Table of Contents
Overview – Spinal Cord
The spinal cord is the primary communication link between the brain and the peripheral nervous system. Encased in the vertebral canal and bathed in cerebrospinal fluid (CSF), it transmits motor signals from the brain to the body and sensory input from the body to the brain. Its segmental organisation gives rise to spinal nerves at every vertebral level, with specialised structures in the lower spine including the cauda equina and filum terminale.
Anatomy & Location
- Begins at the foramen magnum (base of skull)
- Extends down to ~L1 in adults (ending as the conus medullaris)
- Lies within the vertebral canal, surrounded by meninges & CSF
- Gives rise to 31 pairs of spinal nerves, exiting at each vertebral level
Key Terminal Structures
- Cauda equina:
- Bundle of lumbar/sacral nerve rootlets descending beyond the conus
- Filum terminale:
- Fibrous extension anchoring the conus medullaris to the coccyx
Internal Structure of the Spinal Cord
Grey Matter
- Contains neuronal cell bodies
- H-shaped in cross-section
- Dorsal horns → receive sensory information (via dorsal root)
- Ventral horns → contain motor neurons (efferent output via ventral root)
- Lateral horns (T1–L2) → contain autonomic (sympathetic) motor neurons
White Matter
- External to grey matter
- Composed of ascending sensory and descending motor fibre tracts
- Organised into columns (funiculi)
External Structure & Spinal Nerves
- Spinal nerve = dorsal root (sensory) + ventral root (motor)
- Spinal nerves carry mixed (motor + sensory) fibres
- Each spinal nerve divides into:
- Dorsal ramus → supplies posterior body wall & back muscles
- Ventral ramus → supplies limbs, anterior/lateral trunk
Autonomic Structures
- Sympathetic chain: paired ganglia running alongside the vertebral column
- Sympathetic ganglia: relay stations for sympathetic motor fibres
Information Flow Pathways
Somatic Nervous System
Afferent (sensory from skin, muscle, joints):
- Receptor → peripheral axon → dorsal root ganglion (soma)
→ central axon → dorsal horn of grey matter
→ ascending tracts (white matter) → brain
Efferent (motor to skeletal muscle):
- Cell body in ventral horn
→ axon exits via ventral root
→ joins spinal nerve → exits via ventral ramus
→ neuromuscular junction (target muscle)
Autonomic (Visceral) Nervous System
Afferent (from viscera):
- Visceral receptor → peripheral axon → dorsal root ganglion
→ central axon → dorsal horn → ascending tracts → brain
Efferent (to smooth muscle, glands, viscera):
- Cell body in lateral horn (T1–L2)
→ axon exits via ventral root
→ joins spinal nerve → synapses at peripheral autonomic ganglion
→ postganglionic fibre reaches target (e.g. heart, GI tract)
Summary – Spinal Cord
The spinal cord serves as the central conduit for motor output and sensory input between the brain and body. Organised into grey and white matter, and segmented by spinal nerves, it governs both somatic and autonomic functions. The spinal roots, dorsal root ganglia, rami, and associated sympathetic structures enable rapid, precise communication throughout the nervous system. For a broader context, see our Nervous System page.