Spinal Anatomy and Back Muscles: Key Concepts for Students

What are the 5 regions of the spine and how many vertebrae are in each?

Cervical (7), Thoracic (12), Lumbar (5), Sacral (5, fused), Coccygeal (4, fused) — 33 total bones.

What are the two primary spinal curvatures, and are they concave or convex anteriorly?

Thoracic and sacral curvatures — primary (kyphotic), concave anteriorly; present at birth from the fetal position.

What are the two secondary spinal curvatures, and when do they develop?

Cervical and lumbar curvatures — secondary (lordotic), convex anteriorly; develop with acquisition of upright posture and walking.

When does normal cervical lordosis begin to form?

At around 3 months, when the baby begins to raise its head.

When does normal lumbar lordosis begin to form?

At around 1 year, when the baby begins to walk.

What is kyphosis?

An abnormal, exaggerated posterior (outward) curvature of the spine, usually thoracic.

What is lordosis (as a pathology, hyperlordosis)?

An abnormal, exaggerated anterior (inward) curvature of the spine, usually lumbar.

What is scoliosis?

A lateral curvature and rotation of the vertebrae, which can cause uneven shoulders, hips, ribcage, and potentially nerve damage, breathing difficulty, or progressive injury.

What are the components of a typical vertebra's body (centrum)?

The large, weight-bearing anterior part of the vertebra.

What are the components of the neural arch of a typical vertebra?

Lamina (flat, posterior part) and pedicle (connects body to arch).

What does the vertebral foramen form when vertebrae are stacked, and what does it contain?

It forms the vertebral (neural) canal, which contains the spinal cord, meninges, and associated structures.

Name the 7 processes (muscle/joint attachment sites) of a typical vertebra.

Superior articular process (2), Inferior articular process (2), Transverse process (2), Spinous process (1).

What are articulating facets on a vertebra?

Flattened surfaces on the superior/inferior articular processes that allow adjacent vertebrae to articulate with each other (and with ribs, in the thoracic spine).

What is the intervertebral foramen and what passes through it?

The passageway for spinal nerve exit, bordered by the vertebral notches of adjacent vertebrae.

What is the intervertebral disc composed of, and what are its two main parts?

Annulus fibrosus (tough, fibrous outer ring) and nucleus pulposus (pulpy, water-rich interior); the disc is named for the vertebrae between which it lies (e.g., L4-L5).

What makes cervical vertebrae C1-C2 atypical?

C1 (atlas) has no body, pedicle, lamina, or spinous process; C2 (axis) has the odontoid process (dens), a projection that arises from where C1's body would be.

What is the function of the atlas (C1)?

Supports the globe of the head (named for the Greek Titan); allows the head to nod 'yes' (flexion/extension) via its joint with the occipital condyles.

What is the function of the axis (C2) and its dens?

The dens (odontoid process) projects up into the atlas ring; the atlantoaxial joint (pivot joint) allows the head to rotate side to side, shaking 'no'.

What is distinctive about the spinous process of C7 (vertebra prominens)?

It is long and prominent, palpable on the skin surface, nearly horizontal, non-bifurcated, and ends in a tubercle where the ligamentum nuchae attaches.

What is the ligamentum nuchae?

A ligament extending from the external occipital protuberance to the spinous process of C7, serving as a muscle attachment site in the neck.

What is unique about cervical vertebrae's transverse processes?

They contain a transverse foramen, which transmits the vertebral artery and vein (except at C7, where the vertebral artery does NOT pass through).

How many pairs of ribs does the thoracic spine articulate with, and how many thoracic vertebrae are there?

12 thoracic vertebrae, each articulating with a pair of ribs (all costal facets).

What are costal facets/foveae on thoracic vertebrae used for?

Rib articulation sites; normally found only on thoracic vertebrae.

Which thoracic vertebrae are atypical in their rib articulations?

T1 (rib 1 does not articulate with C7) and T9-T12 (atypical; heads of ribs 10-12 articulate with only their own vertebral body).

What distinguishes lumbar vertebrae?

Largest vertebral bodies (support most weight); lack a foramen transversarium (found only in cervical) and lack costal facets on the transverse process (found only in thoracic).

How many vertebrae are fused to form the sacrum?

5 fused vertebrae, forming a large, triangular bone at the base of the spine.

What are the wing-like projections of the sacrum called, and what do they articulate with?

Alae (wings); articulate with the ilium at the L-shaped sacroiliac joints.

What is the sacral promontory?

The most anterior margin of the first sacral vertebra; more pronounced in females for extra room in the birth canal (obstetric relevance).

What passes through the sacral foramina?

Anterior and posterior sacral spinal nerves (S1-S4) and associated blood vessels.

What does the sacral canal contain?

Sacral epidural space, spinal meninges, lumbar and sacral spinal nerves, filum terminale, venous plexus, fatty connective tissue; terminates at the sacral hiatus.

How many vertebrae fuse to form the coccyx?

4 fused vertebrae.

How many fused terminal vertebrae make up the coccyx?

3-5 fused terminal vertebrae

How are cervical spinal nerves named relative to their vertebra?

Named after the vertebra immediately inferior

How are thoracic, lumbar, and sacral spinal nerves named relative to their vertebra?

Named after the vertebra immediately superior to where they exit

Where do spinal nerves exit the vertebral column?

Through the intervertebral foramina

What are the zygapophyseal (facet) joints?

Synovial, plane (gliding) joints between the superior and inferior articular processes of adjacent vertebrae

What is the function of the ligamentum flavum?

Limits spinal flexion by connecting laminae of adjacent vertebrae

What is the function of the anterior and posterior longitudinal ligaments?

Stabilize vertebral bodies and limit extension/flexion

What spinal injury mechanism is associated with hyperextension (whiplash) of the cervical spine?

Tearing of the anterior longitudinal ligament and possible avulsion of the vertebra

What is intervertebral disc herniation?

When the nucleus pulposus protrudes through a tear in the annulus fibrosus

What percentage of vertebral column length is made up by intervertebral discs?

About 25% of column length

What happens to the nucleus pulposus with age?

It loses water content

What are the three main groups of back muscles by depth?

Superficial, Intermediate, Deep

What is the innervation of the trapezius muscle?

Motor innervation: cranial nerve XI; proprioception: anterior rami of C3, C4

What are the actions of the three parts of the trapezius?

Superior: elevates scapula; Middle: retracts scapula; Inferior: depresses scapula

What is the action of latissimus dorsi?

Extends, adducts, and medially rotates the humerus

What is the innervation of levator scapulae?

Dorsal scapular nerve

What is the function of serratus posterior superior?

Elevates ribs 2-5 during inhalation

What muscles make up the spinotransversalis group?

Splenius capitis and splenius cervicis

What three muscles make up the erector spinae group?

Spinalis, longissimus, iliocostalis

What is the Triangle of Auscultation?

An area of thin tissue overlying the pulmonary cavities for better stethoscope auscultation

What is the Lumbar Triangle (of Petit)?

A natural area of weakness in the abdominal wall where hernias can occur