Axial Skeleton Part 2

cervical vertebrae (most mobile)

upper cervical: C1 (atlas) and C2 (axis)

lower cervical: C3 - C7

Cervical segment has most flexibility among all vertebral segments

neck moves 600 times/hour whether awake or sleep

movement includes flexion, extension, lateral flexion, and rotation

atlas

C1

has no vertebral body or spinous process

cradle occiput and transfer forces from occiput to lower cervical

pivot

atlas and axis form _____ joint, allows rotatory movement of the head

odontoid process of axis bone

acts as an axes around which atlas rotates

• kept on its place by transverse ligament of atlas

atlanto-occipital joint (cervical vertebrae)

mainly flexion/extension (nodding)

• around 10-30 degree

• some lateral flexion and rotation also available

atlanto-axial joint

flexion, extension, and lateral flexion are available but predominantly rotation (55-58% of total rotation)

• remaining 40% equally distributed among lower cervical vertebrae

lower cervical

flexion, extension, lateral flexion, and rotation

thoracic vertebrae (flexion is only in lower thoracic)

12 vertebrae, T1 and T12 are slightly different from other thoracic vertebrae

• vertebral body of thoracic vertebrae are wedge-shaped (posterior height is more than anterior) to provide kyphotic posture ,the peak of which occurs at T7

• less flexible and more stable than cervical region because of rib articulation and structure of spinous process

• all motions are possible

upper thoracic (T1-T6)

the flexion/extension ROM is extremely limited but free in lateral flexion and axial rotation

• no flexion component as ribs are attached to sternum

lower thoracic (T9-T12)

has increased amount of flexion/extension

• ribs are free flowing which is why it can move in all directions

lumbar vertebrae

5th lumbar is transitory and different from other lumbar vertebrae as it is wedge shaped (anterior height is more than posterior height)

• intervertebral disc between L5 and S1 is also wedge shaped

• this create lumbosacral angle, for most people it ranges between 21 to 4- degree with average around 30 degree

• an increased angle will result in lordosis and increases shearing stress lumbosacral joint

movements of lumbar vertebrae

all movements are available

• largest flexion is available at lumbosacral joint

• largest lateral flexion and rotation occurs between L2 and L3

sacral region (all on sacroilliac joing)

five sacral vertebrae fused to form triangular structure known as sacrum

• sacroiliac joint is weight bearing joint consisting of anteriorly synovial joint and posteriorly syndesmotic joint

• SI do permit motion but in extremely small amounts

nutation

movement of sacrum on innominate (pelvic and ilium) bones

pelvic tilt (anterior and posterior)

movement of innominate (pelvic and iliac) bones on sacrum

pelvic torsion

asymmetrical movement innominate bone

• one side of pelvis is moving, the other is fixed

muscles and movement of spinal column

moves in all 3 planes: flexion/extension, lateral flexion, and rotation

• the greatest amount of movement available at cervical and lumbar region

• movement are limited in thoracic region due to attachment of ribs

• extremely limited in upper thoracic (T1-T6), comparatively more mobile from T9-T12

• there are no movements at sacrum or coccyx

craniocervical/upper thoracic muslces

sternocleidomastoid

lumbopelvic/lower thoracic muscles

lateral: quadratus lumborum

anterior: abdominal muscles (4 muscles)

sternocleidomastoid

originates from two locations; the manubrium of the sternum and medial 1/3 of clavical

inserts at the mastoid process of the temporal bone of the skull

action of the sternocleidomastoid

bilateral:

• cervical flexion

unilateral:

• ipsilateral lateral flexor

• contralateral rotator

erector spinae

common action: extension of the spine

external oblique

largest and the most superficial of the three flat muscles of the lateral anterior abdomen

8 digitations (each from the external surfaces and inferior borders) from the 5th to 12th ribs

• attaches to the anterior half of the outer lip of the iliac crest and linea alba

external oblique action

bilateral:

• assists in trunk flexion

unilateral:

• ipsilateral lateral flexion and contralateral rotation

internal oblique

perpendicular to the external oblique muscle

• origin: the thoracolumbar fascia of the lower back, the anterior 2/3 of the iliac crest and the inguinal ligament

• the muscle fibers run superior-medialy to insert on the inferior borders of the 10th through 12th ribs and the linea alba

internal oblique action

bilateral:

• helps in flexion

unilateral:

• ipsilateral lateral flexion and ipsilateral rotation

rectus abdominis

paired muscle running vertically one ach side of the anterior wall of the human abdomen, vertically separated by a connective tissue called the linea alba

whole muscle is enveloped within a fibrous structure known as rectus sheath (internal, external, transverse)

• origin: pubic symphysis, pubic crest, and pubic tubercle

• insertion: xiphoid process of sternum and costal cartilages of ribs V to VII

rectus abdominis action

flexion of spine

transverse abdominis

origin: inguinal ligament, iliac crest, thoraco-lumber fascia and 7-12th costal cartilage

insertion: on xiphoid process and linea alba

function:

• maintaining abdominal wall tension

• stabilize the vertebral column

• increase in intraabdominal pressure → decompress intravertebral disc

“natural belt”

one of the most significant muscles → isometric stabilizes

the quadratus lumborum

“hip hiking muscle”

• muscle of the posterior abdominal wall. deepest abdominal muscle but considered a back muscle

• originates from iliolumbar ligament and the internal lip of the iliac crest and inserted at last rib and transverse processes of lumbar vertebrae

action of the quadratus lumborum

bilateral:

• depression of thoracic rib cage

unilateral:

• lateral flexion of vertebral column