Alar plate––According to His’ bipartite division of the
neural tube, that part of the lateral plate neuroepithe-
lium situated above the sulcus limitans. It is hypoth-
esized to be the source of dorsal horn sensory pro-
cessing neurons and some intermediate gray neurons.
In the tripartite division of the spinal cord neuroep-
ithelium in this Atlas, this term is not used. See
Dorsal neuroepithelium and Intermediate neuroep-
ithelium.
Autonomic motoneurons––Preganglionic sympathetic
motoneurons in the lateral horn at thoracic and upper
lumbar levels; preganglionic parasympathetic moto-
neurons in the lateral part of the intermediate gray at
sacral levels. See Lateral horn motoneurons.
Basal plate–– According to His’ bipartite division of the
neural tube, that part of the lateral plate neuroepithe-
lium situated below the sulcus limitans. It is hypoth-
esized to be the source of ventral horn motoneurons,
ventral horn interneurons, and some intermediate
gray neurons. In the tripartite division of the spinal
cord neuroepithelium in this Atlas, this term is not
used. See Ventral neuroepithelium and Intermedi-
ate neuroepithelium.
Cauda equina––Elongated roots of spinal nerves in the
vertebral canal that exit from the spine below the level
of their points of attachment to the spinal cord.
Cellular roof plate––Cells in the roof plate that have
fi brous-like projections into the roof of the spinal
canal. Initially, the cellular roof plate caps the midline
of the spinal cord, but it starts to sink downward at the
end of the fi rst trimester, apparently leaving behind a
string of non-neural cells that form the dorsal median
septum. See Roof plate.
Central autonomic area––Small- and medium-sized neu-
rons that surround the central canal and provide a
bridge between the two wings of the gray matter on
either side of the midline. This area is homologous
to the central gray surrounding the cerebral aqueduct
and fourth ventricle in the brain. It contains the dorsal
and ventral gray commissures that bridge the midline.
These neurons are activated by nociceptive afferents
from small cells in the dorsal root ganglion.
Central cervical nucleus––A cluster of large neurons in
the intermediate gray near the central canal at cervi-
cal levels that is the continuation of Clarke’s column.
Axons of these neurons enter the ipsilateral dorsal spi-
nocerebellar tract.
Cervical enlargement––Includes that part of the spinal
cord from which the nerves of the brachial plexus
arise, from C4 to T1. This part of the spinal cord has a
larger diameter because of the greater amount of gray
and white matter required to innervate the upper limb.
Cervical region––The part of the spinal cord that is con-
tinuous with the medulla of the brain through the fora-
men magnum of the skull. Eight spinal nerves exit
from this region; all nerves except C1 have a dorsal
root ganglion. C1 exits above the fi rst vertebra; C8
exits in the transverse foramen of the C7 vertebra.Clarke’s column––A group of large neurons dorsal to the
central canal in the intermediate gray at thoracic and
upper lumbar levels. Its axons form the ipsilateral
dorsal spinocerebellar tract.Conus medullaris––The cone-shaped terminus of the
spinal cord.Dorsal canal––A transient part of the spinal canal that fi rst
expands then recedes in relation to the changing size
of the dorsal neuroepithelium during the fi rst trimes-
ter.Dorsal funiculus–– Dorsal white matter that caps and fi lls
in the U-shaped space between the paired dorsal horns.
Most of the axons in this funiculus are from large
dorsal root ganglion cells in four subdivisions: fascic-
ulus gracilis, fasciculus cuneatus, dorsal root bifurca-
tion zone, and dorsal root collateralization zone.Dorsal horn––Dorsal wings of the butterfl y-shaped gray
matter that contain sensory processing neurons in lam-
inae I-V. This is the latest differentiating region of the
spinal cord gray matter.Dorsal horn, lamina I––A thin sheet of gray matter that
caps the dorsal surface of the dorsal horn. It contains
the large Waldeyer cells that process nociceptive sen-
sory information. Axons of the Waldeyer cells cross
the midline in the ventral white commissure and enter
the ventral and lateral spinothalamic tracts, or the spi-
nocephalic tracts.Dorsal horn, laminae II-III––See Substantia gelati-
nosa.Dorsal horn, laminae IV-V––A collection of large and
small neurons; also called the nucleus proprius. These
neurons process touch, pressure, and nociceptive input.
At lumbar and thoracic levels, axons of some of the
neurons in lamina IV travel to the medulla in the dorsal
funiculus as a postsynaptic–dorsal column system. At
all levels, some neurons in lamina IV travel in the dor-
solateral region of the lateral funiculus (the spinocer-
vicothalamic pathway) and terminate in a topographic
pattern in the lateral cervical nucleus (Haines, 2000).Dorsal intermediate septum––Aligned non-neural cells
that separate the fasciculus gracilis and fasciculus
cuneatus. There is a slight depression on the surface
of the spinal cord to mark the spot where this septum
joins the pia.GLOSSARY