White matter - wikipedia White matter White matter Micrograph showing white matter with its characteristic fine meshwork - like appearance ( left of image - lighter shade of pink ) and grey matter, with the characteristic neuronal cell bodies ( right of image - dark shade of pink ). HPS stain. Human brain right dissected lateral view, showing grey matter ( the darker outer parts ), and white matter ( the inner and prominently whiter parts ). Details Identifiers Latin substantia alba Dorlands / Elsevier White matter TA A14. 1.00. 009 FMA 83929 Anatomical terminology ( edit on Wikidata ) White matter structure of human brain ( taken by MRI ). White matter refers to areas of the central nervous system ( CNS ) that are mainly made up of myelinated axons, also called tracts. Long thought to be passive tissue, white matter affects learning and brain functions, modulating the distribution of action potentials, acting as a relay and coordinating communication between different brain regions. White matter is named for its relatively light appearance resulting from the lipid content of myelin. However, the tissue of the freshly cut brain appears pinkish white to the naked eye because myelin is composed largely of lipid tissue veined with capillaries. Its white color in prepared specimens is due to its usual preservation in formaldehyde. Contents 1 Structure 1.1 White matter 1.2 Grey matter 1.3 Location 1.4 Myelinated axon length 2 Function 3 Clinical significance 4 Imaging 5 References 6 External links Structure White matter White matter is composed of bundles of myelinated axons, which connect various gray matter areas ( the locations of nerve cell bodies ) of the brain to each other, and carry nerve impulses between neurons. Myelin acts as an insulator, which allows electrical signals to jump, rather than coursing through the axon, increasing the speed of transmission of all nerve signals. The total number of long range fibers within a cerebral hemisphere is 2 % of the total number of cortico - cortical fibers ( across cortical areas ) and is roughly the same number as those that communicate between the two hemispheres in the brain 's largest white tissue structure, the Corpus callosum. Schüz and Braitenberg note `` As a rough rule, the number of fibres of a certain range of lengths is inversely proportional to their length. '' White matter in nonelderly adults is 1.7 -- 3.6 % blood. Grey matter The other main component of the brain is grey matter ( actually pinkish tan due to blood capillaries ), which is composed of neurons. The substantia nigra is a third colored component found in the brain that appears darker due to higher levels of melanin in dopaminergic neurons than its nearby areas. Note that white matter can sometimes appear darker than grey matter on a microscope slide because of the type of stain used. Cerebral - and spinal white matter do not contain dendrites, neural cell bodies, or shorter axons, which can only be found in grey matter. Location White matter forms the bulk of the deep parts of the brain and the superficial parts of the spinal cord. Aggregates of gray matter such as the basal ganglia ( caudate nucleus, putamen, globus pallidus, substantia nigra, subthalamic nucleus, nucleus accumbens ) and brainstem nuclei ( red nucleus, cranial nerve nuclei ) are spread within the cerebral white matter. The cerebellum is structured in a similar manner as the cerebrum, with a superficial mantle of cerebellar cortex, deep cerebellar white matter ( called the `` arbor vitae '' ) and aggregates of grey matter surrounded by deep cerebellar white matter ( dentate nucleus, globose nucleus, emboliform nucleus, and fastigial nucleus ). The fluid - filled cerebral ventricles ( lateral ventricles, third ventricle, cerebral aqueduct, fourth ventricle ) are also located deep within the cerebral white matter. Myelinated axon length Men have more white matter than females both in volume and in length of myelinated axons. At the age of 20, the total length of myelinated fibers in males is 176,000 km while that of a female is 149,000 km. There is a decline in total length with age of about 10 % each decade such that a man at 80 years of age has 97,200 km and a female 82,000 km. Most of this reduction is due to the loss of thinner fibers. Function White matter is the tissue through which messages pass between different areas of gray matter within the central nervous system. The white matter is white because of the fatty substance ( myelin ) that surrounds the nerve fibers ( axons ). This myelin is found in almost all long nerve fibers, and acts as an electrical insulation. This is important because it allows the messages to pass quickly from place to place. Unlike gray matter, which peaks in development in a person 's twenties, the white matter continues to develop, and peaks in middle age. Clinical significance Multiple sclerosis ( MS ) is one of the most common diseases which affect white matter. In MS lesions, the myelin shield around the axons has been destroyed by inflammation. Alcohol use disorders are associated with decrease in white matter volume. Animal studies suggest that alcohol may cause loss of white matter by damaging oligodendrocytes, the glial cell responsible for maintaining myelin. Changes in white matter known as amyloid plaques are associated with Alzheimer 's disease and other neurodegenerative diseases. White matter injuries ( `` axonal shearing '' ) may be reversible, while gray matter regeneration is less likely. Other changes that commonly occur with age include the development of leukoaraiosis, which is a rarefaction of the white matter that can be caused by a variety of conditions, including loss of myelin, axonal loss, and a breakdown of the blood -- brain barrier. Imaging The study of white matter has been advanced with the neuroimaging technique called diffusion tensor imaging where magnetic resonance imaging ( MRI ) brain scanners are used. As of 2007, more than 700 publications have been published on the subject. A 2009 paper by Jan Scholz and colleagues used diffusion tensor imaging ( DTI ) to demonstrate changes in white matter volume as a result of learning a new motor task ( e.g. juggling ). The study is important as the first paper to correlate motor learning with white matter changes. Previously, many researchers had considered this type of learning to be exclusively mediated by dendrites, which are not present in white matter. The authors suggest that electrical activity in axons may regulate myelination in axons. Or, gross changes in the diameter or packing density of the axon might cause the change. A more recent DTI study by Sampaio - Baptista and colleagues reported changes in white matter with motor learning along with increases in myelination. References Jump up ^ Blumenfeld, Hal ( 2010 ). Neuroanatomy through clinical cases ( 2nd ed. ). Sunderland, Mass. : Sinauer Associates. p. 21. ISBN 9780878936137. Areas of the CNS made up mainly of myelinated axons are called white matter. Jump up ^ Douglas Fields, R. ( 2008 ). `` White Matter Matters ''. Scientific American. 298 ( 3 ) : 54 -- 61. Bibcode : 2008SciAm. 298c... 54D. doi : 10.1038 / scientificamerican0308 - 54. Jump up ^ Klein, S.B., & Thorne, B.M. Biological Psychology. Worth Publishers : New York. 2007. ^ Jump up to : Schüz, Almut ; Braitenberg, Valentino ( 2002 ). `` The human cortical white matter : Quantitative aspects of cortico - cortical long - range connectivity ''. In Schüz, Almut ; Braitenberg, Valentino. Cortical Areas : Unity and Diversity, Conceptual Advances in Brain Research. Taylor and Francis. pp. 377 -- 86. ISBN 978 - 0 - 415 - 27723 - 5. Jump up ^ Leenders, K.L. ; Perani, D. ; Lammertsma, A.A. ; Heather, J.D. ; Buckingham, P. ; Jones, T. ; Healy, M.J.R. ; Gibbs, J.M. ; Wise, R.J.S. ; Hatazawa, J. ; Herold, S. ; Beaney, R.P. ; Brooks, D.J. ; Spinks, T. ; Rhodes, C. ; Frackowiak, R.S.J. ( 1990 ). `` Cerebral Blood Flow, Blood Volume and Oxygen Utilization ''. Brain. 113 : 27 -- 47. PMID 2302536. doi : 10.1093 / brain / 113.1. 27. ^ Jump up to : Marner, Lisbeth ; Nyengaard, Jens R. ; Tang, Yong ; Pakkenberg, Bente ( 2003 ). `` Marked loss of myelinated nerve fibers in the human brain with age ''. The Journal of Comparative Neurology. 462 ( 2 ) : 144 -- 52. PMID 12794739. doi : 10.1002 / cne. 10714. Jump up ^ Sowell, Elizabeth R. ; Peterson, Bradley S. ; Thompson, Paul M. ; Welcome, Suzanne E. ; Henkenius, Amy L. ; Toga, Arthur W. ( 2003 ). `` Mapping cortical change across the human life span ''. Nature Neuroscience. 6 ( 3 ) : 309 -- 15. PMID 12548289. doi : 10.1038 / nn1008. Jump up ^ Monnig, Mollie A. ; Tonigan, J. Scott ; Yeo, Ronald A. ; Thoma, Robert J. ; McCrady, Barbara S. ( 2013 ). `` White matter volume in alcohol use disorders : A meta - analysis ''. Addiction Biology. 18 ( 3 ) : 581 -- 92. PMC 3390447. PMID 22458455. doi : 10.1111 / j. 1369 - 1600.2012. 00441. x. Jump up ^ Alfonso - Loeches, Silvia ; Pascual, Maria ; Gómez - Pinedo, Ulises ; Pascual - Lucas, Maya ; Renau - Piqueras, Jaime ; Guerri, Consuelo ( 2012 ). `` Toll - like receptor 4 participates in the myelin disruptions associated with chronic alcohol abuse ''. Glia. 60 ( 6 ) : 948 -- 64. PMID 22431236. doi : 10.1002 / glia. 22327. Jump up ^ Assaf, Yaniv ; Pasternak, Ofer ( 2007 ). `` Diffusion Tensor Imaging ( DTI ) - based White Matter Mapping in Brain Research : A Review ''. Journal of Molecular Neuroscience. 34 ( 1 ) : 51 -- 61. PMID 18157658. doi : 10.1007 / s12031 - 007 - 0029 - 0. Jump up ^ Scholz, Jan ; Klein, Miriam C ; Behrens, Timothy EJ ; Johansen - Berg, Heidi ( 2009 ). `` Training induces changes in white - matter architecture ''. Nature Neuroscience. 12 ( 11 ) : 1370 -- 1. PMC 2770457. PMID 19820707. doi : 10.1038 / nn. 2412. Jump up ^ `` White Matter Matters ''. Dolan DNA Learning Center. Archived from the original on 2009 - 11 - 12. Retrieved 2009 - 10 - 19. Jump up ^ Sampaio - Baptista, C. ; Khrapitchev, A.A. ; Foxley, S. ; Schlagheck, T. ; Scholz, J. ; Jbabdi, S. ; Deluca, G.C. ; Miller, K.L. ; Taylor, A. ; Thomas, N. ; Kleim, J. ; Sibson, N.R. ; Bannerman, D. ; Johansen - Berg, H. ( 2013 ). `` Motor Skill Learning Induces Changes in White Matter Microstructure and Myelination ''. Journal of Neuroscience. 33 ( 50 ) : 19499 -- 503. PMC 3858622. PMID 24336716. doi : 10.1523 / JNEUROSCI. 3048 - 13.2013. External links Wikimedia Commons has media related to White matter. White Matter Atlas WebMD ( 2009 ). `` white matter ''. Webster 's New World Medical Dictionary ( 3rd ed. ). Houghton Mifflin Harcourt. p. 456. ISBN 978 - 0 - 544 - 18897 - 6. Nervous tissue CNS Tissue Types Grey matter White matter Projection fibers Association fiber Commissural fiber Lemniscus Funiculus Fasciculus Nerve tract Decussation Commissure Neuropil Meninges Cell Types Neuronal Pyramidal Purkinje Granule Glial insulating : Myelination : Oligodendrocyte other Astrocyte Radial glial cell Ependymal cells Tanycyte Microglia PNS General Dorsal Root Ganglion Ramus Ventral Root Ramus Ramus communicans Gray White Autonomic ganglion ( Preganglionic nerve fibers Postganglionic nerve fibers ) Connective tissues Epineurium Perineurium Endoneurium Nerve fascicle Neuroglia Myelination : Schwann cell Neurolemma Myelin incisure Node of Ranvier Internodal segment Satellite glial cell Neurons / nerve fibers Parts Soma Axon hillock Axon Telodendron Axon terminals Axoplasm Axolemma Neurofibril / neurofilament Dendrite Nissl body Dendritic spine Apical dendrite / Basal dendrite Types Bipolar Unipolar Pseudounipolar Multipolar Interneuron Renshaw Afferent nerve fiber / Sensory neuron GSA GVA SSA SVA fibers Ia Ib or Golgi II or Aβ III or Aδ or fast pain IV or C or slow pain Efferent nerve fiber / Motor neuron GSE GVE SVE Upper motor neuron Lower motor neuron α motorneuron β motorneuron γ motorneuron Termination Synapse Electrical synapse / Gap junction Chemical synapse Synaptic vesicle Active zone Postsynaptic density Autapse Ribbon synapse Neuromuscular junction Sensory receptors Meissner 's corpuscle Merkel nerve ending Pacinian corpuscle Ruffini ending Muscle spindle Free nerve ending Nociceptor Olfactory receptor neuron Photoreceptor cell Hair cell Taste bud The spinal cord General features Cervical enlargement Lumbar enlargement Conus medullaris Filum terminale Cauda equina Meninges Grey matter Posterior grey column Marginal nucleus Substantia gelatinosa of Rolando Nucleus proprius Spinal lamina V Spinal lamina VI Lateral grey column Intermediolateral nucleus Posterior thoracic nucleus Anterior grey column Interneuron Alpha motor neuron Onuf 's nucleus Gamma motor neuron Other Rexed laminae Central gelatinous substance Gray commissure Central canal Terminal ventricle White matter Sensory Posterior Posterior column - medial lemniscus pathway : Gracile Cuneate Lateral : Spinocerebellar dorsal ventral Spinothalamic lateral anterior Posterolateral Spinotectal Spinoreticular tract Spino - olivary tract Motor Lateral Corticospinal Lateral Extrapyramidal Rubrospinal Olivospinal Raphespinal Anterior Corticospinal Anterior Extrapyramidal Vestibulospinal Reticulospinal Tectospinal Both Anterior white commissure External features Ventral Anterior median fissure Anterolateral sulcus Dorsal Posterior median sulcus Posterolateral sulcus Anatomy of the medulla Grey matter Cranial nuclei afferent : Solitary nucleus tract Dorsal respiratory group Gustatory nucleus Vestibular nuclei Lateral Medial Inferior efferent : Hypoglossal nucleus Nucleus ambiguus Dorsal nucleus of vagus nerve Inferior salivatory nucleus Dorsal Gracile nucleus Cuneate nucleus Accessory cuneate nucleus Ventral Ventral respiratory group Arcuate nucleus of medulla Rostral ventromedial medulla Botzinger complex Pre-Bötzinger complex White matter Dorsal Sensory Sensory decussation Medial lemniscus Juxtarestiform body Ascending dorsal longitudinal fasciculus Medial longitudinal fasciculus Motor Descending dorsal longitudinal fasciculus Medial longitudinal fasciculus Ventral Descending tracts Olivocerebellar tract Rubro - olivary tract Surface Front Pyramid decussation Anterior median fissure Anterolateral sulcus Olive Inferior olivary nucleus Back Posterior median sulcus Posterolateral sulcus Area postrema Vagal trigone Hypoglossal trigone Medial eminence Inferior cerebellar peduncle Grey Reticular formation Gigantocellular Parvocellular Ventral Lateral Paramedian Raphe nuclei Obscurus Magnus Pallidus Perihypoglossal nuclei Anatomy of the pons Dorsal / ( tegmentum ) Surface Cerebellopontine angle Superior medullary velum Sulcus limitans Medial eminence Facial colliculus White : Sensory Trapezoid body Trigeminal lemniscus Dorsal trigeminal tract Ventral trigeminal tract Medial lemniscus Lateral lemniscus Medial longitudinal fasciculus Vestibulo - oculomotor fibers Anterior trigeminothalamic tract Central tegmental tract White : Motor Inferior cerebellar peduncle Vestibulocerebellar tract Medial longitudinal fasciculus Vestibulospinal tract Medial vestibulospinal tract Lateral vestibulospinal tract Grey : Cranial nuclei afferent : GSA Trigeminal Principal Spinal Cochlear nucleus Dorsal Anterior Vestibular nuclei Superior efferent : SVE : Trigeminal motor nucleus Facial motor nucleus GSE : Abducens nucleus GVE : Superior salivary nucleus Inferior salivary nucleus Other Apneustic center Parabrachial area Pneumotaxic center Subparabrachial nucleus Medial parabrachial nucleus Lateral parabrachial nucleus Superior olivary nucleus Caerulean nucleus Ventral / ( base ) Grey Pontine nuclei White : Motor / descending Corticospinal tract Corticobulbar tract Corticopontine fibers MCP Pontocerebellar fibers Surface Basilar sulcus Other grey : Raphe / reticular Reticular formation Caudal Oral Tegmental Paramedian Raphe nuclei Median Anatomy of the midbrain Tectum ( Dorsal ) Surface Corpora quadrigemina : Inferior colliculus Brachium Superior colliculus Brachium Grey matter Pretectal area White : Sensory / ascending Spinotectal tract Central tegmental tract White : Motor / descending Tectospinal tract Peduncle ( Ventral ) Tegmentum White : Sensory / ascending Lemnisci Medial Lateral Ascending MLF Vestibulo - oculomotor fibers Spinothalamic tract Anterior trigeminothalamic tract Dentatothalamic tract White : Motor / descending Rubrospinal tract Rubro - olivary tract Descending MLF Grey : cranial nuclei GSA Mesencephalic - GSE Oculomotor nucleus, Trochlear nucleus - GVE Edinger -- Westphal nucleus Grey : other Periaqueductal gray Raphe nuclei dorsal Ventral tegmental area Rostromedial tegmental nucleus Pedunculopontine nucleus Red nucleus Rostral interstitial nucleus of medial longitudinal fasciculus Parabrachial area Interpeduncular nucleus Midbrain reticular formation Ventricular system Cerebral aqueduct Base White : Motor / descending Cerebral crus : Corticospinal tract Corticobulbar tract Corticopontine tract / Frontopontine fibers / Temporopontine fibers Grey : Substantia nigra Pars compacta Pars reticulata Surface Superior cerebellar peduncle Decussation Interpeduncular fossa Anatomy of the cerebellum Surface Lobes Anterior lobe Posterior lobe Horizontal fissure Flocculonodular lobe Flocculus Nodule Primary fissure Medial / lateral Vermis : anterior Central lobule Culmen Lingula posterior Folium Tuber Uvula Vallecula of cerebellum Hemisphere : anterior Alar central lobule posterior Biventer lobule Cerebellar tonsil Grey matter Deep cerebellar nuclei Dentate interposed Emboliform Globose Fastigial Cerebellar cortex Molecular layer Stellate cell Basket cell Purkinje cell layer Purkinje cell Bergmann glia cell = Golgi epithelial cell Fañanas cell Granule cell layer Golgi cell Granule cell Unipolar brush cell Fibers : Mossy fibers Climbing fiber Parallel fiber White matter Internal Arbor vitae Peduncles Inferior ( medulla ) : Dorsal spinocerebellar tract Olivocerebellar tract Cuneocerebellar tract Juxtarestiform body ( Vestibulocerebellar tract ) Trigeminocerebellar fibers Middle ( pons ) : Pontocerebellar fibers Superior ( midbrain ) : Ventral spinocerebellar tract Dentatothalamic tract Anatomy of the diencephalon of the human brain Epithalamus Surface Pineal gland Habenula Habenular trigone Habenular commissure Grey matter Pretectal area Habenular nuclei Subcommissural organ Thalamus Surface Stria medullaris of thalamus Thalamic reticular nucleus Taenia thalami Grey matter / nuclei paired : AN Ventral VA / VL VP / VPM / VPL Lateral LD LP Pulvinar nuclei Metathalamus MG LG P cell M cell K cell midline : MD Intralaminar Centromedian Midline nuclear group Interthalamic adhesion White matter Mammillothalamic fasciculus Pallidothalamic tracts Ansa lenticularis Lenticular fasciculus Thalamic fasciculus PCML Medial lemniscus Trigeminal lemniscus Spinothalamic tract Lateral lemniscus Dentatothalamic tract Acoustic radiation Optic radiation Subthalamic fasciculus Anterior trigeminothalamic tract Medullary laminae Hypothalamus Surface Median eminence / Tuber cinereum Mammillary body Infundibulum Grey matter Autonomic zones Anterior ( parasympathetic / heat loss ) Posterior ( sympathetic / heat conservation ) Endocrine posterior pituitary : Paraventricular Magnocellular neurosecretory cell Parvocellular neurosecretory cell Supraoptic oxytocin / vasopressin other : Arcuate ( dopamine / GHRH ) Preoptic ( GnRH ) Suprachiasmatic ( melatonin ) Emotion Lateral Ventromedial Dorsomedial White matter afferent Medial forebrain bundle Retinohypothalamic tract efferent Mammillothalamic fasciculus Stria terminalis Dorsal longitudinal fasciculus Pituitary Posterior is diencephalon, but anterior is glandular Subthalamus Subthalamic nucleus Zona incerta Nuclei campi perizonalis ( Fields of Forel ) Commissural fibers in the human brain Corpus callosum Genu Splenium Tapetum Rostrum Archicortex Supracallosal gyrus Lamina terminalis Vascular organ of lamina terminalis Anterior commissure Fornix Fornix Septum pellucidum Septal nuclei Medial septal nucleus Subfornical organ Cave of septum pellucidum Other Posterior commissure Rostral basal ganglia of the human brain and associated structures Basal ganglia Grey matter Striatum Dorsal striatum Putamen Caudate nucleus Ventral striatum Nucleus accumbens Olfactory tubercle Globus pallidus GPe GPi Other Amygdala Claustrum White matter Centrum semiovale Internal capsule Anterior limb Genu Posterior limb Optic radiation Corona radiata External capsule Extreme capsule Pallidothalamic tracts : Thalamic fasciculus Ansa lenticularis Lenticular fasciculus Subthalamic fasciculus Rhinencephalon Grey matter Anterior olfactory nucleus Anterior perforated substance Olfactory bulb White matter Olfactory tract Medial olfactory stria Lateral olfactory stria Olfactory trigone Other basal forebrain Grey matter Substantia innominata Nucleus basalis Nucleus of diagonal band White matter Diagonal band of Broca Stria terminalis Archicortex : Hippocampal formation / Hippocampus anatomy Grey matter Hippocampus proper CA1 CA2 CA3 CA4 Dentate gyrus Fascia dentata Subiculum White matter Alveus Fimbria Perforant path Schaffer collateral Retrieved from `` https://en.wikipedia.org/w/index.php?title=White_matter&oldid=792823546 '' Categories : Central nervous system Neuroanatomy Hidden categories : Wikipedia articles needing page number citations from May 2015 Accuracy disputes from May 2015 Medicine infobox template using Dorlands parameter All articles with unsourced statements Articles with unsourced statements from May 2014 Articles with unsourced statements from May 2015 Talk Contents About Wikipedia Afrikaans 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Question: why is white matter on the inside of the brain
Answer: acting as a relay and coordinating communication between different brain regions