Thespinal cordis a long, thin, tubular structure made up of nervous tissue, that extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column. It encloses the central canal of thespinal cordthat contains cerebrospinal fluid

The spinal cord is the main pathway for information connecting the brain andperipheral nervous system.Much shorter than its protecting spinal column, the human spinal cord originates in the brainstem, passes through theforamen magnum, and continues through to theconus medullarisnear the secondlumbar vertebrabefore terminating in a fibrous extension known as thefilum terminale.

It is about 45cm (18in) long in men and around 43cm (17in) in women,ovoid-shaped, and is enlarged in the cervical and lumbar regions. The cervical enlargement, stretching from the C5 to T1 vertebrae, is where sensory input comes from and motor output goes to the arms and trunk. The lumbar enlargement, located between L1 and S3, handles sensory input and motor output coming from and going to the legs.

The spinal cord is continuous with the caudal portion of the medulla, running from the base of theskullto the body of the first lumbar vertebra. It does not run the full length of the vertebral column in adults. It is made of 31 segments from which branch one pair of sensory nerve roots and one pair of motor nerve roots. The nerve roots then merge into bilaterally symmetrical pairs ofspinal nerves. The peripheral nervous system is made up of these spinal roots, nerves, andganglia.

The dorsal roots are afferentfascicles, receiving sensory information from the skin, muscles, and visceral organs to be relayed to the brain. The roots terminate indorsal root ganglia, which are composed of the cell bodies of the corresponding neurons. Ventral roots consist ofefferent fibersthat arise from motor neurons whose cell bodies are found in the ventral (or anterior) gray horns of the spinal cord.

The spinal cord (and brain) are protected by three layers of tissue or membranes calledmeninges, that surround the canal . Thedura materis the outermost layer, and it forms a tough protective coating. Between the dura mater and the surrounding bone of thevertebraeis a space called theepidural space. The epidural space is filled withadipose tissue, and it contains a network ofblood vessels. Thearachnoid mater, the middle protective layer, is named for its open, spiderweb-like appearance. The space between the arachnoid and the underlyingpia materis called thesubarachnoid space. The subarachnoid space containscerebrospinal fluid(CSF), which can be sampled with alumbar puncture, or "spinal tap" procedure. The delicate pia mater, the innermost protective layer, is tightly associated with the surface of the spinal cord. The cord is stabilized within the dura mater by the connectingdenticulate ligaments, which extend from the enveloping pia mater laterally between the dorsal and ventral roots. Thedural sacends at the vertebral level of the secondsacralvertebra.