Vertebral Column Muscles: Intrinsic

• The vertebral column, also known as the spine, is a complex structure composed of individual bones called vertebrae, separated by intervertebral discs

• These components are held together and moved by numerous muscles, which are essential for posture, balance, and movement

• The muscles of the vertebral column can be broadly classified into two main groups: intrinsic and extrinsic muscles

Intrinsic Muscles of the Vertebral Column

• Intrinsic muscles are those that both originate and insert within the vertebral column

• These muscles are primarily responsible for the movements of the spine and for maintaining posture

• Intrinsic muscles are further divided into superficial, intermediate, and deep layers

Superficial Layer

• Splenius muscles: These include the splenius capitis and splenius cervicis

• They run from the spinous processes of the lower cervical and upper thoracic vertebrae to the skull and transverse processes of upper cervical vertebrae

• Acting together, they extend the head and neck

• Acting individually, they laterally flex and rotate the head to the same side

Intermediate Layer

• Erector spinae muscles: This is a large group of muscles that run along most of the vertebral column

• It is the primary extensor of the back

• The erector spinae is divided into three columns: iliocostalis, longissimus, and spinalis

• Iliocostalis: The iliocostalis is the most lateral of the erector spinae muscles, further divided into iliocostalis lumborum, iliocostalis thoracis, and iliocostalis cervicis

• These muscles extend and laterally flex the vertebral column, and can also be important in respiration

• Longissimus: The longissimus is intermediate in position, divided into longissimus thoracis, longissimus cervicis, and longissimus capitis

• Function to extend and laterally flex the vertebral column and head

• Spinalis: The spinalis is the most medial of the erector spinae muscles, and includes spinalis thoracis, spinalis cervicis, and spinalis capitis

• They primarily extend the vertebral column

Deep Layer

• Semispinalis: This group includes the semispinalis thoracis, semispinalis cervicis, and semispinalis capitis

• These muscles extend and rotate the vertebral column to the opposite side

• Multifidus: Located deep to the semispinalis, the multifidus spans two to four vertebrae

• Stabilizes the vertebrae and assists in extension and rotation

• Rotatores: These are the deepest of the intrinsic back muscles, spanning one or two vertebral segments

• They assist in rotation and stabilize the vertebral column

• Interspinales and Intertransversarii: These small muscles run between the spinous processes (interspinales) and transverse processes (intertransversarii) of adjacent vertebrae

• They help in stabilizing the vertebral column and assist in extension and lateral flexion

• Levatores Costarum: Although primarily involved in rib elevation during respiration, these muscles also contribute to lateral flexion of the vertebral column

Extrinsic Muscles of the Vertebral Column

• Extrinsic muscles of the vertebral column are those that originate outside the vertebral column and insert onto it, or vice versa

• These muscles primarily control movements of the limbs and respiration but also influence the position and stability of the vertebral column

• The extrinsic muscles are divided into superficial and deep groups

Superficial Extrinsic Muscles

• Trapezius: This large, flat muscle covers the upper back and neck

• It extends from the occipital bone to the lower thoracic vertebrae and laterally to the scapula

• It elevates, retracts, and rotates the scapula

• Latissimus Dorsi: This is a broad, flat muscle that covers the lower back

• It extends, adducts, and medially rotates the arm

• Rhomboids (Major and Minor): Located deep to the trapezius, the rhomboids retract and rotate the scapula

• Levator Scapulae: This muscle elevates the scapula and assists in neck flexion

Deep Extrinsic Muscles

• Serratus Posterior Superior: Located deep to the rhomboids, this muscle elevates the ribs, assisting in inspiration

• Serratus Posterior Inferior: Situated at the lower back, this muscle depresses the ribs, aiding in expiration

Anterior Trunk Muscles Influencing the Vertebral Column

• While primarily considered trunk muscles, these also significantly impact the vertebral column

Rectus Abdominis

• A long, paired muscle that runs vertically on the anterior side of the abdomen

• It flexes the vertebral column, particularly the lumbar region, and compresses the abdomen

External Oblique

• Located on the lateral and anterior abdomen, this muscle assists in flexing and rotating the trunk

Internal Oblique

• Deep to the external oblique, it also aids in trunk flexion and rotation

Transversus Abdominis

• The deepest abdominal muscle, it provides core stability and supports the vertebral column by increasing intra-abdominal pressure

Psoas Major and Iliacus

• These muscles are often grouped together as the iliopsoas

• Psoas major originates from the lumbar vertebrae and the iliacus from the iliac fossa

• They are primary hip flexors but also influence lumbar spine stability

Quadratus Lumborum

• Located in the posterior abdominal wall, it extends from the iliac crest to the lumbar vertebrae and the 12th rib

• It laterally flexes the vertebral column and stabilizes the lumbar spine