The thalamus is the structure of the brain, which in prenatal development is formed from the diencephalon, making up the bulk of it 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. Read more about it later in the article.
Location
The thalamus is part of the cerebral hemispheres. It is located lateral to the lateral ventricles - the cavities of the brain that are part of the cerebrospinal fluid (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 nuclei. These formations are necessary for 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 pass from the periphery to the center.
The right and left parts of the thalamus are interconnected by interthalamic gray matter. It is present in 70% of people.
Classification of Thalamus Nuclei
In total, in the visual cusps of the brain there are about 120 nuclei. Depending on their location, they are divided into three groups:
In the lateral group of nuclei, in turn, the medial and lateral cranked bodies, as well as the pillow, are isolated.
There is also a classification depending on the function performed by the kernels :
- specific;
- associative;
- non-specific.
Specific cores
The specific nuclei of the optic tubercle have a number of distinctive features. All formations of this group receive sensory information from the second neurons (nerve cells) of the 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, and the midbrain.
Each of the signals coming from below is processed in the thalamus and then goes to the corresponding region of the cortex. In which area the nerve impulse enters depends on what information it carries. So, information about sounds enters the auditory cortex, about 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, reticular formation, and brain stem nuclei.
The nuclei, which are located in front of the thalamus, provide the conduction of impulses from the limbic cortex through the hippocampus and hypothalamus. After processing the information, it again enters the limbic cortex. Thus, a nerve impulse circulates in a certain circle.
Associative kernels
Associative nuclei are located closer to the posterior-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 is suitable from the underlying formations of the central nervous system. These nuclei are necessary to obtain 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 the cortical region 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 seen objects;
- be aware of the position of your body in space;
- perceive space three-dimensional and so on.
Nonspecific Nuclei
This group of nuclei is called non-specific because it receives information from almost all structures of the central nervous system:
- reticular formation;
- extrapyramidal system nuclei;
- other nuclei of the optic tubercle;
- brain stem structures;
- formations of the limbic system.
Momentum from non-specific nuclei also goes to all areas of the cerebral cortex. Such selectivity, as is the case with associative and specific kernels, is absent here.
Since this particular group of nuclei has the greatest number of connections, it is believed that thanks to it, a coordinated, coordinated work of all parts of the brain is ensured.
Metatalamus
Separately, a group of nuclei of the optic tubercle is called metatalamus. This structure consists of the medial and lateral cranked bodies.
The medial cranked body receives hearing information. From the lower parts of the brain, information flows through the upper humps of the midbrain, and from above the structure receives an impulse from the auditory region of the cortex.
The lateral cranked 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 further goes to the occipital region of the cortex, where the primary center of vision is located.
Thalamus function
How is the processing of sensitive information coming from the periphery, which is then transmitted to the cortex of the forebrain? This is the main role of the visual hillock.
Thanks to this function, damage to the cortex can restore sensitivity through the thalamus. Thus, it is possible to repair pain, temperature sensation, as well as gross touch.
Another important function of the thalamus 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. Also, impulses from the cerebellum, ganglia of the extrapyramidal system, and the cerebral cortex go to it. And these structures, as you know, take part in the implementation of movements.
The visual tubercle is also 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 lesion
Since almost all signals from other structures of the nervous system pass through the thalamus, damage to the optic tubercle can manifest itself in a mass of symptoms. Extensive damage to the thalamus can be diagnosed by the following clinical signs:
- violation of sensitivity, especially deep;
- burning, sharp pains that first appear when touched, and then spontaneously;
- motor disorders, among which there is a so-called thalamic hand, manifested by excessive flexion of the fingers in the metacarpophalangeal and extension in the interphalangeal joints;
- visual disturbances - hemianopsia (loss of visual fields from the opposite side of the lesion).
Thus, the thalamus is an important structure of the brain, which ensures the integration of all processes in the body.