Spinal Cord and Nerve Roots

• The spinal cord extends from the medulla oblongata to the spinal column level L1

Spinal Cord

• Below L1 is the cauda equina, a collection of spinal nerves
• Enlargements occur in the cervical and lumbar regions
• Meningeal coverings protect the cord and cauda equina forming the thecal sac
• The spinal cord ends at L1, however can vary from upper L1 to middle of L2
• The tapered end includes sacral function
• Connective tissue called the filum terminale anchors the spinal cord to the inferior sacrum
• Same three meningeal layers cover the cortex and spinal cord, the lumbar cistern
• The lumbar cistern is the thecal sac
• Nerve roots leave at each vertebra formed of two roots.

Nerve Roots

• Incoming sensory fibers form the dorsal nerve root which contains the dorsal root ganglion, housing sensory cell bodies
• Sensory nerve roots enter the dorsal horn of the spinal cord via the dorsal root entry zone
• Motor nerve roots leave the anterior horn
• Axons come from alpha and gamma motor neurons.
• Roots exit above their respective vertebra with one exception
• C8 roots exit above T1
• All other roots exit below their respective vertebra

Spinal Cord Enlargements

• The cervical enlargement corresponds with large nerves supplying the upper limbs, extending from C3-T2, associated with high input/output
• The lumbar enlargement commences at T11-L1, which tapers to the conus medularis beginning the cauda equina formation
• The cauda equina is also known as a "horse's tail"

Additional Information

• The central nervous system is completely surrounded and sealed by meninges
• Meninges consist of multiple layers of connective tissue surrounding the spinal cord and brain: pia mater, arachnoid mater, and dura mater
• Spaces around the meninges include the epidural space(anesthesia injected), the subdural space(serous fluid), and the subarachnoid space(CSF)
• Cauda equina cross sections at lumbar levels L1-L5 show nerve roots diagrammed and labeled
• In the L1-L2 image, the conus medullaris (end of spinal cord) is labeled C and the dura forms the thecal sac

Grey and White Matter

• White matter contains both sensory and motor axons transmitting information up and down the spinal cord, noting the larger proportion of grey matter at enlargements
• Grey matter is shaped like a butterfly and contains nerve cell bodies
• Internal cord anatomy includes neuronal bodies and ascending/descending axonal fibers
• External cord anatomy includes all components encased in the meninges, nerve roots, anterior spinal artery, and dorsal spinal arteries

Spinal Cord Blood Supply

• Blood flows through the anterior spinal artery upward
• Cervical and lumbar regions have more blood flow
• Fewer arteries supply the thoracic region

Spinal Artery Details

• The ventral aspect is perfused by one anterior spinal artery while the dorsal aspect is perfused by two posterior spinal arteries
• There is both a centrifugal system (central artery supply) and a centripetal system (vasocorona supply), which supply distinct territories
• There is an intermediate zone that is able to be supplied by either system

Artery of Adamkiewicz

• The largest anterior segmental artery, supplies the lower 2/3 of spinal cord via the anterior spinal artery
• Usually originates around T8-L1
• Damage or obstruction can result in incontinence and impaired lower motor function, though sensory function is often preserved
• The artery is predominately left-sided and between T10-T8, and associates with thoracic watershed strokes

Spinal Gray Matter Lamina

• Spinal cord gray matter forms layers (lamina) numbered I-X from posterior to anterior
• Lamina I-IV are primarily sensory and VIII-IX are primarily motor
• Lamina VIII and IX is an important area for the spine because it is the location of the LMN (lower motor neurons)
• Posterior nuclei include the posteromarginal nuclei, substantia gelatinosa, and proper sensory nuclei
• Intermedial nuclei include the intermedial grey
• Anterior nuclei include the ventral horn, spinal nerves, and commissural

Spinal Cord Sensory Input Pathways

• Only the first order neuron cell body (DRG) is in the dorsal columns and is present at the level of entry
• Both the first order and second order neuron cell bodies are present at the level of entry, with the second in the spinal gray matter, in spinothalamic pathways
• Reflex arcs note lateral corticospinal descending motor tract feedback which controls reflex arcs