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Figure 2. Median sagittal section of the cerebral hemisphere showing major gyri
Figure 1. Lateral aspect of the cerebral hemispheres showing major gyri and sulci.
and sulci.
The cerebral hemispheres develop from the embryological telencephalon. It Is the largest part of the forebrain. The cerebral cortex is highly
convoluted and has a complex patter of ridges (gyri/gyrus) and furrows (sulci/sulcus). Gyri and sulci serve to increase the surface are of the cerebral
cortex and up to 70% of which is hidden in the depth of sulci. The cerebral cortex consist of the grey matter which is top layers layer of the cerebral
hemisphere. Underneath the grey matter there is white matter which consists of nerve fibers that pass between the cerebral cortex and subcortical
structures, and the fibers are condensed into a broad sheet – the internal capsule. Between internal capsule and cerebral cortex there are fibers that
radiate in and out and are called – the corona radiata. Within the white matter there are some embedded nuclei structures that have extensive
connections with the cerebral cortex such as caudate nucleus, putamen, and globus pallidus which compose the basal ganglia.
Within the cerebral hemisphere there is large C-shaped cavity of the lateral ventricles which are part of the ventricular system. The two cerebral
hemispheres are separated by the great longitudinal fissure which accommodates the meningeal falx cerebri. The hemispheres are connected by
the corpus callosum which is a sheet of commissural fibers which course between corresponding cerebral cortices.
• Gyri, sulci and lobes of the cerebral hemisphere
The cerebral cortex is divided into four lobes – frontal, parietal, temporal, and occipital lobes. The lateral fissure is the deepest cleft on the lateral
surface of the cerebral cortex which separates the temporal lobe below from the frontal and parietal lobe from above. Within the depth of the lateral
fissure there is insula. Opercula is the part of the frontal, parietal, and temporal lobe that overly the insula. The central sulcus marks the boundary
between the frontal and parietal lobes. The central sulcus extends onto the medial surface of the hemispheres within the great longitudinal fissure.
The frontal lobe occupies the entire region in front of the central sulcus. In front of the centra sulcus there is precentral gyrus which contains the
primary motor cortex. While the rest of the frontal lobe consists of convolutions named superior, middle, and inferior frontal gyri.
Behind the central sulcus above the lateral fissure there is parietal lobe. The anterior part of the parietal lobe contains postcentral gyrus which
corresponds to the primary somatosensory cortex. Behind the postcentral gyrus on the lateral surface of the hemisphere the intraparietal sulcus
divides the parietal lobe into superior and inferior parietal lobules.
On the lateral surface of the hemispheres there is deep parieto-occipital sulcus which marks the divide between parietal and occipital lobes. The
occipital lobe has calcarine sulcus on the medial surface which indicated position of the primary visual cortex.
The temporal lobe is located beneath the lateral fissure and merges with parietal and occipital lobes posteriorly. The temporal lobe is divides into
three principal gyri, which course parallel to the lateral fissure: the superior, middle, and inferior temporal gyri. The superior temporal gyri
correspond to the primary visual cortex. While the transverse temporal gyri and Heschel’s convolutions correspond to structures of the secondary
visual cortex which are located superiorly beneath the lateral fissure.
On the medial surface of the hemispheres, some parts of the frontal, parietal, and temporal lobes comprise the limbic system. Curving around and
coursing in parallel with corpus callosum there is cingulate gyrus which is separated from the rest of the cerebral cortex by the cingulate sulcus. The
cingulate gyrus courses posteriorly and inferiorly around the posterior part/splenium of the corpus callosum and is continuous with the
parahippocampal gyrus of the temporal lobe. Deep to the parahippocampal gyrus there is hippocampus which id formed by the curving of the
inferomedial part of the temporal lobe. The cingulate gyrus, hippocampus, and the parahippocampal gyrus comprise the limbic lobe of the cerebral
cortex.
Focal cerebra lesions
Focal cerebral lesions are stoke and tumor which produce 3 types of symptoms:
1. Focal epileptic seizures – discharge of a group/s of neurons in the cerebral cortex that produce paroxysmal attack s that last for a brief period
and reflect function of neurons involved. The patient experiences attacks of abnormal movement and sensations (simple focal seizures) or
alterations in perception, behavior, and mood (complex partial seizures). Focal seizures may trigger generalized (tonic-clonic) seizures.
2. Sensory motor deficits. Which is characterized by the loss of sensation/movement which can be detected during clinical neurological
examination.
3. Psychological deficits. Leads to the breakdown of processes such as language, perception, and memory, which can be detected during
psychological evaluation.
The focal lesion can be space occupying – the syndrome of raised intracranial pressure is the result. A unilateral cerebral hemisphere lesion
leads to mental impairments (aphasia) a contralateral spastic hemiparesis, hyperreflexia, and an extensor plantar response (upper motor neuron
lesion) and contralateral hemisensory loss. A vascular destruction to the internal capsule such as infraction or hemorrhage leads to stroke.
, Figure 4. Coronal section of the cerebral hemisphere.
Figure 3. Coronal section of the cerebral hemisphere.
Figure 6. Coronal section of the cerebral hemisphere.
Figure 5. Coronal section of the cerebral hemisphere.
Figure 8. Coronal section of the cerebral hemisphere.
Figure 7. Coronal section of the cerebral hemisphere.
Figure 9. Coronal section of the cerebral hemisphere. Figure 10. Coronal section of the cerebral hemisphere.
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