Myelinated, so axons thatĪre wrapped in myelin. The central nervous system, is most of the "myelinated axons". And then there are otherĪreas called "white matter". In the central nervous system are found in the gray matter. In the central nervous system, which is mostly the brainĪnd the spinal cord, there are areas called "gray matter" gray matter, that contain most of the "neuron somas". The disadvantage of laminae is that, unlike nuclei, laminar boundaries are not evident in normal sections.Voiceover: In this video, I'm gonna talk about Laminae offer the advantage of including all regions of gray matter. An alternative of method of categorizing gray matter involves defining spinal laminae (below), as opposed to nuclei. Much of the spinal gray matter is outside of recognizable nuclei. Motor nuclei are somatotopically arranged. Lateral collections of motor neurons, which innervate limb muscle, are seen in segments of the cervical and lumbosacral enlargements. Medial motor nuclei innervate muscles of the trunk and are found in all spinal segments. The ventral horn contains somatic efferent motor neurons. The intermediolateral nucleus, which forms a lateral horn, is composed of sympathetic preganglionic neurons. In the intermediate substance, one nucleus is found only in thoracic and cranial lumbar segments of the spinal cord. The nucleus thoracicus, located medially in the base of the dorsal horn, is present in thoracolumbar segments axons from the nucleus form the dorsal spinocerebellar tract (Note: nucleus thoracicus projection neurons are large but sparse and not evident in some sections). The remainder of the dorsal horn may be considered nucleus proprius. A population of small neurons forms a very distinctive substantia gelatinosa (lamina II). The dorsal horn surface is capped by a marginal nucleus (lamina I) which is thin and not distinct in transverse sections. Some nuclei (columns of cell bodies) are present throughout the spinal cord, other nuclei have more restricted segmental distributions. The cell body clusters are called nuclei. Columns of neuron cell bodies, when transected, appear as clusters of neuron cell body profiles within gray matter. The gray matter "horns" are actually profiles of gray columns. Spinal neurons within the gray matter are either efferent neurons (axons enter ventral roots), projection neurons (axons join white matter tracts), or interneurons (axons remain within gray matter).
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