Projection (nervous system)

from Wikipedia, the free encyclopedia

Projection means forwarding, local relocation. The term originating from optics was u. a. taken over from neurophysiology and neuroanatomy . It is derived from Latin pro = 1) before, in the face of 2) for; to protect; and Latin iacere = to throw; Latin proiectio = the (spatial) stepping forward, reproaching, stretching out (e.g. a limb); Latin proicere = to reproach, to throw away (e.g. food), to throw out, to throw away, to spurn, to humiliate oneself. By definition, projection is initially a physiological term , as it describes a specific function, namely e.g. B. the "relocation of a sensory impression to a certain point". Projection centers are primary brain centers, also called primary cortex . These centers can have both motor and sensory qualities. The term projection centers thus specifically refers to both the motor cortex and the sensory projection centers . Projection trajectories consist of those short or long nerve fibers that make up the specific function of the respective primary cortex. It is therefore a matter of the specifically motor, sensory or vegetative pathways, e.g. B. to the visual radiation . These tracks gave rise to the designation projection , as they have to "branch out" to the more extensive, ribbon-like or fan-shaped projection fields .

Basic concept of functional neuroanatomy

As an anatomical term , projection first came into use in modern brain anatomy. The physiological concept of projection makes it possible to anatomically follow and understand spatial relationships better. This concept is based on localization theory . In neurology, this is understood to be the most exact local assignment of somatic and psychological functions to certain areas in the central nervous system. It assumes that there are certain centers of nerve cells in the brain that perform a specific function at a certain point. The optical performance of the visual cortex may serve as an example . A z. For example, an image created on the retina of the eye from a large number of different pixels is forwarded via projection paths, which consist of a large number of neurites , to very specific fields of the central nervous system (CNS) responsible for information processing (point-to-point transmission ). Projection tracts would thus nervous lines which an articulated image or a single multi-element mosaic composite information further convey a "particular location of the body" to a different location in the form of nerve impulses. One speaks of topically structured information, which is also received and processed by topically structured receiving organs. In the case of optical vision, this "receiving organ" is the primary visual cortex. It represents the specific brain center for the visual function. The physiological organization of the point-to-point imaging during vision is called retinotopy . This organizational principle can also be found in a similar form in the other sensory activities.

A distinction must be made between ascending projection trajectories that run from the periphery to the brain centers and descending projection trajectories that run in the opposite direction from the brain centers to the periphery.

These descending orbits seem to contradict the definition of mosaic-like composed information insofar as we are dealing here with quasi-punctiform efferents that emanate from an exactly localizable center, e.g. T. for the last information before the motor execution. The impulses of the specifically motor cortex are not only the result of a "sensorimotor short circuit", as this would be understandable based on the pure localization theory - namely in the sense of the reflex arc and as an expression of the topographically corresponding sensory and motor homunculi . Rather, they are primarily to be assessed and understood as an expression of finely tuned sequences of movements, cf. PMA and SMA . The design principle of the somatotopic structure of the pyramidal trajectory would also contradict a purely “punctual” understanding of the effectoral performance of these “individual” projection trajectories in the sense of a pure input / output mechanism of these motor centers as isolated and absolutely effective neuronal modules . The organization of the point-to-point transmission must be seen and understood in connection with the integrative performance of the brain, as it is accomplished by the association centers .

Projection tracks and projection centers

General and concept development

Fig. 1. How a pinhole camera works
Fig. 2. Projector based on the principle of shadow projection

Projection trajectories and projection centers form a common unit, which is why there is something forced about a separate representation. The concept of ascending and descending projection paths represented here follows on from the representations by Voss and Herrlinger as well as by Sobotta and Becher and Benninghoff and Goerttler. Some authors such as Robert F. Schmidt and Wilfrid Jänig reserve the term projection only for descending nerve tracts and in particular do not use it for the ascending spino-thalamic and thalamo-cortical tracts. The representation in the Roche Lexicon of Medicine from 1987 (2nd edition) only mentions the ascending portions of the projection trajectories and the centers in the cerebral cortex, not the descending portions. It describes projection physiologically as “localization of a sensation in space or on the body surface, e.g. B. based on the position of the corresponding light stimulus in the retinal image ”. From the 4th edition of the lexicon in 1999, ascending and descending projection paths are mentioned.

Projection tracks

Fig. 3. Pyramidal path

The anatomical name "projection pathways" (Tractus nervosi projectionis) is a name for certain nerve pathways according to the Paris nomenclature ( PNA ). The nerve tracts deserve this name in purely descriptive terms due to the fan-like expansion of one of the most important projection trajectories in the motor cortex of the endbrain, the fanning of the pyramidal tract (Fig. 3) or the corona radiata . This fanning out of paths is similar to the divergent bundle of rays from a projector for the enlarged display of image material (Fig. 2).

A peculiarity and peculiarity of the projection tracks from a purely anatomical point of view is that they run in different halves of the body and z. T. have mixed proportions from different halves of the body. A somatotopic structure can also be recognized in this. In this way, projection paths differ from association paths, which by definition only run in one half of the body and only have parts of one half of the body.

Optic fibers e.g. B. are projection tracks, which come in different compositions from fibers of the right and left eye. The visual field of each eye is broken down into different sections, of which the nerve fibers responsible for different visual field sections are composed differently and thus also come from different halves of the body . This composition of the projection tracks differs before and after the intersection in the optic chiasm . The visual path is thus formed according to the physiological expediencies of the visual field. By merging the so-called image sections of the field of view, a “larger overall image” can be perceived than can be perceived by each individual eye. This also creates an overall picture of "spatial depth". Projection fibers are distinguished from association fibers and commissure fibers . Projection fibers are often long conduction paths , be it pyramidal paths or long sensory paths, which connect the sensory organs with the brain or with the relevant sensory projection center . In view of the “length” criterion, it does not matter that the ascending projection paths in the thalamus in particular are interrupted and switched to another neuron.

Association fibers connect individual sections of a hemisphere with one another , i.e. a primary cortical field with the secondary one. Commissure fibers connect individual sections of one hemisphere to the other . These fibers run over the bar ( corpus callosum ) to the other hemisphere. According to Benninghoff-Goertler's textbook, the commissure systems also consist of association fibers.

Ascending projection tracks

Ascending projection tracks (corticopetal or afferent tracks) convey impressions from the environment ( sensory and sensory projection) or from the inner world ( visceral projection ) to certain areas of nerve cells in the central nervous system. These end points or receiving organs of the transmission in the brain centers are called sensory projection centers or sensory projection fields.

Excursus on the terminology of ›center‹, ›field‹ and ›cortex‹ : The term field does justice to the idea of ​​a spatially extended topical structure within an association of nerve cells in a certain cortex area and thus enables a structured “mapping” of sensory physiological data such as B. an acoustic sound effect, such as a chord or a visually perceptible object, such as a table. - The term center, on the other hand, suggests a point-like origin of light rays according to the pinhole camera principle (Fig. 1). This designation of a nervous center does justice to the integration of the services of different nerve cells within a regional association of specifically differentiated nerve cells, such as optical cortical centers. The deliberately controlled movement of a finger z. B. starts from a very narrowly circumscribed, so to speak, point-like center in the motor cerebral cortex. Since these centers are located in specific regions of the cerebral cortex and perform very specific services, they are also referred to as primary cortical centers or, for short, primary cortex . The primary cortex, which can be assigned to the projection fields, is contrasted with the secondary and tertiary cortex. These fields in turn provide integration services with regard to various sensory modalities . So requires z. B. the perception of an optical object - z. B. a table - an interplay of optical and acoustic bark fields. As a result, in the example chosen, the concept formation is used to mentally reproduce the word 'table' and, if necessary, to pronounce this word, cf. in addition the → perception theory .
However, by definition, secondary and tertiary centers no longer belong to the projection fields, even if they are in multiple neural connections with them. They belong to the association cortex . These secondary and tertiary centers are reminiscent of the technical principle of shadow projection (Fig. 2). In the primary and secondary centers of the brain, different, specialized and differentiated services are performed locally in the brain (→ topistic brain research ). This is not just about innate specific sensory performance or specific motor performance (PS and EPS), but about complex learned tasks such as a. Language, body scheme and understanding of symbols , which can be disturbed in neuropsychological syndromes . These functions have also been referred to as representations of an internal map or as representations of realities of the second order . According to definition, nervous connections between these half-sided and only half-connected fields are referred to as association trajectories , and nervous connections between these half-sided association fields are referred to as → commissure trajectories .
Some authors also count the commissure trajectories among the association trajectories, others distinguish them from them. According to the principles of topistic brain research, however, the commissure tracts fulfill similar functions as the association tracts, as they not only take into account the alignment between the left and right hemispheres, but also the functional differentiation of both hemispheres in particular.
Here, however, it is primarily a conceptual separation between the association cortex and the projection cortex , which is shaped by the thought of specific sensory modalities and the distinction between motor and sensory functions. A histological distinction is not possible, but cytoarchitectural differences are being explored. So it is largely a macroscopic anatomical-topographical description . Empirical conclusions about the function of these fields can only be drawn from the failure symptoms occurring in the case of circumscribed damage.

Descending projection trajectories

Impulses from the cerebral cortex are transmitted to the periphery via descending projection paths (corticofugal or efferent paths) (motor projection). For example, when nerve cells are stimulated at a specific point in the brain, certain functionally related muscle groups can contract. While only simple movements can be triggered from the anterior central turn, the parts of the frontal convolutions connected and further adjoining via association fibers ( fibrae arcuatae ) appear as secondary centers ( association centers ) for more complex movements ( eupractical combinations of movements ) corresponding, simultaneous turning movements of the head called. The secondary center for this is in the medial frontal gyrus . As in the case of ascending projection paths, a somatotopically structured field of excitations also arises for the descending projection paths, which is responsible for complex functions. Even for simple movements, the pyramidal tract shows a somatotopic structure in the internal capsule, see Chap. Motor cortex . A distinction must be made between pyramidal and extrapyramidal paths ( PS and EPS ) for the descending projection paths .

Projection centers

Certain central nervous structures represent as projection centers either

  1. represents the end point of the sensory pathways in the brain emanating from the sense organs (to prepare for sensory perception) or
  2. the starting point for voluntary specific muscle actions ( motor performance of the CNS starting from the frontal centers for will formation) or else
  3. a switching point of the vegetative nervous system that z. B. leads to hormonal or immunological regulatory mechanisms and uses information from higher centers.

Sensory are those nerve tracts whose excitation leads to a sensation that can be further processed and consciously perceived (→ perception ). In contrast to this, the sensory pathways, which are also centripetal,do not necessarilyconveya conscious arousal success. The term projection center is largely used synonymously with projection field , for a more detailed distinction see the excursus on these technical termsmentioned above. Corresponding to the model adjustment of the reflex arc , projection centers represent the connecting link between ascending and descending projection trajectories. They are thus part of the control circuit on the animal level . This control loop has also been referred to as a psychic reflex arc . The individual projection centers aresubdividedinto topical fields ( projection fields)as a neural association, see → Topistic brain research .

Sensory cortex

The primary sensory cortex is to be understood as the end point of the sensory conduction pathways emanating from the sense organs (synonym: primary sensory cortex, = primary sensory cerebral cortex, = sensory projection center). The sensory bark includes u. a. the body feeling sphere ending in the rear central turn (somatosensory cortex field). The centers superordinate to the primary cortex are also connected to the sensory projection centers (secondary and tertiary cortex). They are called association areas, see the preceding excursus on center and field . It is in these secondary and tertiary centers that the transmitted afferents of the sensory systems are integrated. Such an integration would be e.g. B. the fusion of the two-dimensional images to a spatial image in the case of the visual path or the recognition of characters, which goes beyond the 'mere seeing' of these characters in the sense of unprocessed and neglected sensations.

Motor cortex

From the motor brain centers , the motor projection paths receive the central nervous impulse responsible for muscle action, see also sensorimotor cortex . The main motor area is the pre-central region ( area pyramidalis and extrapyramidal areas ). A large part of all voluntary movements start from the regio praecentralis, from here they are controlled. It is therefore referred to as the primary motor cortex analogous to the sensory cortex area. There are also different levels of projection (primary and secondary centers) in the area of ​​motor skills, depending on the formation of the neuron chain responsible for muscle action . The pyramidal and extra pyramidal motor systems differ with regard to these “additional” switching centers to the next neuron in the projection chain. Pyramidal and extrapyramidal tracks are to be assessed as descending projection fibers. The most important path for voluntary motor skills is the pyramidal path . The pyramidal tract shows a somatotopic structure in its course through the internal capsule . The pathways belonging to the pyramidal tract system (PS) are not interrupted by synaptic connections or by switching to other neurons on their way to the motor nuclei in the midbrain, the medulla oblongata and the spinal cord ( Brodmann areas 4 and 8). This allows a relatively quick reaction. The pathways of the extrapyramidal system (EPS) are interrupted at least once on their way to the motor nuclei by synaptic switching to another neuron. This switching takes place in the thalamus, the lens nucleus or in the bridge (Brodmann areas 1–6, 19 and 22). This corresponds to the function of the EPS, which is more influenced by vegetative influences, cf. also limbic system , reticular formation and reflex activity . PS and EPS can be seen as antagonistic systems to a certain extent. Both systems inhibit one another. If the PS is damaged z. B. a significant increase in reflexes.

Visceral projection centers

The center of the ascending visceral projections, i.e. the sensations and pain emanating from the vessels, bones, and internal organs, is most likely the hypothalamus . It goes without saying that the pain sensations of the skin or the projections of somatic sensations are not considered here. These visceral afferents are coupled with those from the endocrine system and put in the service of the vegetative and animal body functions. Along with the hypothalamus, other centers also seem to exist via z. T. phylogenetically associated with very old pathways. These are:

  1. the anterior cingulate gyrus
  2. the rostral thalamic nucleus
  3. the dorsoventral thalamic nucleus
  4. the anterior temporal pole
  5. the front island

The prefrontal areas on the convexity of the frontal lobe adjacent to the orbitocingular region can be named as further association centers . These play a role in the integration of the affects (will and drive formation).

Attempts have been made to eliminate deep visceral pain through leukotomy .

Organizational principle

Fig. 4. Neural network , drawn by Sigmund Freud in 1895. The arrows show the diagram of a transmission (projection) of neuronal excitation through the processes of the nerve cells ( dendrites and neurites ). The area around the neurites α (alpha), δ (delta) and b receives impulses on different projection levels of processing

The organizational principle of the projection tracks, projection centers and the associated services corresponds to the principle of structural functionalism . Max Neuburger presented the development of medicine as undulating movements between the view based on purely anatomical localization ( topical diagnostics ) and a physiological way of thinking in the sense of a "general functional pathology ".

The concept of the projection tracks and the services performed in the projection centers corresponds to this idea. Somatotopic or anatomical points of view on the one hand and functional or physiological points of view on the other complement each other to a mutual gain in knowledge. It is a requirement of reason to reconcile morphological conditions with physiological performance characteristics. This is also one of the basic ideas of Benninghoff-Goerttler's anatomical textbook. If this principle is applied to the projection centers, the conclusion is that there is a service chain or a neural network . By “shifting a sensory impression to a certain point” (Triepel) a second record is made. With this new writing of a sensory stimulus or a draft of an action, there is the possibility of its qualitatively new and different processing through these centers and other adjacent areas of association.

This principle was formulated by Sigmund Freud in 1915. As is well known, Freud had neuropathological experience. With regard to the question of the anatomical topics of qualities of consciousness, he distinguished between various possibilities. In principle, he differentiated the possibility of a second writing of an idea in another place (different topics depending on the different qualities of consciousness - this would come very close to the principle of somatotopically structured association centers) from a merely functional change in state without losing the place of the first writing (constant topology in each case different dynamic cast), cf. Fig. 4. In 1952, the neurophysiologist Herbert Hensel also delimited two possible variations for differentiating between sensory qualities. Basically, he differentiated a perception of stimuli in specific cortical centers as a result of different localization of these centers from a distinction as a result of different forms of excitation in one and the same center.

Individual evidence

  1. ↑ Hermann Triepel: Dictionary of anatomical terms. Springer-Verlag, 2013, ISBN 978-3-642-97798-5 , p. 73 ( limited preview in the Google book search).
  2. ^ A b Hermann Triepel , Robert Herrlinger : The anatomical names. Your derivation and pronunciation. Bergmann, Munich 1962, p. 59
  3. ↑ a b c d e Alfred Benninghoff , Kurt Goerttler : Textbook of Human Anatomy. Shown with preference given to functional relationships. Volume 3: Nervous System, Skin and Sensory Organs. Urban & Schwarzenberg, Munich 1964, pp. 133 (a), 240 (d), 242 ff. (A) (c) (e), in particular p. 247 ff. (A).
  4. ↑ a b Helmut Ferner : Anatomy of the nervous system and the human sense organs. Reinhardt, Munich 1964, p. 162 f.
  5. ↑ a b c Hermann Voss , Robert Herrlinger : Taschenbuch der Anatomie. Nervous system, sensory system, skin system, increment system. Volume III. Fischer, Jena 1964, p. 20 (c), 62 ff. (A) (b)
  6. ↑ Johannes Sobotta , H. Becher: Atlas of the human anatomy. 3rd part: central nervous system a. a. Urban & Schwarzenberg, Munich 1962, Figs. 215-217 and 299; Text p. 330 f.
  7. ↑ a b c Robert F. Schmidt (Ed.): Outline of Neurophysiology. Springer Berlin 1979, ISBN 3-540-07827-4 , pp. 188 (a), 282 (b) (c).
  8. ↑ Norbert Boss (Ed.): Roche Lexicon Medicine. Hoffmann-La Roche AG and Urban & Schwarzenberg, Munich 1987, ISBN 3-541-13191-8 , p. 1401.
  9. ↑ Otto Bach : About the subject dependence of the image of reality in psychiatric diagnosis and therapy. In: Psychiatry Today, Aspects and Perspectives. Festschrift for Rainer Tölle. Urban & Schwarzenberg, Munich 1994, ISBN 3-541-17181-2 , pp. 1-6.
  10. ↑ Roger Wolcott Sperry et al .: The two brains of humans. In: Image of Science. 9, 1972, pp. 920-927.
  11. ↑ a b Peter Duus : Neurological-topical diagnostics. Anatomy, physiology, clinic. Thieme, Stuttgart 1990, ISBN 3-13-535805-4 , p. 387 ff.
  12. ^ Max Neuburger (ed.): Handbook of the history of medicine. Jena 1902.
  13. ↑ Manfred Spitzer : Spirit on the Net. Spectrum, Heidelberg 1996, ISBN 3-8274-0109-7 . P. 97 ff.
  14. ↑ Erwin H. Ackerknecht : Brief history of psychiatry. Enke, Stuttgart 1985, ISBN 3-432-80043-6 , p. 91, quote: "In 1885 Freud, who was barely 30 years old, became a lecturer in neuropathology ..."
  15. ↑ Sigmund Freud : The Unconscious. (1915 e) In: The Unconscious. Writings on psychoanalysis. Fischer 1963, pp. 15-19.
  16. ↑ Herbert Hensel : Erg. Physiol. 47, 166, 1952.
  17. ^ Hermann Rein , Max Schneider : Human Physiology. 15th edition. Springer, Berlin 1964, p. 650.