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Spinal cord
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Spinal cord
The spinal cord (in yellow) connects the brain to nerves throughout the body.
Details
Part of
Central nervous system
Identifiers
Latin
medulla spinalis
MeSH
D013116
NeuroNames
22
TA
A14.1.02.001
FMA
7647
Anatomical terminology
[edit on Wikidata]
The spinal cord is a long, thin, tubular bundle of nervous tissue and support cells that extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column. The brain and spinal cord together make up the central nervous system (CNS). In humans, the spinal cord begins at the occipital bone where it passes through the foramen magnum, and meets and enters the spinal canal at the beginning of the cervical vertebrae. The spinal cord extends down to between the first and second lumbar vertebrae where it ends. The enclosing bony vertebral column protects the relatively shorter spinal cord. It is around 45 cm (18 in) in men and around 43 cm (17 in) long in women. Also, the spinal cord has a varying width, ranging from 13 mm (1⁄2 in) thick in the cervical and lumbar regions to 6.4 mm (1⁄4 in) thick in the thoracic area.
The spinal cord functions primarily in the transmission of nerve signals from the motor cortex to the body, and from the afferent fibers of the sensory neurons to the sensory cortex. It is also a center for coordinating many reflexes and contains reflex arcs that can independently control reflexes and central pattern generators.[1]
Contents
[hide]
1 Structure
1.1 Spinal cord segments
1.2 Development
1.3 Blood supply
2 Function
2.1 Somatosensory organization
2.2 Motor organization
2.3 Spinocerebellar tracts
3 Clinical significance
3.1 Injury
3.2 Treatment
3.3 Lumbar puncture
3.4 Tumours
4 Additional images
5 See also
6 References
7 External links
Structure[edit]
Diagram of the spinal cord showing segments
The spinal cord is the main pathway for information connecting the brain and peripheral nervous system.[2][3] Much shorter than its protecting spinal column, the human spinal cord originates in the brainstem, passes through the foramen magnum, and continues through to the conus medullaris near the second lumbar vertebra before terminating in a fibrous extension known as the filum terminale.
It is about 45 cm (18 in) long in men and around 43 cm (17 in) in women, ovoid-shaped, and is enlarged in the cervical and lumbar regions. The cervical enlargement, stretching from the C5 to T1 vertebrae, is where sensory input comes from and motor output goes to the arms and trunk. The lumbar enlargement, located between L1 and S3, handles sensory input and motor output coming from and going to the legs.
The spinal cord is continuous with the caudal portion of the medulla, running from the base of the skull to the body of the first lumbar vertebra. It does not run the full length of the vertebral column in adults. It is made of 31 segments from which branch one pair of sensory nerve roots and one pair of motor nerve roots. The nerve roots then merge into bilaterally symmetrical pairs of spinal nerves. The peripheral nervous system is made up of these spinal roots, nerves, and ganglia.
The dorsal roots are afferent fascicles, receiving sensory information from the skin, muscles, and visceral organs to be relayed to the brain. The roots terminate in dorsal root ganglia, which are composed of the cell bodies of the corresponding neurons. Ventral roots consist of efferent fibers that arise from motor neurons whose cell bodies are found in the ventral (or anterior) gray horns of the spinal cord.
The spinal cord (and brain) are protected by three layers of tissue or membranes called meninges, that surround the canal . The dura mater is the outermost layer, and it forms a tough protective coating. Between the dura mater and the surrounding bone of the vertebrae is a space called the epidural space. The epidural space is filled with adipose tissue, and it contains a network of blood vessels. The arachnoid mater, the middle protective layer, is named for its open, spiderweb-like appearance. The space between the arachnoid and the underlying pia mater is called the subarachnoid space. The subarachnoid space contains cerebrospinal fluid (CSF), which can be sampled with a lumbar puncture, or "spinal tap" procedure. The delicate pia mater, the innermost protective layer, is tightly associated with the surface of the spinal cord. The cord is stabilized within the dura mater by the connecting denticulate ligaments, which extend from the enveloping pia mater laterally between the dorsal and ventral roots. The dural sac ends at the vertebral level of the second sacral vertebra.
In cross-section, the peripheral region of the cord contains neuronal white matter tracts containing sensory and motor axons. Internal to this peripheral region is the grey matter, which contains the nerve cell bodies arranged in the three grey columns that give the region its butterfly-shape. This central region surrounds the central canal, which is an extension of the fourth ventricle and contains cerebrospinal fluid.
The spinal cord is elliptical in cross section, being compressed dorsolaterally. Two prominent grooves, or sulci, run along its length. The posterior median sulcus is the groove in the dorsal side, and the anterior median fissure is the groove in the ventral side.
Spinal cord segments[edit]
The human spinal cord is divided into segments where pairs of spinal nerves (mixed; sensory and motor) form. Six to eight motor nerve rootlets branch out of right and left ventro lateral sulci in a very orderly manner. Nerve rootlets combine to form nerve roots. Likewise, sensory nerve rootlets form off right and left dorsal lateral sulci and form sensory nerve roots. The ventral (motor) and dorsal (sensory) roots combine to form spinal nerves (mixed; motor and sensory), one on each side of the spinal cord. Spinal nerves, with the exception of C1 and C2, form inside the intervertebral foramen (IVF). These rootlets form the demarcation between the central and peripheral nervous systems.
A model of segments of the human spine and spinal cord, nerve roots can be seen extending laterally from the (not visible) spinal cord.
The grey column, (as three regions of grey columns) in the center of the cord, is shaped like a butterfly and consists of cell bodies of interneurons, motor neurons, neuroglia cells and unmyelinated axons. The anterior and posterior grey column present as projections of the grey matter and are also known as the horns of the spinal cord. Together, the grey columns and the gray commissure form the "grey H."
The white matter is located outside of the grey matter and consists almost totally of myelinated motor and sensory axons. "Columns" of white matter carry information either up or down the spinal cord.
The spinal cord proper terminates in a region called the conus medullaris, while the pia mater continues as an extension called the filum terminale, which anchors the spinal cord to the coccyx. The cauda equina ("horse's tail") is a collection of nerves inferior to the conus medullaris that continue to travel through the vertebral column to the coccyx. The cauda equina forms because the spinal cord stops growing in length at about age four, even though the vertebral column continues to lengthen until adulthood. This results in sacral spinal nerves originating in the upper lumbar region.
Within the CNS, nerve cell bodies are generally organized into functional clusters, called nuclei. Axons within the CNS are grouped into tracts.
There are 31 spinal cord nerve segments in a human spinal cord:
8 cervical segments forming 8 pairs of cervical nerves (C1 spinal nerves exit the spinal column between the foramen magnum and the C1 vertebra; C2 nerves exit between the posterior arch of the C1 vertebra and the lamina of C2; C3–C8 spinal nerves pass through the IVF above their corresponding cervical vertebrae, with the exception of the C8 pair which exit between the C7 and T1 vertebrae)
12 thoracic segments forming 12 pairs of thoracic nerves
5 lumbar segments forming 5 pairs of lumbar nerves
5 sacral segments forming 5 pairs of sacral nerves
1 coccygeal segment
Spinal cord segments in some common species [4]
Species
Cervical
Thoracic
Lumbar
Sacral
Caudal/Coccygeal
Total
Dog 8 13 7 3 5 36
Cat 8 13 7 3 5 36
Cow 8 13 6 5 5 37
Horse 8 18 6 5 5 42
Pig 8 15/14 6/7 4 5 38
Human 8 12 5 5 1 31
In the fetus, vertebral segments correspond with spinal cord segments. However, because the vertebral column grows longer than the spinal cord, spinal cord segments do not correspond to vertebral segments in the adult, particularly in the lower spinal cord. For example, lumbar and sacral spinal cord segments are found between vertebral levels T9 and L2, and the spinal cord ends around the L1/L2 vertebral level, forming a structure known as the conus medullaris.
Although the spinal cord cell bodies end around the L1/L2 vertebral level, the spinal nerves for each segment exit at the level of the corresponding vertebra. For the nerves of the lower spinal cord, this means that they exit the vertebral column much lower (more caudally) than their roots. As these nerves travel from their respective roots to their point of exit from the vertebral column, the nerves of the lower spinal segments form a bundle called the cauda equina.
There are two regions where the spinal cord enlarges:
Cervical enlargement – corresponds roughly to the brachial plexus nerves, which innervate the upper limb. It includes spinal cord segments from about C4 to T1. The vertebral levels of the enlargement are roughly the same (C4 to T1).
Lumbar enlargement – corresponds to the lumbosacral plexus nerves, which innervate the lower limb. It comprises the spinal cord segments from L2 to S3 and is found about the vertebral levels of T9 to T12.
Development[edit]
Spinal cord seen in a midsection of a five-week-old embryo
Spinal cord seen in a midsection of a 3 month old fetus
The spinal cord is made from part of the neural tube during development. There are four stages of the spinal cord that arises from the neural tube: The neural plate, neural fold, neural tube, and the spinal cord. Neural differentiation occurs within the spinal cord portion of the tube.[5] As the neural tube begins to develop, the notochord begins to secrete a factor known as Sonic hedgehog or SHH. As a result, the floor plate then also begins to secrete SHH, and this will induce the basal plate to develop motor neurons. During the maturation of the neural tube, its lateral walls thicken and form a longtitudinal groove called the sulcus limitans. This extends the length of the spinal cord into dorsal and ventral portions as well.[6] Meanwhile, the overlying ectoderm secretes bone morphogenetic protein (BMP). This induces the roof plate to begin to secrete BMP, which will induce the alar plate to develop sensory neurons. Opposing gradients of such morphogens as BMP and SHH form different domains of dividing cells along the dorsal ventral axis.[7] Dorsal root ganglion neurons differentiate from neural crest progenitors. As the dorsal and ventral column cells proliferate, the lumen of the neural tube narrows to form the small central canal of the spinal cord.[8] The alar plate and the basal plate are separated by the sulcus limitans. Additionally, the floor plate also secretes netrins. The netrins act as chemoattractants to decussation of pain and temperature sensory neurons in the alar plate across the anterior white commissure, where they then ascend towards the thalamus. Following the closure of the caudal neuropore and formation of the brain's ventricles that contain the choroid plexus tissue, the central canal of the caudal spinal cord is filled with cerebrospinal fluid.
Earlier findings by Viktor Hamburger and Rita Levi-Montalcini in the chick embryo have been confirmed by more recent studies which have demonstrated that the elimination of neuronal cells by programmed cell death (PCD) is necessary for the correct assembly of the nervous system.[9]
Overall, spontaneous embryonic activity has been shown to play a role in neuron and muscle development but is probably not involved in the initial formation of connections between spinal neurons.
Blood supply[edit]
The spinal cord is supplied with blood by three arteries that run along its length starting in the brain, and many arteries that approach it through the sides of the spinal column. The three longitudinal arteries are the anterior spinal artery, and the right and left posterior spinal arteries.[10] These travel in the subarachnoid space and send branches into the spinal cord. They form anastamoses (connections) via the anterior and posterior segmental medullary arteries, which enter the spinal cord at various points along its length.[10] The actual blood flow caudally through these arteries, derived from the posterior cerebral circulation, is inadequate to maintain the spinal cord beyond the cervical segments.
The major contribution to the arterial blood supply of the spinal cord below the cervical region comes from the radially arranged posterior and anterior radicular arteries, which run into the spinal cord alongside the dorsal and ventral nerve roots, but with one exception do not connect directly with any of the three longitudinal arteries.[10] These intercostal and lumbar radicular arteries arise from the aorta, provide major anastomoses and supplement the blood flow to the spinal cord. In humans the largest of the anterior radicular arteries is known as the artery of Adamkiewicz, or anterior radicularis magna (ARM) artery, which usually arises between L1 and L2, but can arise anywhere from T9 to L5.[11] Impaired blood flow through these critical radicular arteries, especially during surgical procedures that involve abrupt disruption of blood flow through the aorta for example during aortic aneursym repair, can result in spinal cord infarction and paraplegia.
Function[edit]
Somatosensory organization[edit]
Spinal cord tracts.
Somatosensory organization is divided into the dorsal column-medial 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.
In the dorsal column-medial leminiscus tract, a primary neuron's axon enters the spinal cord and then enters the dorsal column. If the primary axon enters below spinal level T6, the axon travels in the fasciculus gracilis, the medial part of the column. If the axon enters above level T6, then it travels in the fasciculus cuneatus, which is lateral to the fasciculus gracilis. Either way, the primary axon ascends to the lower medulla, where it leaves its fasciculus and synapses with a secondary neuron in one of the dorsal column nuclei: either the nucleus gracilis or the nucleus cuneatus, depending on the pathway it took. At this point, the secondary axon leaves its nucleus and passes anteriorly and medially. The collection of secondary axons that do this are known as internal arcuate fibers. The internal arcuate fibers decussate and continue ascending as the contralateral medial lemniscus. Secondary axons from the medial lemniscus finally terminate in the ventral posterolateral nucleus (VPLN) of the thalamus, where they synapse with tertiary neurons. From there, tertiary neurons ascend via the posterior limb of the internal capsule and end in the primary sensory cortex.
The proprioception of the lower limbs differs from the upper limbs and upper trunk. There is a four-neuron pathway for lower limb proprioception. This pathway initially follows the dorsal spino-cerebellar pathway. It is arranged as follows: proprioceptive receptors of lower limb → peripheral process → dorsal root ganglion → central process → Clarke's column → 2nd order neuron → medulla oblogata (Caudate nucleus) → 3rd order neuron → VPLN of thalamus → 4th order neuron → posterior limb of internal capsule → corona radiata → sensory area of cerebrum.
The anterolateral system works somewhat differently. Its primary neurons axons enter the spinal cord and then ascend one to two levels before synapsing in the substantia gelatinosa. The tract that ascends before synapsing is known as Lissauer's tract. After synapsing, secondary axons decussate and ascend in the anterior lateral portion of the spinal cord as the spinothalamic tract. This tract ascends all the way to the VPLN, where it synapses on tertiary neurons. Tertiary neuronal axons then travel to the primary sensory cortex via the posterior limb of the internal capsule.
Some of the "pain fibers" in the ALS deviate from their pathway towards the VPLN. In one such deviation, axons travel towards the reticular formation in the midbrain. The reticular formation then projects to a number of places including the hippocampus (to create memories about the pain), the centromedian nucleus (to cause diffuse, non-specific pain) and various parts of the cortex. Additionally, some ALS axons project to the periaqueductal gray in the pons, and the axons forming the periaqueductal gray then project to the nucleus raphes magnus, which projects back down to where the pain signal is coming from and inhibits it. This helps control the sensation of pain to some degree.
Motor organization[edit]
Actions of the spinal nerves edit
Level
Motor function
C1–C6
Neck flexors
C1–T1
Neck extensors
C3, C4, C5
Supply diaphragm (mostly C4)
C5, C6
Move shoulder, raise arm (deltoid); flex elbow (biceps)
C6
externally rotate (supinate) the arm
C6, C7
Extend elbow and wrist (triceps and wrist extensors); pronate wrist
C7, C8
Flex wrist; supply small muscles of the hand
T1–T6
Intercostals and trunk above the waist
T7–L1
Abdominal muscles
L1–L4
Flex thigh
L2, L3, L4
Adduct thigh; Extend leg at the knee (quadriceps femoris)
L4, L5, S1
abduct thigh; Flex leg at the knee (hamstrings); Dorsiflex foot (tibialis anterior); Extend toes
L5, S1, S2
Extend leg at the hip (gluteus maximus); flex foot and flex toes
The corticospinal tract serves as the motor pathway for upper motor neuronal signals coming from the cerebral cortex and from primitive brainstem motor nuclei.
Cortical upper motor neurons originate from Brodmann areas 1, 2, 3, 4, and 6 and then descend in the posterior limb of the internal capsule, through the crus cerebri, down through the pons, and to the medullary pyramids, where about 90% of the axons cross to the contralateral side at the decussation of the pyramids. They then descend as the lateral corticospinal tract. These axons synapse with lower motor neurons in the ventral horns of all levels of the spinal cord. The remaining 10% of axons descend on the ipsilateral side as the ventral corticospinal tract. These axons also synapse with lower motor neurons in the ventral horns. Most of them will cross to the contralateral side of the cord (via the anterior white commissure) right before synapsing.
The midbrain nuclei include four motor tracts that send upper motor neuronal axons down the spinal cord to lower motor neurons. These are the rubrospinal tract, the vestibulospinal tract, the tectospinal tract and the reticulospinal tract. The rubrospinal tract descends with the lateral corticospinal tract, and the remaining three descend with the anterior corticospinal tract.
The function of lower motor neurons can be divided into two different groups: the lateral corticospinal tract and the anterior cortical spinal tract. The lateral tract contains upper motor neuronal axons which synapse on dorsal lateral (DL) lower motor neurons. The DL neurons are involved in distal limb control. Therefore, these DL neurons are found specifically only in the cervical and lumbosacral enlargements within the spinal cord. There is no decussation in the lateral corticospinal tract after the decussation at the medullary pyramids.
The anterior corticospinal tract descends ipsilaterally in the anterior column, where the axons emerge and either synapse on lower ventromedial (VM) motor neurons in the ventral horn ipsilaterally or descussate at the anterior white commissure where they synapse on VM lower motor neurons contralaterally . The tectospinal, vestibulospinal and reticulospinal descend ipsilaterally in the anterior column but do not synapse across the anterior white commissure. Rather, they only synapse on VM lower motor neurons ipsilaterally. The VM lower motor neurons control the large, postural muscles of the axial skeleton. These lower motor neurons, unlike those of the DL, are located in the ventral horn all the way throughout the spinal cord.
Spinocerebellar tracts[edit]
Proprioceptive information in the body travels up the spinal cord via three tracks. Below L2, the proprioceptive information travels up the spinal cord in the ventral spinocerebellar tract. Also known as the anterior spinocerebellar tract, sensory receptors take in the information and travel into the spinal cord. The cell bodies of these primary neurons are located in the dorsal root ganglia. In the spinal cord, the axons synapse and the secondary neuronal axons decussates and then travel up to the superior cerebellar peduncle where they decussate again. From here, the information is brought to deep nuclei of the cerebellum including the fastigial and interposed nuclei.
From the levels of L2 to T1, proprioceptive information enters the spinal cord and ascends ipsilaterally, where it synapses in Clarke's nucleus. The secondary neuronal axons continue to ascend ipsilaterally and then pass into the cerebellum via the inferior cerebellar peduncle. This tract is known as the dorsal spinocerebellar tract.
From above T1, proprioceptive primary axons enter the spinal cord and ascend ipsilaterally until reaching the accessory cuneate nucleus, where they synapse. The secondary axons pass into the cerebellum via the inferior cerebellar peduncle where again, these axons synapse on cerebellar deep nuclei. This tract is known as the cuneocerebellar tract.
Motor information travels from the brain down the spinal cord via descending spinal cord tracts. Descending tracts involve two neurons: the upper motor neuron (UMN) and lower motor neuron (LMN).[12] A nerve signal travels down the upper motor neuron until it synapses with the lower motor neuron in the spinal cord. Then, the lower motor neuron conducts the nerve signal to the spinal root where efferent nerve fibers carry the motor signal toward the target muscle. The descending tracts are composed of white matter. There are several descending tracts serving different functions. The corticospinal tracts (lateral and anterior) are responsible for coordinated limb movements.[12]
Clinical significance[edit]
A congenital disorder is diastematomyelia in which part of the spinal cord is split usually at the level of the upper lumbar vertebrae. Sometimes the split can be along the length of the spinal cord.
Injury[edit]
Main article: Spinal cord injuries
Spinal cord injuries can be caused by trauma to the spinal column (stretching, bruising, applying pressure, severing, laceration, etc.). The vertebral bones or intervertebral disks can shatter, causing the spinal cord to be punctured by a sharp fragment of bone. Usually, victims of spinal cord injuries will suffer loss of feeling in certain parts of their body. In milder cases, a victim might only suffer loss of hand or foot function. More severe injuries may result in paraplegia, tetraplegia (also known as quadriplegia), or full body paralysis below the site of injury to the spinal cord.
Damage to upper motor neuron axons in the spinal cord results in a characteristic pattern of ipsilateral deficits. These include hyperreflexia, hypertonia and muscle weakness. Lower motor neuronal damage results in its own characteristic pattern of deficits. Rather than an entire side of deficits, there is a pattern relating to the myotome affected by the damage. Additionally, lower motor neurons are characterized by muscle weakness, hypotonia, hyporeflexia and muscle atrophy.
Spinal shock and neurogenic shock can occur from a spinal injury. Spinal shock is usually temporary, lasting only for 24–48 hours, and is a temporary absence of sensory and motor functions. Neurogenic shock lasts for weeks and can lead to a loss of muscle tone due to disuse of the muscles below the injured site.
The two areas of the spinal cord most commonly injured are the cervical spine (C1–C7) and the lumbar spine (L1–L5). (The notation C1, C7, L1, L5 refer to the location of a specific vertebra in either the cervical, thoracic, or lumbar region of the spine.) Spinal cord injury can also be non-traumatic and caused by disease (transverse myelitis, polio, spina bifida, Friedreich's ataxia, spinal cord tumor, spinal stenosis etc.)[13]
In the U.S., 10,000–12,000 people become paralyzed annually as a result of various injuries to the spinal cord.[citation needed]
Treatment[edit]
Real or suspected spinal cord injuries need immediate immobilisation including that of the head. Scans will be needed to assess the injury. A steroid, methylprednisolone, can be of help as can physical therapy and possibly antioxidants.[citation needed] Treatments need to focus on limiting post-injury cell death, promoting cell regeneration, and replacing lost cells. Regeneration is facilitated by maintaining electric transmission in neural elements.
Lumbar puncture[edit]
The spinal cord ends at the level of vertebrae L1–L2, while the subarachnoid space —the compartment that contains cerebrospinal fluid— extends down to the lower border of S2.[13] Lumbar punctures in adults are usually performed between L3–L5 (cauda equina level) in order to avoid damage to the spinal cord.[13] In the fetus, the spinal cord extends the full length of the spine and regresses as the body grows.
Tumours[edit]
Spinal tumours can occur in the spinal cord and these can be either inside (intradural) or outside (extradural) the dura mater.
Additional images[edit]
Spinal Cord Sectional Anatomy. Animation in the reference.
Diagrams of the spinal cord.
Cross-section through the spinal cord at the mid-thoracic level.
Cross-sections of the spinal cord at varying levels.
Cervical vertebra
A portion of the spinal cord, showing its right lateral surface. The dura is opened and arranged to show the nerve roots.
The spinal cord with dura cut open, showing the exits of the spinal nerves.
The spinal cord showing how the anterior and posterior roots join in the spinal nerves.
The spinal cord showing how the anterior and posterior roots join in the spinal nerves.
A longer view of the spinal cord.
Projections of the spinal cord into the nerves (red motor, blue sensory).
Projections of the spinal cord into the nerves (red motor, blue sensory).
Cross-section of rabbit spinal cord.
Cross-section of adult mouse spinal cord: astrocytes (red) and neurons (green)
Cross section of adult rat spinal cord stained using Cajal method.
[show]Dissection images
An overview of the spinal cord.
Sagittal section of pig vertebrae showing a section of the spinal cord.
The base of the brain and the top of the spinal cord
Spinal cord. Spinal membranes and nerve roots.Deep dissection. Posterior view.
Spinal cord. Spinal membranes and nerve roots.Deep dissection. Posterior view.
Spinal cord. Spinal membranes and nerve roots.Deep dissection. Posterior view.
Spinal cord. Spinal membranes and nerve roots.Deep dissection. Posterior view.
Spinal cord. Spinal membranes and nerve roots.Deep dissection. Posterior view.
Spinal cord. Spinal membranes and nerve roots.Deep dissection. Posterior view.
Spinal cord. Spinal membranes and nerve roots.Deep dissection. Posterior view.
Cerebrum.Inferior view.Deep dissection
Cerebrum.Inferior view.Deep dissection
Spinal cord. Brachial plexus. Cerebrum.Inferior view.Deep dissection.
Spinal cord. Brachial plexus. Cerebrum.Inferior view.Deep dissection.
Spinal cord
Medulla spinalis of 8-week-old human embryo
See also[edit]
Wikimedia Commons has media related to Spinal cord.
This article uses anatomical terminology; for an overview, see Anatomical terminology.
Neutral spine
Brown–Séquard syndrome
Hereditary spastic paraplegia (HSP, or familial spastic paraplegia – FSP, Strümpell–Lorrain syndrome)
Poliomyelitis, Post-polio syndrome
Upper-limb surgery in tetraplegia
Redlich–Obersteiner's zone
Subacute combined degeneration of spinal cord
Tethered spinal cord syndrome
References[edit]
Jump up ^ Maton, Anthea; et al. (1993). Human biology and health (1st ed.). Englewood Cliffs, N.J.: Prentice Hall. pp. 132–144. ISBN 0-13-981176-1. CS1 maint: Explicit use of et al. (link)
Jump up ^ Myers, Gary. Exploring Psychology. Worth Publishers. p. 41. ISBN 978-1429216357.
Jump up ^ Squire, Larry Squire; et al. (2013). Fundamental neuroscience (4th ed.). Amsterdam: Elsevier/Academic Press. p. 628. ISBN 978-0-12-385-870-2. CS1 maint: Explicit use of et al. (link)
Jump up ^ "Spinal Cord Gross Anatomy". Retrieved December 27, 2015.
Jump up ^ Kaufman, Bard. "Spinal Cord – Development and Stem Cells". Life Map Discovery Compendium. Retrieved 12 Dec 2015.
Jump up ^ Kaufman, Bard. "Spinal Cord-Development and Stem Cells". Stem Cell Development Compendium. Retrieved 2 Dec 2015.
Jump up ^ Than-Trong, Emmanuel; Bally-Cuif, Laure (2015-08-01). "Radial glia and neural progenitors in the adult zebrafish central nervous system". Glia. 63 (8): 1406–1428. doi:10.1002/glia.22856. ISSN 1098-1136. PMID 25976648.
Jump up ^ Saladin. Anatomy & Physiology The Unity of Form and Function. Mc Graw Hill.
Jump up ^ Cowan, WM (2001). "Viktor Hamburger and Rita Levi-Montalcini: the path to the discovery of nerve growth factor". Annual Review of Neuroscience. 24: 551–600. doi:10.1146/annurev.neuro.24.1.551. PMID 11283321.
^ Jump up to: a b c Moore, Keith; Anne Agur (2007). Essential Clinical Anatomy, Third Edition. Lippincott Williams & Wilkins. p. 298. ISBN 0-7817-6274-X.
Jump up ^ Biglioli, Paolo; et alia (April 2004). "Upper and lower spinal cord blood supply: the continuity of the anterior spinal artery and the relevance of the lumbar arteries". Journal of Thoracic and Cardiovascular Surgery. 127 (4): 1188–1192. doi:10.1016/j.jtcvs.2003.11.038. PMID 15052221.
^ Jump up to: a b Saladin. Anatomy and Physiology, 5th Ed.
^ Jump up to: a b c Le, Tao (10 January 2014). First Aid for the USMLE Step 1 2014 / Edition 24. McGraw-Hill Professional Publishing. ISBN 9780071831420.
External links[edit]
Spinal Cord Histology – A multitude of great images from the University of Cincinnati
Spinal Cord Medical Notes – Online medical notes on the spinal cord
"The Nervous System: Sensory and Motor Tracts of the Spinal Cord" (PDF). Napa Valley College / Southeast Community College Lincoln, Nebraska. Retrieved 20 May 2013.
eMedicine: Spinal Cord, Topographical and Functional Anatomy
WebMD. May 17, 2005. Spina Bifida – Topic Overview Information about spina bifida in fetuses and throughout adulthood. WebMD children's health. Retrieved March 19, 2007.
Potential for spinal injury repair Retrieved February 6, 2008.
4000 sets of digital images, showing spatial expression patterns for various genes in adult and juvenile mouse spinal cords from the Allen Institute for Brain Science
Spinal cord photomicrographs
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v
t
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The spinal cord
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GND: 4050831-6
NDL: 00570617
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text:
Sphere of influence
From Wikipedia, the free encyclopedia
Jump to: navigation, search
For other uses, see Sphere of influence (disambiguation).
A 1912 newspaper cartoon highlighting the United States' influence in Latin America following the Monroe Doctrine.
In the field of international relations, a zone of influence (SOI) is a spatial region or concept division over which a state or organization has a level of cultural, economic, military, or political exclusivity, accommodating to the interests of powers outside the borders of the state that controls it.
While there may be a formal alliance or other treaty obligations between the influenced and influence, such formal arrangements are not necessary and the influence can often be more of an example of soft power. Similarly, a formal alliance does not necessarily mean that one country lies within another's sphere of influence. High levels of exclusivity have historically been associated with higher levels of conflict.
In more extreme cases, a country within the "sphere of influence" of another may become a subsidiary of that state and serve in effect as a satellite state or de facto colony. The system of spheres of influence by which powerful nations intervene in the affairs of others continues to the present. It is often analyzed in terms of superpowers, great powers, and/or middle powers.
An example of spheres of influence was China in the late 19th and early 20th Century, when Britain, France, Germany, and Russia (later replaced by Japan) had de facto control over large swaths of territory. These were taken by unequal treaties or as very long term "leases".[1] These powers (and the United States) might have their own courts, post offices, commercial institutions, railroads, and gunboats in what was on paper Chinese territory. However, the foreign powers and their influence in some cases could have been exaggerated.[2] The system ended with the Second World War.
For another example, during the height of its existence in World War II, the Japanese Empire had quite a large sphere of influence. The Japanese government directly governed events in Korea, Vietnam, Taiwan, and parts of China. The "Greater East Asia Co-Prosperity Sphere" could thus be quite easily drawn on a map of the Pacific Ocean as a large "bubble" surrounding the islands of Japan and the Asian and Pacific nations it controlled.
Sometimes portions of a single country can fall into two distinct spheres of influence. In the colonial era the buffer states of Iran and Thailand, lying between the empires of Britain/Russia and Britain/France respectively, were divided between the spheres of influence of the imperial powers. Likewise, after World War II, Germany was divided into four occupation zones, which later consolidated into West Germany and East Germany, the former a member of NATO and the latter a member of the Warsaw Pact.
The term is also used to describe non-political situations, e.g., a shopping mall is said to have a sphere of influence which designates the geographical area where it dominates the retail trade.
Contents
[hide]
1 Historical remnants
2 Molotov-Ribbentrop Pact
3 End of World War II
4 Cold War
5 1990s to present
6 United States
7 Corporations
8 Other examples
9 See also
10 References
11 External links
Historical remnants[edit]
A map of colonial Africa in 1897 showing the European "sphere[s] of influence".
Many areas of the world are considered to have inherited culture from a previous sphere of influence, that while perhaps today halted, continues to share the same culture. Examples include the Anglosphere, Arab World, Eurosphere, Francophonie, Françafrique, Germanosphere, Indosphere, Latin Europe/Latin America, Lusophonie, Turkosphere, Chinese cultural sphere, Slavisphere, Hispanophone, Malay World, as well as many others.
Molotov-Ribbentrop Pact[edit]
According to a secret protocol attached to the Molotov-Ribbentrop pact of 1939 (revealed only after Germany's defeat in 1945), Northern and Eastern Europe were divided into Nazi and Soviet spheres of influence.[3] In the North, Finland, Estonia, and Latvia were assigned to the Soviet sphere.[3] Poland was to be partitioned in the event of its "political rearrangement"—the areas east of the Narev, Vistula, and San Rivers going to the Soviet Union while Germany would occupy the west.[3] Lithuania, adjacent to East Prussia, would be in the German sphere of influence, although a second secret protocol agreed in September 1939 assigned Lithuania to the USSR.[4] Another clause of the treaty stipulated that Bessarabia, then part of Romania, would join the Moldovan ASSR and become the Moldovan SSR under the control of Moscow.[3] The Soviet invasion of Bukovina on 28 June 1940 violated the Molotov-Ribbentrop Pact, as it went beyond the Soviet sphere of influence as agreed with the Axis.[5] The USSR continued to deny the existence of the Pact's protocols until after the dissolution of the USSR when the Russian government fully acknowledged the existence and authenticity of the secret protocols.[6]
End of World War II[edit]
From 1941 and the German attack on the Soviet Union, the Allied Coalition operated on the unwritten assumption that the Western Powers and the Soviet Union had each its own sphere of influence. The presumption of the US-British and Soviet unrestricted rights in their respective spheres started causing difficulties as the Nazi-controlled territory shrank and the allied powers successively liberated other states. The wartime spheres lacked a practical definition and it had never been determined if a dominant allied power was entitled to unilateral decisions only in the area of military activity, or could also force its will regarding political, social and economic future of other states. This overly informal system backfired during the late stages of the war and afterwards, when it turned out that the Soviets and the Western Allies had very different ideas concerning the administration and future development of the liberated regions and of Germany itself.[7]
Cold War[edit]
During the Cold War the Baltic states, Central Europe, some countries in Eastern Europe, Cuba, Laos, Vietnam, North Korea, and, until the Sino-Soviet split, the People's Republic of China, among other countries at various times, were said to lie under the Soviet sphere of influence. Western Europe, Oceania, Japan, and South Korea, among other places, were often said to lie under the sphere of influence of the United States. However, the level of control exerted in these spheres varied and was not absolute. For instance, France and Great Britain were able to act independently to invade (with Israel) the Suez Canal (they were later forced to withdraw by joint U.S. and Soviet pressure). Later, France was also able to withdraw from the military arm of the North Atlantic Treaty Organisation (NATO). Cuba often took positions that put it at odds with its Soviet ally, including momentary alliances with the People's Republic of China, economic reorganizations, and providing support for insurgencies in Africa and the Americas without prior approval from the Soviet Union.[citation needed]
With the end of the Cold War, the Eastern Bloc fell apart, effectively ending the Soviet sphere of influence. Then in 1991, the Soviet Union collapsed, replaced by the Russian Federation and several other ex-Soviet Republics who became independent states.
1990s to present[edit]
See also: Foreign relations of Russia
After the fall of the Soviet Union, the countries of Eastern Europe, the Caucasus, and Central Asia that became independent were often portrayed as part of the Russian Federation's "sphere of influence". According to Ulrich Speck, writing for Carnegie Europe, "After the breakup of the Soviet Union, the West's focus was on Russia. Western nations implicitly treated the post-Soviet countries (besides the Baltic states) as Russia's sphere of influence."[8]
In 1997, NATO and Russia signed the Founding Act on Mutual Relations, Cooperation and Security, stating the "aim of creating in Europe a common space of security and stability, without dividing lines or spheres of influence limiting the sovereignty of any state."[9]
In 2009, Russia asserted that the European Union desires a sphere of influence and that the Eastern Partnership is "an attempt to extend" it.[10] In March 2009, Sweden's foreign minister Carl Bildt stated that "The Eastern Partnership is not about spheres of influence. The difference is that these countries themselves opted to join".[10]
Following the 2008 Russo-Georgian War, Václav Havel and other former central and eastern European leaders signed an open letter stating that Russia had "violated the core principles of the Helsinki Final Act, the Charter of Paris... -all in the name of defending a sphere of influence on its borders."[11] In April 2014, NATO stated that "Contrary to [the Founding Act], Russia now appears to be attempting to recreate a sphere of influence by seizing a part of Ukraine, maintaining large numbers of forces on its borders, and demanding, as Russian Foreign Minister Sergei Lavrov recently stated, that “Ukraine cannot be part of any bloc.”"[12] Criticising Russia in November 2014, German Chancellor Angela Merkel said that "old thinking about spheres of influence, which runs roughshod over international law" put the "entire European peace order into question".[13] In January 2017, British Prime Minister Theresa May said, "We should not jeopardise the freedoms that President Reagan and Mrs Thatcher brought to Eastern Europe by accepting President Putin's claim that it is now in his sphere of influence."[14]
United States[edit]
See also: Foreign relations of the United States, Carter Doctrine, and Monroe Doctrine
Corporations[edit]
In corporate terms, the sphere of influence of a business, organization or group can show its power and influence in the decisions of other businesses/organizations/groups. Influence shows in several ways, such as in size, frequency of visits, etc. In most cases, a company described as "bigger" has a larger sphere of influence.
For example, the software company Microsoft has a large sphere of influence in the market of operating systems; any entity wishing to sell a software product may weigh up compatibility with Microsoft's products as part of a marketing plan.[citation needed]
In another example, retailers wishing to make the most profits must ensure they open their stores in the correct location. This is also true for shopping centers that, to reap the most profits, must be able to attract customers to their vicinity.[citation needed]
There is no defined scale measuring such spheres of influence. However, one can evaluate the spheres of influence of two shopping centers by seeing how far people are prepared to travel to each shopping center, how much time they spend in its vicinity, how often they visit, the order of goods available, etc.[citation needed]
Other examples[edit]
An 1878 British cartoon about The Great Game between the United Kingdom and Russia over influence in Central Asia
For historical and current examples of significant battles over spheres of influence see:
The Great Game
Geostrategy in Central Asia
See also[edit]
Geopolitics
National interest
Balance of power in international relations
Eurosphere
Lateral pressure theory
Unequal treaty
References[edit]
Jump up ^ Spheres of Influence in China
Jump up ^ Patrick Fuliang Shan, “What was the ‘Sphere of Influence’? A Study of Chinese Resistance to the Russian Empire in North Manchuria, 1900-1917,” The Chinese Historical Review, (Fall 2006, vol. 13, no. 2), pp.271-291.
^ Jump up to: a b c d Text of the Nazi-Soviet Non-Aggression Pact, executed August 23, 1939
Jump up ^ Christie, Kenneth, Historical Injustice and Democratic Transition in Eastern Asia and Northern Europe: Ghosts at the Table of Democracy, RoutledgeCurzon, 2002, ISBN 0-7007-1599-1
Jump up ^ Brackman, Roman The Secret File of Joseph Stalin: A Hidden Life (2001) p. 341
Jump up ^ Etkind, Alexander; Finnin, Rory; Blacker, Uilleam; Julie Fedor; Simon Lewis; Maria Mälksoo; Matilda Mroz (2013). Remembering Katyn. John Wiley & Sons. ISBN 9780745662961.
Jump up ^ Norman Davies, Europe at War 1939–1945: No Simple Victory, pp. 172-174. Penguin Books, New York 2006, ISBN 978-0-14-311409-3
Jump up ^ Speck, Ulrich (9 December 2014). "The EU Must Prepare for a Cold Peace With Russia". Carnegie Europe.
Jump up ^ "Founding Act on Mutual Relations, Cooperation and Security between NATO and the Russian Federation signed in Paris, France". NATO. 27 May 1997.
^ Jump up to: a b Pop, Valentina (21 March 2009). "EU expanding its 'sphere of influence,' Russia says". EUObserver.
Jump up ^ Valdas Adamkus, Martin Bútora, Emil Constantinescu, Pavol Demeš, Luboš Dobrovský, Mátyás Eörsi, István Gyarmati, Václav Havel, Rastislav Káčer, Sandra Kalniete, Karel Schwarzenberg, Michal Kováč, Ivan Krastev, Aleksander Kwaśniewski, Mart Laar, Kadri Liik, János Martonyi, Janusz Onyszkiewicz, Adam Daniel Rotfeld, Vaira Vīķe-Freiberga, Alexandr Vondra, Lech Wałęsa (15 July 2009). "An Open Letter to the Obama Administration from Central and Eastern Europe". Gazeta Wyborcza. CS1 maint: Uses authors parameter (link)
"An Open Letter". Radio Free Europe.
Jump up ^ "Russia's accusations - setting the record straight, Fact Sheet - April 2014". NATO. 12 May 2014.
Jump up ^ Rettman, Andrew (17 November 2014). "Merkel: Russia cannot veto EU expansion". EUobserver.
Jump up ^ "FULL TEXT: Theresa May's speech to the Republican 'Congress of Tomorrow' conference". Business Insider. 26 January 2017. Archived from the original on 27 January 2017.
External links[edit]
Wikimedia Commons has media related to Spheres of influence.
The CommonCensus Map Project – Calculates the spheres of influence for American cities based on voting
Russia - a counterbalancing agent to the Asia.
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