Lamina VII contains the nucleus dorsalis of Clark (Clark's column), a group of relatively large multipolar or oval nerve cells that extends from C8 through 元 or L4.
Lamina VI, seen only at cord enlargements, receives group I muscle afferents in its medial zone, and descending spinal terminations in its lateral zone. The nucleus reticularis is present in the broad lamina V, which is divided into medial and lateral zones, except in thoracic segments. This receives inputs concerning movement, position, vibration and two-point discrimination from the dorsal white column.
Ventral to the substantia gelatinosa, extending through III and IV, is the largest dorsal horn nucleus, the nucleus pro-prius, which also exists at all cord levels.
Both I and II are rich in substance P, considered to be an excitatory neurotransmit-ter of pain impulses, in opioid receptors and the enkephalin. Near the apex, in lamina II, is the substan-tia gelatinosa, which is found throughout the length of the cord, and which receives touch, temperature and pain afferents, as well as inputs from descending fibers. These cells respond to thermal and other noxious stimuli, and receive axosomatic connections from lamina II. Lamina I is at the apex of the dorsal horn, and contains the posterior marginal nucleus. Most laminae are present throughout the cord, but VI, for example, is apparently absent from T4 to L2. The gray matter is divided arbitrarily into nine visually distinct laminae, labeled I through IX, and an area X, which surrounds the central canal. The overall arrangement of the gray matter of the cord was systematized by Rexed, who proposed the generally accepted laminar arrangement, commonly referred to as the cytoarchitectonic organization of the spinal cord. Structurally, the gray matter is composed of neuronal cell nuclei, their processes, neuroglia (see p. These are the cervical and lumbosacral, which innervate upper and lower limb muscles, respectively.) (The size of the gray matter is greatest at segments that innervate the most skeletal muscle. The lower wings of the butterfly shape are formed by the ventral (anterior) horns of the gray matter. In the thoracic and upper lumbar segments the gray matter extends on both sides to form lateral horns. These are linked by a thin gray commissure in which lies the central canal. The gray matter of the cord is butterfly-shaped, with the so-called dorsal (posterior) horns forming the upper wings of the butterfly shape.
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