The Human Brain: Chapter 1: The Spinal Cord

1-3 Dorsal view of the lower part of the medulla oblongata and the upper six segments of the cervical spinal cord of a newborn infant

The posterior white columns (funiculi) lie alongside the posterior median sulcus. Their constituent bundles in the spinal cord can be followed upward without interruption into the lower closed part of the medulla oblongata. The 6th segment of the cervical cord has not been stripped of its pia mater. On each side of the posterior median sulcus are two longitudinally running fasciculi, the gracile and cuneate, separated by the shallow posterior intermediate sulcus. These fasciculi are composed of sensory axons that arise from cell bodies in the dorsal root ganglia of the spinal nerves and enter the spinal cord via the dorsal nerve roots. At the medullary level both fascicles spread out and diverge from the median plane. Each terminates in an elongated and often poorly defined swelling produced by the gracile or cuneate nucleus, in which the primary proprioceptive and exteroceptive fibers end, and from which secondary axons-most of them carrying sensory signals onward to the thalamus-arise. Lateral to each cuneate fasciculus an extensive series of dorsal nerve rootlets can be seen alongside the posterior lateral sulcus of the spinal cord. Each group of dorsal nerve rootlets is associated with the corresponding segmental nerve. Note that the upper rootlets run almost transversely, but that the lower ones become progressively longer and more oblique. From its beginning at the 5th cervical segment, the spinal root of the accessory nerve increases in thickness as fibers join it from higher segments. The root lies dorsal to the rootlets of the 1st cervical nerve and the vertebral artery and can be followed through the foramen magnum into the cranial cavity.

On each side a series of spinal ganglia penetrate the intervertebral foramina. The ganglion associated with the 1st cervical nerve is small and fusiform, and immediately below it is the ventral motor root of the 1st cervical nerve. The other cervical ganglia are larger. The nerve roots and ganglia are enclosed in tubular extensions of dura, which merges with the epineurium that envelops the spinal nerves. The 1st cervical nerves are related closely to the vertebral arteries. The latter ascend through the transverse foramina of the cervical vertebrae, as shown on the left side of the preparation.

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