital bone (superior nuchal line), Nuchal ligament, Vertebra prominens (spinous process of C7 vertebra), Spinous processes of T1-12 vertebrae

• Insertion: Clavicle (lateral), Scapula (spine and acromion)

• Innervation: Accessory nerve (CN XI)

Trapezius m.

• Action: Protraction (abduction) of scapula, Superior rotation of scapula (directs glenoid cavity superiorly), Stabilizes scapula (holds it against thoracic wall)

• Origin: Ribs 1-9

• Insertion: Scapula (medial border)

• Innervation: Long thoracic nerve

Serratus anterior m.

• Action: Dome of diaphragm flattens during inspiration, Contraction increases vertical dimension of thoracic cavity

• Origin: Sternal part (not always present): xiphoid process, Costal part: ribs 5-10 and their costal cartilage, Lumbar part: arcuate ligaments and L1-3 vertebral bodies

• Insertion: Central tendon

• Innervation: Phrenic nerve

Diaphragm

• Action: Muscles of respiration

• Location: Found between ribs 1-11

• Innervation: Intercostal nerves (ventral rami of T1-11 spinal nerves)

Intercostal mm.

• Action: Superior fibers: elevation of scapula; superior rotation of scapula (glenoid cavity directed superiorly), Middle fibers: retraction (adduction) of scapula, Inferior fibers: depression of scapula

• Origin: Occipital bone (superior nuchal line), Nuchal ligament, Vertebra prominens (spinous process of C7 vertebra), Spinous processes of T1-12 vertebrae

• Insertion: Clavicle (lateral), Scapula (spine and acromion)

• Innervation: Accessory nerve (CN XI)

Trapezius m.

• Action: Unilateral: lateral flexion of vertebral column, Bilateral: extension of vertebral column, Depression of ribs

• Origin: Common origin and ribs

• Insertion: Ribs, Transverse processes (cervical)

• Innervation: Dorsal rami of spinal nerves

Iliocostalis part of erector spinae m.

• Action: Unilateral: lateral flexion of vertebral column and rotation of head to same side, Bilateral: extension of vertebral column and head, Depresses ribs

• Origin: Iliac crest, Dorsal sacrum, Sacral and lumbar spinous processes, Supraspinous ligament

• Insertion: Transverse processes (cervical and thoracic), ribs, and mastoid process

• Innervation: Dorsal rami of spinal nerves

Longissimus part of erector spinae m.

• Action: Retraction (adduction) of scapula, Elevation of scapula

• Origin: Spinous processes of T2-5 vertebrae

• Insertion: Scapula (medial border)

• Innervation: Dorsal scapular nerve

Rhomboid major m.

• Action: Retraction (adduction) of scapula, Elevation of scapula

• Origin: Spinous processes of C7-T1 vertebrae

• Insertion: Scapula (medial border)

• Innervation: Dorsal scapular nerve

Rhomboid minor m.

• Action: Unilateral: rotation of head to opposite side, Bilateral: extension of head and neck

• Origin: Transverse processes of C7-T6 vertebrae

• Insertion: Occipital bone

• Innervation: Cervical spinal nerves (dorsal rami)

Semispinalis capitis m.

• Action: Unilateral: lateral flexion of vertebral column, Bilateral: extension of vertebral column

• Origin: Spinous processes and nuchal ligament

• Insertion: Spinous processes (cervical and thoracic) and occipital bone

• Innervation: Dorsal rami of spinal nerves

Spinalis part of erector spinae m.

• Action: Superior fibers: elevation of scapula; superior rotation of scapula (glenoid cavity directed superiorly), Middle fibers: retraction (adduction) of scapula, Inferior fibers: depression of scapula

• Origin: Occipital bone (superior nuchal line), Nuchal ligament, Vertebra prominens (spinous process of C7 vertebra), Spinous processes of T1-12 vertebrae

• Insertion: Clavicle (lateral), Scapula (spine and acromion)

• Innervation: Accessory nerve (CN XI)

Trapezius m.

• Action: Unilateral: rotation of trunk, Bilateral: flexion of trunk (sit-ups), Compression of anterior abdominal wall and viscera (increases intra-abdominal pressure)

• Origin: Ribs and costal cartilages 5-12

• Insertion: Linea alba, Ilium (crest)

• Innervation: Ventral rami of T8-L1 spinal nerves

External abdominal oblique m.

• Action: Unilateral: rotation of trunk, Bilateral: flexion of trunk (sit-ups), Compression of anterior abdominal wall and viscera (increases intra-abdominal pressure)

• Origin: Inguinal ligament, Ilium (crest), Thoracolumbar fascia

• Insertion: Linea alba, Costal cartilages 7-10

• Innervation: Ventral rami of T8-L1 spinal nerves

Internal abdominal oblique

• Action: Unilateral: lateral flexion of trunk, Bilateral: extension of trunk, Fix/depress rib 12

• Origin: Ilium (crest)

• Insertion: Rib 12, L1-4 vertebrae (transverse processes)

• Innervation: Ventral rami of T12-L4 spinal nerves

Quadratus lumborum m.

• Action: Flexion of trunk (sit-ups), Compression of anterior abdominal wall

• Origin: Pubis (crest and symphysis)

• Insertion: Sternum (xiphoid process), Costal cartilages 5-7

• Innervation: Ventral rami of T7-12 spinal nerves

Rectus abdominis m.

• Action: Compression of anterior abdominal wall and viscera (increases intra-abdominal pressure)

• Origin: Ilium (crest), Inguinal ligament, Thoracolumbar fascia, Costal cartilages 7-12

• Insertion: Pubis (body), Linea alba, Sternum (xiphoid process)

• Innervation: Ventral rami of T8-L1 spinal nerves

Transversus abdominis m.

• Location: Neck, Between occipital bone and T1 vertebra

• Description: Seven individual vertebrae, Characteristic features include transverse foramen and bifid (split) spinous process on C3-C6

Cervical vertebra (holistic view)

• Location: Posterior pelvic wall, Lower back, inferior to S5 vertebra

• Description: Small, triangular bone, Consists of three to five, variably fused, poorly developed vertebrae

• Also known as: "Tailbone"

Coccyx

• Location: Lower back, Between T12 and S1 vertebrae

• Description: Five individual vertebrae, Characteristic features include large size, kidney bean-shaped body, and a thick, blunt spinous process

Lumbar vertebra

• Location: Lower back, Between L5 and Co1 vertebrae, Posterior wall of pelvis

• Description: Five fused vertebrae, Triangular bone wedged between hip bones

Sacrum

• Location: Vertebrae (posterior aspect)

• Description: Unpaired, posterior projection from midline of vertebral arch, Has characteristic thick, blunt form

Spinous process of lumbar vertebra (holistic view)

• Location: Trunk, Between C7 and L1 vertebrae

• Description: 12 individual vertebrae, Characteristic features include costal demifacets (or facets) for articulation with head of rib, spinous process slopes inferiorly, and heart-shaped vertebral body

Thoracic vertebra

• Location: Lateral aspect of cervical vertebra

• Description: Prominent, paired, laterally-directed process

• Comment: Provides attachment for intrinsic and extrinsic back muscles

Transverse process of cervical vertebra

• Location: Neck, Between occipital bone and T1 vertebra

• Description: Seven individual vertebrae, Characteristic features include transverse foramen and bifid (split) spinous process on C3-C6

Cervical vertebra

• Location: Vertebrae (posterior aspect)

• Description: Unpaired, posterior projection from midline of vertebral arch, Usually bifid

Spinous process of cervical vertebra

• Location: Cervical vertebra, Superior articular process

• Description: Smooth area

• Comment: Provides articulation between adjacent vertebrae

Superior articular facet of cervical vertebra

• Location: Cervical vertebra (superior aspect)

• Description: Paired process at junction of pedicle and lamina, Has superiorly-directed articular facet (smooth area)

Superior articular process of cervical vertebra

• Location: Cervical vertebra, Transverse process

• Description: Foramen in each transverse process

• Comment: Vertebral artery passes through transverse foramina of C1-6 vertebrae (not through C7 transverse foramen)

Transverse foramen of cervical vertebra

• Location: Neck, Between occipital bone and axis (C2 vertebra)

• Description: Ring-shaped vertebra, Characteristic features include transverse foramen, Lacks vertebral body, spinous process, or lamina

• Also known as: C1 vertebra

Atlas

• Location: Atlas (C1 vertebra), Superior aspect of lateral mass

• Description: Superior-facing, smooth concavity, Receives corresponding occipital condyle of occipital bone

• Function: Part of atlanto-occipital joint

• Comment: Adapted for "nodding" movements of head

Superior articular facet of atlas

• Location: Atlas, Transverse process

• Description: Foramen in each transverse process of atlas

• Comment: Vertebral artery passes through transverse foramina of C1-6 vertebrae (not through C7 transverse foramen), Atlas also known as C1 vertebra

Transverse foramen of atlas

• Location: Atlas

• Description: Large foramen formed by anterior and posterior arches of atlas

• Comment: Vertebral canal formed by combined vertebral foramina, Contains spinal cord, meninges, spinal nerve roots, blood vessels, and fat, Atlas also known as C1 vertebra

Vertebral foramen of atlas

• Location: Neck, Between atlas (C1 vertebra) and C3 vertebra

• Description: Characteristic features include transverse foramen, bifid (split) spinous process, and dens (prominent superior projection from body)

• Also known as: C2 vertebra

Axis (C2 vertebra)

• Location: Axis (anterior aspect)

• Description: Has superior projection (dens), Attached to pedicle on either side, Separated from body of C3 by intervertebral disc

Body of axis

• Location: Axis (C2 vertebra)

• Description: Prominent, finger-like projection from superior aspect of body of axis (C2 vertebra)

• Also known as: Odontoid process

• Comment: Represents body of atlas (C1 vertebra), No other vertebra has a dens

Dens

• Location: Axis (posterior)

• Description: Unpaired posterior midline projection from vertebral arch, Process has characteristic bifid (split) form

Spinous process of axis

• Location: Axis, Superior articular process

• Description: Smooth area

Superior articular facet of axis

• Location: Thoracic vertebra (anterior aspect)

• Description: Progressive increase in size from superior to inferior, Contains paired costal demifacets on each side, Attached to pedicle on either side

• Comment: Supports body weight

Body of thoracic vertebra

• Location: T1-T12 vertebrae

• Description: Paired plates that form dorsal wall of vertebral canal, Connects pedicle to spinous process

Lamina of thoracic vertebra

• Location: T1-T12 vertebrae

• Description: Short, thick pillar, Connects vertebral body to lamina on each side

Pedicle of thoracic vertebra

• Location: Thoracic vertebra

• Description: Unpaired posterior midline projection from vertebral arch, Has characteristic long, slender form, Processes of inferior thoracic vertebrae directed inferiorly

Spinous process of thoracic vertebra

• Location: Thoracic vertebra (superior aspect)

• Description: Paired process at junction of pedicle and lamina, Has posteriorly-directed articular facet (smooth area

Superior articular process of thoracic vertebra

• Location: Thoracic vertebral body (lateral aspect), At junction with pedicle

• Description: Smooth area

Superior costal facet of thoracic vertebra

• Location: Thoracic vertebra 1-10, Transverse process

• Description: Smooth area

Transverse costal facet of thoracic vertebra

• Location: Thoracic vertebra

• Description: Large foramen formed by vertebral arch and posterior aspect of vertebral body

Vertebral foramen of thoracic vertebra

• Location: Vertebra (anterior aspect)

• Description: Oval ventral portion, Forms ventral wall of vertebral canal

• Comment: Supports body weight

Body of lumbar vertebra

• Location: Lumbar vertebra, At junction of pedicles and laminae

• Description: Paired processes, Has laterally-directed articular facet (smooth area)

Inferior articular process of lumbar vertebra

• Location: L1-L5 vertebrae

• Description: Paired plate that forms dorsal wall of vertebral canal, Connects pedicle to spinous process

Lamina of lumbar vertebra

• Location: Lower back, Between T12 and S1 vertebrae

• Description: Five individual vertebrae, Characteristic features include large size, kidney bean-shaped body, and a thick, blunt spinous process

Lumbar vertebra

• Location: Vertebrae L1-5 (lateral aspect)

• Description: Short, thick pillar, Connects vertebral body to lamina on each side

• Comment: Adjacent pedicles contribute to each intervertebral foramen

Pedicle of lumbar vertebra

Location: Vertebrae (posterior aspect)

Description: Unpaired, posterior projection from midline of vertebral arch, Has characteristic thick, blunt form

Spinous process of lumbar vertebra

• Location: Lumbar vertebra (superior aspect)

• Description: Paired process at junction of pedicle and lamina, Has medially-directed articular facet (smooth area)

Superior articular process of lumbar vertebra

• Location: Lateral aspect of lumbar vertebra

• Description: Prominent, paired, laterally-directed process

• Comment: Provides attachment for intrinsic back muscles and ligaments

Transverse process of lumbar vertebra

• Location: Lumbar vertebra

• Description: Large foramen formed by vertebral arch and posterior aspect of vertebral body

Vertebral foramen of lumbar vertebra

• Location: Sacrum (base)

• Description: Paired, wing-like, laterally projecting masses, Modification of S1 vertebral transverse process

• Comment: Base of sacrum is superior surface of S1 vertebra, Latin: ala = wing

Ala of sacrum

• Location: Sacrum (anterior surface)

• Description: Four pairs of openings, Communicate with sacral canal

• Function: Transmit ventral rami of S1-4 spinal nerves

Anterior sacral foramen

• Location: Sacrum (lateral surface)

• Description: Paired, elongated, ear-shaped, lateral surface of sacrum

• Function: Articulation with ilium (synovial sacroiliac joint)

• Comment: Latin: auris = ear

Auricular surface of sacrum

• Location: Posterior pelvic wall, Lower back, inferior to S5 vertebra

• Description: Small, triangular bone, Consists of three to five, variably fused, poorly developed vertebrae

• Also known as: "Tailbone"

• Comment: Rudiment of the tail in other vertebrates

Coccyx (Tailbone)

• Location: Sacrum, Along dorsal midline

• Description: Prominent, interrupted longitudinal ridges, Formed by three or four spinous tubercles, Represent fused spinous processes of S1-3(4) vertebrae

• Function: Attachment for aponeurosis of erector spinae muscles

Median sacral crest

• Location: Sacrum (posterior surface)

• Description: Four pairs of openings, Communicate with sacral canal

• Function: Transmit dorsal rami of S1-4 spinal nerves

Posterior sacral foramen

• Location: Sacrum (anterior)

• Description: Prominent, projecting edge of base of sacrum formed by superior border of S1 vertebral body. Forms posterior part of pelvic brim at midline

• Comment: Sacral promontory is landmark for establishing female pelvic dimensions

Promontory of sacrum

• Location: Sacrum (posterior surface)

• Description: Arched opening, Communicates with sacral canal

• Function: Transmits filum terminale

Sacral hiatus

Location: Lower back, Between L5 and Co1 vertebrae, Posterior wall of pelvis

Description: Five fused vertebrae, Triangular bone wedged between hip bones

Sacrum (posterior view)

• Location: Sacrum (base)

• Description: Paired, superiorly-directed process, Has articular facet

• Function: Articulation with inferior articular process of L5 vertebra

• Comment: Base of sacrum is superior surface of S1 vertebra

Superior articular process of sacrum