Histology of Spinal Cord
Dr. Muhammad Rafique
• • • • • • Introduction of Spinal Cord Division of Spinal Cord Division of White Matter Division of Gray Matter Different Nuclei of Gray Column Rexed Classification
Cross Section of Spinal Cord
In cross sections of the spinal cord, white matter is peripheral and gray matter is central, assuming the shape of an H. In the horizontal bar of this H is an opening, the central canal, which is a remnant of the lumen of the embryonic neural tube. It is lined with ependymal cells
Division of Gray Matter
The gray matter of the legs of the H forms the anterior horns. These contain motor neurons whose axons make up the ventral roots of the spinal nerves. Gray matter also forms the posterior horns (the arms of the H), which receive sensory fibers from neurons in the spinal ganglia (dorsal roots).
Anterior Horn Cells
Spinal cord neurons are large and multipolar, especially in the anterior horns, where large motor neurons are found.
The spinal cord is the main pathway for information connecting the brain and peripheral nervous system. The length of the spinal cord is much shorter than the length of the bony canal. The human spinal cord extends from the medulla oblongata and continues through the conus medullaris near the first or second lumbar vertebra, terminating in a fibrous extension known as the filum terminale.
It is about 45 cm long in men and 43 cm long in women, ovoidshaped. In cross-section, the peripheral region of the cord contains neuronal white matter tracts containing sensory and motor neurons. Internal to this peripheral region is the gray, butterflyshaped central region made up of nerve cell bodies. This central region surrounds the central canal, which is an anatomic extension of the spaces in the brain known as the ventricles and, like the ventricles, contains cerebrospinal fluid.
Somatosensory organization is divided into the dorsal columnmedial lemniscus tract (the touch/proprioception/vibration sensory pathway) and the anterolateral system, or ALS (the pain/temperature sensory pathway). Both sensory pathways use three different neurons to get information from sensory receptors at the periphery to the cerebral cortex. These neurons are designated primary, secondary and tertiary sensory neurons. In both pathways, primary sensory neuron cell bodies are found in the dorsal root ganglia, and their central axons project into the spinal cord.
Principles of Cord Organization
1) Longitudinal Arrangement Fibers (White Matter) – White Column / Fasciculus Cell Groups (Gray Matter) -Gray Column / Nucleus 2) Transverse Arrangement Afferent & Efferent Fiber Crossing (Commissural and Decussating) Fibers 3) Somatotopical Arrangement
The inner part of the cord, or gray matter, contains the cell bodies and dendrites of the spinal neurons. There are three basic kinds of spinal neurons: 1.) Those with axons that leave the cord via the ventral roots (motoneurons and autonomic preganglionic neurons); 2.) Tract cells that project mainly to supraspinal regions such as the cerebellum and thalamus, although some of these also have intraspinal corrections via axon collaterals; and 3.) Spinal interneurons with axons that project entirely within the cord
Division of Gray Matter
• Classically, the gray matter is divided into two major parts, called the dorsal (DH) and ventral horns (VH). The dorsal horn contains most of the tract cells that process incoming sensory information and project upward via the corresponding white matter tracts. The ventral horn contains the motoneurons, grouped together in the motor nuclei, and the autonomic preganglionic neurons that control functions such as control of blood pressure and gastrointestinal activity.
Marginal nucleus of spinal cord
The marginal nucleus of spinal cord, or posteromarginal nucleus, or Substantia Marginalis, Rexed lamina I, is located at the most dorsal aspect of the dorsal horn of the spinal cord. The neurons located here receive input primarily from Lissauer's tract and relay information related to pain and temperature sensation
The posterolateral tract (fasciculus of Lissauer, Lissauer's tract, tract of Lissauer, dorsolateral fasciculus, zone of Lissauer) is a small strand situated in relation to the tip of the posterior column close to the entrance of the posterior nerve roots.
It contains centrally projecting axons carrying non-discriminative pain and temperature information (location, intensity and quality), which enter the spinal column ascend or descend one or two spinal segments in this tract before penetrating the grey matter of the dorsal horn where they synapse on second-order neurons.
Substantia gelatinosa of Rolando
The apex of the posterior horn of the gray matter of the spinal cord is capped by a V-shaped or crescentic mass of translucent, gelatinous neuroglia, termed the substantia gelatinosa of Rolando, which contains both neuroglia cells, and small nerve cells. The gelatinous appearance is due to a very low concentration of myelinated fibers. It receives pain fibers. It corresponds to Rexed lamina II.
Nucleus proprius of spinal cord
• The Nucleus proprius is a layer of the spinal cord adjacent to the substantia gelatinosa. Nucleus proprius constitutes the bulk of the dorsal horn and receives inputs from the dorsal root ganglions that carry sensory information, such as light touch, as well as pain and temperature information.
Nucleus proprius of spinal cord
Cells in this nucleus project to deeper laminae of the spinal cord, to the posterior column nuclei, and to other supraspinal relay centers including the midbrain, thalamus, and hypothalamus. Rexed laminae III, IV, and V make up the nucleus propius. Nucleus proprius (NP), along with nucleus dorsalis (ND) are involved in sensing fine touch and proprioception.
Dorsal nucleus, posterior thoracic nucleus) is a group of interneurons found in Lamina VII, also known as the intermediate zone, of the spinal cord. It occupies the medial part of the base of the posterior horn and appears on the transverse section as a well-defined oval area.
It begins below at the level of the second or third lumbar nerve, and reaches its maximum size opposite the twelfth thoracic nerve. Above the level of the ninth thoracic nerve its size diminishes, and the column ends opposite the last cervical or first thoracic nerve. Nerve cells in Clarke’s column are most abundant between the lower thoracic and upper lumbar segments. Cell bodies are of medium size and oval- or pyriformshape
The gray commissure is a thin strip of gray matter that surrounds the central canal of the spinal cord and, along with the anterior white commissure, connects the two halves of the cord. It comprises lamina X in the Rexed classification. Divided into two areas, anterior and posterior gray commissure.
It a term referring to a disorder in which a cyst or cavity forms within the spinal cord. This cyst, called a syrinx, can expand and elongate over time, destroying the spinal cord. This damage may result in loss of sensation of pain and temperature, hot or cold, especially in the hands. As these sensation crossed to opposite site in gray commissure
Lamina I: posteromarginal nucleus
Lamina Lamina Lamina Lamina
II: substantia gelatinosa III, IV: nucleus proprius V, VI VII: intermediate gray
Clarke’s column (Nucleus dorsalis; C8-L2,
sensory relay) intermediolateral cell column -sympathetic T1-L2, parasympathetic in sacral cord)
Lamina VIII Lamina IX: anterior horn motor neurons Lamina X: gray commissure
The Rexed laminae comprise a system of ten layers of grey matter (I-X), identified in the early 1950s by Bror Rexed to label portions of the spinal cord. Similar to Brodmann areas, they are defined by their cellular structure rather than by their location, but the location still remains reasonably consistent.
Laminae of Posterior or Dorsal Horn
Laminae I-VI: Posterior/dorsal horn • Lamina I: Marginal nucleus of spinal cord or posteromarginal nucleus • Laminae II: Substantia gelatinosa of Rolando • Laminae III & IV:
Laminae of Anterior Horn
VII-IX: Anterior/ventral horn Lamina VII: intermediolateral nucleus, nucleus dorsalis Lamina VIII: motor interneurons Lamina IX: motor neurons which also contain the Onuf's nucleus in the sacral region Lamina X: neurons bordering Central canal