General structure of the hemispheres
The cerebrum (cerebrum) is a derivative of the telencephalon. The right and left hemispheres (hemispheria cerebri dextrum et sinistrum) are separated by the deep longitudinal cerebral fissure — fissura longitudinalis cerebri. The hemispheres are separated from the underlying cerebellum by the transverse fissure (fissura transversa cerebri).
Three main systems are distinguished in the structure of each hemisphere:
- Cerebral cortex (cortex cerebri or pallium);
- Basal nuclei (nuclei basales);
- Rhinencephalon (rhinencephalon), which occupies the most ventral position.
Aggregations of gray matter from these three systems form the internal white matter of the hemispheres. Cavities, known as the two lateral ventricles (ventriculi laterales), are located inside the telencephalon; the left one is conventionally considered the first.
Surfaces, borders, and poles
Each hemisphere has a complex three-dimensional shape, which anatomically features three surfaces connected by borders, and projecting poles.
Surfaces:
- Superolateral (facies superolateralis hemispherii) — convex, facing the internal surface of the cranial vault bones.
- Inferior (facies inferior hemispherii) — its anterior and middle parts lie on the cranial base, while the posterior parts rest on the cerebellar tentorium.
- Medial (facies medialis hemispherii) — flat, facing toward the longitudinal cerebral fissure.
These surfaces form three borders: the superior border (margo superior), inferolateral border (margo inferior), and inferomedial border (margo medialis). The latter is additionally divided into medial occipital and medial orbital borders.
The most projecting parts of the hemispheres are called poles. These include the frontal pole (polus frontalis), occipital pole (polus occipitalis), and temporal pole (polus temporalis).
Lobes of the cerebrum
The hemisphere is traditionally divided into five lobes:
- Frontal lobe (lobus frontalis);
- Parietal lobe (lobus parietalis) — located posterior to the central sulcus. It is separated from the temporal lobe by the lateral sulcus, and partially demarcated from the occipital lobe by the parieto-occipital sulcus. The intraparietal sulcus runs through its thickness, dividing the lobe into superior and inferior parietal lobules.
- Temporal lobe (lobus temporalis) — has the clearest boundaries. On its superolateral surface run the superior and inferior temporal sulci, which form the superior, middle, and inferior temporal gyri.
- Occipital lobe (lobus occipitalis) — on its convex surface, it lacks clear boundaries with the parietal and temporal lobes. The pattern of its sulci and gyri is extremely individual and variable.
- Insular lobe or insula (lobus insularis / insula) — located deep within the lateral fossa of the cerebrum (fossa lateralis cerebri) and physically separates the frontal lobe from the temporal lobe.
Main sulci, gyri, and their functions
The surface of the hemispheres is furrowed by sulci (sulci), between which lie gyri (gyri). Each cortical area is responsible for specific functions.
| Surface | Sulcus | Gyrus or structure | Main function |
|---|---|---|---|
| Superolateral | Sulcus centralis | Gyrus precentralis (frontal lobe) | Primary motor cortex (voluntary movements) |
| Superolateral | Sulcus centralis | Gyrus postcentralis (parietal lobe) | Primary somatosensory cortex |
| Superolateral | Sulcus temporalis superior | Gyrus temporalis superior | Hearing, sensory speech |
| Medial | Sulcus cinguli | Gyrus cinguli | Limbic system (emotions, motivation) |
| Medial | Sulcus calcarinus | Cuneus, gyrus lingualis | Primary visual cortex |
| Inferior | Sulcus olfactorius | Gyrus rectus | Smell |
| Inferior | Sulcus hippocampi | Gyrus dentatus | Memory and learning |
Insular lobe (Insula)
The insula lies at the floor of the lateral fossa of the brain. It has the shape of a three-sided pyramid, the apex of which is directed upward and laterally — directly toward the lateral sulcus.
At its periphery, the insula is surrounded by the frontal, parietal, and temporal lobes, which form the walls of the lateral sulcus. Its base is bounded by the circular sulcus of the insula (sulcus circularis insulae), which gradually flattens and disappears on the inferior surface.
On the surface of the insula itself runs the central sulcus of the insula (sulcus centralis insulae). It divides the lobe into two parts:
- Anterior (larger) part — contains several short gyri (gyri breves insulae).
- Posterior (smaller) part — formed by a single long gyrus (gyrus longus insulae).
Briefly: answers to topical questions
Which gyri and lobules are located in the parietal lobe?
The following gyri and lobules are distinguished in the parietal lobe:
- Postcentral gyrus (gyrus postcentralis) — located posterior to the central sulcus.
- Superior parietal lobule (lobulus parietalis superior) — separated by the intraparietal sulcus.
- Inferior parietal lobule (lobulus parietalis inferior) — includes the supramarginal and angular gyri.
- Precuneus (precuneus) — a quadrilateral surface on the medial side.
- Paracentral lobule (lobulus paracentralis) — its posterior part also belongs to the parietal lobe.
Which structures belong to the basal nuclei of the telencephalon?
The basal nuclei of the telencephalon include three main accumulations of gray matter:
- Corpus striatum (corpus striatum) — includes the caudate nucleus (nucleus caudatus) and lentiform nucleus (nucleus lentiformis).
- The claustrum (claustrum) is located lateral to the lentiform nucleus.
- The amygdaloid body (corpus amygdaloideum) is located in the region of the temporal pole.
Which anatomical structures are part of the olfactory brain (rhinencephalon)?
The rhinencephalon is divided into two topographical divisions: peripheral and central.
- The peripheral division (lobus olfactorius) includes the olfactory bulb (bulbus olfactorius), olfactory tract (tractus olfactorius), olfactory trigone (trigonum olfactorium), and anterior perforated substance (substantia perforata anterior).
- The central division is represented by cerebral gyri, which include the parahippocampal gyrus (gyrus parahippocampalis), dentate gyrus (gyrus dentatus), and cingulate gyrus (gyrus fornicatus) with the uncus (uncus).
Which sulci and gyri are located on the inferior surface of the frontal lobe?
The following sulci and gyri are located on the inferior (basal) surface of the frontal lobe:
- The olfactory sulcus (sulcus olfactorius) runs parallel to the medial margin of the hemisphere.
- The gyrus rectus (gyrus rectus) lies medial to the olfactory sulcus, continuing as the superior frontal gyrus.
- The orbital sulci (sulci orbitales) have a characteristic H-shape and are located lateral to the olfactory sulcus.
- The orbital gyri (gyri orbitales) are divided by the orbital sulci into anterior, posterior, medial, and lateral gyri.
Which gyri are found on the medial surface of the hemisphere?
The following gyri and lobules are located on the medial surface of the cerebral hemisphere:
- The paracentral lobule (lobulus paracentralis) corresponds to the medial surface of the upper ends of the central gyri.
- The precuneus (precuneus) is a quadrilateral surface posterior to the paracentral lobule.
- The cuneus (cuneus) is a distinct area of the occipital lobe cortex.
- The cingulate gyrus (gyrus fornicatus) consists of the cingulate gyrus (gyrus cinguli), isthmus (isthmus), and parahippocampal gyrus (gyrus parahippocampalis).
- The lingual gyrus (gyrus lingualis) borders the cuneus inferiorly and posteriorly.
To easily remember the three main systems of the hemispheres, use the mnemonic: Cortex, Rhinencephalon, Basal nuclei.
Class and exam questions
What forms the cavity of the telencephalon?
The cavity of the telencephalon consists of the two lateral ventricles (ventriculi laterales). By convention, the left ventricle is considered the first and the right the second.
Which structure separates the frontal lobe from the temporal lobe?
The frontal and temporal lobes are separated by the lateral sulcus of the cerebrum, deep within which lies the insular lobe (insula).
Where is the olfactory brain located?
The olfactory brain (rhinencephalon) occupies the most ventral (inferior) position in the structure of the cerebral hemispheres.
What else to study on this topic
- Structure and functions of the basal nuclei (nuclei basales)
- Architectonics of the cerebral white matter
- Anatomy of the olfactory brain (rhinencephalon)
- Limbic system and parahippocampal gyrus
- Individual variability of occipital lobe sulci
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