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 WALLThe anterior abdominal wall is composed of skin, fascia and 4 pairs of muscles.

Tendinous Intersections – bands of connective tissue that divides the rectus abdominisLinea Alba – tough fibrous band extending from xiphoid process to pubic symphysis

Rectus AbdominisOrigin – Pubis and Pubic SymphysisInsertion – Costal Cartilage and Xiphoid ProcessAction – Flexes vertebral column and compresses abdomen

Tendinous Intersections

Linea Alba

External ObliqueOrigin – Lower 8 ribsInsertion – Crest of Ilium and Linea AlbaAction – Compresses abdomen, flexes vertebral column. Singularly rotates vertebral column

Internal ObliqueOrigin – Ilium, inguinal ligamentInsertion – Costal Cartilage and linea albaAction - Compresses abdomen, flexes vertebral column. Singularly rotates vertebral column

Transverse AbdominisOrigin – Ilium, inguinal ligament, lumbar fascia, and costal cartilageInsertion – Xiphoid Process, linea alba and pubisAction – Compress Abdomen

Muscles Used in BreathingThese 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

DiaphragmOrigin – xiphoid process, costal cartilage and lumbar vertebraeInsertion – central tendonAction – increases the vertical dimension of the thoracic cavity resulting in inhalation.

External and Internal Intercostals

Origin – ribsInsertion – ribsAction:

External – increases the anteroposterior and lateral dimensions of thoracic cage resulting in inhalationInternal – 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 minorOrigin – Ribs 3-5Insertion – ScapulaAction – depresses scapula, moves it laterally and forward

Serratus AnteriorOrigin – Upper 8 or 9 ribsInsertion – ScapulaAction – Moves scapula laterally and forward.

AKA: “the boxer’s muscle” because it is important in horizontal arm movements like punching.

TrapeziusOrigin – occipital bone, spines of C7 and thoracic vertebraeInsertion – clavicle and scapulaAction – Elevates clavicle, moves scapula medially

Levator ScapulaeOrigin – C1 – C5Insertion – ScapulaAction – elevates scapula

Rhomboid MajorOrigin – Spines of T2-T5Insertion – ScapulaAction – Elevates scapula, moves it medially