The spinal cord is a delicate cylinder of nervous tissue that runs from the brainstem down through the vertebral canal. In adults, it typically extends from the foramen magnum of the skull down to the level of the first or second lumbar vertebra (L1-L2). It is housed within the bony vertebral column, which provides sturdy structural protection against physical trauma.
At its inferior end, the cord tapers into a conical structure called the conus medullaris. Extending from this tip is the filum terminale, a strand of fibrous tissue that anchors the spinal cord to the coccyx. Because the bony vertebral column grows faster than the nervous tissue during development, the lower lumbar and sacral nerve roots angle sharply downward inside the canal, forming a bundle known as the cauda equina, which resembles a horse's tail.
Three protective membrane layers called meninges wrap around the spinal cord, continuous with those covering the brain.
Between the dura mater and the bone of the vertebral vertebrae lies the epidural space, which contains fat and blood vessels and serves as the common site for administering epidural anesthesia during labor. Between the arachnoid and pia mater is the subarachnoid space, filled with cerebrospinal fluid (CSF) that cushions the cord against shock.
A cross-section of the spinal cord reveals an inner core of grey matter shaped roughly like a butterfly or the letter H, surrounded by outer white matter.
The grey matter consists primarily of neuronal cell bodies, neuroglia, and unmyelinated axons. It is subdivided into horns: the posterior (dorsal) horns contain sensory nuclei, the anterior (ventral) horns contain motor neuron cell bodies, and the lateral horns (present in thoracic and lumbar segments) house autonomic motor neurons.
The white matter is arranged into columns or funiculi—posterior, lateral, and anterior—containing myelinated nerve fibers traveling up and down the central nervous system.
White matter pathways transmit signals between the brain and the body via two main route types:
Damage to these tracts disrupts communication, leading to sensory deficits or paralysis below the level of the lesion.
Thirty-one pairs of mixed spinal nerves emerge from the spinal cord, connecting it to different regions of the body. They are categorized by region:
| Region | Number of Pairs |
|---|---|
| Cervical | 8 |
| Thoracic | 12 |
| Lumbar | 5 |
| Sacral | 5 |
| Coccygeal | 1 |
Each spinal nerve is formed by the union of a posterior (sensory) root—which features a swelling called the dorsal root ganglion containing sensory cell bodies—and an anterior (motor) root. A dermatome is a specific strip of skin supplied by a single spinal nerve, which helps clinicians map nerve root damage.
A spinal reflex is a fast, predictable, automatic response to a stimulus that bypasses conscious thought to protect the body from harm. The pathway it travels is called a reflex arc, consisting of five basic components:
The knee-jerk patellar reflex is a classic example of a simple monosynaptic stretch reflex.
Injuries to the spinal cord can result from trauma, tumors, or vascular accidents, leading to profound clinical challenges. Transection or severe compression of the cord causes paralysis and sensory loss below the injury site. Quadriplegia (tetraplegia) involves impairment of all four limbs, typically resulting from cervical cord damage, while paraplegia affects the lower body, occurring from thoracic, lumbar, or sacral injuries.
During acute spinal trauma, patients may experience spinal shock, a temporary loss of all reflex activity and flaccid paralysis below the lesion. Nurses must carefully monitor respiratory status in high cervical injuries, as innervation to the diaphragm via the phrenic nerve (C3-C5) may be compromised.