Spinal cord

The spinal cord ( medulla spinalis or medulla dorsalis Latin, Greek ῥαχίτης μύελος rhachítes mýelos or νωτιαῖος μύελος nōtiaios mýelos ) is the part of the central nervous system (CNS) of vertebrates, which runs within the vertebral canal. As part of the CNS, the spinal cord is surrounded by the same skins as the brain.

• 2.1 Grey Matter 2.1.1 cell types
• 2.1.2 dorsal horn
• 2.1.3 anterior horn
• 2.1.4 lateral horn

• 2.2.1 Important ascending pathways
• 2.2.2 Important descending pathways

Location, shape, and structure

The spinal cord of man reaches the unborn child from the foramen magnum of the skull until the sacrum, the infant up to the lower lumbar vertebrae, in the adult it ends at the level of first to second lumbar vertebra (L1- L2). This can be explained by the fact that the spine in the course of human development grows faster than the spinal cord and therefore the longitudinal growth of the spinal cord behind the spine remains (so-called medulla spinalis ascensus, "Rise of the spinal cord ").

By this phenomenon, the roots of the spinal nerves have to because they are " their" original intervertebral foramen emerge despite the ascensus yet from a downward ( caudal ) toward increasingly longer path within the spinal canal to cover before they can leave him. From the 1st lumbar vertebra, after the end of the spinal cord, run only the roots of the spinal nerves down in the spinal canal. They form the cauda equina (from the Latin cauda "tail ", " tail " and equus "horse", " horse's tail "). The spinal cord is like the brain of cerebrospinal fluid ( CSF) surrounding it. When lumbar puncture can puncture at the level of 3 / 4 Lumbar vertebral body cerebrospinal fluid removed and / or drugs are injected without injuring the spinal cord.

The ascensus occurs in the other mammals on also, but here the spinal cord ends at the level of the posterior lumbar vertebrae. In the other vertebrates, this phenomenon does not occur.

Wrap

The spinal cord ( meninges medullae spinalis ) behave in principle as the meninges. Again, we distinguish the outer dura mater, the middle arachnoid ( arachnoid ) and the directly adjacent to the spinal cord pia mater. Compared to the membranous sheath in the area of the brain, there are two structural features. Firstly, the dura mater is not adherent to the spinal canal, so that between the bone and dura mater a filled with connective tissue and fat space is formed, called the epidural space or epidural space, in which a dense venous plexus lies. In the epidural is a local anesthetic can be introduced ( apply ) and thus the exiting nerve off ( epidural ). A second structural feature are segmental bridges between pia and dura mater, called the ligamentum denticulatum ( " toothed belt "). These triangular in plan structures serve the suspension stabilizing the spinal cord in the subarachnoid space filled with cerebrospinal fluid ( space between the arachnoid and pia mater).

External appearance

The spinal cord is a long strand, which is significantly thickened in two places: at the intumescentia cervical and the lumbosacral intumescentia ( intumescentia (lat. ) = swelling ). The swellings arise from the fact that in these areas, those spinal nerves leave the spinal cord innervating the arms and legs, which requires a larger number of neurons than for example the innervation of the trunk. On the downside, the spinal cord tapers off as Mark cone ( conus medullaris ) and continues in the approximately 1 millimeter thick terminal filament ( filum terminale ) continued, still contains only glial cells and is attached in humans to the rear surface of the second Steißwirbels.

Front ( in animals below) runs from top to bottom, a small furrow, the anterior median fissure (animals: the ventral median fissure ). On the back side of the median sulcus extends posteriorly. On both sides there are three strands (Latin funiculi ) can be demarcated from each other: Para Median of median fissure of the anterior column ( anterior funiculus ), behind the dorsal columns ( posterior funiculus ) and between the two of the lateral column ( funiculus lateralis). The dorsal roots of the spinal nerves exit respectively of in-furrow (Latin sulcus ) between the rear and side strand ( sulcus lateralis posterior), the ventral roots between the side and the front line ( sulcus lateralis anterior). The front and dorsal roots of the spinal nerves from the spinal cord occur continuously as Fila radicularia and unite only at the level of the intervertebral foramen ( intervertebral foramina ) of the vertebrae of the spinal nerves.

In birds in the area of ​​the so-called lumbosacral intumescentia Glykogenkörper ( Corpus gelatinosum ) is intercalated between the posterior columns of both sides. It is a jelly-like, ovoid formation of glycogen glial cells, their functional significance has not been elucidated. In the domestic fowl, it is about 1 cm long and 4 mm wide.

Structure

• Cervical vertebrae ( cervical part )
• Thoracic vertebrae ( thoracic part )
• Lumbar ( lumbar part )
• Tailbone ( coccyx )

The spinal cord is divided according to the exit for the spinal nerves into five sections, which can be divided into a number of segments:

• Neck or cervical spinal cord ( cervical part ): in mammals 8 segments (C1 - C8)
• Chest or thoracic spinal cord ( thoracic part ): segments according to the number of vertebrae in humans 12 (Th1 - Th12 )
• Lumbar or lumbar spinal cord ( lumbar part ): segments according to the number of vertebrae in humans 5 (L1 -L5)
• Cross or sacral spinal cord ( sacral Pars ): segments according to the number of vertebrae in humans 5 (S1- S5)
• Tail or Kokzygealmark ( Pars coccyx ): constructed rudimentary in humans, one segment ( Co1 )

This classification does not depend on the position of the sections in the spinal canal, but only after the exit for the spinal nerves of the spinal column. A segment corresponding to the spinal cord section that provides the fibers for each left and right spinal nerves. From the first Thorakalsegment the spinal nerve is named with its associated segment of the overlying vertebrae in the cervical area, however, according to the underlying vertebrae, because the first spinal nerve emerges not below but above the first cervical vertebra ( atlas). Thus, the cervical spinal cord has eight segments in seven vertebrae, in contrast to the remaining sections, in which the number of market segments coincides with the number of vertebrae. This can be explained this apparent discrepancy to the fact that parts of the occipital bone ( occipital bone ) can be considered as evolutionary vertebrae.

Feinbau

The spinal cord consists of gray matter and white matter. The gray matter consists mainly of nerve cell bodies ( perikarya ), the white matter of axons.

Gray matter

The gray matter in the form of a butterfly in the spinal cord cross section. The front, wider wing part is called the anterior horn ( Cornu anterior, ventral in animals Cornu ), the rear, narrower part of the dorsal horn ( Cornu posterior or dorsal). In the field of thoracic and Lumbalmarks is located between the front and rear horn, the smaller the lateral horn ( Cornu lateral). The two butterfly wings are connected by a cross connection ( commissure grisea ). In the middle of the commissure grisea the central canal, which is filled with cerebrospinal fluid and represents the inner subarachnoid space of the spinal cord runs. The gray matter can be divided into ten layers ( laminae Latin ), which are also known by other names in some cases. So lamina II is often referred to in the literature as the substantia gelatinosa Rolandi ( after its discoverer Luigi Rolando ). The laminae I-VII are located in the dorsal horn, the laminae VIII and IX in the ventral horn. The lamina X is the commissure grisea. Functionally, individual nerve nuclei can be distinguished ( see picture).

Cell types

In addition to the root cells, whose axons form the ventral root, there are in the gray matter a variety of other cells.

The so-called single cells make their own apparatus of the spinal cord dar. This realizes the integration benefits of the spinal cord, for example, for the generation of reflections. To own apparatus further includes switching cells, cells and association Kommissurenzellen. The extensions of the switching cells (or interneurons ) leave the gray matter not, but run ipsilateral (on the same side of the body ) within a spinal segment. You make the connection between cells of the same segment and mediate eg reflexes. Important interneurons are also the Renshaw cells, which have an inhibitory feedback effect on motor neurons. The association cells ( propriospinal neurons ) connect different spinal cord segments. Your projections leave the gray matter also not even to extend ipsilateral. The Kommissurenzellen intersect with their axons to the other side of the body (contralateral ) within a spinal segment. They ensure that the excitation pulses reach the other side of the spinal cord.

Strand cells ( projection neurons ) are only partially for its own apparatus of the spinal cord. They leave with their neurites and drag the gray matter in the white matter. Here they move into strands and transmit information to other spinal cord segments and the brain.

Association, stranded and Kommissurenzellen are involved in triggering the foreign reflexes.

Dorsal horn

The posterior horn receives on the back side ( dorsal), sensory root of the spinal nerve sensory information from the periphery. This information is passed in the direction of the brain, but partly also processes already in the spinal cord.

The dorsal root is formed by axons pseudounipolarer neurons whose cell bodies lie outside the spinal cord in the spinal ganglion. Their axons pass over the dorsal ( sensory) roots in the spinal cord, where a portion of the posterior horn on a second neuron is switched. Other Hinterwurzelaxone run without switching to the medulla oblongata.

The dorsal horn, which shows embryologically from the wing panel, consists of dorsal to ventral are switched ( from the back towards the belly ) of a thin zona marginalis, to which the substantia gelatinosa followed in the Schmerzafferenzen the skin receptors on the second neuron before they move to the thalamus in the lateral spinothalamic tract. Here inhibit interneurons that are activated by the transmitter serotonin, pain transmission through the release of endorphins. Thereby, the substantia gelatinosa is clinically highly relevant and provides a starting point for the explanation of mechanisms of the controversial acupuncture or pain-inhibiting effect of some antidepressants.

In the laminae 3 and 4 of the nucleus proprius, which can be found in full height of the spinal cord is located. He is goal sensitive afferents of depth perception and forms in its cranial ( leading to the head) during the anterior spinocerebellar tract.

Laminae 5 and 6, finally, include the nucleus dorsalis ( Stilling - Clarke), who also is called the posterior thoracic nucleus. Just as the nucleus proprius of the dorsal nucleus receives afferents in depth sensitivity (muscle spindles, joint and tendon receptors), which are passed through the posterior spinocerebellar tract to the cerebellum.

Anterior horn

The anterior horn is formed from the base plate and contains cell bodies whose axons than radix anterior spinal cord exit to innervate the skeletal muscles. In the stratification the anterior horns consist of laminae 8 and 9 Here, the large multi-polar α - motoneurons and the somewhat smaller ɣ motoneurons and Renshaw cells occur. Here, the impulses coming from the brain pathways ( pyramidal and extrapyramidal pathways ), and send the impulses of muscle reflexes and are called " common final pathway motor " to the success of organ - the skeletal muscles - routed.

Lateral horn

In the area of ​​breast Marks and, somewhat less clearly, in the spinal cord is located between the front and the dorsal horn lying, called the lateral horn, which is made from the cell bodies of vegetative neurons and is part of the sympathetic nervous system. Your efferent fibers leave the spinal cord via the ventral root, pull the sympathetic chain and in part connected there to the second neuron. The radical drawn to the prevertebral ganglion to be connected there. Sympathetic afferent fibers pass from the periphery to the dorsal root to the lateral horn. An equivalent station are in the sacral spinal cord cell bodies of parasympathetic neurons to form but without a recognizable lateral horn. The axons as pelvic splanchnic nerves to the pelvic ganglion and on the intramural ganglia.

White matter

In the white matter of the spinal cord ascending run (mostly sensory) pathways that pull to the brain, and descending ( mostly motor ) tracks that come from the brain. Cause of the white color is the myelination of axons.

Important ascending pathways

The rear train rail passes epikritische sensitivity and depth sensitivity of the information in each of the same side of the body in the Extended spinal cord (medulla oblongata ) in the brain. The cell bodies of the running in the dorsal column axons train are in the spinal ganglia. There is no change in the dorsal horn, but in the medulla oblongata, the gracile nucleus for information of the lower body and in the cuneate nucleus of the upper half of the body. The posterior column can be divided into a fasciculus gracilis and cuneatus a fasciculus, the fiber end at the corresponding nuclei. Shortly after the switchover to the second neuron cross the fibers on the opposite side. This crossing is eponymous for the lemniscal system.

The spinothalamic tract ( anterolateral sensitive rail system or front rail train ) carries impulses of protopathic sensitivity (rough pressure, temperature and pain sensation) from the cells of the dorsal horn to the thalamus; it is part of extralemniskalen system. The fibers cross at the level of the source segment to the other side.

The spinocerebellar tract ( lateral cerebellar path ) arises mainly from the dorsal nucleus of the posterior horn and ends in the cerebellum. It runs either uncrossed or crossed the side twice and forwards proprioceptive ( = information about the location and position of the joints, muscles, tendons ) information.

Important descending pathways

The pyramidal tract ( corticospinal tract ) extends from the motor cortex of the cerebral cortex to the anterior horn.

When extrapyramidal pathways is any motor pathways, which do not belong to pyramidal tract. They include the rubrospinalis tract, the vestibulospinal tract, the reticulospinal tract and the tract tectospinal. They all also terminate in the ventral horn.

Neurotransmitters in the spinal cord

The major inhibitory neurotransmitter in the spinal cord is glycine. Interneurons and, for example, the Renshaw cells are glycinerg, that is, they set glycine from their synaptic terminals freely.

Embryology and malformations

The spinal cord is formed when vertebrate embryo from the neural folds of the ectoderm, immediately above the notochord. The neural folds close to the neural tube, a liquid-filled channel, which is surrounded by an epithelium. In case of malfunctions of this closure various forms of dysraphism occur. It can be an open spina bifida ( "open back " ) arise, the vertebral arches remain incomplete at the dorsal side. Only the spinal meninges ( meningocele ) or in addition, the spinal cord ( meningomyelocele ) can bulge outward through this defect. There, where the neural groove does not close itself, creates a Myeloschisis ( rachischisis ). If this defect in the rostral ( anterior ) end of the neural groove, there is even a lack of education of the brain ( anencephaly ).

From the neuroepithelium of the neural and glial cells differentiate. The dorsal root ganglia and sympathetic neurons arise from the so-called neural crest. The neural tube to emerge from the mesenchyme, the somites, from which the spine is formed, among other things.

First, leave Proneurone ( the precursors of neurons ), the neuroepithelium and form a cladding layer ( mantle zone ) from which the gray matter is created. Most of these axons Proneurone grow towards the surface and form the boundary layer ( marginal zone ), which is the white substance later.

Within the cladding layer evolve through cell proliferation and migration, two thickenings, the wing plate ( Alarplatte ) and the base ( basal plate ) which have gradually the later appearance of a butterfly. The boundary layer is divided by the further ingrowth of ascending and descending axons whose myelination and the magnification of the wing and base plates in three strands: dorsal column, lateral column and the anterior funiculus.

When Tethered cord remains under the relative shortening of the spinal cord.

Blood supply

Three arteries supply the spinal cord: the front the anterior spinal artery, posterior spinal arteries rear two. In animals with horizontal body position is instead spoken of the ventral spinal artery and dorsalis.

These three arteries arise in the neck area on both sides of the laterally extending into the spinal vertebral arteries. In the thoracic and lumbar segmental they receive inflows from the intercostal ( intercostal arteries posterior ) and the lumbar arteries ( arteries, lumbar ). The largest and most important segment of artery is the Adamkiewicz artery ( radicularis magna), which is usually between the 9th and 12th thoracic segment. A closure of this vessel is particularly influential to the blood supply of the thoracic spinal cord.

In the region between the 4th and 6th thoracic vertebrae, the training of such flows is small, so that when a vessel closure, this section is particularly at risk of suffering a spinal cord infarction.

The venous blood is removed two large veins, the partially parallel to the artery: Vena anterior spinal and spinal posterior vena.

Phylogenesis

In the form described here, the spinal cord is made up of all representatives of the skull Animals ( gnathostomata ), and there are slight differences in each case in detail in the different taxa.

In the basal chordates, to which the acrania ( Acrania ) and tunicates ( Tunicata ) belong, there is no differentiated spinal cord. Here there is instead only the neural tube, which is the later spinal cord homologous. At its front end, it has a thickening, which is called the cerebral vesicles, however, has in common with the vertebrate brain not much. The neural tube itself is made ​​up of some highly differentiated neurons, via interconnections and functions the same, however, is little known. The Hauptaxone emanate from the so-called colossal cells, which are large and intermediate neurons whose axons form ventromediane giant fibers. Segmental located dorsal nerve roots, which correspond to the later dorsal root ganglia, due to the offset myomeres but offset from each other. During this construction consists in the acrania to the adult animal, he finds himself at the Tunicata only in the larval state.

In the hagfish ( Myxinoida ) and lampreys ( Petromyzontida ) representing as jawless ( Agnatha ), the most primitive taxa of the skull Animals ( Craniata ), there is already a spinal cord, in which the neural tube, as in the later vertebrates represents only the lumen. The hagfish is it structured band-shaped and has several motor neurons and interneurons without a segmental arrangement, the roots of the spinal nerves unite only in the somatic musculature and a number of organs are innervated by spinal nerves directly. The spinal cord of the lamprey is similar, however, already clear that of the later vertebrates. It has a separation in white and gray matter and the cell bodies of Riesenaxone lie primarily in the brainstem. On the other hand, the interconnection of the neurons in the spinal column is so complex that the animals even after a disconnection, the same can swim in front of the brain, such as by removing the head, nor coordinated. The dorsal and ventral roots of the spinal nerves unite with the animals near the spinal cord, but do not occur segmentally produced in the same amount from the spinal cord.

The cartilaginous fishes ( Chondrichthyes ), to which the sharks and rays belong to possess a spinal cord with segmental spinal nerves, as is typical for the skull animals. With them, however, some features are available. Even with them, the spinal cord is very strong autonomous and a shark can still use coordinated swim when the spinal cord is severed at the neck. Unlike all other vertebrates, the number of sensory and motor root ganglia during the growth of life-long. In addition to other differences in the fine structure, such as a separate descending strand of the nuclei of the cranial nerve VIII, the cartilaginous fishes possess a caudal neurosekretorisches system, which plays an important role in osmoregulation and in reproduction.

All of the following taxa from the Strahlenflossern to the amphibians, the various Reptilientaxa as well as the birds and the mammals, the spinal cord has the same design and function as the basic pattern shown and differs only in very specific details from each other.

Spinal cord injury

Damage to the spinal cord ( myelopathy ) can

• Pressure ( tumor, herniated disc, wobbler syndrome, cauda equina syndrome, whiplash ),
• Transection (spina neutralization with subsequent paraplegia),
• Inflammation ( myelitis, multiple sclerosis),
• Infections such as neurosyphilis ( tabes dorsalis),
• Circulatory disorders ( Fibrokartilaginöse embolism),
• Degenerative processes ( Degenerative myelopathy dogs, cauda equina syndrome of dogs), syringomyelia or
• Congenital malformation such as the Chiari malformation type II or III

Caused.

Examination of the spinal cord

The spinal cord itself is the clinical examination by its position in the bony spinal canal is not directly accessible. However, reflex tests and the distribution pattern of paralysis ( paresis ) or dysesthesias give the neurologist important clues to the nature and location of the injury. Neurophysiological investigation methods such as motor and somatosensory evoked potentials allow a functional examination of individual railway systems of the spinal cord, such as the corticospinal tract and the posterior funiculus. Investigations of reflex pathways on motor neurons in the spinal cord are possible with the help of the H- reflex and F- wave.

Structural changes can be seen, however, with the imaging techniques, especially magnetic resonance imaging, computed tomography and myelography. Abnormalities in the vascular system of the spinal cord can also be presented with angiography. Evidence of inflammation can also supply the lumbar puncture and examination of the spinal fluid.