Review of Brain Structures From a Mid-sagittal View
Midsagittal section of the brain
The midsagittal section of the brain shows the three major parts of the brain, which are the cerebrum, cerebellum, and brainstem. These brain parts are marked with visible gross features similar the gyri (singular: gyrus) and sulci (singular: sulcus) of the cerebrum. They are each also divided into subparts or regions for simplified localization of structures, for case, the brainstem is composed of the midbrain, pons and medulla oblongata, while the cerebrum is divisible into lobes.
Sulci are pocket-sized grooves that split and ascertain gyri; large grooves, chosen fissures, carve up the cerebral cortex into lobes, and too the cerebrum into the right and left cerebral hemispheres forth the midsagittal airplane. The fissure involved in this division is called the medial longitudinal fissure. From the midsagittal section of the brain both white and gray matter tin be observed, as well as of import spaces such as the third and fourth ventricles.
| Diencephalon and brainstem | Nuclei - thalamic, hypothalamic, pineal gland, superior and junior colliculi, nucleus gracilis Optic chiasm, ventricular system, cognitive channel |
| Cerebellum | Vermis - lingula, primal, culmen, declive, folium, tuber, pyramid, uvula, nodule), folia Fissures - primary and posterolateral Lobules - anterior, posterior, floculonodular Superior medullary vellum, arbor-vitae |
| Cerebrum | Corpus callosum, third ventricle, interventricular foramen of Monro, thalamus, hypothalamus, cerebral aqueduct Sulci & gyri - cingulate sulcus and gyrus, callosal sulcus, medial frontal gyrus, suprasplenial sulcus, parieto-occipital sulcus, calcarine cleft Lobules - paracentral, precuneus, cuneus, isthmus |
| Important Brodmann areas | Surface area 4 - primary motor cortex Areas six, 8, 44, 45 - motor association cortex Areas 1, 2, 3 - primary somatosensory cortex Area 17 - visual area Areas 17, 18 - occipital middle field Area 18, nineteen - psychovisual area |
Contents
- Diencephalon, brainstem and related structures
- Cerebellum
- Cerebrum
- Important functional areas of the cerebrum
- Motor surface area (primary motor cortex)
- Premotor area (motor association cortex)
- Sensory area (main somatosensory cortex)
- Visual areas
- Occipital center field
- Prefrontal areas (prefrontal cortex)
- Olfactory cortex
- Summary
- Sources
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Diencephalon, brainstem and related structures
The diencephalon is part of the "old brain" lying between the cerebrum and the brainstem and is equanimous of the thalamus, the hypothalamus, and the epithalamus. These can be seen in a midsagittal aspect upon sectioning of the third ventricle. The brainstem is the "bridge" between the cognitive hemispheres and the spinal cord. It is made upwardly of the midbrain, pons and the medulla oblongata. They are continuous above with the cerebral hemispheres, below with the spinal cord and posteriorly with the cerebellum.
The midsagittal section of the diencephalon and brainstem show some important masses of grayness matter projecting onto the median plane. Some nuclei that can be observed include:
- The thalamic and hypothalamic nuclei bordering the tertiary ventricle.
- The pineal gland which is the principal component of the epithalamus.
- The superior and inferior colliculi, two posterior bulges situated on either side of the midsagittal line.
- The nucleus gracilis lying immediately lateral to the posterior median fissure.
Just anterior to the pituitary, and junior to the hypothalamus, the optic chiasm passes, where fretfulness from each heart cross over assuasive binocular vision. Vascular systems relating to the claret supply and the cerebrospinal fluid can be observed progressing through the brainstem. The major blood vessel is the basilar artery, in the anterior pontine, which progresses into the posterior of the Circle of Willis. The ventricular organization - excluding the lateral ventricles - can as well be observed passing from the third ventricle, via the cerebral aqueduct, to the fourth ventricle and beyond to the fundamental culvert. The central canal runs through the medulla to become the central culvert of the spinal cord.
Cerebellum
The cerebellum (or small encephalon) weighs about ten% of the cerebral hemispheres and weighs approximately 150 k in adults. It has a superficial layer of grey matter, the cerebellar cortex, and like other parts of the brain, it is marked by numerous fissures. The cerebellum lies posterior to the brainstem and is separated from the cerebrum by a fold of dura mater chosen the tentorium cerebelli.
The cerebellum consists of 2 hemispheres separated past the medially positioned vermis. The cerebellum likewise has superior and inferior surfaces. The surface of the cerebellum is marked by a series of fissures that run more or less parallel to one another. The fissures subdivide the surface of the cerebellum into narrow leaf-similar bands or folia. The long axis of the majority of folia is approximately transverse. Sagittal sectioning of the cerebellum reveals the invaginations of the folia, which have a tree-like advent and to which the term arbor-vitae (tree of life) is ascribed.
The deepest fissures, such as the principal crack (fissure prima) and the posterolateral cleft, divide the cerebellum into lobules: the inductive, posterior, and flocculonodular. The medial vermis is similarly divisible into lobules, although to a greater extent than the lateral hemispheres. The lobules of the vermis are the:
- lingula
- primal
- culmen
- uncomplicated
- folium
- tuber
- pyramids
- uvula
- nodule
Collectively the lateral hemispheres and vermis form the highly active relay station that is the corpus cerebella. The anterior and posterior lobes together form the corpus cerebelli.
Cerebrum
The cerebrum is comprised of gyri and sulci, with divisions between lobes primarily identified by fissures. When observed from the medial view different aspects of the cortices tin be observed as they progress into the midsagittal cleft, and indeed some cortices not otherwise observable tin be seen, such every bit the olfactory cortex. The midsagittal aspect of the cerebrum also reveals structures spanning the fissure, such as the corpus callosum.
The corpus callosum (a grouping of commissural fibres) is a prominent structure on this midsagittal surface. The third ventricle of the brain, as well as some other related structures similar the interventricular foramen (of Monro) – through which the 3rd ventricle communicates with the lateral ventricles - can likewise be seen on the medial surface. Other structures seen on this surface include the thalamus, hypothalamus and cerebral aqueduct (of Sylvius).
The thalamus, hypothalamus and the basal ganglia are three distinct masses of gray matter like the cerebral cortex. They are located deep in the cognitive cortex and inside the white matter of the cerebrum. These deep structures contribute only a small-scale portion of the cerebrum's gray matter, while the cognitive cortex forms the largest portion of the cerebrum's grey matter.
Surrounding the superior surfaces of the corpus callosum, sulci and gyri form medial walls of the median fissure cogent the folds of the cerebral cortex. The most prominent of the sulci is the cingulate sulcus (sulcus cinguli), which follows a curved course parallel to the upper convex margin of the corpus callosum. Anteriorly, the sulcus cinguli ends below the rostrum of the corpus callosum, and posteriorly, it turns up to reach the superomedial edge, a footling backside the upper cease of the fundamental sulcus. The area between the cingulate sulcus and the corpus callosum is the gyrus cinguli (or cingulate gyrus). Hence this gyrus is divers by the cingulate sulcus superiorly, and the corpus callosum inferiorly (specifically by the callosal sulcus which wounds around the corpus callosum).
Above the cingulate sulcus, upward to the limit of the superomedial border (superomedial edge) is an area which consists of two parts. The large anterior part, chosen the medial frontal gyrus, lies anterior to the paracentral lobule, which is wound around the end of the key sulcus. The paracentral lobule is separated from the anterior part by a very short sulcus which is continuous with the cingulate sulcus. Between the parieto-occipital sulcus and paracentral lobule is a quadrilateral surface area called the precuneus. Anteroinferiorly, the precuneus is separated from the posterior part of the gyrus cinguli by the suprasplenial (or subparietal) sulcus. The precuneus and the posterior role of the paracentral lobule form the medial surface of the parietal lobe.
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Further posterior to the paracentral lobule and gyrus cinguli are two major sulci that cutting off a triangular surface area. This area is called the cuneus. This triangular surface area is defined anterosuperiorly by the parieto-occipital sulcus (which crosses the superomedial edge to appear as a very brusque sulcus on the superolateral surface), inferiorly by the calcarine fissure, and posteriorly by the superomedial edge of the cognitive cortex. The calcarine fissure extends forward beyond its junction with the parieto-occipital sulcus and ends a little below the splenium of the corpus callosum (posterior office of the corpus callosum) to define a pocket-sized area called the isthmus which lies between it (calcarine scissure) and the splenium of the corpus callosum.
Important functional areas of the cerebrum
Cortices of the cerebral cortex have long been divisible by their specific functions. These areas can be defined in terms of the gyri and sulci described above. Nevertheless, upon investigation of the microscopic structure of the cerebral cortex, at that place is considerable variation from region to region and that definition of these functional areas is not bars to the boundaries of gyri and sulci, simply often cross them. Virtually of these authors have likewise worked out "maps" of the cognitive cortex indicating areas of the differing structure. The all-time-known scheme is that by Brodmann, who represented different areas of the cortex past numbers.
Motor expanse (principal motor cortex)
This is the area corresponding to area iv of Brodmann and possibly to the part of area six which lies in the precentral gyrus. The motor area is located in the precentral gyrus on the superolateral surface and in the anterior function of the paracentral lobule on the medial surface. This area of the cortex is responsible for initiation of voluntary move. Within the motor surface area, subpopulations of neurons are responsible for activating different areas of the torso.
Each neuronal population responsible for activating a concrete area neighbors the population that activates the concrete area adjacent, this is chosen the topographical arrangement, and in this mode, the brain forms a representation of the trunk. While topographic organization depicted in the "Homunculus" shows the clan betwixt the concrete torso areas and their representations, it as well depicts the size of the excitability of each representation, and the relative control the neuronal populations take over each physical location. The topographical motor representation of the body begins with the toes and anxiety deep in the paracentral lobule, and progresses into the legs and genitalia superiorly, before progressing laterally and inferiorly with the rest of the body. As indicated by the homunculus, the lower limbs have a relatively small neuronal motor input.
Premotor area (motor association cortex)
This is the area corresponding to areas 6, eight, 44 & 45 of Brodmann. It is located just anterior to the motor area, occupying the posterior parts of the superior, middle and junior frontal gyri. The part of the premotor area located in the superior and eye frontal gyri corresponds to area 6 and eight of Brodmann.
Sensory surface area (primary somatosensory cortex)
This functional surface area is located in the postcentral gyrus. Information technology corresponds to area one, 2 and 3 of Brodmann. It extends to the medial surface, from the lateral surface, where information technology lies in the posterior function of the paracentral lobule. As with the motor area, the concept of Homunculus, and associated topographical system - chosen somatotopic organization - applies to the sensory area. The somatotopic representation denoted by the homunculus displays a similar organization to the motor cortex, with the legs, and genitalia beingness visible from the midsagittal aspect, and beingness responsible for sensations of those regions. The surface area of the cortex that receives sensations from a particular part of the body is non proportional to the size of that role, but rather to the complexity of sensations received from it (e.g., the hands have high cortical investment, whereas the feet, with a similar mass, take very footling cortical investment). Immediately posterior to the somatosensory area is the Sensory Association Cortex. This cortex is responsible for the processing of multisensory information.
Visual areas
The areas concerned with vision are located in the occipital lobe, mainly on the medial surface, both to a higher place and below the calcarine sulcus (area 17). Surface area 17 extends into the cuneus, and into the lingual gyrus. Posteriorly, it may extend onto the superolateral surface where it is limited anteriorly by the lunate sulcus. Surface area 17 is continuous, both above and below with area 18 and beyond this surface area with expanse 19. Areas 18 and 19 are described every bit psychovisual areas (or visual association areas) and are responsible for the interpretation of visual impulses reaching expanse 17. The pathways leading to the eyes and visual areas can as well exist observed from a midsagittal attribute, peculiarly at the optic chiasm.
Occipital eye field
Fibers from the visual areas attain the frontal heart field which is concerned with eye movements. The visual areas are therefore regarded equally partly motor in function. This view is substantiated by the fact that movements of the eyeballs and head can be produced by stimulation of areas 17 and 18 which constitutes an occipital eye field. Efferents from the visual areas as well reach the superior colliculus, the pretectal region, and the nuclei of cranial fretfulness supplying muscles that movement the eyeballs.
Therefore, as a way of summary, the visual areas tin exist categorized equally follows:
- Visual area – surface area 17 – sensory.
- Occipital eye field – area 17 & eighteen – motor.
- Psychovisual area – expanse 18 & xix – sensory.
Prefrontal areas (prefrontal cortex)
The part of the frontal lobe excluding the motor, premotor and motor clan cortex is referred to as the prefrontal area. It includes the parts of the frontal gyri anterior to the motor association surface area, most of the anterior parts of the orbital gyri, most of the medial frontal gyrus, and the anterior part of the gyrus cinguli. This area is concerned with normal expression of emotions, the ability to predict consequences of deportment, and complex thoughts. The medial part of the prefrontal area is associated with auditory and visual functions.
Olfactory cortex
This region of the cognitive cortex plays a role in olfaction (the sense of smell). It receives direct fibres from the olfactory bulb. The olfactory cortex is composed of the prepiriform cortex (which includes the lateral olfactory gyrus and the gyrus ambiens), gyrus semilunaris, inductive olfactory nucleus, likewise equally the entorhinal area.
Summary
- A midsagittal section of the encephalon shows the cerebrum, cerebellum and the brainstem.
- The brain is divided into the prosencephalon, mesencephalon, and rhompbencephalon.
- The prosencephalon is further divided into the telencephalon (cognitive hemispheres) and Diencephalon (thalami, neurohypophysis, pineal body,..etc).
- The mesencephalon is a synonym to midbrain (peduncles and collicules).
- The rhombencephalon containing the pons, cerebellum, and medulla.
- Important functional areas of the cerebrum incude:
- Motor Area (Primary Motor Cortex)
- Pre-motor Area (Motor Association Cortex)
- Sensory Area (Principal Somatosensory Cortex)
- Visual Areas
- Occipital eye field
- Prefrontal Areas (Prefrontal Cortex)
- Olfactory Cortex
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