Principle Skeletal Muscles 2
Muscles that act on the abdominal
wall, muscles used in breathing
and muscles that move the
pectoral girdle
MUSCLES THAT ACT ON THE
ANTERIOR ABDOMINAL WALL
The anterior abdominal wall is
composed of skin, fascia and 4 pairs of
muscles.
Tendinous Intersections – bands of
connective tissue that divides the rectus
abdominis
Linea Alba – tough fibrous band extending
from xiphoid process to pubic symphysis
Rectus Abdominis
Origin – Pubis and Pubic Symphysis
Insertion – Costal Cartilage and Xiphoid
Process
Action – Flexes vertebral column and
compresses abdomen
Linea Alba
Tendinous Intersections
External Oblique
Origin – Lower 8 ribs
Insertion – Crest of Ilium and Linea
Alba
Action – Compresses abdomen, flexes
vertebral column. Singularly rotates
vertebral column
Internal Oblique
Origin – Ilium, inguinal ligament
Insertion – Costal Cartilage and linea
alba
Action - Compresses abdomen, flexes
vertebral column. Singularly rotates
vertebral column
Transverse Abdominis
Origin – Ilium, inguinal ligament,
lumbar fascia, and costal cartilage
Insertion – Xiphoid Process, linea alba
and pubis
Action – Compress Abdomen
Muscles Used in Breathing
These muscles alter the size of the
thoracic cavity so that breathing can
occur. Inhalation occurs when the
thoracic cavity increases in size and
exhalation occurs when the thoracic
cavity decreases in size
Diaphragm
Origin – xiphoid process, costal
cartilage and lumbar vertebrae
Insertion – central tendon
Action – increases the vertical
dimension of the thoracic cavity
resulting in inhalation.
External and Internal
Intercostals
Origin – ribs
Insertion – ribs
Action:
External – increases the anteroposterior
and lateral dimensions of thoracic cage
resulting in inhalation
Internal – decreases the antroposterior and
lateral dimensions resulting in forceful
exhalation
Muscles that Move the
Pectoral Girdle
These muscles are divided into anterior
(pectoralis minor and serratus anterior) and posterior
(trapezius, levator scapulae and rhomboid major) thoracic
muscles based on their location.
The main action of the muscles is to hold the
scapula in place so that is can function as a
stable origin for the muscles that move the
humerus
Pectoralis minor
Origin – Ribs 3-5
Insertion – Scapula
Action – depresses scapula, moves it
laterally and forward
Serratus Anterior
Origin – Upper 8 or 9 ribs
Insertion – Scapula
Action – Moves scapula laterally and
forward.
AKA: “the boxer’s muscle” because it is
important in horizontal arm movements like
punching.
Trapezius
Origin – occipital bone, spines of C7
and thoracic vertebrae
Insertion – clavicle and scapula
Action – Elevates clavicle, moves
scapula medially
Levator Scapulae
Origin – C1 – C5
Insertion – Scapula
Action – elevates scapula
Rhomboid Major
Origin – Spines of T2-T5
Insertion – Scapula
Action – Elevates scapula,
moves it medially