The axons of the column cells form longitudinal ascending tracts that ascend in the white columns and terminate upon neurons located rostrally in the brain stem, cerebellum or diencephalon. Some column cells send their axons up and down the cord to terminate in gray matter close to their origin and are known as intersegmental association column cells.
Other column cell axons terminate within the segment in which they originate and are called intrasegmental association column cells. Still other column cells send their axons across the midline to terminate in gray matter close to their origin and are called commissure association column cells.
The propriospinal cells are spinal interneurons whose axons do not leave the spinal cord proper. Some of these fibers also are found around the margin of the gray matter of the cord and are collectively called the fasciculus proprius or the propriospinal or the archispinothalamic tract. The prominent nuclear groups of cell columns within the spinal cord from dorsal to ventral are the marginal zone, substantia gelatinosa, nucleus proprius, dorsal nucleus of Clarke, intermediolateral nucleus and the lower motor neuron nuclei.
The axons of its neurons contribute to the lateral spinothalamic tract which relays pain and temperature information to the diencephalon Figure 3.
Substantia gelatinosa is found at all levels of the spinal cord. Located in the dorsal cap-like portion of the head of the dorsal horn, it relays pain, temperature and mechanical light touch information and consists mainly of column cells intersegmental column cells.
These column cells synapse in cell at Rexed layers IV to VII, whose axons contribute to the ventral anterior and lateral spinal thalamic tracts. The homologous substantia gelatinosa in the medulla is the spinal trigeminal nucleus.
Nucleus proprius is located below the substantia gelatinosa in the head and neck of the dorsal horn. This cell group, sometimes called the chief sensory nucleus, is associated with mechanical and temperature sensations.
It is a poorly defined cell column which extends through all segments of the spinal cord and its neurons contribute to ventral and lateral spinal thalamic tracts, as well as to spinal cerebellar tracts. The axons originating in nucleus proprius project to the thalamus via the spinothalamic tract and to the cerebellum via the ventral spinocerebellar tract VSCT. Dorsal nucleus of Clarke is a cell column located in the mid-portion of the base form of the dorsal horn. The axons from these cells pass uncrossed to the lateral funiculus and form the dorsal posterior spinocerebellar tract DSCT , which subserve unconscious proprioception from muscle spindles and Golgi tendon organs to the cerebellum, and some of them innervate spinal interneurons.
The dorsal nucleus of Clarke is found only in segments C8 to L3 of the spinal cord and is most prominent in lower thoracic and upper lumbar segments. The homologous dorsal nucleus of Clarke in the medulla is the accessory cuneate nucleus, which is the origin of the cuneocerebellar tract CCT. Intermediolateral nucleus is located in the intermediate zone between the dorsal and the ventral horns in the spinal cord levels. Extending from C8 to L3, it receives viscerosensory information and contains preganglionic sympathetic neurons, which form the lateral horn.
A large proportion of its cells are root cells which send axons into the ventral spinal roots via the white rami to reach the sympathetic tract as preganglionic fibers. Similarly, cell columns in the intermediolateral nucleus located at the S2 to S4 levels contains preganglionic parasympathetic neurons Figure 3. Lower motor neuron nuclei are located in the ventral horn of the spinal cord. The a motor neurons are the final common pathway of the motor system, and they innervate the visceral and skeletal muscles.
The distribution of cells and fibers within the gray matter of the spinal cord exhibits a pattern of lamination. The cellular pattern of each lamina is composed of various sizes or shapes of neurons cytoarchitecture which led Rexed to propose a new classification based on 10 layers laminae.
This classification is useful since it is related more accurately to function than the previous classification scheme which was based on major nuclear groups Figure 3. Laminae I to IV, in general, are concerned with exteroceptive sensation and comprise the dorsal horn, whereas laminae V and VI are concerned primarily with proprioceptive sensations.
Lamina VII is equivalent to the intermediate zone and acts as a relay between muscle spindle to midbrain and cerebellum, and laminae VIII-IX comprise the ventral horn and contain mainly motor neurons. The axons of these neurons innervate mainly skeletal muscle. Lamina X surrounds the central canal and contains neuroglia. Rexed lamina I — Consists of a thin layer of cells that cap the tip of the dorsal horn with small dendrites and a complex array of nonmyelinated axons.
Cells in lamina I respond mainly to noxious and thermal stimuli. Lamina I cell axons join the contralateral spinothalamic tract; this layer corresponds to nucleus posteromarginalis. Rexed lamina II — Composed of tightly packed interneurons. This layer corresponds to the substantia gelatinosa and responds to noxious stimuli while others respond to non-noxious stimuli. The majority of neurons in Rexed lamina II axons receive information from sensory dorsal root ganglion cells as well as descending dorsolateral fasciculus DLF fibers.
High concentrations of substance P and opiate receptors have been identified in Rexed lamina II. The lamina is believed to be important for the modulation of sensory input, with the effect of determining which pattern of incoming information will produce sensations that will be interpreted by the brain as being painful.
Rexed lamina III — Composed of variable cell size, axons of these neurons bifurcate several times and form a dense plexus. Rexed lamina IV — The thickest of the first four laminae.
In addition, dendrites of neurons in lamina IV radiate to lamina II, and respond to stimuli such as light touch. The ill-defined nucleus proprius is located in the head of this layer. Some of the cells project to the thalamus via the contralateral and ipsilateral spinothalamic tract. Rexed lamina V — Composed neurons with their dendrites in lamina II. This lamina covers a broad zone extending across the neck of the dorsal horn and is divided into medial and lateral parts.
Many of the Rexed lamina V cells project to the brain stem and the thalamus via the contralateral and ipsilateral spinothalamic tract.
Moreover, descending corticospinal and rubrospinal fibers synapse upon its cells. Rexed lamina VI — Is a broad layer which is best developed in the cervical and lumbar enlargements. Lamina VI divides also into medial and lateral parts. Group Ia afferent axons from muscle spindles terminate in the medial part at the C8 to L3 segmental levels and are the source of the ipsilateral spinocerebellar pathways. Many of the small neurons are interneurons participating in spinal reflexes, while descending brainstem pathways project to the lateral zone of Rexed layer VI.
Rexed lamina VII — This lamina occupies a large heterogeneous region. This region is also known as the zona intermedia or intermediolateral nucleus. Its shape and boundaries vary along the length of the cord. Lamina VII neurons receive information from Rexed lamina II to VI as well as visceral afferent fibers, and they serve as an intermediary relay in transmission of visceral motor neurons impulses.
The dorsal nucleus of Clarke forms a prominent round oval cell column from C8 to L3. The large cells give rise to uncrossed nerve fibers of the dorsal spinocerebellar tract DSCT. Cells in the lateral horn of the cord in segments T1 and L3 give rise to preganglionic sympathetic fibers to innervate postganglionic cells located in the sympathetic ganglia outside the cord.
Lateral horn neurons at segments S2 to S4 give rise to preganglionic neurons of the sacral parasympathetic fibers to innervate postganglionic cells located in peripheral ganglia.
Rexed lamina VIII — Includes an area at the base of the ventral horn, but its shape differs at various cord levels. In the cord enlargements, the lamina occupies only the medial part of the ventral horn, where descending vestibulospinal and reticulospinal fibers terminate. The neurons of lamina VIII modulate motor activity, most probably via g motor neurons which innervate the intrafusal muscle fibers. Its size and shape differ at various cord levels.
Rexed lamina X — Neurons in Rexed lamina X surround the central canal and occupy the commissural lateral area of the gray commissure, which also contains decussating axons.
In summary, laminae I-IV are concerned with exteroceptive sensations, whereas laminae V and VI are concerned primarily with proprioceptive sensation and act as a relay between the periphery to the midbrain and the cerebellum.
All visceral motor neurons are located in lamina VII and innervate neurons in autonomic ganglia. Surrounding the gray matter is white matter containing myelinated and unmyelinated nerve fibers. These fibers conduct information up ascending or down descending the cord. The white matter is divided into the dorsal or posterior column or funiculus , lateral column and ventral or anterior column Figure 3.
The anterior white commissure resides in the center of the spinal cord, and it contains crossing nerve fibers that belong to the spinothalamic tracts, spinocerebellar tracts, and anterior corticospinal tracts. Three general nerve fiber types can be distinguished in the spinal cord white matter: 1 long ascending nerve fibers originally from the column cells, which make synaptic connections to neurons in various brainstem nuclei, cerebellum and dorsal thalamus, 2 long descending nerve fibers originating from the cerebral cortex and various brainstem nuclei to synapse within the different Rexed layers in the spinal cord gray matter, and 3 shorter nerve fibers interconnecting various spinal cord levels such as the fibers responsible for the coordination of flexor reflexes.
Ascending tracts are found in all columns whereas descending tracts are found only in the lateral and the anterior columns.
Four different terms are often used to describe bundles of axons such as those found in the white matter: funiculus, fasciculus, tract, and pathway. Funiculus is a morphological term to describe a large group of nerve fibers which are located in a given area e.
Within a funiculus, groups of fibers from diverse origins, which share common features, are sometimes arranged in smaller bundles of axons called fasciculus, e. Fasciculus is primarily a morphological term whereas tracts and pathways are also terms applied to nerve fiber bundles which have a functional connotation.
A tract is a group of nerve fibers which usually has the same origin, destination, and course and also has similar functions.
The tract name is derived from their origin and their termination i. Cervical Radiculopathy Interactive Video. You are here Conditions Spine Anatomy. Cervical Spinal Nerves share pin it Newsletters.
Peer Reviewed. Video: Cervical Nerve Anatomy Learn how 8 pairs of spinal nerves in the neck play an important role in sending messages to and from the spinal cord. Magee DJ. Cervical Spine. In: Magee DJ, ed. Orthopedic Physical Assessment. Louis, MO. Saunders Elsevier; One pair of coccygeal Co1 nerves meets in the area of the tailbone.
By way of the peripheral nervous system PNS , nerve impulses travel to and from the brain through the spinal cord to a specific location in the body. The PNS is a complex system of nerves that branch off from the spinal nerve roots. These nerves travel outside of the spinal canal to the upper extremities arms, hands and fingers , to the muscles of the trunk, to the upper and lower extremities arms, hands, fingers, legs, feet and toes and to the organs of the body.
Any interruption of spinal cord function by disease or injury at a particular level may result in a loss of sensation and motor function below that level. Depending on the severity of the disease or injury, the loss of function may be permanent. Did you know you can support education and research for neurosurgical conditions while you shop, at no extra cost to you? Register with AmazonSmile to designate the NREF as your charity, and a percentage of your purchase is donated automatically.
Annulus fibrosus — The fibrous, ring-like outer portion of an intervertebral disc. Arachnoiditis — Inflammation of the arachnoid membrane the middle of the three protective layers called the meninges ; most commonly seen around the spinal cord and cauda equina. Arthritis — Inflammation of a joint, usually accompanied by swelling, pain and restriction of motion.
Bone spur — Bony growth or rough edge of bone. Cauda equina — The collection of nerves at the end of the spinal cord that resembles a horse's tail. Cervical spine — The neck region of the spine consisting of the first seven vertebrae. Coccyx — More commonly known as the tailbone, this is a bony structure in the region of the spine below the sacrum. Conus medullaris — The cone-shaped bottom of the spinal cord, usually at the level of L1.
Disc Intervertebral — A tough, elastic cushion located between the vertebrae in the spinal column; acts as a shock absorber for the vertebrae. Disc degeneration — The deterioration of a disc. A disc in the spine may wear out over time.
A deteriorated disc may or may not cause pain. Facet — A joint formed when a posterior structure of a vertebra that joins with a facet of an adjacent vertebra; this joint allows for motion in the spinal column. Each vertebra has a right and left superior upper facet and a right and left inferior lower facet.
Foramen — An opening in the vertebrae of the spine through which the spinal nerve roots travel. Joint — The junction of two or more bones that permits varying degrees of motion between the bones. Lamina — The flattened or arched part of the vertebral arch that forms the roof or back part of the spinal canal. Ligament — Fibrous connective tissue that links bones together at joints or that passes between bones of the spine.
Lumbar spine — The lower back region of the spine; consists of the five vertebrae between the ribs and the pelvis.
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