Thalamus

	Email		Print
	Bookmark		Link

Thalamus

The thalamus (from Greek

Greek language

Greek is an Indo-European languages native to the southern Balkan peninsula, the language of the Greek people. It forms an independent branch within Indo-European....
???aµ?? = room, chamber, IPA= /'?æl?m?s/) is a pair and symmetric part of the brain. It constitutes the main part of the diencephalon

Diencephalon

The diencephalon is the region of the brain that includes the thalamus, hypothalamus, epithalamus, prethalamus or subthalamus and pretectum. The diencephalon is located at the midline of the brain, above the mesencephalon of the brain stem....
.

he caudal (tail) to rostral (head) sequence of neuromeres, the diencephalon is located between the mesencephalon

Mesencephalon

In biological anatomy, the mesencephalon comprises the tectum , tegmentum, the ventricular mesocoelia , and the cerebral peduncles, as well as several nuclei and fasciculi....
(cerebral peduncule, belonging to the brain stem

Brain stem

The brain stem is the lower part of the brain, adjoining and structurally continuous with the spinal cord. The brain stem provides the main motor and sensory innervation to the face and neck via the cranial nerves....
) and the cerebrum. The diencephalon

Diencephalon

Epithalamus

The epithalamus is a Dorsum posterior segment of the diencephalon which includes the habenula, the stria medullaris and the pineal body. Its function is the connection between the limbic system to other parts of the brain....
(essentially the habenula

Habenula

In neuroanatomy, habenula originally denoted the stalk of the pineal gland , but gradually came to refer to a neighboring group of nerve cells with which the pineal gland was believed to be associated, the habenular nucleus....
and annexes) and the perithalamus (prethalamus

Prethalamus

The prethalamus or subthalamus is part of the diencephalon and therefore part of the brain.Developmental biologist prefer the term prethalamus, as it can be genetically defined , whereas anatomists often use the expression subthalamus....
formerly described as ventral thalamus) containing the zona incerta

Zona incerta

The zona incerta is a small region of gray matter that is part of the subthalamus....
and the "reticulate nucleus" (not the reticular, term of confusion).

Discussion

Ask a question about 'Thalamus'

Start a new discussion about 'Thalamus'

Answer questions from other users

Full Discussion Forum

Encyclopedia

The thalamus (from Greek

Greek language

Diencephalon

Location and topography

In the caudal (tail) to rostral (head) sequence of neuromeres, the diencephalon is located between the mesencephalon

Mesencephalon

Brain stem

Diencephalon

Epithalamus

Habenula

Prethalamus

Zona incerta

The zona incerta is a small region of gray matter that is part of the subthalamus....
and the "reticulate nucleus" (not the reticular, term of confusion). Due to their different ontogenetic origins, the epithalamus and the perithalamus are formally distinguished from the thalamus proper.

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 human beings.

Anatomy

The thalamus comprises a system of lamellae (made up of myelinated

Myelin

Myelin is an electrically-insulating dielectric material that forms a layer, the myelin sheath. Usually, myelin surrounds only the axon of a neuron....
fibers

Axon

An axon or nerve fiber is a long, slender projectionof a nerve cell, or neuron, that conducts action potentialaway from the neuron's cell body or soma....
) separating different thalamic subparts. Other areas are defined by distinct clusters of neuron

Neuron

Neurons are responsive cell in the nervous system that process and transmit information by electrochemical Signal . They are the core components of the brain, the vertebrate spinal cord, the invertebrate ventral nerve cord, and the peripheral nerves....
s, such as the periventricular gray, the intralaminar elements, the "nucleus limitans", and others. These latter structures, different in structure from the major part of the thalamus, have been grouped together into the allothalamus
Allothalamus

The Allothalamus is a division used by some researchers in describing the thalamus.....
as opposed to the isothalamus
Isothalamus

The isothalamus is a division used by some researchers in describing the thalamus..The isothalamus constitutes 90% or more of the thalamus, and despite the variety of functions it serves, follows a simple organizational scheme....
. This distinction simplifies the global description of the thalamus.

See also List of thalamic nuclei

List of thalamic nuclei

This traditional list does not accord strictly with human thalamic anatomy.Nucleus groups of the thalamus include:*anterior nuclear group**anteroventral nucleus...
.

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. These are all branches of the posterior cerebral artery

Posterior cerebral artery

The posterior cerebral artery is one of a pair of blood vessels that supplies oxygenated blood to the posterior aspect of the brain in human anatomy]....
.

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

Prethalamus

The prethalamus or subthalamus is part of the diencephalon and therefore part of the brain.Developmental biologist prefer the term prethalamus, as it can be genetically defined , whereas anatomists often use the expression subthalamus....
" inputs are processed into a form readable by the cerebral cortex

Cerebral cortex

The cerebral cortex is a structure within the brain that plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness....
. 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

Sleep

Sleep is the natural state of bodily rest observed in humans and other animals. It is common to all mammals and birds, and is also seen in many reptiles, amphibians and fish....
and wakefulness. Thalamic nuclei have strong reciprocal connections with the cerebral cortex, forming thalamo-cortico-thalamic circuits

Thalamo-cortico-thalamic circuits

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....
that are believed to be involved with consciousness

Consciousness

Consciousness is a difficult term to define, because the word is used and understood in a wide variety of ways, so that it frequently happens that what one person sees as a definition of consciousness is seen by others as about something else altogether....
. The thalamus plays a major role in regulating arousal, the level of awareness, and activity. Damage to the thalamus can lead to permanent coma

Coma

In medicine, a coma is a profound state of unconsciousness. A comatose person cannot be awakened, fails to respond normally to pain or light, does not have sleep-wake cycles, and does not take voluntary actions....
.

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

Auditory system

The auditory system is the sensory system for the sense of hearing ....
, somatic, visceral, gustatory and visual system

Visual system

The visual system is the part of the central nervous system which allows organisms to visual perception.It interprets the information from visible light to build a representation of the world surrounding the body....
s where localised lesions provoke particular sensory deficits. 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

Tremor is an unintentional, somewhat rhythmic, muscle movement involving to-and-fro movements of one or more body parts. It is the most common of all involuntary movements and can affect the hands, arms, head, face, vocal cords, trunk, and legs....
. The role of the thalamus in the more anterior pallidal and nigral territories in the basal ganglia

Basal ganglia

The basal ganglia are a group of Nucleus in the brain interconnected with the cerebral cortex, thalamus and brainstem. Mammalian basal ganglia are associated with a variety of functions: motor control, cognition, emotions, and learning....
system disturbances is recognized but still poorly known. The contribution of the thalamus to vestibular or to tectal functions is almost ignored. 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.

Pathology

Cerebrovascular accidents (stroke

Stroke

A stroke is the rapidly developing loss of brain function due to a disturbance in the blood supply to the brain. According to the National Stroke Association, a "stroke" occurs when a blood clot blocks and artery or a blood vessel breaks, interrupting blood flow to an area of the brain....
s) can cause thalamic syndrome, which results in a contralateral hemianaesthesia, burning or aching sensation on one half of a body (painful anaesthesia) often accompanied by mood swings

Mood disorder

A mood disorder is the term given for a group of diagnoses in the Diagnostic and Statistical Manual of Mental Disorders classification system where a disturbance in the person's Mood is hypothesised to be the main underlying feature....
. Ischemia of the territory of the paramedian artery, if bilateral, causes serious troubles including akinetic mutism

Akinetic mutism

Akinetic mutism is a medicine term describing patients who tend neither to speak nor move . It is the result of severe frontal lobe damage in which the pattern of inhibitory control is one of increasing passivity and gradually decreasing speech and motion....
accompanied or not by oculomotor troubles. It is also related to Thalamocortical Dysrhythmia

Thalamocortical Dysrhythmia

Thalamocortical Dysrhythmia is a theoretical framework in which neuroscientists try to explain the positive and negative symptoms induced by neurological disorders like Parkinsons, Pain and nociception, Tinnitus, Epilepsy as well as neuropsychiatric disorders like Clinical depression and schizophrenia....
.

Korsakoff's Syndrome

Korsakoff's syndrome

Korsakoff's syndrome , is a brain disorder caused by the lack of thiamine in the brain. The syndrome is named after Sergei Korsakoff, the Neuropsychiatry who popularized the theory....
stems from mammillary bodies, mammilothalamic, or thalamic lesions.

Development

The thalamic complex is composed of the perithalamus (or prethalamus, previously also known as ventral thalamus), the zona limitans intrathalamica

Zona limitans intrathalamica

The zona limitans intrathalamica is a compartment and primary developmental boundary in the vertebrate forebrain that serves as a signaling center and a restrictive border between the thalamus and the prethalamus ....
(ZLI) and the thalamus (dorsal thalamus).

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

Fate mapping

Fate mapping is a wikt:technique that is used to show how a cell or tissue moves and what it will become during normal development. Fate mapping was developed by Walter Vogt as a means by which to trace the development of specific regions of the early embryo....
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.

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

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.

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

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.

In humans, a common genetic variation in the promotor region of the serotonin transporter

Serotonin transporter

The serotonin transporter is a monoamine transporter protein.This protein is an integral membrane protein that transports the neurotransmitter serotonin from synaptic spaces into presynaptic neurons....
(the SERT-long and -short allele: 5-HTTLPR

5-HTTLPR

5-HTTLPR is a degenerate repeat polymorphism region in SLC6A4, the gene that codes for the serotonin transporter.Since the polymorphism was identified in the middle of the 1990s,...
) has been shown to affect the development of several regions of the thalamus in adults. People who inherit two short allele

Allele

An allele is one member of a pair or series of different forms of a gene. Usually alleles are coding region, but sometimes the term is used to refer to a junk DNA....
s (SERT-ss) have more neurons and a larger volume in the pulvinar and possibly the limbic regions of the thalamus. 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.

Thalamus

Location and topography

Anatomy

Arterial supply

Function

Pathology

Development

See also

Additional images

External links