What is the anatomy of the spinal cord?

Spinal Cord Anatomy Overview

The spinal cord is a cylindrical structure of the central nervous system that extends from the medulla oblongata at the foramen magnum to approximately the L1-L2 vertebral level in adults, serving as the primary conduit for motor and sensory information between the brain and peripheral nervous system. 1, 2

Gross Anatomical Features

Location and Extent

• The spinal cord terminates at the conus medullaris, which normally ends at the L1-L2 disc space in adults (with the lowest normal position being the middle third of L2 vertebra by 2 months after birth) 3
• The cord extends through the vertebral canal, protected by the bony spinal column 4
• Below the conus medullaris, nerve roots continue as the cauda equina 1

Meningeal Coverings (Outer to Inner)

• Dura mater (outermost protective layer) 4
• Arachnoid mater (middle layer) 4
• Pia mater (innermost layer, directly adherent to cord surface) 4

Cross-Sectional Anatomy

White Matter (Peripheral)

The white matter contains the major ascending and descending neural pathways arranged in specific tracts 5, 4:

Descending Motor Pathways:

• Corticospinal tracts (lateral and anterior): Carry upper motor neuron signals; damage causes ipsilateral motor deficits 5

Ascending Sensory Pathways:

• Dorsal columns (gracilis and cuneatus fasciculi): Transmit touch, vibration, and proprioception; damage causes ipsilateral sensory loss 5
• Spinothalamic tracts (lateral and anterior): Carry pain and temperature sensation; damage causes contralateral sensory deficits 5

Gray Matter (Central)

The central gray matter has a characteristic butterfly or H-shaped appearance on cross-section 2, 4:

• Posterior (dorsal) horn: Contains sensory neurons (laminae 1-5) that process incoming sensory information 5
• Anterior (ventral) horn: Contains lower motor neurons (primarily lamina 9) that innervate skeletal muscles 5
• Central commissure: Contains crossing fibers; damage produces a suspended bilateral "girdle" sensory level 5
• Lateral horn (T1-L2 levels): Contains autonomic preganglionic neurons 5

Segmental Organization

Nerve Root Anatomy

• Anterior (ventral) roots: Emerge at regular, regionally-modulated intervals without strict segmental boundaries 6
• Posterior (dorsal) roots: Show somewhat more segmental organization, though patterns vary individually 6
• Spinal nerves: Form when anterior and posterior roots combine at the intervertebral foramen 6

Important Clinical Concept

• While the cord appears segmentally organized due to paired nerve roots, developmental and anatomical evidence suggests the cord is actually organized regionally rather than in discrete segments 6
• The visual segmented appearance results from axon bundling toward vertebral foramina rather than true internal segmentation 6

Embryological Development

Primary Neurulation (Weeks 2-4)

• The neural plate elevates and folds to form the neural tube 3
• Neural folds converge and fuse in the midline 3
• Cutaneous ectoderm separates (dysjunction) to form overlying skin 3
• Forms the spinal cord from cervical through S2 levels 3

Secondary Neurulation (Week 4 onward)

• Forms the cord below S2 and the filum terminale from the caudal cell mass 3
• Occurs beneath fully formed skin, producing "closed" malformations when disrupted 3

Clinical Imaging Correlates

MRI as Gold Standard

• MRI is the definitive imaging modality for spinal cord evaluation, providing superior visualization of cord parenchyma, nerve roots, and surrounding soft tissues 3
• MRI can assess for cord edema, abnormal signal, enhancement patterns, masses, and compression 3
• Contrast administration enhances detection of inflammatory, infectious, and neoplastic processes 3

CT Limitations

• CT inadequately visualizes the spinal cord and nerve roots compared to MRI 3
• CT is primarily useful for bony evaluation but cannot assess cord pathology adequately 3

Common Clinical Syndromes

Central Cord Syndrome

• Most common incomplete spinal cord injury pattern, especially in older adults 3
• Characterized by disproportionately greater upper extremity weakness than lower extremity weakness, bladder dysfunction, and variable sensory loss 3
• Typically results from hyperextension injury in a spondylotic or congenitally narrow canal 3

Tethered Cord Syndrome

• Results from abnormal fixation preventing normal cord ascent during growth 3
• Causes physical stretching leading to impaired blood flow and metabolic dysfunction 3
• Clinical manifestations include pain, sensorimotor deficits, bladder/bowel dysfunction, and progressive orthopedic deformities 3