What is central sulcus

Telencephalon - anatomy and function of the cerebrum

Table of Contents


Image: “Illustration from Anatomy & Physiology, Connexions Web site” by OpenStax College. License: CC BY 3.0


Embryological development of the telencephalon

The brain, the spinal cord and the central nervous system arise from the embryological development Neural tubewhich emerged from the dorsal surface ectoderm. Three primary ones develop from the cranial portion of the neural tube Cerebral vesicles.

One of these cerebral vesicles develops into Prosencephalon (Forebrain). The other two cerebral vesicles make up that Rhombencephalon (Hindbrain) or that Mesencephalon (Midbrain). The prosencephalon develops into the diencephalon and telencephalon.

Division of the telencephalon into further hemispherical segments

Depending on the age of the respective part, the telencephalon is evolutionarily divided into three further sections.
The oldest section is dated Palleocortex formed, which in the adult brain is formed by the olfactory brain (Rhinencephalon) is represented. The olfactory brain becomes the Olfactory bulb, as well as the Olfactory tract, the Septum and cortical portions of the Amygdala assigned.
The Archicortex (old part) develops from the medial sections of the embryonic brain and forms the in the adult brain Hippocampus with the Cornu ammonis (Ammon's horn), the Fornix (Bow) and that Indusium griseum ("Gray veil").

The Hippocampus makes up the largest part of the archicortex and plays an important role in memory formation, especially in the transfer of information from short to long-term memory.
The transfer is thereby carried out by the Papez neuron circle which consists of the afferents and efferents of the hippocampus. The afferents of the hippocampus originate mainly from the Entorhinal region, through which, in turn, information from the olfactory brain, the Amygdala and the Neocortex mediated.

Other afferents reach the hippocampus via the Thalamus, as well as the Cingulate gyrus. The efferents emanating from the hippocampus run mainly over the Fornixto then go to the Corporamamillaria to end. Starting from the corpora mamillaria, the Papez neuron circle closes through the connection to the thalamus via the Mamillothalamic Fasciculus (Vicq-d’Azyr bundle).


The largest part of the telencephalon is made up of the Neocortex (youngest proportion) to which the Insula and the Corpus striatum of the adult brain.

The neocortex can be divided into 50 areas, which are called Brodmann areas are designated. Certain functions can be assigned to these areas. An example of this would be the Broca and Wernicke areas, which represent the two language centers of the brain. The Broca area is through the Brodmann area 44/45  formed, whereas that Wernicke area in the area 22 is located.

Histological structure of the cerebral cortex

The two historically older parts, i.e. the paleopallium and archipallium, have a different structure than the neocortex in terms of the histological structure of the cortex. Thus, the cortex of the neocortex consists of six layers and is also called Isocortex whereas the bark of Paleo and Archipallium is called Allocortex and consists of three layers.

There are two types of neurons within the neocortex: one is the Pyramidal cellswhich make up the majority of the neurons (85%) and via the transmitters Glutamate and Aspartate act excitatory, as well as the Non-pyramidal cells which via the transmitter GABA have an inhibitory effect.

Macroscopic structure of the telencephalon

The telencephalon consists of two Hemispheres, as well as six cerebral lobes per hemisphere. The right and left hemispheres are through the Cerebral longitudinal fissure (Hemispherical gap) separated from each other and stand over the Corpus callosum (Bars) functionally connected to each other.

There is one for each hemispheres dominanthemisphere. This is where the processing of linguistic and arithmetical services takes place. Functions such as reading and writing are also located here. The majority of right-handers have the dominant hemisphere on the left and only a small proportion of left-handers on the right hemisphere.

The six cerebral lobes include the Frontal-, the Parietal-, the Temporal-, the Occipital, the Island rag, as well as the limbic lobes. In addition, each hemisphere has three surfaces (facies) and two edges (margo). The facies include the Facies medialis, superolateralis and the Inferior facies. To the edges belong the Margo superior (Coat edge) and the Margo inferolateralis.

Image: “Lobes of cerebral Cortex” by Phil Schatz. License: CC BY 4.0

The lobes are separated from one another on the outside by the so-called primary furrows (sulci cerebri). These include the Central sulcus (= Rolando groove) between the parietal and frontal lobes, the Lateral sulcus between the temporal, frontal and parietal lobes and the Parietooccipital sulcus between the parietal and occipital lobes.
The Sulcus calcarinus also belongs to the primary furrows and divides the occipital lobe into an upper and a lower part.

In addition to the primary furrows, there are also secondary and tertiary furrows, with the secondary furrows dividing the individual lobes even further. The tertiary furrows start from these.

In addition to the sulci cerebri, the surface of the brain has a further surface enlargement in the form of cerebral convolutions (Gyri cerebri) on. An example of this would be the precentral gyrus and the postcentral gyrus, which are discussed further below in the article.

Structure of the frontal lobe


In the area of ​​the frontal lobe there are various functional centers that can be assigned to specific areas of the cortex or specific gyri. Depending on the gyri, between the Frontal superior gyri and medius, the Inferior frontal gyrus, as well as the Precentral gyrus differentiated.

Function of the gyri frontales superior et medius

In the area of ​​the gyri frontales superior and medius is the so-called frontal association cortex localizes. Starting from the Brodmann areas, the frontal association cortex is located within theAreas 9-11. Within the association cortex there is a processing of higher mental abilities such as planned actions.

Symptoms of damage to the frontal association cortex

If this area is damaged, there are, among other things, deficits in the planning of actions. In addition, it can be too general Drive malfunctionswhich, in addition to a reduction in spontaneous movements, are presented by a reduced ability to think and concentrate.
With lesions predominantly in the orbital portion of the frontal lobe (Area 11) there is predominantly an impairment of the Affect state. This can lead to disinhibited, suspicious and irascible behavior, but also to exaggerated cheerfulness on the part of the person concerned.

Notice: Association fields are not assigned to a specific cortical area and do not receive any information from the thalamus.

Function of the inferior frontal gyrus

The inferior frontal gyrus can be divided into further sections. It is between the Parsorbitalis, the Parsopercularis and the Parstriangularis differentiated.

In the area of ​​the Brodmann area 44 is located within the inferior frontal gyrus Broca centerwhich, along with the Wernicke Center, is counted among the language centers. The two language centers are explained in more detail in the article "Telencephalon - language centers, structure of the limbic system and the basal ganglia".

Function of the frontal gyrus medius

Another center, which is located in the area of ​​the frontal lobe, is that frontal eye field. This is synonymous with the Brodmann area 8 and is located within the frontal gyrus medius. Its function is to control voluntary eye movements.

To do this, it receives afferents from the primary and secondary Visual cortex and gives efferents over the Colliculi superiores to the brain muscle nuclei of the cranial nerves III, IV and VI. These cranial nerves are responsible for the innervation of the Eye muscle nuclei responsible.

Function of the precentral gyrus


The Precentral gyrus, as well as the premotor cortex (Area 6), as well as the supplementary motorcortex (Area 6) are assigned to the motor system. In the area of ​​the precentral gyrus, which is located in front of (= prae) the central sulcus, the primary somatomotor cortex (Area 4). Starting from this, the pyramid track (Corticospinal tract) as efference to the respective body parts.

The motor cortex itself receives afferents from the area of ​​the Thalamus (Ncl. Ventralis anterolateralis), as well as from the Postcentral gyrus (see basal ganglia loop).

The premotor, as well as the supplementarymotorcortex have comparable afferents. The efferents go from the premotor cortex over the Frontopontinus tract to the cerebellum, which then projects back into the primarily motor cortex. This creates a kind of control mechanism or fine regulation of movements.

In the area of ​​the supplementary motor cortex on the other hand, motion sequences are saved or planned.

Clinical symptoms of damage to the pyramidal tract

In order to derive the symptoms of damage to the pyramidal path, two factors are of particular importance: on the one hand, the fact that the pyramidal path is at the level of the Medulla oblongata 80% crosses on the opposite side (Decussatio pyramidalis) and, on the other hand, that the respective body parts are organized in the area of ​​the precentral gyrus somatotopically. This somatotopic division is made with the help of the motor Homunculus shown.
Due to the fact that in the area of ​​the medulla oblongata 80% of the fibers of the pyramidal tract cross on the opposite side and the remaining portions (20%) also cross in the course, motor failures occur on the contralateral side of the body if the pyramidal tract is damaged centrally.

These motor deficits appear in the form of paresis, with damage to the pyramidal tract, i.e. the 1. Motoneuons, in the course of a spasticParesis occurs. At the beginning, however, there is initially flaccid paresis due to the “spinal shock”. The spastic paresis usually only develops within a time frame of 3-4 weeks.

A lasting one flaccid paresis occurs when the 2. Motor neurons. The two forms of paresis can be distinguished from one another on the basis of clinical parameters.

Image: “Scheme of the Babinski reflex with German labeling” by derivative work: Roxbury-de (talk) Objaw_babinskiego.png: Original uploader was Malki at pl.wikipedia - Objaw_babinskiego.png. License: CC BY-SA 3.0

Clinically, a spastic paresis manifests itself e.g. through increased reflexes and weakened resp. missing external reflexes, as well as existing pathological reflexes. The pathological reflexes include the Babinski reflex, in which dorsiflexion of the big toe occurs when the lateral sole of the foot is wiped. The remaining toes remain in their original position or spread apart in a fan shape.

At a go limp or peripheral Paresis on the other hand it comes to one Loss of self-reflexes, whereas the external reflexes are usually not affected. Pathological reflexes also do not occur in peripheral paresis. Additionally, flaccid paresis leads to one neurogenic atrophy of the muscles, whereas the muscles are usually not affected by the increase in tone in spastic paresis. At most, immobilization in the context of spastic paresis can also lead to muscle atrophy, albeit lighter.

The Homunuclus also allows conclusions to be drawn about the respective central damage location. If there is damage in the area of ​​the edge of the jacket, which is caused by the A. cerebri anterior is taken care of, there is, for example, a spastic paresis of the legs.

Structure of the parietal lobe


The postcentral gyrus, the secondary somatosensory cortex, and the parietal association cortex are located within the parietal lobe.

Function of the postcentral gyrus


The postcentral gyrus includes the somatosensory Cortex. Here sensory afferents (pain, tactile and temperature senses) transmitted from the periphery are processed. These afferents arrive mainly via the Nucleus ventralis posteromedialis and the Posterolateral ventral nucleus of the thalamus to the somatosensory cortex, whereby the thalamus acts as a kind of filter ("gateway to consciousness").

Starting from the somatosensory cortex, the efferent fibers pull towards the secondarysomatosensitive Cortex, as well as to the motorcortex (Pre-central gyrus).
The fibers in the area of ​​the postcentral gyrus are organized somatotopically, like the fibers of the precentral gyrus, so that in addition to the motor homunculus there is sensory homunculus exists.

The homunculus makes it clear that individual areas, regardless of their anatomical size, are more or less sensory innervated. For example, the hands and tongue have a relatively large innervation area reflected in the homunculus, whereas the thighs, for example, only make up a relatively small area.

Image: “Illustration from Anatomy & Physiology, Connexions Web site” by OpenStax College. License: CC BY 3.0

Function of the secondary somatosensitive cortex

The information emanating from the somatosensory cortex is interpreted and classified in the area of ​​the secondary somatosensitive cortex (areas 5 and 7).

Function of the parietal association cortex

In addition to the frontal association cortex (see above), there is also a parietal association cortex, which is composed of the Angular gyrus, as well as the Supramarginal gyrus of the parietal lobe.

The angular gyrus (area 39), which curves around the end of the Superior temporal sulcus winds between the secondary auditory cortex and the secondary visual cortex. This also explains the importance of the parietal association cortex in functions such as reading or writing.
The supramarginal gyrus (area 40) lies at the end of the Lateral sulcus and encloses this.

Popular exam questions about the telencephalon

The solutions can be found below the references.

1. Which statement about the telencephalon is incorrect?
  1. Historically, the telencephalon is divided into the paleo-, archi- and neocortex.
  2. The paleocortex is the oldest section of the telencephalon.
  3. The neocortex can be histologically divided into six layers.
  4. The archicortex has three layers.
  5. The telencephalon emerges from the prosencephalon together with the rhombencephalon.
2. Which statement about the frontal lobe is incorrect?
  1. The precentral gyrus is part of the frontal lobe.
  2. The frontal eye field, which corresponds to area 6 according to Brodmann, is located within the frontal lobe.
  3. The Broca center is located in the area of ​​the inferior frontal gyrus.
  4. The Wernicke center is located in the area of ​​the frontal gyrus medius.
  5. Damage to the frontal lobe can lead to changes in the affect state.
3. Which statement about the parietal lobe is correct?
  1. This is where the motor cortex is located.
  2. The angular gyrus is located behind the central sulcus.
  3. The primary and secondary somatosensitive cortex lie within the parietal lobe.
  4. The postcentral gyrus corresponds to the Brodmann area 22.
  5. In contrast to the motor system, there is no somatotopic structure in the somatosensitive cortex.

 



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Last minute anatomy, F. Rengier, C. Jaschinski, H. Holtmann - Elsevier

MEDI-LEARN Anatomy 3, CNS Part 2, 3rd edition, A. Martin - MEDI-LEARN

Neurology, 12th edition, W. Gehlen, H.-W. Delank - Thieme

Physiology, 6th edition, R. Klinke, H.-C. Pape, A. Kurtz, S. Silbernagl - Thieme

Prometheus, head and neuroanatomy, M. Schünke and others - Thieme

Pocket textbook anatomy, J. Kirsch and others - Thieme

Solutions to the questions: 1E, 2D, 3C

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