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The spinal cord is another major component of the CNS. While cerebral development stems from neural tube elongations culminating in primary and subsequent secondary vesicles, the spinal cord sustains the tubular configuration and solely differentiates into specific domains. During neonatal maturation, distinctive anatomical attributes progressively manifest across the surface of the spinal cord.
The spinal cord is a longitudinally oriented, cylindrical neural structure that extends from the foramen magnum at the base of the skull to the conus medullaris, a cone-shaped terminal end of the spinal cord near the first or second lumbar vertebra (Figure 27). Similar to the brain, a series of protective layers envelop the spinal cord, collectively called the meninges. The outermost layer is the dura mater, a tough and fibrous membrane that encases the spinal cord and forms a protective sheath. Adjacent to the dura mater lies the arachnoid mater, characterized by a delicate and avascular nature. The subarachnoid space between the arachnoid and pia mater contains CSF, providing buoyancy and cushioning to the spinal cord. The innermost layer, the pia mater, adheres closely to the surface of the spinal cord, following its contours (Figure 28). This layer is richly vascularized and facilitates the exchange of nutrients and waste products between the spinal cord and the surrounding CSF. Moreover, the pia mater extends inferiorly, forming the filum terminale and the denticulate ligaments, which anchor the spinal cord within the vertebral canal. Below the conus medullaris, a cluster of nerves known as the cauda equina ("horse's tail") emerges from the lumbar and sacral segments. The cervical and lumbar enlargements correspond to nerve supply for the upper and lower limbs, respectively. Comprising ventral and dorsal roots that have descended beyond the spinal cord proper ultimately course through the vertebral canal before exiting through their respective intervertebral foramina (Figure 27).
The anatomical boundary of the spinal cord involves its division into distinct regions predicated upon its spatial relationship with the vertebral column. The nomenclature assigned to a specific spinal cord region corresponds to the level at which spinal nerves traverse the intervertebral foramina. The cervical region is positioned immediately adjacent to the brainstem, followed sequentially by the thoracic, lumbar, and sacral regions. Notably, the length of the spinal cord does not mirror the entire vertebral column due to its limited elongation following the initial year or two of growth, while the skeletal structure continues expanding. The spinal nerves emanating from the spinal cord traverse the intervertebral foramina at their designated levels. Concurrently, as the vertebral column grows, these nerves undergo concomitant elongation, culminating in an elongated bundle of nerves, the cauda equina. The sacral spinal cord is localized at the level of the upper lumbar vertebral bodies, L1 to L2. Subsequently, the spinal nerves extend from their origins to align with the appropriate level of the vertebral column.
As shown in Figure 29, the anterior median fissure delineates the anterior midline, while the posterior midline is restricted by the posterior median sulcus. Axons enter the posterior aspect of the spinal cord via the dorsal (posterior) nerve root, identifiable by the posterolateral sulcus on each side. The exit of axons from the anterior part occurs through the ventral (anterior) nerve root. Sensory functions are primarily attributed to the posterior regions, whereas motor functions are predominantly associated with the most anterior regions.
Gray Matter
In cross-sectional representation, the gray matter configuration within the spinal cord exhibits a pattern where bilateral expansion mirrors its presence on the opposite side, delineating a bulbous "H" contour. As illustrated in Figure 29, the gray matter is further partitioned into distinct regions known as horns. The posterior horn serves as the locus for sensory information processing. The anterior horn generates motor commands, with the axons stemming from these neurons propagating motor signals to skeletal muscles. Limited to the thoracic, upper lumbar, and sacral segments, the lateral horn constitutes a crucial element of the sympathetic division within the autonomic nervous system.
White Matter
In a manner analogous to partitioning gray matter into horns, the white matter within the spinal cord is compartmentalized into columns (Figure 29). The columns extend linearly as contiguous bands of white matter. Enclosed within these columns are ascending bundles of nerve fibers responsible for conveying sensory data to the brain, while descending counterparts transmit motor directives originating from the brain. Positioned between the two posterior horns of gray matter lie the posterior columns. The anterior columns are between the two anterior horns, bordered by the axons of motor neurons emanating from that specific gray matter region. The white matter bilaterally within the spinal cord, flanked by the posterior horn and the axons of anterior horn neurons, constitutes the lateral columns. Comprising axons of ascending tracts, the posterior columns facilitate the transmission of sensory information. Conversely, the anterior and lateral columns contain diverse groups of axons, including both ascending and descending tracts.49
Regional Vertebral Characteristics
It is essential to discuss the details of a vertebra in relation to the location of the spinal cord to recognize the landmarks. A typical vertebra comprises a vertebral body, a vertebral arch featuring two pedicles and two laminae, and an arrangement of seven processes—articular, transverse, and spinous—that serve as points of attachment for articulation and musculature (Figure 30). The intervertebral discs demarcate and separate the vertebral bodies from one another. In instances where two adjacent vertebrae engage in articulation, the configuration of the pedicles delineates the contours of the intervertebral foramina, through which spinal nerves find passage. Combining the body of the vertebra with the vertebral arch yields the vertebral foramen, a spacious central aperture that encompasses and safeguards the spinal cord.50
Dorsal Root Ganglion
A ganglion is an assemblage of neuron cell bodies in the PNS. These ganglia can be classified into sensory and autonomic categories based on their primary functional roles. Sensory ganglia include dorsal (posterior) root ganglia, which exemplify the most prevalent type. These ganglia encapsulate cell bodies of neurons whose axons serve as sensory terminations in the periphery, such as within the skin, extending into the CNS via the dorsal nerve root. This ganglion constitutes a localized enlargement of the nerve root. Microscopic examination reveals neuron cell bodies and bundled posterior nerve root fibers (Figure 31). Notably, the cells within the dorsal root ganglion exhibit a unipolar configuration, reflecting their morphological classification. Analogous to the dorsal root ganglion, another variant is the cranial nerve ganglion associated with cranial nerves. While the roots of cranial nerves reside within the cranial cavity, the ganglia are situated outside the cranial vault. For instance, the trigeminal ganglion is superimposed upon the temporal bone, with its corresponding nerve anchored to the mid-pons region of the brainstem. Neurons in cranial nerve ganglia also exhibit a unipolar configuration.
Another key classification comprises the autonomic nervous system, consisting of the sympathetic and parasympathetic divisions. The sympathetic chain ganglia form a sequential series aligned alongside the vertebral column, receiving central inputs from the lateral horn of the thoracic and upper lumbar spinal cord. Additionally, three paravertebral ganglia are situated within the cervical region. Functionally akin to the chain ganglia, the prevertebral ganglia form another triad of autonomic ganglia external to the chain but share similar functions, positioned anterior to the vertebral column. Neurons within these autonomic ganglia exhibit a multipolar morphology with dendrites radiating around the cell body, facilitating synapses with spinal cord neurons. Subsequently, neurons within the chain, paravertebral and prevertebral ganglia project to cranial and cervical areas, thoracic and abdominal regions, and pelvic cavities to regulate the sympathetic aspect of homeostatic mechanisms.53
This page titled 3.11: The Spinal Cord was last modified on Sun, 13 Sep 2026 13:28:35 GMT and is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Chaya Gopalan (Consortium of Academic and Research Libraries in Illinois (CARLI)) .
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