The telencephalon
The telencephalon
The telencephalon or endbrain
It controls human mental and intellectual activity.
The telencephalon includes the
cerebral hemispheres
their commissures and
cavities
Each cerebral hemisphere has an external layer of neurons, the cortex or pallium,
an internal mass of neuronal processes, deeply situated basal nuclei (núclei basáles) and rhinencéphalon.
The lateral ventricles (ventriculi lateráles) are the cavity of the telencephalon.
Two hemispheres are connected by córpus callósum that consists of transverse white fibers.
Anterior part of the corpus callosum flexes inferiorly and forms the genu, génu córporis callósi.
Under the corpus callosum is fórnix, which consists of two bundles of white fibers.
- Anteriorly these fibers diverge and form colúmnae fórnicis,
- posteriorly – crúrae fórnicis.
- Between colú mnae fórnicis and génu córporis callósi is a transparent lamina – septum pellúcidum.
The brain cortex
The brain cortex, pállium is a layer of gray matter that covers the surface of each hemisphere.
a layer of gray matter that covers the surface of each hemisphere. The cerebral cortex consists of 6 layers:
1) molecular;
2) external glandular;
3) the layer of medium sized and small pyramidal neurons;
4) internal glandular;
5) the layer of the largest pyramidal cells (cells of Betz);
6) multiform.
The first and second layers contain associative neurons,
the third and fourth – sensory neurons,
the fifth and sixth – motor neurons.
right and left hemisphere are separated by the longitudinal fissure, fissúra longitudinális
Each hemisphere has three surfaces:
superolateral,
medial and
inferior
(fácies súperolateralis, mediális et inférior)
three margins:
superior,
inferior and
medialis (márgo supérior, mediális et inférior)
three poles:
frontal,
occipital and
temporal
(pólus frontális, occipitális et temporális).
cerebral cortex has folds and grooves. This pattern increases the surface area of the cortex.
-The folds are called gyri.
- Grooves between folds are termed sulci
Permanent (primary) sulci divide each hemisphere into 5 lobes:
- parietal lobe, lóbus parietális;
- occipital lobe, lóbus occipitális;
- temporal lobe, lóbus temporális
- insula.
The frontal lobe is separated from the parietal lobe by the central sulcus súlcus centrális or sulcus Rolandi.
- The lateral cerebral sulcus (sulcus of Sylvii), súlcus cérebri laterális separates the frontal lobe from the temporal lobe.
- The parietooccipital sulcus, súlcus parietooccipitális separates the parietal lobe from the occipital lobe.
This sulcus lies at the medial surface and only a small portion reaches the superolateral surface of the hemisphere.
The superolateral surface
Lateral surface of the frontal lobe has the precentral sulcus, súlcus precentrális which runs parallel to the central sulcus, in front of it.
The precentral gyrus, gyrus precentrális lies between the two sulci
- Here, in the third and fourth layer of the brain cortex terminate pathways, which bring stimuli from muscles and joints (cortical center of the motor analyzer).
- Processes of the fifth’s layer neurons form motor pyramidal pathway which regulates voluntary movements (primary motor area).
- Lesions of this area lead to paralysis of the opposite half of the body.
The area in front of the precentral sulcus is divided into superior, middle and inferior frontal gyri, gyrus frontális supérior, médius et inferior by the superior and inferior fontal sulci, súlcus frontális supérior et inférior.
The anterior horizontal, rámus antérior and anterior ascending, rámus ascéndens rami of the lateral sulcus subdivide the inferior frontal gurys into three parts: párs operculáris, párs trianguláris and párs orbitális.
The posterior third of the middle frontal lobe contains the center of writing (the cortical center of written speech motor analyzer).
- This area sends stimuli to the nuclei of the oculomotor nerves, and also is connected with the visual center in the occipital lobe and the motor area that controls voluntary contraction of neck and upper limbs muscles in the precentral gyrus.
- Agraphia is a loss of ability to express thoughts in writing.
The triangular and opercular parts of the inferior frontal lobe contain the motor speech area or Broca’s area.
- Its location has functional asymmetry.
Damage to the motor speech area in the left hemisphere results in motor aphasia, an inability to properly articulate or form words and amusia, an inability to sing.
The person knows what he wishes to say but can’t speak.
Damage to the motor speech area in the right hemisphere results in timbre and voice intonation disturbances.
The triangular and opercular parts of the inferior frontal lobe contain the motor speech area or Broca’s area.
- Its location has functional asymmetry.
Damage to the motor speech area in the left hemisphere results in motor aphasia, an inability to properly articulate or form words and amusia, an inability to sing.
The person knows what he wishes to say but can’t speak.
Damage to the motor speech area in the right hemisphere results in timbre and voice intonation disturbances.
Immediately anterior to the primary motor area is a premotor association area.
- It generates impulses that cause specific group muscles to contract in a specific sequence – for example to write a word.
- It controls the learned skilled movements and serves as a memory bank for such movements.
involved in planning and organizing movements and actions
The frontal pole area regulates the activity of the emotional zones in the cerebrum (limbic system) and controls the psychoactive state.
- Damage to this area causes different personality disorders, difficulty in interpreting feedback from the environment, IQ decrease and leads to dramatic change in social behavior, "behavioral sponteneity".
The superior and inferior temporal sulci, súlcus temporális supérior et inferior divide the temporal lobe into the superior, middle and inferior temporal gyri, gyrus temporális supérior, médius et inférior.
The internal surface of the superior temporal gyrus, faced towards the insula, has transverse temporal gyri, gyri temporáles transvérsae (Heschl's gyri).
Heschl's gyri contain cortical end of the auditory analyzer (primary auditory area).
It interprets the basic characteristics of sound as pitch and rhythm. Damage to this area causes deafness.
The posterior third of the superior temporal gyrus contains sensory speech area, Wernicke’s (posterior language) area.
- Damage to this gnostic area results in sensory aphasia, faulty understanding of spoken or written words.
- Such a patient may produce strings of words that have no meaning.
- The deficiency may be word deafness, an inability to understand spoken words, or word blindness, an inability to understand written words, or both.
The middle and inferior temporal gyri contain the cortical end of the vestibular analyzer (primary vestibular area). Injury to it causes disequilibrium.
Anterior part of the parietal lobe has the postcentral sulcus, súlcus postcentrális which runs parallel to the central sulcus, behind it.
- The postcentral gyrus, gyrus postcentrális lies between the two sulci.
- The area behind the postcentral gyrus is divided into the superior and inferior parietal lobules, lóbules parietáles supérior et inférior by the intraparietal sulcus.
- The inferior parietal lobule has the supramarginal gyrus, gyrus supramarginális placed above the
upturned ends of the lateral sulcus and the angular gyrus, gyrus anguláris that lies near the end of the superior temporal gyrus.
The postcentral gyrus and the superior temporal lobule contain the primary somatosensory area or general sensory area (touch, pain, proprioreceprion and temperature).
- The size of the cortical area receiving impulses from a particular body part depends on the number of receptors present there than on the size of the part.
- For example a larger portion of the sensory area receives stimuli from lips and fingers than from thorax and hip (somatotoFig principle).
- Damage to this area causes loss of sensation (anesthesia).
Injury to the superior parietal lobule leads to pain sensitivity decrease and stereognosis breach – inability to identify an object by touch without visual input.
The inferior temporal lobule in the supramarginal gyrus contains the center of praxia, which regulates the ability to perform complicated movements and learned skilled movements.
- Neurons of this area communicate with the frontal lobe and with all sensory areas of the posterior half of the brain.
- Apraxia is characterized by loss of the ability to execute or carry out learned purposeful movements, despite having the desire and the physical ability to perform the movements.
The angular gyrus contains the reading center (visual center of the written speech).
- Alexia occurs when damage to the angular gyrus causes a patient to lose the ability to read.
The lateral surface of the occipital lobe has a prominent transverse occipital sulcus, súlcus occipitális transvérsus. Other sulci are of individual variation.
The inferior surface
The inferior surface of the hemisphere has a fossa, which is the continuation of the lateral fissure.
- This is the lateral cerebral fossa, fóssa cérebri laterális which separates the inferior surface into anterior and posterior parts
Anterior part has the olfactory sulcus, súlcus olfactórius which is parallel to the medial border of the hemisphere.
- It contains olfactory bulb and tract (parts of the rhinencephalon).
- Medially from the olfactory sulcus is the gyrus rectus.
- Laterally – inconstant orbital sulci and gyri, súlci et gyri orbitáles.
Posterior part of the inferior surface has two sulci:
- the lateral one is the occipitotemporal sulcus, súlcus occipitotemporális, which separates gyrus occipitotemporális laterális et mediális and
- the medial one is the collateral sulcus, súlcus collaterális which continues forward as the rhinal sulcus, súlcus rinális.
- The sulcus medial to the collateral sulcus is the hippocampal sulcus, súlcus hippocámpi, which separates the hemisphere from the brain stem.
- The uncus contains primary gustatory and
olfactory areas (cortical center for the gustatory
and olfactory analyzers).
- Medially from the súlcus collaterális
is gyrus linguális.
The medial surface
Above the corpus callosum lies the súlcus corpóris callósi
The cingulated sulcus, súlcus cinguli starts in front of the genu and parallel to the sulcus corporis callosum.
- it continues as the isthmus and then as the gyrus parahippocampális.
- Gurus cinguli, the isthmus and the gyrus parahippocampális form the gyrus fornicátus, which is one of the limbic system structures.
The medial surface of the frontal lobe has the paracentral lobule, lóbulus paracentrális.
- It is the U-shaped area limited by the ramus
marginalis and sulcus precentralis.
- Behind the paracentral lobule lies the précuneus.
The calcarine sulcus, súlcus calcarinus begins a little below the splenium and runs towards the occipital pole.
- The cortex near the calcarine sulcus contains the primary visual area (the cortical end of the visual analyzer).
- Injury to this area causes blindness.
The triangular area between the parieto-occipital sulcus and the calcarine sulcus is called the cuneus.
- The gyrus lingualis lies between the calcarine sulcus and the collateral sulcus.
