Doctors Network: Muscles of trunk

Muscles of back

Superficial layer:

trapezius

latissimus dorsi

levator scapulae

rhomboid muscle

Deep layer:

eretor spinae

Superficial group

Trapezius

a large, triangular m. lying on the back of the neck and thorax;

Origin:

external occipital protuberance, superior nuchal line, ligamentum nuchae, the spinous processes of 7th cervical vertebrae and all thoracic vertebrae;

Insertion:

lateral 1/3 of clavicle, acromion and spine of scapula.

Action:

raises, descends, and rotates the scapula and extends the head.

superficial group

Latissimus Dorsi

It is a largest and triangular m. lying the back and lateral wall of thorax;

Origins: the spinous processes of lower 6 thoracic vertebrae and all lumbar vertebrae;

Insertion: inserted into the floor of the intertubercular sulcus

Action:

Extend, adduct， and rotate the shoulder joint medially

superficial group

Levator scapulae

Origin : the transverse processes of the upper 4 cervical vertebrae;

Insertion : superior angle of scapula.

Action : raise the scapula.

rhomboideus

Lies deep to the trapezius. Adduct the scapular by pulling it medially toward the vertebral column.

The deep group

Position :

It lies in the vertebral groove on each side of vertebral spines.

Action : extend the spinal column and head.

Thoracolumbar fascia

Wrap the surrounding of erector muscle of spine. It can be divided into three layers：

Superficial layer：posterior to the erector spinae；

Middle layer ：separate the erector spinae and the quadratus lumborum

Deep layer：anterior to the quadratus lumborum

Muscles of thorax

Extrinsic muscles

Pectoralis major

Pectoralis minor

Serratus anterior

Pectoralis major

Origin: medial half of clavicle, sternum, 1th-6th costal cartilages.

Insertion: crest of greater tubercle of humerus.

Action: flexes, adducts and rotates arm medially; arm fixed, elevates trunk; elevates ribs 1-6, aidding in forced inspiration.

Pectoralis minor

Deep to the pectoralis major

Origin: 3rd-5th ribs

Insertion: coracoid process of scapula

Action:

Draw the scapula forwards and downwards, when the scapula is fixed it helps the inspiration (by elevation the ribs)

Serratus anterior

It overlies the lateral wall of thorax

Origin: external surfaces of the upper 8~9 ribs

Insertion: medial border of scapula

Action: holds the scapula against the chest wall；Pulls the scapula forwards in throwing and pushing.

Intrinsic muscles

External Intercostale muscles

Origin: lower border of rib

Insertion: upper border of rib below origin

external intercostals membrane.

Action: elevate ribs adding in forced inspiration

Internal Intercostale muscles

Origin: upper border of rib；

Insertion: lower border of rib above origin

Replaced posteriorly by internal intercostals membrane.

Action: depress ribs for forced expiration

Diaphragm

Position and division:

dome-shaped between thorax and abdomen, consists of

Central tendon

muscular part

Sternal part:

Costal part:

Lumbar part: arises by left and right crus from upper 2-3 lumbar vertebrae

Insertion: central tendon

Openings of diaphragm:

Aortic hiatus

at the level of 12th thoracic vertebra, the thoracic aorta and thoracic duct pass through it.

Esophageal hiatus

at the level of 10th thoracic vertebra, the esophagus and vagus n. pass throught it.

Vena caval foramen

at the level of 8th thoracic vertebra, inferior vena cava through it.

Action:

Contraction: the dome moving downward, increases the volume of thoracic cavity which results in inspiration.

Relaxation: the dome returns to the former position, reduces the volume of the thoracic cavity, resulting in expiration.

Weak areas:

triangular spaces without muscular tissue

Lumbocostal triangle: between costal and lumbar parts.

Sternocostal triangle: between costal and sternal parts.

Muscles of abdomen

Anterolateral group

Obliquus externus abdominis

Obliquus internus abdominis

Transversus abdominis

Rectus abdominis

Obliquus externus abdominis

Origin:

Arises from the lower 8 ribs, and the muscular fibers run obliquely from the superolateal

to the inferomedial, the anterior part of the m. change gradually into aponeurosis, which pass over the rectus Abdominis;

Insertion: Linea alba

Structures

formed by aponeurosis of this m. include：

Inguinal ligament

Superficial inguinal ring － triangular-shaped hiatus above pubic tubercle

Lacunar ligament

Obliquus internus abdominis

Origin: thoracolumbar fascia, iliac crest and the lateral half of the ingunal lig.

Insertion: Linea alba

The muscular fibers run upwards and forwards, and become the aponeurosis close the lateral border of the rectus abdominis. Its aponeurosis divided into two layers to inclose the rectus abdominis.

Transversels abdominis:

is the deepest one of the three flat abdominal m.

Origin:

it arises from the costal cartilages of the lower 6 ribs，the thoracolumbar fascia , the iliac crest and the lateral 1/3 of the ingunal lig.

Insertion: Linea alba

The muscular fibers run transversly, and pass deep to rectus abdominis.

Inguinal falx (conjoined tendon) :

is a common aponeurosis joined by obliquus internus abdominis and transverse abdominis, it turns downwards to insert the pubic crest and pecten pubis.

Cremaster : around the spermatic cord and testis

Rectus abdominis:

is a long, broad, strap m. and the principal vertical one of the anterior abdominal wall.

Origin: it arises from pubic symphysis and pubic crest.

Insertion: xiphoid process and 5th to 7th costal cartilages.

The two muscles are separated by the linea alba and enclosed in the rectus sheath.

The Sheath of rectus abdominis

Anterior layer:

formed by the aponeurosis of obliquus externus abdominis ； anterior leaf of aponeurosis

of obliquus internus abdominis

Posterior layer: formed byposterion leaf of aponeurosis of obliquus internusabdominis;

aponeurosis of transverses abdominis

The Sheath of rectus abdominis

arcuate line or semicircular line

at about 4-5cm below the umbilicus, the lower free border of the posterior layer of the sheath present arcuated.

Below this line the rectus abdominis in contact with transverse fascia directly.

Linea alba

tendinous raphe between right and left rectus abdominis from xiphoid process to pubic symphysis.

The functions of the four pairs of muscles

Support and protect the abdominal viscera

Maintain and increase intra-abdominal pressure, aid in vomiting, coughing, sneezing, defecation, urination and childbirth.

Flex, lateral flex, and rotate vertebral column

Inguinal canal

Position:

oblique passage about 4cm long, and passes downwards and medially, it lies parallel to, and immediately above medial half of inguinal lig. It has two openings and four walls.