310
UNIT TWO
Erector spinae
muscles run longitudinally along the
back, with origins and insertions at many places on the axial
skeleton. These muscles extend and rotate the head and
maintain the erect position of the vertebral column. Erector
spinae can be subdivided into lateral, intermediate, and
medial groups (table 9.5).
Muscles That Move the Pectoral Girdle
The muscles that move the pectoral girdle are closely asso-
ciated with those that move the arm. A number of these
chest and shoulder muscles connect the scapula to nearby
bones and move the scapula upward, downward, forward,
and backward (
f
gs. 9.27, 9.28, 9.29
; reference plates 68, 69;
table 9.6
). Muscles that move the pectoral girdle include the
following:
Trapezius
Levator scapulae
Rhomboid major
Serratus anterior
Rhomboid minor
Pectoralis minor
the sternocleidomastoid on one side contracts, the face turns
to the opposite side. When both muscles contract, the head
bends toward the chest. If other muscles F
x the head in posi-
tion, the sternocleidomastoids can raise the sternum, aiding
forceful inhalation (see F
g. 9.28 and table 9.5).
The
splenius capitis
(sple
ne-us kap
ı
˘-tis) is a broad,
straplike muscle in the back of the neck. It connects the base
of the skull to the vertebrae in the neck and upper thorax.
A splenius capitis acting singly rotates the head and bends
it toward one side. Acting together, these muscles bring the
head into an upright position (see F
g. 9.26 and table 9.5).
The
semispinalis capitis
(sem
e-spi-na
lis kap
ı
˘-tis) is
a broad, sheetlike muscle extending upward from the verte-
brae in the neck and thorax to the occipital bone. It extends
the head, bends it to one side, or rotates it (see F
g. 9.26
and table 9.5).
The
quadratus lumborum
(kwod-ra
tus lum-bo
rum)
is located in the lumbar region. When the quadratus lum-
borum muscles on both sides contract the vertebral column
is extended. When the muscle on only one side contracts,
the vertebral column is fl
exed laterally.
TABLE
9.5
|
Muscles That Move the Head and Vertebral Column
Muscle
Origin
Insertion
Action
Nerve Supply
Sternocleidomastoid
Anterior surface of sternum and upper
surface of clavicle
Mastoid process of
temporal bone
Pulls head to one side, F
exes
neck or elevates sternum
Accessory, C2 and C3
cervical nerves
Splenius capitis
Spinous processes of lower cervical and
upper thoracic vertebrae
Occipital bone
Rotates head, bends head to
one side, or extends neck
Cervical nerves
Semispinalis capitis
Processes of lower cervical and upper
thoracic vertebrae
Occipital bone
Extends head, bends head to
one side, or rotates head
Cervical and thoracic
spinal nerves
Quadratus lumborum
Iliac crest
Upper lumbar vertebrae
and twelfth rib
Aids in breathing, extends lumbar
region of vertebral column
Thoracic and lumbar
spinal nerves
Erector spinae
(divides into three columns)
Iliocostalis (lateral) group
Iliocostalis lumborum
Iliac crest
Lower six ribs
Extends lumbar region of
vertebral column
Lumbar spinal nerves
Iliocostalis thoracis
Lower six ribs
Upper six ribs
Holds spine erect
Thoracic spinal nerves
Iliocostalis cervicis
Upper six ribs
±ourth through sixth
cervical vertebrae
Extends cervical region of
vertebral column
Cervical spinal nerves
Longissimus (intermediate) group
Longissimus thoracis
Lumbar vertebrae
Thoracic and upper lumbar
vertebrae and ribs 9 and 10
Extends thoracic region of
vertebral column
Spinal nerves
Longissimus cervicis
±ourth and ²
fth thoracic vertebrae
Second through sixth
cervical vertebrae
Extends cervical region of
vertebral column
Spinal nerves
Longissimus capitis
Upper thoracic and lower cervical
vertebrae
Mastoid process of
temporal bone
Extends and rotates head
Cervical spinal nerves
Spinalis (medial) group
Spinalis thoracis
Upper lumbar and lower thoracic vertebrae
Upper thoracic vertebrae
Extends vertebral column
Spinal nerves
Spinalis cervicis
Ligamentum nuchae and seventh cervical
vertebra
Axis
Extends vertebral column
Spinal nerves
Spinalis capitis
Upper thoracic and lower cervical vertebrae
Occipital bone
Extends vertebral column
Spinal nerves
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