Thalamus is a structure of the brain, which in fetal development is formed from the diencephalon, making up its bulk in an adult. It is through this formation that all information from the periphery is transmitted to the cortex. The second name of the thalamus is visual tubercles. More about it later in the article.
Location
The thalamus is part of the forebrain. It is located lateral to the lateral ventricles - brain cavities that are part of the CSF (cerebrospinal fluid) circulation system. Below it is the hypothalamus, from which the visual tubercles are separated by a furrow.
Above and somewhat outside of the thalamus are the basal ganglia. These formations are necessary for the implementation of precise, coordinated movements. These structures are separated from each other by an internal capsule - a bundle of white matter of the forebrain, through which the pathways from the periphery to the center pass.
The right and left parts of the thalamus are interconnected by the interthalamic gray matter. It is present in 70%people.
Classification of the nuclei of the thalamus
In total, there are about 120 nuclei in the visual tubercles of the brain. Depending on their location, they are divided into three groups:
- medial;
- lateral;
- front.
In the lateral group of nuclei, in turn, the medial and lateral geniculate bodies, as well as the pillow are distinguished.
There is also a classification depending on the function performed by the cores:
- specific;
- associative;
- non-specific.
Specific cores
Specific nuclei of the thalamus have a number of distinctive features. All formations of this group receive sensory information from the second neurons (nerve cells) of sensitive pathways. The second neuron, in turn, can be located in the spinal cord or in one of the structures of the brain stem: the medulla oblongata, the bridge, the midbrain.
Each of the signals coming from below is processed in the thalamus and then goes to the corresponding area of the cortex. Which area a nerve impulse enters depends on what information it carries. So, information about sounds enters the auditory cortex, about the objects seen - into the visual cortex, and so on.
In addition to impulses from the second neurons of the pathways, specific nuclei are responsible for the perception of information coming from the cortex, the reticular formation, the nuclei of the brain stem.
The nuclei, which are located in front of the thalamus, provideconduction of impulses from the limbic cortex through the hippocampus and hypothalamus. After processing the information, it again enters the limbic cortex. Thus, the nerve impulse circulates in a certain circle.
Associative cores
Associative nuclei are located closer to the postero-medial part of the thalamus, as well as in the pillow area. The peculiarity of these structures is that they do not participate in the perception of information that comes from the underlying formations of the central nervous system. These nuclei are needed to receive already processed signals in other nuclei of the thalamus or in the overlying brain structures.
The essence of the "associativity" of these nuclei is that any signals are suitable for them, and neurons are able to adequately perceive them. Signals from these structures arrive in cortical areas with the corresponding name - associative zones. They are located in the temporal, frontal and parietal parts of the cortex. Thanks to these signals, a person is able to:
- recognize objects;
- associate speech with movements and objects seen;
- be aware of the position of your body in space;
- to perceive space as three-dimensional and so on.
Non-specific nuclei
This group of nuclei is called non-specific because it receives information from almost all structures of the central nervous system:
- reticular formation;
- nuclei of the extrapyramidal system;
- other thalamus nuclei;
- brain stem structures;
- Formations of the limbic system.
The impulse from non-specific nuclei also goes to all areas of the cerebral cortex. Such selectivity, as in the case of associative and specific nuclei, is absent here.
Since it is this group of nuclei that has the most connections, it is believed that thanks to it, the coordinated work of all parts of the brain is ensured.
Metalalamus
Separately allocate a group of nuclei of the thalamus called metathalamus. This structure consists of the medial and lateral geniculate bodies.
The medial geniculate body receives information about hearing. From the lower parts of the brain, information enters through the upper humps of the midbrain, and from above the structure receives an impulse from the auditory cortex.
The lateral geniculate body belongs to the visual system. Sensitive information to the nuclei of this group comes from the retina through the optic nerves and the optic tract. The information processed in the thalamus then goes to the occipital region of the cortex, where the primary center of vision is located.
Thalamus functions
How is the processing of sensitive information coming from the periphery, which is then transmitted to the forebrain cortex? This is the main role of the thalamus.
Thanks to this function, when the cortex is damaged, it is possible to restore sensitivity through the thalamus. Thus, the reparation of pain, temperature sensation, as well as coarse touch is possible.
Another important featurethalamus is the coordination of movements and sensitivity, that is, sensory and motor information. This is due to the fact that not only sensory impulses enter the thalamus. It also receives impulses from the cerebellum, ganglia of the extrapyramidal system, and the cerebral cortex. And these structures, as you know, take part in the implementation of movements.
Also, the thalamus is involved in maintaining conscious activity, regulating sleep and wakefulness. This function is carried out due to the presence of connections with the blue spot of the brain stem and the hypothalamus.
Symptoms of defeat
Since almost all signals from other structures of the nervous system pass through the thalamus, damage to the thalamus can manifest itself with a host of symptoms. Extensive involvement of the thalamus can be diagnosed by the following clinical features:
- violation of sensitivity, first of all - deep;
- burning, sharp pains that first appear when touched, and then spontaneously;
- motor disorders, among which there is the so-called thalamic hand, manifested by excessive flexion of the fingers in the metacarpophalangeal joints and extension in the interphalangeal joints;
- visual disorders - hemianopsia (loss of visual fields from the side opposite from the lesion).
Thus, the thalamus is an important brain structure that ensures the integration of all processes in the body.
