WordNet

(physical chemistry) a sample of matter in which substances in different phases are in equilibrium; "in a static system oil cannot be replaced by water on a surface"; "a system generating hydrogen peroxide"
instrumentality that combines interrelated interacting artifacts designed to work as a coherent entity; "he bought a new stereo system"; "the system consists of a motor and a small computer"
a group of independent but interrelated elements comprising a unified whole; "a vast system of production and distribution and consumption keep the country going" (同)scheme
a complex of methods or rules governing behavior; "they have to operate under a system they oppose"; "that language has a complex system for indicating gender" (同)system of rules
a group of physiologically or anatomically related organs or parts; "the body has a system of organs for digestion"
a procedure or process for obtaining an objective; "they had to devise a system that did not depend on cooperation"
the living body considered as made up of interdependent components forming a unified whole; "exercise helped him get the alcohol out of his system"
use or deal in (as of stock or commercial transaction) in a pyramid deal
(stock market) a series of transactions in which the speculator increases his holdings by using the rising market value of those holdings as margin for further purchases
a polyhedron having a polygonal base and triangular sides with a common vertex
increase rapidly and progressively step by step on a broad base
arrange or build up as if on the base of a pyramid
enlarge ones holdings on an exchange on a continued rise by using paper profits as margin to buy additional amounts
resembling a pyramid (同)pyramidic, pyramidical

PrepTutorEJDIC

〈C〉(関連した部分から成る)『体系』,系統,組織[網],装置 / 〈C〉(教育・政治などの)『制度』,機構;《the~》体制 / 〈C〉(思想・学問などの)『体系』,学説 / 〈C〉(…の)『方法』,方式,やり方《+of doing》 / 〈U〉正しい方針(筋道,順序) / 〈U〉《the~》(身体の)組織,系統 / 〈U〉《the~,one's~》身体,全身
(エジプト・メキシコなどの)『ピラミッド』 / ピラミッド形の物 / (幾何の)角錐(かくすい) / ピラミッド形になる / 〈物価などが〉上昇する,増加する / …‘を'ピラミッド形にする(積み上げる)
ピラミッド[状]の

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2015/03/01 08:45:16」(JST)

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The pyramidal tracts (pyramides)^{[citation needed]} include both the corticospinal and corticobulbar tracts. These are aggregations of upper motor neuron nerve fibres that travel from the cerebral cortex and terminate either in the brainstem (corticobulbar) or spinal cord (corticospinal) and are involved in control of motor functions of the body.

The corticobulbar tract conducts impulses from the brain to the cranial nerves.^[1] These nerves control the muscles of the face and neck and are involved in facial expression, mastication, swallowing, and other functions.

The corticospinal tract conducts impulses from the brain to the spinal cord. It is made up of a lateral and anterior tract. The corticospinal tract is involved in voluntary movement. The majority fibres of the corticospinal tract cross over in the medulla, resulting in muscles being controlled by the opposite side of the brain. The corticospinal tract also contains Betz cells (the largest pyramidal cells), which are not found in any other region of the body.

The pyramidal tracts are named because they pass through the pyramids of the medulla.

The myelination of the pyramidal fibres is incomplete at birth and gradually progresses in caudo-cranial direction and thereby progressively gaining functionality. Most of the myelination is complete by two years of age and thereafter it progresses very slowly in cranio-caudal direction up to twelve years of age.

Structure

The term pyramidal tracts refers to upper motor neurons that originate in the cerebral cortex and terminate in the spinal cord (corticospinal) or brainstem (corticobulbar). Nerves emerge in the cerebral cortex, pass down and may cross sides in the medulla, and travel as part of the spinal cord until they synapse with interneurons in the middle part of the spinal cord, known as grey matter.^[2]

There is some variation in terminology. The pyramidal tracts definitively encompass the corticospinal tracts. Many, but not all authors also consider the tracts to include the corticobulbar tracts.^[3]

Corticospinal tract

Nerve fibres in the corticospinal tract originate from pyramidal cells in layer V of the cerebral cortex. Fibres arise from the primary motor cortex (about 30%), supplementary motor area and the premotor cortex (together also about 30%), and the somatosensory cortex, parietal lobe, and cingulate gyrus supplies the rest.^[2] The cells have their bodies in the cerebral cortex, and the axons form the bulk of the pyramidal tracts.^[4] The nerve axons travel from the cortex through the posterior limb of internal capsule, through the cerebral peduncle and into the brainstem and anterior medulla. Here they form two prominences called the pyramids of the medulla. Below the prominences, the majority of axons cross over to the opposite side from which they originated. The axons that cross over move to the outer part of the medulla and form the lateral corticospinal tract, whereas the fibres that remain form the anterior corticospinal tract^[2] About 80% of axons cross over and form the lateral corticospinal tract; 10% do not cross over and join the tract, and 10% of fibres travel in the anterior corticospinal tract.^{[citation needed]}

The nerve axons traveling down the tract are referred to as upper motor neurons. These axons travel down the tracts in the white matter of the spinal cord until they reach the vertebral level of the muscle that they will innervate.^[5] At this point, the axons synapse with lower motor neurons. The majority of axons do not directly synapse with lower motor neurons, but instead synapse with an interneuron that then synapses with a lower motor neuron. This generally occurs in the anterior horn of the spinal cord.^[2] Nerve axons of the lateral corticospinal tract that did not cross over in the medulla do so at the level of the spinal cord they terminate in.^[6]

These tracts contain more than 1 million axons and the majority of the axons are myelinated. The corticospinal tracts myelinate largely during the first and second years after birth. The majority of nerve axons are small (<4μm) in diameter. About 3% of nerve axons have a much larger diameter (16μm) and arise from Betz cells, mostly in the leg area of the primary motor cortex. These cells are notable because of their rapid conduction rate, over 70m/sec, the fastest conduction of any signals from the brain to the spinal cord.^[2]

Horizontal section through the lower part of the pons, showing the fibers of the corticospinal tract (#19) passing through the pontine nuclei

Corticobulbar tract

Fibres from the wikt:ventral motor cortex travel with the corticospinal tract through the internal capsule, but terminate in a number of locations in the midbrain (cortico-mesencephalic tract), pons (Corticopontine tract), and medulla oblongata (cortico-bulbar tract).^[6] The upper motor neurons of the corticobulbar tract synapse with interneurons or directly with the lower motor neurons located in the motor cranial nerve nuclei, namely oculomotor, trochlear, motor nucleus of the trigeminal nerve, abducens, facial nerve and accessory and in the nucleus ambiguus to the hypoglossal, vagus and accessory nerves.^[6] These nuclei are supplied by nerves from both sides of the brain, with the exception of the parts of the facial nerve that control muscles of the lower face. These muscles are only innervated by nerves from the contralateral (opposite) side of the cortex.^[6]

Function

The nerves within the corticospinal tract are involved in movement of muscles of the body. Because of the crossing-over of fibres, muscles are supplied by the side of the brain opposite to that of the muscle.^[2] The nerves within the corticobulbar tract are involved in movement in muscles of the head. They are involved in swallowing, phonation, and movements of the tongue.^[6] By virtue of involvement with the facial nerve, the corticobulbar tract is also responsible for transmitting facial expression.^[5] With the exception of lower muscles of facial expression, all functions of the corticobulbar tract involve inputs from both sides of the brain.^[5]

The term extrapyramidal motor system is used to refer to tracts within the spinal cord involved in voluntary movement but not part of the pyramidal tracts.^[2] Their functions include the control of posture and muscle tone.^{[citation needed]}

Clinical significance

If fibres of the corticospinal tracts are damaged anywhere along their course from the cerebral cortex to the lower end of the spinal cord, this will give rise to an upper motor neuron syndrome. A few days after the injury to the upper motor neurons, a pattern of motor signs and symptoms appears, including spasticity, hyperactive reflexes, a loss of the ability to perform fine movements, and an extensor plantar response known as the Babinski sign.^[7] Symptoms generally occur alongside other sensory problems. Causes of damage may include masses such as strokes, subdural hemorrhage, absesses and tumours, inflammation such as meningitis and multiple sclerosis, and trauma to the spinal cord, including from slipped discs.^[4]

If the corticobulbar tract is damaged on only one side, then only the lower face will be affected, however if there is involvement of both the left and right tracts, then the result is pseudobulbar palsy. This causes problems with swallowing, speaking, and emotional lability.^[4]

Additional images

Dissection of brain-stem. Lateral view.
Superficial dissection of brain-stem. Ventral view.
The motor tract.
Diagram of the principal fasciculi of the spinal cord, from Gray's anatomy

References

^ Chapter 9 of "Principles of Physiology" (3rd edition) by Robert M. Berne and Mathew N. Levy. Published by Mosby, Inc. (2000) ISBN 0-323-00813-5.
^ ^a ^b ^c ^d ^e ^f ^g Hall, Arthur C. Guyton, John E. (2005). Textbook of medical physiology (11th ed.). Philadelphia: W.B. Saunders. pp. 687–690. ISBN 978-0-7216-0240-0.
^ Anthoney, Terence R. (1994). Neuroanatomy and the neurologic exam : a thesaurus of synonyms, similar-sounding non-synonyms, and terms of variable meaning. Boca Raton: CRC Press. pp. 458–460. ISBN 9780849386312.
^ ^a ^b ^c Fauci, Anthony S.; Harrison, T. R., eds. (2008). Harrison's principles of internal medicine (17th ed.). New York: McGraw-Hill Medical. pp. 147–149. ISBN 978-0-07-147692-8.
^ ^a ^b ^c Arslan, Orhan (2001). Neuroanatomical Basis of Clinical Neurology. CRC Press. p. 368. ISBN 1439806136.
^ ^a ^b ^c ^d ^e Young, Paul A. (2007). Basic clinical neuroscience (2nd ed.). Philadelphia, Pa.: Lippincott Williams & Wilkins. pp. 69–70. ISBN 9780781753197.
^ Neuroscience (2. ed.). Sunderland, Mass: Sinauer Assoc. 2001. pp. Damage to Descending Motor Pathways: The Upper Motor Neuron Syndrome. ISBN 0-87893-742-0. |first1= missing |last1= in Authors list (help)

External links

959774759 at GPnotebook
Illustration and text: 01Pyramid at the University of Wisconsin–Madison Medical school
McGill
Stained brain slice images which include the "Corticospinal tract" at the BrainMaps project

UpToDate Contents

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Accumulation of GABAergic Neurons, Causing a Focal Ambient GABA Gradient, and Downregulation of KCC2 Are Induced During Microgyrus Formation in a Mouse Model of Polymicrogyria.

Wang T1, Kumada T, Morishima T, Iwata S, Kaneko T, Yanagawa Y, Yoshida S, Fukuda A.Author information 1Department of Neurophysiology, Hamamatsu University School of Medicine, Hamamatsu, Shizuoka 431-3192, Japan.AbstractAlthough focal cortical malformations are considered neuronal migration disorders, their formation mechanisms remain unknown. We addressed how the γ-aminobutyric acid (GABA)ergic system affects the GABAergic and glutamatergic neuronal migration underlying such malformations. A focal freeze-lesion (FFL) of the postnatal day zero (P0) glutamic acid decarboxylase-green fluorescent protein knock-in mouse neocortex produced a 3- or 4-layered microgyrus at P7. GABAergic interneurons accumulated around the necrosis including the superficial region during microgyrus formation at P4, whereas E17.5-born, Cux1-positive pyramidal neurons outlined the GABAergic neurons and were absent from the superficial layer, forming cell-dense areas in layer 2 of the P7 microgyrus. GABA imaging showed that an extracellular GABA level temporally increased in the GABAergic neuron-positive area, including the necrotic center, at P4. The expression of the Cl(-) transporter KCC2 was downregulated in the microgyrus-forming GABAergic and E17.5-born glutamatergic neurons at P4; these cells may need a high intracellular Cl(-) concentration to induce depolarizing GABA effects. Bicuculline decreased the frequency of spontaneous Ca(2+) oscillations in these microgyrus-forming cells. Thus, neonatal FFL causes specific neuronal accumulation, preceded by an increase in ambient GABA during microgyrus formation. This GABA increase induces GABAA receptor-mediated Ca(2+) oscillation in KCC2-downregulated microgyrus-forming cells, as seen in migrating cells during early neocortical development.
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Although focal cortical malformations are considered neuronal migration disorders, their formation mechanisms remain unknown. We addressed how the γ-aminobutyric acid (GABA)ergic system affects the GABAergic and glutamatergic neuronal migration underlying such malformations. A focal freeze-lesion (
PMID 23246779

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「pyramidal tract」

Corticospinal tract
	Deep dissection of brain-stem. Lateral view. ("pyramidal tract" visible in red, and "pyramidal decussation" labeled at lower right.)
	Spinal cord tracts, with pyramidal tracts labeled at upper left
Details
Latin	tractus corticospinalis
Identifiers
Gray's	p.759
MeSH	A08.186.854.633
NeuroNames	ancil-373
NeuroLex ID	Pyramidal tract
TA	A14.1.04.102
FMA	72634
	Anatomical terms of neuroanatomy

　　[★] 錐体路

(解剖)錐体路

関: corticobulbar tract、corticospinal tract、pyramidal、pyramidal decussation、pyramidal system

「system」

　　[★]

n.

系、システム、体系、体制、方式

関: method、series、strain

「pyramidal」

　　[★]

adj.

錐体の、錐体路の

関: cone、petrosal、pyramid、pyramidal system、pyramidal tract

「pyramid」

　　[★]

関: 虫部錐体、錐体

[1] Chapter 9 of "Principles of Physiology" (3rd edition) by Robert M. Berne and Mathew N. Levy. Published by Mosby, Inc. (2000) ISBN 0-323-00813-5.

[GUYTONHALL2005-2] ^ ^a ^b ^c ^d ^e ^f ^g Hall, Arthur C. Guyton, John E. (2005). Textbook of medical physiology (11th ed.). Philadelphia: W.B. Saunders. pp. 687–690. ISBN 978-0-7216-0240-0.

[3] Anthoney, Terence R. (1994). Neuroanatomy and the neurologic exam : a thesaurus of synonyms, similar-sounding non-synonyms, and terms of variable meaning. Boca Raton: CRC Press. pp. 458–460. ISBN 9780849386312.

[HARRISONS2008-4] Fauci, Anthony S.; Harrison, T. R., eds. (2008). Harrison's principles of internal medicine (17th ed.). New York: McGraw-Hill Medical. pp. 147–149. ISBN 978-0-07-147692-8.

[Arslan2001-5] Arslan, Orhan (2001). Neuroanatomical Basis of Clinical Neurology. CRC Press. p. 368. ISBN 1439806136.

[YOUNG2007-6] Young, Paul A. (2007). Basic clinical neuroscience (2nd ed.). Philadelphia, Pa.: Lippincott Williams & Wilkins. pp. 69–70. ISBN 9780781753197.

[7] Neuroscience (2. ed.). Sunderland, Mass: Sinauer Assoc. 2001. pp. Damage to Descending Motor Pathways: The Upper Motor Neuron Syndrome. ISBN 0-87893-742-0. |first1= missing |last1= in Authors list (help)

リンク元	「pyramidal tract」
関連記事	「system」「pyramidal」「pyramid」

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案内

pyramidal system