Central canal

At a glance

English

Central canal

Latin (TA2)

Canalis centralis

System

Nerve

Region

Head

Side

Single, on the midline

About the central canal

The central canal, or ependymal canal, is the small tube at the core of the spinal cord. It is what remains in the adult of the cavity of the embryonic neural tube, the same cavity that widens into the ventricles inside the brain. It contains cerebrospinal fluid and is lined by the same ependyma as the ventricular system. In many adults it becomes partly or completely closed along much of its length.

Its upper end opens at the obex, the point in the lower medulla where the floor of the fourth ventricle narrows to a point. From there it runs down the whole cord, lying in the grey commissure that joins the two halves of the grey matter. In cervical and thoracic segments it sits towards the front, in roughly the anterior third of the cord; in the lumbar cord it is more central and a little wider; and in the conus medullaris, where the cord tapers, it lies further back. Near the conus it swells into a spindle-shaped terminal ventricle, sometimes called the fifth ventricle, about 8 to 10 mm long, which is clear in the fetus and young child but usually gone in adults.

Under the microscope the canal is lined by columnar ependymal cells bearing cilia. Around them is a ring of pale tissue, the central gelatinous substance, made mostly of neuroglia with a few nerve cells and fibres and crossed by the deep processes of the ependymal cells. It is distinct from the substantia gelatinosa of the posterior horn, which lies further back.

The canal matters clinically when it widens. In hydromyelia, extra fluid stretches the canal itself; in syringomyelia, a fluid cavity forms in or beside it, most often in the lower neck and upper thoracic segments. Such a cavity first damages the pain and temperature fibres that cross in the anterior white commissure in front of the canal, giving loss of these sensations in a cape over the shoulders and arms on both sides, with weakness later as the anterior horns are involved. Related problems include Chiari malformation, spina bifida with myelomeningocele, a tethered cord, tumours of the cord, and occasionally an enlarged terminal ventricle.

Course and supply

Supplies

Holds and carries cerebrospinal fluid received from the fourth ventricle, contributing to the fluid environment of the cord.

Blood supply

No supply of its own; the surrounding grey matter is fed by the anterior spinal artery through its central (sulcal) branches.