What is the significance of the spinal cord

What is a spinal cord injury? What causes spinal cord injury? What is paralysis? What is paraplegia? What is tetraplegia? What recovery is expected following spinal cord injury? C1-C7 nerves exit above their vertebrae whereas the C8 nerve exits below the C7 vertebra. It leaves between the C7 vertebra and the first thoracic vertebra.

Therefore, each subsequent nerve leaves the cord below the corresponding vertebra. In the thoracic and upper lumbar regions, the difference between the vertebrae and cord level is three segments.

Therefore, the root filaments of spinal cord segments have to travel longer distances to reach the corresponding intervertebral foramen from which the spinal nerves emerge. The lumbosacral roots are known as the cauda equina Figure 3. Each spinal nerve is composed of nerve fibers that are related to the region of the muscles and skin that develops from one body somite segment.

A spinal segment is defined by dorsal roots entering and ventral roots exiting the cord, i. B Drawing of the spinal vertebrate.

C Section of the spinal cord, its meninges and the dorsal and ventral roots of three segments. A dermatome is an area of skin supplied by peripheral nerve fibers originating from a single dorsal root ganglion. If a nerve is cut, one loses sensation from that dermatome. Because each segment of the cord innervates a different region of the body, dermatomes can be precisely mapped on the body surface, and loss of sensation in a dermatome can indicate the exact level of spinal cord damage in clinical assessment of injury Figure 3.

It is important to consider that there is some overlap between neighboring dermatomes. Most axons in the ventral roots arise from motor neurons in the ventral horn of the spinal cord and innervate skeletal muscle. Others arise from the lateral horn and synapse on autonomic ganglia that innervate visceral organs. The ventral root axons join with the peripheral processes of the dorsal root ganglion cells to form mixed afferent and efferent spinal nerves, which merge to form peripheral nerves.

Knowledge of the segmental innervation of the cutaneous area and the muscles is essential to diagnose the site of an injury. A transverse section of the adult spinal cord shows white matter in the periphery, gray matter inside, and a tiny central canal filled with CSF at its center.

Surrounding the canal is a single layer of cells, the ependymal layer. The shape and size of the gray matter varies according to spinal cord level. At the lower levels, the ratio between gray matter and white matter is greater than in higher levels, mainly because lower levels contain less ascending and descending nerve fibers.

The gray matter mainly contains the cell bodies of neurons and glia and is divided into four main columns: dorsal horn, intermediate column, lateral horn and ventral horn column. The dorsal horn is found at all spinal cord levels and is comprised of sensory nuclei that receive and process incoming somatosensory information.

From there, ascending projections emerge to transmit the sensory information to the midbrain and diencephalon. The intermediate column and the lateral horn comprise autonomic neurons innervating visceral and pelvic organs. The ventral horn comprises motor neurons that innervate skeletal muscle. At all the levels of the spinal cord, nerve cells in the gray substance are multipolar, varying much in their morphology. The axons of Golgi type I are long and pass out of the gray matter into the ventral spinal roots or the fiber tracts of the white matter.

The axons and dendrites of the Golgi type II cells are largely confined to the neighboring neurons in the gray matter. A more recent classification of neurons within the gray matter is based on function. These cells are located at all levels of the spinal cord and are grouped into three main categories: root cells, column or tract cells and propriospinal cells. The root cells are situated in the ventral and lateral gray horns and vary greatly in size.

The root cells contribute their axons to the ventral roots of the spinal nerves and are grouped into two major divisions: 1 somatic efferent root neurons, which innervate the skeletal musculature; and 2 the visceral efferent root neurons, also called preganglionic autonomic axons, which send their axons to various autonomic ganglia.

The column or tract cells and their processes are located mainly in the dorsal gray horn and are confined entirely within the CNS. 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.

There are 31 pairs of spinal nerves that are distributed in a systematic way. The spinal cord and the brain together constitute the Central Nervous System.

It is an incredibly complex and intricate mesh of nerves. It would be almost impossible to survive without the CNS-that is how vital it is to the body. That explains why a damaged CNS cripples all the basic body functions even if the person is alive. The spinal cord controls all the reflex actions that are done involuntarily and rapidly.

The spinal cord controls all voluntary reflexes as well. The spinal cord is essentially the information processing center of your body. The electrical currents traversing up and down the spinal cord allow the body to connect and communicate with the brain. The spinal cord carries messages to the brain that allow you to recognize and process information like:. In a city like Chennai, where there are many hospitals and doctors to deal with spinal cord injuries, HAMSA stands a cut above the rest as first-ever spinal cord rehabilitation center in Chennai.

Services in HAMSA are on par with international standards and extend to include brain injury and stroke patients. Supervised by a deeply committed team of experts, HAMSA offers holistic, medical-based practices and comprehensive patient care to provide and promote a quick and complete recovery from spinal cord injuries.

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