Projection areas

Projection means conduction, local relocation. A native of the optics term was adopted, inter alia, of the neurophysiology and neuroanatomy. It is derived from the Latin pro = 1) before, in the face of 2) for; to protect; and Latin iacere = throw; Latin proiectio = the (spatial ) emergence Let accuse, stretching out (eg a limb ); Latin proicere = accuse throw (eg food), throw out, throw away, spurn, humiliate yourself. Projection is defined to be initially a physiological concept, as it describes a specific function, namely, for example, the " laying of a sensory impression to a certain place ." Projection centers are primary centers of the brain, also called primary cortex. These centers may have both motor and sensory qualities. Thus, the term projection specifically refers centers both on the motor cortex as well as on the sensory projection centers. Projection tracts consist of those short or long nerve fibers that make up the specific function of each primary cortex. It therefore is the specific motor, sensory or autonomic pathways, such as the optic radiation. These tracks gave rise to the term projection as they " branch " must to the more areally, band - or fan-shaped spread projection fields.

• 2.3.1 Sensory Cortex
• 2.3.2 Motor Cortex
• 2.3.3 Visceral projection centers

Fundamental concept of functional neuroanatomy

As an anatomical term projection has become common only in modern brain anatomy. The physiological concept of projection makes it possible to track and understand spatial relationships anatomically better. This concept is based on the localization theory. This is understood in the central nervous system in neurology the locally exact possible mapping of somatic and mental functions to particular areas. It assumes that there are certain centers of nerve cells in the brain to accomplish a specific service at a specific location. As an example, like the optical power of the visual cortex are used. An example on the retina of the eye arisen from a variety of image points image to very specific charge of information processing fields of the central nervous system (CNS) is projection tracts, which consist of a large number of neurites, forwarded ( point-to -point transmission ). Projection tracts would thus be nervous lines which convey a more structured image or a mosaic of many individual elements, composite information from a " certain part of the body " to another location in the form of nerve impulses. One speaks of topically structured information, which are each incorporated and processed by topically structured receiving organs. This " receiving body" is the primary visual cortex in the case of the optical sight. It provides the specific brain center for the visual function represents the physiological organization of the point-to- point mapping in vision called retinotopy. This organizing principle is detectable in similar form in the other sensory abilities.

A distinction must be ascending projection pathways that extend from the periphery to the brain centers of descending projection tracts that run in the reverse direction from the brain centers to the periphery.

These descending pathways seem the definition mosaic composite information to contradict the sense that it is here to quasi point-like efferent fibers emanating from a precisely localized center, so some to last information before motor execution. However, the pulses of specific motor cortex are not only the result of a " sensory-motor short-circuit ," as this would be understandable due to the pure localization theory - namely, within the meaning of the reflex arc and as an expression of topographically corresponding sensory and motor homunculi. Rather, they are primarily to evaluate an expression finely tuned movements and understand, see PMA and SMA. Also the shape principle of somatotopic structure of the pyramidal tract contrary to a pure " ad hoc " understanding of the effector performance of these " individual " projection tracts in the sense of a pure input / output mechanism of the motor centers as isolated and absolutely effective neural modules. The organization of the point-to -point transmission must be seen and understood in the context of the integrative performance of the brain, as it is done by the association centers.

Projection tracts and projection centers

General and concept development

Projection tracts and projection centers form a common unit, which is why a separate presentation somewhat Forced adheres. The here presented concept of the ascending and descending projection tracts closes the representations of Voss and Mr. Linger as Sobotta and cup or by Benninghoff and Goerttler. Some authors such as Robert F. Schmidt and Wilfrid Jänig retain the term projection only descending nerve pathways before and use it in particular to the ascending spino - thalamic and thalamo - cortical pathways. The representation in the Roche Lexicon of Medicine from 1987 (2nd edition) mentions only the ascending portions of the projection tracts and centers in the cerebral cortex, not the descending portions. It describes projection physiologically as " localization of a sensation in the room or on the body surface, eg on the basis of the position of the corresponding light stimulus in the retinal image ." From the 4th edition of the lexicon in 1999, ascending and descending projection tracts are mentioned.

Projection paths

The anatomical name " projection tracts " ( tract nervosi projectionis ) is a designation of certain nerve pathways after the Paris nomenclature (PNA ). This name earn the nerves already in purely descriptive terms due to the fan-like spread of the main projection pathways in the motor cortex of the telencephalon, the fanning out of the pyramidal tract (Fig. 3 ) or the corona radiata. This fanning of Railways has similarity with the divergent beam of a projector to the enlarged view of image material ( Fig. 2).

A particularity and peculiarity of the projection tracts in purely anatomical point of view is that they run in different halves of the body and partly have mixed components from different sides of the body. Also it can be a somatotopic structure are detected. In this way, projection tracts differ from the association tracts, which is defined to run in only one half of the body and only holds shares of a body.

Projection fibers are distinguished from association fibers and commissural fibers. Projecting fibers are often long line paths, whether they are paths or pyramid long sensory pathways that connect the sense organs to the brain or to the relevant sensory projection center. It does, in view of the criterion " length" does not matter that in particular the ascending projection pathways are interrupted in the thalamus and can be switched to another neuron.

Association fibers connect individual sections of a hemisphere with each other, so as a primary cortical area with the secondary. Commissural connect individual sections of one hemisphere to the other. These fibers extend above the bars ( corpus callosum ) to the other hemisphere. According to the textbook by Benninghoff - Goertler made ​​the Kommissurensysteme of association fibers.

Ascending projection tracts

Ascending projection tracts ( corticopetale or afferent pathways ) convey impressions from the environment (sensory and sensory projection) or from the inner world ( visceral projection) to certain parts of nerve cells in the central nervous system. These terminals and receiving bodies of the transmission in the brain centers are called sensory projection centers or sensory projection fields.

Descending projection tracts

Impulses of the cerebral cortex to the periphery are transmitted via descending projection tracts ( corticofugale or efferent pathways ) ( motorized projection). It can contract certain functionally associated muscle groups at a circumscribed spot of the brain located at about irritation of nerve cells. While only simple movements are triggered by the anterior central gyrus, the above association fibers ( arcuate fibers ) show connected and on adjacent parts of the frontal gyri as secondary centers ( association areas ) for more complicated movements ( eupraktische movement combinations ) An example of this are the conjugate movements of the eyeballs and called corresponding simultaneous rotational movements of the head. The secondary center of this lies in the gyrus frontalis medius. The result is similar to that of the ascending projection pathways somatotopically a structured field of excitations for the descending projection tracts, which is responsible for complex functions. Even for simple movements can the pyramidal tract in a somatotopic structure of the internal capsule recognize, see chap. Motor cortex. In the descending projection paths pyramidal and extrapyramidal pathways (PS and EPS) can be distinguished.

Projection centers

Certain central nervous structures represent a projection centers either

Sensory are those nerve pathways whose excitation leads to a sensation that can be further processed and consciously perceived (→ perception. Contrast, the also centripetally extending sensory tracts convey not necessarily equipped with awareness excitation success. The term projection center is largely used synonymously with projection field, for a more detailed distinction, see the outlined above digression on these terms. According to the model adjustment of the reflex arc set projection centers, the link between ascending and descending projection tracts; they are therefore part of the control loop on the animal level. individual projection centers are as neuronal association in topical fields ( projection fields) divided, see → Topistische brain research.

Sensory Cortex

Under the primary sensory cortex of the terminal of the sense organs each outgoing sensory pathways is to understand ( Synonyms: primary sensory cortex, primary sensory cortex =, = sensory projection center ). For the sensory cortex counts, inter alia, the ending in the posterior central somaesthetic ( Somatosensory cortical area ). With the sensory projection centers of the primary cortex parent centers are connected ( secondary and tertiary cortex). They are called association areas, see the above digression to center field. In these secondary and tertiary centers, the integration of continuous -led afferents of sensory systems is performed. Such integration would, for example, the merger of the two-dimensional images into a three-dimensional image in the case of the visual pathway or the recognition of scripts, which goes beyond the mere seeing ' those signs within the meaning of unprocessed and not noticed sensations.

Motor cortex

Of the motor centers of the brain 's motor projection tracts receive the responsible for muscle action central nervous impulse, see also sensorimotor cortex. The motor main area is the Regio precentral (area pyramidalis and the areae extrapyramidal ). From the precentral regions the majority of all voluntary movements have their origin, from where it can be controlled. They are therefore referred to as primary motor cortex analogous to sensory beef area. In the area of ​​motor skills there are different stages of the projection (primary and secondary centers), depending on the training of the muscle action for the neuron chain. Pyramidal and Extrapyramidalmotorisches system differ in terms of these " extra" Umschaltzentren to the next neuron in the chain projection. Pyramidal and extrapyramidal pathways are to be regarded as descending projection fibers. The most important for voluntary motor car is the pyramidal tract. The pyramidal tract has in its course through the internal capsule to a somatotopic structure. The pyramidal tract to the system (PS ) associated tracks are on their way to the motor nuclei in the midbrain, the medulla oblongata and the spinal cord not by synaptic connections or by switching to other neurons interrupted ( Brodmann's areas 4 and 8). This allows a relatively fast response manner. The orbits of the extrapyramidal system (EPS ) can be interrupted at least once on their way to the motor nuclei by synaptic switching to another neuron. This switchover takes place, inter alia, in the thalamus, the lenticular nucleus or in the bridge ( Brodmann areae 1-6, 19 and 22). This corresponds to the more co-determined by the autonomic influences functions of the EPS, see also the limbic system, reticular formation and reflex activity. PS and EPS can be considered in some respects as antagonistic systems. Both systems inhibit one another. When damage occurs, for example, the PS a significant increase in reflex.

Visceral projection centers

The center of the ascending visceral projections, so that of the blood vessels, bone, and internal organs outgoing sensations and pain is most likely the hypothalamus. It is understood that the pain sensations of the skin or the projections of somatic sensations in this case do not qualify. This visceral afferents are coupled with those of the endocrine system and placed at the service of the vegetative and the animal body functions. The hypothalamus also centers on some seem phylogenetically very old associated tracks. These are:

Another association centers of the adjacent orbito - cingulate region prefrontal areas can be named on the convexity of the frontal lobe. These play a role in the integration of affect ( the will and drive education).

Attempts have been made must be remedied by lobotomy deep visceral pain.

Organizing principle

The organizing principle of the projection tracts, projection centers and the related receivables corresponds to the principle of structural functionalism. Max Neuburger has the development of medicine represented as wave motion between the built-up on a purely anatomical localization way of looking at (topical diagnostics) and a physiological mode of representation in the sense of " general functional pathology ".

The concept of projection tracts and accomplished in the projection centers receivables corresponds to this thought. Somatotopic and anatomical aspects on the one hand and functional and physiological considerations on the other hand combine to form a mutual gain of knowledge. It is a requirement of reason to bring morphological conditions with physiological Leistungseigentümlichkeiten consistent. This is also one of the basic ideas of the anatomical textbook of Benninghoff - Goerttler. Applying this principle to the projection centers, we obtain the conclusion that here there is a power chain or a neural network. Through the " relocation of a sensory impression to a certain place " ( Triepel ), a second transcript. This new transcript of a sensory stimulus or an action design is the possibility of its qualitatively new and different processing by these centers and other adjacent association areas.

This principle has already been formulated by Sigmund Freud in 1915. Freud possessed known about neuropathological experience. On the issue of anatomical Topik of qualities of consciousness, he distinguished between different possibilities. He distinguished in principle the possibility of the second record of an idea in another place (different Topik depending on different qualities of consciousness - this would amount to the principle somatotopically structured association centers quite close ) from a merely functional change of state without the location of the first transcript to lose (constant Topik at each A variety of dynamic instrumentation), see Figure 4 neurophysiologist Herbert Hensel 1952 also excluded from two variations for the differentiation of sensory qualities of each other. Basically, he picked a perception of stimuli in specific cortical centers due to different localization of these centers of a distinction due to various forms of excitation in a demselbsen center and from each other.