Trunk + Back Muscle

Muscles of the Trunk: how many compartment?

1. Posterior (back) compartment

2. Anterior chest compartment

3. Anterolateral abdomen compartment

Posterior compartment: muscles of the back exist in how many layers?

• Back muscles exist in 3 layers with largely separate functions

Superficial layer: mostly move scapula and shoulder girdle

Intermediate layer: respiratory

Deep layer: move/stabilize spinal column

Superficial muscles of the back

- Trapezius, Latissimus dorsi are most superficial

• Then Levator scapulae, Rhomboid major, Rhomboid minor

Trapezius: Orgin and Insertion

• Origin: Occipital bone, ligamentum nuchae, spinous processes of thoracic vertebrae, thoracolumbar fascia

• Insertion: clavicle, and acromion process and spine of scapula

Trapezius: Function

Superior fibers

• Draws scapula superomedially (elevation &

retraction)

• Extension of head and neck

• (Unilateral) lateral flexion/rotation of head and

neck

Middle fibers

• Draws scapula medially, rotates as arm is raised

Inferior fibers

• Draws scapula inferomedially (depression)

Latissimus Dorsi: Orgin and Insertion

• Origin: spinous processes of lower thoracic and lumber vertebrae,

thoracolumbar fascia, ribs 8-12

• Insertion: bicipital/intertubercular groove of humerus

Latissimus Dorsi: Function

Arm/shoulder adduction & extension, some medial/internal rotation of arm

Levator Scapula: OI

• Origin: transverse processes of C1-C4

• Insertion: superior angle and medial border of scapula

Levator Scapula: F

Elevate scapula, downward rotation of scapula, lateral flexion of neck

Rhomboid Minor: OI

• Origin: C7-T1 spinous process

• Insertion: medial border of scapula

Rhomboid Minor: F

Retraction, elevation of scapula

Rhomboid Major: OI

• Origin:T2-T6 spinous process

• Insertion: medial border of scapula

Rhomboid Major: F

Retraction, elevation, downward rotation of scapula

Intermediate muscles of the back

1. Serratus Posterior Superior

2. Serratus Posterior Inferior

Serratus Posterior Superior

• Origin: Ligamentum nuchae, C7-T3 spinous process

• Insertion: superior border of ribs 2-5

• Function: Elevate the ribs

Serratus Posterior Inferior

• Origin: T11-T12 spinous process

• Insertion: Inferior border of ribs 9-12

• Function? Depress the ribs

Deep muscles of the back

1. Splenius Capitus

2. Quadratus Lumborum

3. Erector spinae group

• Iliocostalis

• Longissimus

• Spinalis

Splenius capitis

• Origin: C7-T3 & nuchal ligament

• Insertion: occipital bone, mastoid process of temporal bone

• Function:

Unilateral: lateral flexion and rotation of head

Bilateral: extension of neck/head

Quadratus Lumborum

• Origin: iliac crest

• Insertion: inferior border of rib 12, transverse processes of vertebrae L1-L4

• Function:

Unilateral: lateral flexion of trunk

Bilateral: trunk extension

Erector spinae muscles

• are a group of muscles: Iliocostalis, Longissimus, Spinalis

• Origin & insertion: (in general) originate from the lumbar & lower thoracic regions and insert onto the upper thoracic and cervical regions

• Function:

Extensors of the spine, maintain posture and balance

Movement of the vertebral column

Vertebral column largely moved DIRECTLY by:

• Erector spinae group

• Small inter-vertebral muscles (not discussed)

• Low back muscles (e.g., Quadratus Lumborum)

Vertebral column moved INDIRECTLY by:

• Abdominal muscles

• Pectoral girdle muscles

• Pelvic girdle muscles

• Lower limb muscles

Pectoralis Major

• Origin: cartilages of ribs 1-6, sternum, inferior medial portion of clavicle

• Insertion: greater tubercle, intertubercular groove of humerus

• Function: Shoulder flexion, adduction, medial rotation

Pectoralis Minor

• Origin: anterior & superior surface of ribs 3-5

• Insertion: coracoid process of scapula

• Function:

Scapular protraction, superior rotation of scapula

Serratus Anterior

• Origin: anterior & superior surface of ribs 1-8

• Insertion: anterior surface of scapula's medial border, superior angle, inferior angle

• Function:

Scapular protraction

MOVEMENT of the back

Intercostal muscles

3 layers of muscles between the ribs:

• External Intercostals

• Internal Intercostals

• Innermost Intercostals

• Function:

External: elevate ribs (breathing in)

Internal, innermost: depress ribs (breathing out)

Other breathing muscles

Anterior (chest) compartment

Anterolateral abdomen compartment

External and Internal Abdominal Obliques

• Attachment points: (generally) ribs, aponeurosis, thoracolumbar fascia

Linea alba, anterior half of iliac crest, pubis, inguinal ligament

• Function:

Unilateral: Trunk lateral flexion, trunk rotation

Bilateral: Trunk flexion

Aponeurosis (Rectus Sheath)

• An extension of the tendons of the abdominal muscles

• Its function is to protect the contents it encloses

Linea Alba

• Attachment site for multiple abdomen muscles

• A thin band of connective tissue running from from the xyphoid process to the pubic symphysis

• It separates the left and right sides of your rectus abdominis (six-pack abs)

Diastasis recti

• Increased distance between left and right rectus abdominus muscles

• Cause by weakness in ligaments and muscles of abdomen due to

stretching during pregnancy

lnguinal ligament

• Defines the lower abdomen, before the creases of the thigh

• Separates trunk from leg

• Anchors the abdominal muscles to the hips

Rectus Abdominus

• Origin: pubic symphysis

• Insertion: xiphoid process, costal cartilages of ribs 5-7

• Function:

Trunk flexion

Transverse Abdominis

• Origin: costal cartilages of ribs 7-12, thoracolumbar fascia, iliac crest

• Insertion: aponeurosis, Linea alba, pubis

• Function:

Unilateral: Trunk rotation

Bilateral: compresses organs, posture, expiration