The spinal cord is made of both gray and white matter. Gray matter consists of neurons, neuronal processes, and neuroglia. It is butterfly or H-shaped. White matter surrounds gray matter and is made up of neuronal processes (myelinated and unmyelinated), neuroglia, and blood vessels. The proportion of gray to white matter varies at different levels of the spinal cord. The ratio of gray to white matter is greatest at the cervical and lumbar regions.
Gray matter can be categorized into columns (or horns) and laminae (Figure 122-1). The columns include a ventral (or anterior) column, which contains motor neurons, and an intermediolateral gray column, which contains preganglionic cells for the autonomic nervous system. The intermediolateral gray column contains preganglionic sympathetic neurons from T1-L2 and contains parasympathetic neurons at S2-S4. In addition, a dorsal (or posterior) gray column is involved in sensory processing. Lissauer tract lies in this area and is part of the pain pathway. The anterior and posterior horns are united by a gray commissure that contains a small, central canal.
Laminae of spinal cord gray matter. (Reproduced with permission from Waxman SG, Clinical Neuroanatomy, 27th ed. McGraw-Hill Companies, Inc. 2013. All rights reserved.)
There are 10 laminae (layers of nerve cells), also known as Rexed laminae that make up the gray matter. Each of these laminae is involved in sensory or motor pathways (Table 122-1).
TABLE 122-1Laminae (Gray Matter) |Favorite Table|Download (.pdf) TABLE 122-1 Laminae (Gray Matter)
|Laminae ||Sensory or Motor ||Other Info/Function |
|I ||Sensory ||Respond to noxious stimuli—mediate pain, temperature, and touch. Substance P found in high concentrations |
|II ||Sensory ||Substantia gelatinosa. Responds to noxious stimuli—pain and temperature. Substance P and glutamate found in high concentrations |
|III and IV ||Sensory ||Together known as nucleus proprius. Convey position and light sense |
|V ||Sensory ||Respond to noxious and visceral afferent stimuli |
|VI ||Sensory ||Respond to mechanical signals from joints and skin. Located only in cervical and lumbar spinal segments |
|VII ||Motor, autonomic ||Contains cells of dorsal nucleus, which give rise to posterior spinocerebellar tract. Also contains intermediolateral nucleus (intermediolateral cell column) in thoracic and lumbar regions which contains sympathetic fibers |
|VIII and IX ||Motor ||Medial and lateral components. Medial—axial muscles. Lateral—distal muscles. Flexor muscles innervated by motor neurons closer to central canal (more ventral) |
|X ||Autonomic ||Small neurons/remnants around central canal |
The white matter is divided into columns, including the dorsal, lateral, and ventral columns (Figure 122-2). Each column contains tracts, which are groups of nerve fibers that have similar destinations in relaying sensory and motor information. For instance, the dorsal column can be divided into a medial tract (fasciculus gracilis) and a ...