Thalamus

Anatomy

The two thalami are the principal parts of diencephalon. In the caudal order of the neuromères (tail) with oral examination (stops), the diencephalon is located in front of the cerebral stalks (which form the mésencéphale, the high part of the cerebral trunk) and behind of the télencéphale. The diencephalon includes/understands several parts in addition to thalamus: the ventral thalamus or périthalamus (made " core réticulaire" and of the shingles incerta) and the épithalamus (primarily constituted of the habenula and its appendices). Perished and épithalamus must be formally separate thalamus itself. The " term; métathalamus" who gathered the two geniculate bodies, left thalamus, is not recognized more. The thalami are oblique and symmetrical nervous masses located on both sides third ventricle. It are sometimes (30% of the cases) dependant between them by the interthalamic commissure which crosses the third ventricle. The interior of thalamus is separated by limiting parts, of the plates of white substance or the particular neuronal small islands. Since Burdach (1822), Dejerine (1901) Foix and Nicolesco (1925) one uses this bulk-heading to distinguish and name the thalamic parts. There are others " elements limitants" , neuronal these, like the gray substance périventriculaire, the elements intralaminaires or the " nucleus limitans". Since they do not have the same neuronal constitution as that of the major part of thalamus, following Vogts for the cortex, it was proposed to gather them in an opposite allothalamus with the isothalamus (Percheron, 2003). The allothalamus is a heterogeneous unit which includes/understands Formatio Paramediana (periventricular), Formatio Intralaminaris-limitans and the regio Centralis which corresponds to the " complex center median-parafasciculaire" who has in fact three subdivisions in the higher primate. The allothalmus will be studied later on.

*Isothalamus The remainder of thalamus (more than 90%) is isothalmic. In spite of a large variety of related systems, the isothalamus is made little of arranged elements in a relatively simple way, using few mediators. The analysis will study initially the constituent elements then the afférences distinguished in subcorticales and cortical. The constituent neurons belong to two generated highly differentiated. The first, most, correspond to the thalamocorticaux neurons (or principal) which are very characteristic within the neurons. They are said " radiés" or " touffus" because their dendritic arborisation starts from thick trunks and short follow-ups of long and stiff distal branches. The number of branches and the diameter of the arborisation depend on the system anatomofonctionnel considered and the animal specie. The neurons thalamocortco have the characteristic not to have collateral a axonales initial, which implies that a neuron thalamocortical does not inform its neighbors of only it makes. In a more general way there are practically no isothalamic connections between elements. The thalamocorticaux neurons have long thick and myelinized axons. Their mediator is the glutamate. The other genus neuronal consists of " microneurones". They have dendritic branches and axonales short. They contribute thus to the local circuitery (interneurones). Their percentage compared to the thalamocorticaux neurons depends on the system (about 25% in the areas sensorimotrice and on the animal specie, with a strong increase in the higher primates. Their short axons have as a target dendrites of the thalamocorticaux neurons and others microneurones. Their mediator is the GABA. Among the subcortical related axons one must distinguish those which come from the perithalamus (réticulé core in particular). The neurons perithalamic receive afférences (collateral) thalamocorticaux axons. It re-emit in return of the axons towards the cortex forming circuits thus. Their mediator is also the GAGA. There are in the perithalamic evolution an opposite evolution of the neurons which decline and an increase in microneurones.

This list corresponds in the disorder has a Anglo-Saxon tradition not or badly adapted to the description of thalamus of the man. See human Thalamus

Nuclear groups off the thalamus include:

Anterior nuclear group

Medial nuclear group

Medial nucleus
Midline nuclear group

Paratenial nucleus
Parventricular nucleus
Reuniens nucleus
Rhombodoidal nucleus

Intralaminar nuclear group

Centromedian nucleus
Parafascicular nucleus
Paracentral Central nucleus
side Central nucleus
medial Side nucleus

nuclear group

Side dorsal Side nucleus
posterior nucleus
Ventral Pulvinar

nuclear group

Ventral anterior Ventral nucleus
side Ventral nucleus
posterior Ventral nucleus

posterolateral - receives sensory information from the body
Ventral posteromedial - receives sensory information from the face

Metathalamus

Medial geniculate body - receives auditory information (via brachium from inferior colliculus off Midbrain)
Side geniculate body - receives visual information from the Optic leaflet

Thalamic reticular nucleus -->

Function

the thalamus is used to filter information which arrives at the cerebral cortex

Pathology

Cerebral vascular accidents peuvent being at the origin of the syndrome thalamic , which results in a feeling from burn or pain in a half of the body, often accompanied by turbid emotional.

See too

List of the areas of the human brain

External bond

diaporamic of thalamus, by Dr. Dominique Hasboun (course under video requiring the video decoder free Distens)
Anatomy of thalamus, on Neuranat, by Dr. Dominique Hasboun
human Thalamus
High-Resolution Cytoarchitectural Primate Brain Atlases

Random links: