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Spinal nerves

The spinal nerves are 31 pairs of mixed peripheral nerves that emerge from the spinal cord through the intervertebral foramina. Each spinal nerve is formed by the union of a dorsal (posterior) root, which carries sensory (afferent) fibers, and a ventral (anterior) root, which carries motor (efferent) fibers. These roots merge just distal to the dorsal root ganglion to form a mixed spinal nerve, which then divides into branches.

There are 31 pairs of spinal nerves:

  • 8 cervical (C1–C8)

  • 12 thoracic (T1–T12)

  • 5 lumbar (L1–L5)

  • 5 sacral (S1–S5)

  • 1 coccygeal (Co1)

Each spinal nerve is relatively short and quickly divides into:

  • A dorsal ramus (innervates back muscles and skin of posterior trunk)

  • A ventral ramus (innervates anterior trunk and limbs; forms major nerve plexuses such as cervical, brachial, lumbar, and sacral plexuses)

  • A meningeal branch (re-enters the vertebral canal to supply meninges and blood vessels)

  • A ramus communicans (connects to the sympathetic chain for autonomic fibers)

Clinically, spinal nerves are crucial in motor control, sensory function, and autonomic regulation. Compression or injury (e.g., herniated disc, foraminal stenosis, or trauma) leads to radiculopathy, characterized by pain, sensory loss, and weakness along the nerve’s dermatome or myotome.

Synonyms

  • Nervi spinales

  • Mixed spinal nerves

  • Segmental nerves

Function

  • Provide motor innervation to skeletal muscles (via ventral root fibers)

  • Transmit sensory information (pain, touch, temperature, proprioception) from body to spinal cord (via dorsal root fibers)

  • Carry autonomic fibers (sympathetic/parasympathetic) for visceral function

  • Serve as the communication link between central nervous system and periphery

MRI Appearance

T1-weighted images:

  • Spinal nerves appear as linear low-signal structures emerging from the spinal cord into the foramina

  • Surrounded by epidural and foraminal fat (hyperintense), which provides natural contrast

T2-weighted images:

  • Nerve roots and spinal nerves appear as low-to-intermediate signal linear structures within bright cerebrospinal fluid (CSF)

  • Pathology (e.g., edema, compression, inflammation) may show signal alteration or distortion

STIR:

  • Fat suppression enhances visualization of nerves against foraminal fat

  • Useful for detecting nerve inflammation, radiculitis, or edema

T1 Post-Gadolinium (Gd-enhanced MRI):

  • Normal spinal nerves show mild uniform enhancement

  • Abnormal enhancement indicates neuritis, infection, tumor infiltration, or postoperative scar

MRI Non-Contrast 3D Imaging:

  • High-resolution 3D sequences map spinal nerve roots in multiple planes

  • Useful for surgical planning, nerve root anomalies, and congenital conditions

CT Appearance

Non-contrast CT:

  • Spinal nerves themselves are not well visualized due to limited soft tissue contrast

  • Indirectly assessed by observing bony foraminal narrowing or fractures

CT Post-Contrast (CT Myelography):

  • Contrast within CSF outlines nerve roots as filling defects or displaced structures

  • Especially useful in patients who cannot undergo MRI

  • Detects nerve compression from disc herniation, tumors, or stenosis

MRI images

Spinal nerves anatomy MRI axial image -img-00000-00000

MRI images

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CT images

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MRI image

Spinal nerves MRI sag anatomy image -img-00000-00000