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Brain: Thalamus
MRI cross-section of human brain, with thalamus marked.
Scheme showing the course of the fibers of the lemniscus; medial lemniscus in blue, lateral in red. The medial lemniscus, also known as Reil's band or Reil's ribbon, is a pathway in the Brainstem that carries sensory information from the gracile The lateral lemniscus is a tract of Axons in the Brainstem that carries information about sound from the Cochlear nucleus to various brainstem nuclei and
Latin thalamus dorsalis
Gray's subject #189 808
NeuroNames hier-283
MeSH Thalamus
For the computer game developer, see Thalamus Ltd. Latin ( lingua Latīna, laˈtiːna is an Italic language, historically spoken in Latium and Ancient Rome. This is a list of the subjects in Gray's Anatomy: IX Neurology NeuroNames is a system of nomenclature for the human and/or macaque Brain. Medical Subject Headings ( MeSH) is a huge Controlled vocabulary (or metadata system for the purpose of indexing journal articles and books Thalamus Ltd (also known as Thalamus) was a British computer game developer that published titles for a number of 8-bit and 16-bit platforms

The thalamus (from Greek θάλαμος = room, chamber, IPA= /ˈθæləməs/) is a pair and symmetric part of the brain. Greek (el ελληνική γλώσσα or simply el ελληνικά — "Hellenic" is an Indo-European language, spoken today by 15-22 million people mainly It constitutes the main part of the diencephalon. The diencephalon (or interbrain is the region of the Brain that includes the Thalamus, Hypothalamus, Epithalamus, Prethalamus or

Contents

Location and topography

In the caudal (tail) to rostral (head) sequence of neuromeres, the diencephalon is located between the mesencephalon (cerebral peduncule, belonging to the brain stem) and the cerebrum. Neuromeres are morphologically or molecularly defined Transient segments of the early developing Brain. In biological anatomy the mesencephalon (or midbrain) comprises the Tectum (or corpora quadrigemini Tegmentum, the ventricular mesocoelia (or "iter" The cerebral peduncle, by most classifications is everything in the Mesencephalon except the Tectum. The brain stem (or brainstem) is the lower part of the Brain, adjoining and structurally continuous with the Spinal cord. The diencephalon includes also the dorsally located epithalamus (essentially the habenula and annexes) and the perithalamus (prethalamus formerly described as ventral thalamus) containing the zona incerta and the "reticulate nucleus" (not the reticular, term of confusion). The diencephalon (or interbrain is the region of the Brain that includes the Thalamus, Hypothalamus, Epithalamus, Prethalamus or The epithalamus is a dorsal posterior segment of the Diencephalon (a segment in the middle of the Brain also containing the Hypothalamus In Neuroanatomy, habenula (diminutive of Latin habena meaning rein originally denoted the stalk of the Pineal gland (pineal habenula pedunculus of pineal The' Prethalamus (formerly described as ventral thalamus) or Subthalamus is part of the Diencephalon and therefore part of the Brain The zona incerta is a small region of Gray matter that is part of the Subthalamus. Due to their different ontogenetic origins, the epithalamus and the perithalamus are formally distinguished from the thalamus proper. Ontogeny, as opposed to Phylogeny, refers to the history of an organism from birth as opposed to its genetic makeup

Phylogenetic modifications are such that this article essentially deals with the human thalamus and may differ in comparison with accounts in non-upper primate species. In normal humans, the two thalami are prominent bulb-shaped masses, about 5. 7 cm in length, located obliquely (about 30°) and symmetrically on each side of the third ventricle. The two can adhere on a variable extent in 30% of humans. This adhesio interthalamica (interthalamic adhesion, or massa intermedia) does not contain interthalamic neural connection in our species. The medial surface of the Thalamus constitutes the upper part of the lateral wall of the Third ventricle, and is connected to the corresponding surface of the opposite thalamus

Anatomy

The thalamus comprises a system of lamellae (made up of myelinated fibers) separating different thalamic subparts. Myelin is an electrically-insulating Dielectric Phospholipid layer that surrounds only the Axons of many Neurons It is an outgrowth An axon or nerve fiber is a long slender projectionof a nerve cell or Neuron, that conducts electrical impulses away from the neuron's Cell Other areas are defined by distinct clusters of neurons, such as the periventricular gray, the intralaminar elements, the "nucleus limitans", and others. Neurons (ˈnjuːɹɒn also known as neurones and nerve cells) are responsive cells in the Nervous system that process and transmit information [1] These latter structures, different in structure from the major part of the thalamus, have been grouped together into the allothalamus as opposed to the isothalamus. The Allothalamus is a division used by some researchers in describing the Thalamus. The isothalamus is a division used by some researchers in describing the Thalamus. [2] This distinction simplifies the global description of the thalamus.

See also List of thalamic nuclei. This traditional list does not accord strictly with human thalamic anatomy

Arterial supply

The thalamus derives its blood supply from a number of arteries including polar and paramedian arteries, inferolateral (thalamogeniculate) arteries, and posterior (medial and lateral) choroidal arteries. [3] These are all branches of the posterior cerebral artery. In Human anatomy, the posterior cerebral artery is the Blood vessel that supplies oxygenated Blood to the posterior aspect of the brain ( Occipital

Function

The thalamus is known to have multiple functions. Deduced from the design of the isothalamus, it is generally believed to act as a translator for which various "prethalamic" inputs are processed into a form readable by the cerebral cortex. The' Prethalamus (formerly described as ventral thalamus) or Subthalamus is part of the Diencephalon and therefore part of the Brain The cerebral cortex is a structure within the Brain that plays a key role in Memory, Attention, perceptual Awareness, Thought, The thalamus is believed to both process and relay sensory information selectively to various parts of the cerebral cortex, as one thalamic point may reach one or several regions in the cortex.

The thalamus also plays an important role in regulating states of sleep and wakefulness. Sleep is a Natural state of bodily rest observed throughout the animal kingdom [4] Thalamic nuclei have strong reciprocal connections with the cerebral cortex, forming thalamo-cortico-thalamic circuits that are believed to be involved with consciousness. Thalamo-cortico-thalamic circuits consist of looped neural pathways that connect the Thalamus to the Cerebral cortex, and connect the cerebral cortex back to the thalamus Consciousness has been defined loosely as a constellation of attributes of Mind such as Subjectivity, Self-awareness, Sentience, and the The thalamus plays a major role in regulating arousal, the level of awareness, and activity. Damage to the thalamus can lead to permanent coma. In Medicine, a coma (from the Greek koma, meaning deep sleep is a profound state of Unconsciousness.

Many different functions are linked to the system to which thalamic parts belong. This is at first the case for sensory systems (which excepts the olfactory function) auditory, somatic, visceral, gustatory and visual systems where localised lesions provoke particular sensory deficits. The auditory system is the Sensory system for the sense of hearing. In Anatomy, a viscus (ˈvɪskəs ( Plural: viscera /ˈvɪsərə/ is an internal organ of an animal (including humans in particular an internal Taste (or more formally gustation) is a form of direct Chemoreception and is one of the traditional five Senses The visual system is the part of the Nervous system which allows organisms to see. A major role of the thalamus is devoted to "motor" systems. This has been and continues to be a subject of interest for investigators. VIm, the relay of cerebellar afferences, is the target of stereotactians particularly for the improvement of tremor. Tremor is an unintentional somewhat rhythmic muscle movement involving to-and-from movements (oscillations of one or more parts of the body The role of the thalamus in the more anterior pallidal and nigral territories in the basal ganglia system disturbances is recognized but still poorly known. The globus pallidus ( Latin for "pale globe" is a sub- cortical structure of the Brain. The substantia nigra ( Latin for "black substance" Sömmering) or locus niger is a heterogeneous portion of the midbrain, separating The basal ganglia (or basal nuclei) are a group of nuclei in the Brain interconnected with the Cerebral cortex, Thalamus and The contribution of the thalamus to vestibular or to tectal functions is almost ignored. The tectum (Latin roof) is a region of the Brain, specifically the dorsal part of the Mesencephalon (midbrain The thalamus has been thought of as a "relay" that simply forwards signals to the cerebral cortex. Newer research suggests that thalamic function is more complicated. [5]

Pathology

Cerebrovascular accidents (strokes) can cause thalamic syndrome,[6] which results in a contralateral hemianaesthesia, burning or aching sensation on one half of a body (painful anaesthesia) often accompanied by mood swings. A stroke is the rapidly developing loss of brain functions due to a disturbance in the blood vessels supplying blood to the brain A mood disorder is the term given for a group of diagnoses in the DSM IV TR classification system where a disturbance in the person's emotional mood is hypothesised Ischaemia of the territory of the paramedian artery, if bilateral, causes serious troubles including akinetic mutism accompanied or not by oculomotor troubles. Akinetic mutism is a medical term describing Patients who tend neither to speak ( mutism) nor move ( Akinesia) It is also related to Thalamocortical Dysrhythmia. Thalamocortical Dysrhythmia (TCD is a theoretical framework in which neuroscientists try to explain the positive and negative symptoms induced by neurological disorders like Parkinson's

Korsakoff's Syndrome stems from mammillary bodies, mammilothalamic, or thalamic lesions. Korsakoff's syndrome or "Korsakov's syndrome" ( Korsakoff's psychosis, amnesic-confabulatory syndrome) is a brain disorder caused by the lack of thiamine

Development

The thalamic complex is composed of the perithalamus (or prethalamus, previously also known as ventral thalamus), the zona limitans intrathalamica (ZLI) and the thalamus (dorsal thalamus). The zona limitans intrathalamica (ZLI is a transverse boundary located between the Prethalamus (previously also known as ventral thalamus and the functional distinct Thalamus [7][8]

The ZLI is a transverse boundary located between the perithalamus and the functional distinct thalamus. Besides its morphological characteristics, it bears the hallmarks of a signalling centre. Fate mapping experiments in chicks have shown that the ZLI is cell lineage restricted at its boundaries and therefore can be termed a true developmental compartment in the forebrain. [9]

Besides morphological characteristics, the ZLI is the only structure in the alar plate of the neural tube that expresses signaling molecules. [10]

In mice, the function of signaling at the ZLI has not been addressed directly due to a complete absence of the diencephalon in Shh mutants. [11]

Studies in chicks have shown that Shh is both necessary and sufficient for thalamic gene induction. [12]

In zebrafish, it was shown that the expression of two Shh genes, shh-a and shh-b (formerly described as twhh) mark the ZLI territory, and that Shh signaling is sufficient for the molecular differentiation of both the prethalamus and the thalamus but is not required for their maintenance and Shh signaling from the ZLI/alar plate is sufficient for the maturation of prethalamic and thalamic territory while ventral Shh signals are dispensable. The zebrafish or zebra danio, Danio rerio, a Tropical Freshwater Fish belonging to the minnow family ( Cyprinidae) [13]

In humans, a common genetic variation in the promotor region of the serotonin transporter (the SERT-long and -short allele: 5HTTLPR) has been shown to affect the development of several regions of the thalamus in adults. The Serotonin transporter (SERT is a Monoamine transporter Protein. People who inherit two short alleles (SERT-ss) have more neurons and a larger volume in the pulvinar and possibly the limbic regions of the thalamus. An allele (ˈæliːl (UK /əˈliːl/ (US (from the Greek αλληλος allelos, meaning each other) is one member of a pair or series of different forms Enlargement of the thalamus provides an anatomical basis for why people who inherit two SERT-ss alleles are more vulnerable to major depression, posttraumatic stress disorder, and suicide. Major depressive disorder, also known as major depression, unipolar depression, unipolar disorder, clinical depression, or simply depression Post traumatic stress disorder It is a severe and ongoing emotional reaction to [14]

References

  1. ^ Jones Edward G. (2007) "The Thalamus" Cambridge Uni. Press
  2. ^ Percheron, G. (2003) "Thalamus". In Paxinos, G. and May, J. (eds). The human nervous system. 2d Ed. Elsevier. Amsterdam. pp. 592-675
  3. ^ Percheron, G. (1982) The arterial supply of the thalamus. In Schaltenbrand and Walker, A. E. (eds) Stereotaxy of the human brain. Thieme . Stuttgart. pp. 218-232
  4. ^ Steriade, M. and Llinas, R. (1988) "The functional states of the thalamus and the associated neuronal interplay". Physiological Review 68: 699-742
  5. ^ Your Brain Boots Up Like a Computer | LiveScience
  6. ^ Dejerine, J. and Roussy. G. (1906) Le syndrome thalamique. Rev. Neurol. 14: 521-532
  7. ^ Kuhlenbeck, H. (1937). The ontogenetic development of diencephalic centres in the bird's brain (chick) and comparison with the reptilian and mammalian diencephalon. J. Comp. Neurol. 66
  8. ^ Shimamura, K. , Hartigan, D. J. , Martinez, S. , Puelles, L. and Rubenstein, J. L. (1995). Longitudinal organization of the anterior neural plate and neural tube. Development 121,3923 -3933.
  9. ^ Zeltser, L. M. , Larsen, C. W. and Lumsden, A. (2001). A new developmental compartment in the forebrain regulated by Lunatic fringe. Nat. Neurosci. 4, 683-684.
  10. ^ Puelles, L. and Rubenstein, J. L. (2003). Forebrain gene expression domains and the evolving prosomeric model. Trends Neurosci. 26,469 -476.
  11. ^ Ishibashi, M. and McMahon, A. P. (2002). A sonic hedgehog-dependent signalling relay regulates growth of diencephalic and mesencephalic primordia in the early mouse embryo. Development 129,4807 -4819.
  12. ^ Kiecker, C. and Lumsden, A. (2004). Hedgehog signalling from the ZLI regulates diencephalic regional identity. Nat. Neurosci. 7,1242 -1249.
  13. ^ Scholpp S, Wolf O, Brand M, Lumsden A. Hedgehog signalling from the zona limitans intrathalamica orchestrates patterning of the zebrafish diencephalon'. Development. 2006 Mar;133(5):855-64[1]
  14. ^ Young KA, Holcomb LA, Yazdani U, Bonkale W, Hicks PB and German DC. 5HTTLPR polymorphism and enlargement of the pulvinar: Unlocking the backdoor to the limbic system. Biol Psychiatry. 2007. 61: 813-8 PMID 17083920.

See also

Additional images

Schematic representation of the chief ganglionic categories (I to V). The primate basal ganglia system is a symmetrical major cerebral system that has only recently been recognized Anatomical regions of the brain are listed vertically following hierarchies that are standard in Neuroanatomy. This traditional list does not accord strictly with human thalamic anatomy

Deep dissection of brain-stem. Lateral view.

Deep dissection of brain-stem. Ventral view.

Mesal aspect of a brain sectioned in the median sagittal plane.

Dissection showing the ventricles of the brain.

Coronal section of brain immediately in front of pons.

Coronal section of brain through intermediate mass of third ventricle.

Coronal section of lateral and third ventricles.

Section of brain showing upper surface of temporal lobe.

Horizontal section of right cerebral hemisphere.

The left optic nerve and the optic tracts.

Parts of the thalamus

Projections of the thalamus

Parts of the thalamus

Thalamus

Human brain frontal (coronal) section

External links


BrainMaps is an NIH -funded interactive zoomable high-resolution digital brain atlas and virtual microscope that is based on more than 20 million megapixels (50 terabytes

Dictionary

thalamus

-noun

  1. (anatomy) Either of two large, ovoid structures of grey matter within the forebrain that relay sensory impulses to the cerebral cortex.
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