Back Muscles and Movement

• The neck and back's musculoskeletal axis provides trunk support comprised of bones (vertebrae), muscles, and spinal nerves that connect body regions and protect the nervous system

Back Movements

• Extrinsic muscles move the upper limbs and ribs
• Intrinsic muscles maintain posture and move the vertebral column
• Movements include flexion (anterior bending), extension, lateral flexion, and rotation
• Muscles are arranged in three layers: extrinsic muscles, intermediate muscles, and intrinsic muscles
• Extrinsic muscles are superficial and aid upper limb movement
• Intermediate muscles aid movement of the thoracic wall in respiration
• Intrinsic muscles are deep and provide support and movement for the vertebral column and head

Superficial Layer

• The superficial layer facilitates upper limb movement via the shoulder, consisting of two layers of muscles

First Layer

• Includes the trapezius and latissimus dorsi:

Trapezius

• Originates from the superior nuchal line, ligamentum nuchae, and spinous processes of C7-T12
• It inserts on the lateral 1/3rd of the clavicle, acromion process, and superior border of the spine of the scapula
• Acts to retract, laterally rotate, elevate, and depress the scapula

Latissimus Dorsi

• Originates from the spinous processes of T7-L5, sacral iliac crests, and inferior four ribs (via thoracolumbar fascia)
• Insertion occurs at the intertubercular sulcus of the humerus
• Acts to extend, adduct, and medially rotate the arm at the shoulder, drawing the arm inferiorly and posteriorly

Second Layer

• Includes the rhomboid major, rhomboid minor, and levator scapulae:

Rhomboid Major

• Originates from the spinous processes of T2-T5
• The insertion is on the medial border of the scapula, inferior to the spine
• Stabilizes, elevates, adducts, and downwardly rotates the scapula

Rhomboid Minor

• Originates from the spinous processes of C7-T1
• Insertion on the medial border of the scapula, superior to the spine
• Stabilizes, elevates, adducts, and downwardly rotates the scapula

Levator Scapulae

• Originates from the transverse processes of C1-C4
• Insertion is on the superior medial border of the scapula
• Elevates and downwardly rotates the scapula

Intermediate Layer

• Muscles consist of two thin muscular sheets in the superior and inferior regions of the back, located immediately deep to the superficial group
• It is involved in movements of the thoracic cage
• Includes serratus posterior superior and serratus posterior inferior muscles

Serratus Posterior Superior

• Originates from the lower part of the ligamentum nuchae and spinous processes of C7-T3
• Insertion occurs on the superior border of ribs 2-5 posteriorly
• Elevates ribs 2-5

Serratus Posterior Inferior

• Originates from the spinous processes of T11-L3
• Insertion occurs on the inferior border of ribs 9-12 posteriorly
• Depresses ribs 9-12

Deep Intrinsic Muscles

• The muscles extend from the pelvis to the skull, keeping the body erect, and are arranged in three layers

Superficial Layer: Spinotransversalis

• Transverse FROM the spine
• These muscles act to extend the neck
• Includes the splenius capitis and splenius cervicis.

Splenius Capitis

• Originates from the nuchal ligament and spinous processes of C7-T4
• Insertion on the occipital bone and mastoid process

Splenius Cervicis

• Originates from the spinous processes of T3-T6
• Insertion on the transverse process of C2

Intermediate Layer: Erector Spinae Muscles

• Action bilaterally extends the vertebral column and the head
• Action unilaterally, lateral flexion of vertebral column
• Consists of three muscles: iliocostalis, longissimus, and spinalis

Iliocostalis

• It is the lateral intermediate part of deep layer
• Originates from the iliac crest/ribs
• Insertion is on the posterior angles of the ribs

Longissimus

• Origin occurs on the transverse processes of thoracic and lumbar vertebrae
• Insertion is on the cervical vertebrae and mastoid process

Spinalis

• Occurs medially within the intermediate part of deep layer
• Originates from the ligamentum nuchae, spinous processes of C7 and T10-L2
• Insertion occurs on the spinous processes of superior vertebrae and the occipital bone

Deep Layer: Transversospinalis

• Transverse TOWARD the spine
• Consists of three muscles: semispinalis, multifidus, and rotatores

Semispinalis

• Extends and contralaterally rotates the head and vertebral column
• Originates from the transverse processes of C4-T10
• Insertion occurs on the spinous processes of C1-T4 and the midline of the skull between the nuchal lines

Multifidus

• Stabilizes the vertebral column
• Originates from the sacrum and posterior ilium, transverse processes of C4-C7, and thoracic/lumbar vertebrae
• Insertion is on the spinous processes of 2-4 vertebrae above

Rotatores

• Stabilizes the vertebral column
• Originates from the transverse processes of all vertebrae
• Insertion occurs on the laminae and spinous processes of vertebrae directly above

Overview of Layers and Muscles

• Superficial layer contains trapezius, latissimus dorsi, rhomboid major/minor, and levator scapulae
• Intermediate layer contains serratus posterior superior/inferior
• Deep layer contains splenius capitis/cervicis (superficial), iliocostalis/longissimus/spinalis (intermediate), and multifidus/semispinalis/rotatores (deep)

Additional Muscles

• Quadratus lumborum and psoas major are functionally significant in the back

Quadratus Lumborum

• Part of the abdominal wall
• Originates from the iliac crest and iliolumbar ligament
• Inserts on the inferior border of the 12th rib and L1-L4 transverse processes
• Unilateral action: lateral flexion of the lumbar spine, Bilateral action: extension of lumbar vertebraea

Psoas Major

• Arises on the transverse processes of lumbar vertebrae
• Inserts on the lesser trochanter of the femur
• Flexes the trunk on the hip

Thoracolumbar Fascia

• It is a layer of dense fascia that covers the muscle
• It is prominent in the sacral, lumbar, and thoracic regions
• Provides attachment for upper limb and abdominal wall muscles
• A tough sheath around back muscles with 3 layers
• Posterior is posterior to erector spinae muscles, attaches mainly to lumbar/thoracic spinous processes & medial sacral crest
• Middle & anterior are anterior & posterior to quadratus lumborum, attaching to transverse processes of lumbar vertebrae