Medial Surface of Left Cerebral Hemisphere
The medial surface of the cerebral hemisphere is visualized by sectioning the brain in the midline (midsagittal plane). It helps us understand the gross anatomy of the hemispheres, the diencephalon, the brainstem, and the ventricles.
The presence of the corpus callosum is the most conspicuous feature seen on the medial surface of the cerebral hemisphere. The sulci and gyri on the medial surface are located above, in front and behind the corpus callosum.
The following areas are visualized:
- Medial frontal gyrus
- Paracentral lobule
- Cingulate gyrus
- Lingual gyrus
- Hippocampal gyrus
Additionally, inside each cerebral hemisphere is a space filled with CSF, the lateral ventricle. The lateral ventricle of one hemisphere is separated from the other by a curtain called the septum pellucidum. The fornix, a fiber tract of the limbic system, is located in the free lower edge of the septum. The third ventricle is also visualized here in the midline, thereby revealing the diencephalic region. On this medial view, the thalamus (part of the diencephalon) is separated from the hypothalamus by a groove, the hypothalamic sulcus. This sulcus extends from the foramen of Monro to the aqueduct of the midbrain. The optic chiasma is found at the anterior aspect of the hypothalamus, and behind it is the mammillary body.
Corpus callosum :
The corpus callosum is the largest commissure of the brain connecting the cerebral cortex of the two cerebral hemispheres. The parts of the corpus callosum are rostrum, genu, trunk/body and splenium. The genu and the splenium can be appreciated in the midline in the horizontal section of the cerebrum. The genu is located anteriorly and medial to the frontal lobes while the splenium is located posteriorly and medial to the occipital lobes.
The corpus callosum is mainly responsible for the transfer of interhemispheric information that is essential for bilateral responses and in learning processes.
Medial frontal gyrus :
The medial frontal gyrus is situated in the medial surface of the cerebral hemisphere anterior to the paracentral lobule. It lies in between the cingulate sulcus and superomedial border of the cerebral hemisphere. It plays a role in executive mechanisms.
Paracentral lobule :
The paracentral lobule is situated on the medial surface of the cerebral hemisphere and is the continuation of the precentral and postcentral gyri. It is a small part that lies around the upper part of the central sulcus. It controls the motor and sensory innervations of the contralateral lower extremity. It is also considered as the cortical center for the control of defecation and urination.
Cingulate gyrus :
The cingulate gyrus is the area between the cingulate sulcus and corpus callosum. It is a component of the limbic system and is involved in processing emotions and behavior regulation. It also helps to regulate autonomic motor function.
The precuneus is a quadrangular area between the parieto-occipital sulcus and paracentral lobule. It lies in front of the cuneus. It is involved with episodic memory, visuospatial processing, reflections upon self, and aspects of consciousness.
The cuneus is a triangular area between the posterior part of the calcarine sulcus and the parieto-occipital sulcus. It is a smaller lobe in the occipital lobe of the brain and is a site for basic visual processing.
Lingual gyrus :
The lingual gyrus is the area between the collateral and calcarine sulci posteriorly. It is involved in processing vision, especially related to letters. It is also thought to play a role in analysis of logical conditions (i.e., logical order of events) and encoding visual memories.
The hippocampal gyrus (or parahippocampal gyrus) is a cortical grey matter that surrounds the hippocampus and is part of the limbic system. It lies anterior to the ligual gyrus. The region plays an important role in memory encoding and retrieval.
The lateral ventricles are the two largest ventricles of the brain and contain cerebrospinal fluid (CSF). There are two lateral ventricles one in each cerebral hemisphere. Each lateral ventricle is a roughly C-shaped cavity situated within each cerebral hemisphere. The lateral ventricle surrounds the thalamus, the lentiform nucleus, and the caudate nucleus. Each lateral ventricle is divided into four parts: central part or body, anterior horn, posterior horn, and inferior horn. Each lateral ventricle communicates with the third ventricle through the interventricular foramen (of Monroe). Most of the CSF in the CNS is produced by the choroid plexus of two lateral ventricles.
The septum pellucidum is a membranous septum separating the anterior horns of the left and right lateral ventricles of the brain. It runs as a sheet from the corpus callosum down to the fornix.
The fornix is a C-shaped bundle of nerve fibers (projection fibers) in the brain that acts as the major output tract of the hippocampus. It connects the hippocampus with the mammillary body. The fornix also carries some afferent fibers to the hippocampus from structures in the diencephalon and basal forebrain. The fornix is part of the limbic system.
The thalami are a pair of ovoid diencephalic structures located bilaterally, with respect to the third ventricle. Functionally, the thalamus is considered as the great sensory gateway (except olfactory) to the cerebral cortex. The thalami act as a relay station for afferent and efferent fibers communicating between the cortex and subcortical and structures. It is separated from the putamen by the posterior limb of the internal capsule.
The hypothalamus is a small part of the diencephalon which lies below the thalamus. It forms the floor and lower parts of lateral walls of the third ventricle. The hypothalamus controls three systems: autonomic nervous system, endocrine system and limbic system. It helps to maintain homeostasis
Foramen of Monro :
The foramen of Monroe or the interventricular foramen is a short conduit of the CSF between each of the lateral ventricles with the third ventricle of the brain.
Aqueduct of the midbrain :
The aqueduct of midbrain or the cerebral aqueduct is a conduit of the CSF that connects the third ventricle with the fourth ventricle of the brain.
The optic chiasma is the part of the brain where the optic nerves cross. It is located at the base of the brain immediately inferior to the hypothalamus.
Mammillary body :
The mammillary bodies are a pair of small round bodies, located at the base of the brain. They are located at the ends of the anterior arches of the fornix. The mammillary bodies are a part of the limbic system.