Gross Anatomy of the Cerebral Hemispheres
The cerebral hemispheres make up the largest portion of the brain and are separated by a deep midline sagittal fissure called the longitudinal cerebral fissure.
The surface of each cerebral hemisphere is thrown into folds or gyri (sing: gyrus) which are separated from each other by sulci (sing: sulcus) or deeper fissures.
For descriptive purpose, the cerebral hemisphere is divided into lobes which are named according to the overlying cranial bones.
Main Sulci & Fissures
The surfaces of the cerebral hemispheres contain many fissures and sulci.
- Central sulcus
- Lateral sulcus
- Parieto-occipital sulcus
- Calcarine sulcus
These four sulci separates the cerebral lobes from each other.
- arises about the middle of the hemisphere, beginning near the longitudinal cerebral fissure
- extends downward and forward to about 2.5 cm above the lateral cerebral sulcus
- separates the frontal lobe from the parietal lobe
- separates anterior motor and posterior general sensory areas
Lateral cerebral sulcus (Sylvian sulcus)
- A deep cleft found mainly on the inferior and lateral surface of the cerebral hemisphere
- Consists of a short stem which on reaching the lateral surface divides into three rami – anterior horizontal ramus, anterior ascending ramus and posterior ramus
- separates the temporal lobe from the frontal and parietal lobes
- the insula, a portion of cortex, lies deep within the fissure.
- Circular sulcus (circuminsular sulcus) surrounds the insula and separates it from the adjacent frontal, parietal, and temporal lobes.
Parieto-occipital sulcus
- Begins on the superior medial border about 5cm anterior to occipital lobe
- passes downward and anteriorly as a deep cleft along the medial surface of the cerebral hemisphere.
- separates the parietal lobe from the occipital lobe
Calcarine sulcus
- begins on the medial surface of the hemisphere near the occipital pole
- extends forward to an area slightly below the splenium of the corpus callosum.
Lobes of the cerebral hemisphere
Frontal Lobe
The frontal lobe extends from the frontal pole to the central sulcus and the lateral fissure. The lobe is divided into four gyri by three sulci. The precentral sulcus runs parallel to the central sulcus - precentral gyrus lies between them.
The superior and inferior frontal sulci extend forward and downward from the precentral sulcus, dividing the lateral surface of the frontal lobe into three parallel gyri: the superior, middle, and inferior frontal gyri.
Frontal Lobe
The frontal lobe extends from the frontal pole to the central sulcus and the lateral fissure. The lobe is divided into four gyri by three sulci. The precentral sulcus runs parallel to the central sulcus - precentral gyrus lies between them.
The superior and inferior frontal sulci extend forward and downward from the precentral sulcus, dividing the lateral surface of the frontal lobe into three parallel gyri: the superior, middle, and inferior frontal gyri.
The inferior frontal gyrus is divided into three parts: The orbital part lies rostral to the anterior horizontal ramus; the triangular part, wedge-shaped portion lies between the anterior horizontal and anterior ascending rami; and the opercular part is between the ascending ramus and precentral sulcus.
Inferior surface of the frontal lobe presents the olfactory sulcus medial to which lies the gyrus rectus and laterally lie a number of orbital gyri.
The cingulate gyrus is the crescent-shaped, or arched, convolution on the medial surface between the cingulate sulcus and the corpus callosum.
The paracentral lobule is on the medial surface of the hemisphere and is the continuation of the precentral and postcentral gyri.
Parietal Lobe
The parietal lobe extends from the central sulcus to the parieto-occipital fissure; laterally, it extends to the level of the lateral cerebral fissure.
Presents two sulci and three gyri
The postcentral sulcus lies behind the postcentral gyrus – postcentral gyrus lies between them.
The intraparietal sulcus is a horizontal groove that runs posteriorly from the postcentral sulcus.
The superior parietal lobule lies above the horizontal portion of the intraparietal sulcus and the inferior parietal lobule lies below it.
The supramarginal gyrus is the portion of the inferior parietal lobule that arches above the ascending end of the posterior ramus of the lateral cerebral fissure. The angular gyrus arches above the end of the superior temporal sulcus and becomes continuous with the middle temporal gyrus. The precuneus is the posterior portion of the medial surface between the parieto-occipital fissure and the ascending end of the cingulate sulcus.
Occipital Lobe
The occipital lobe is situated behind the parieto-occipital fissure.
The calcarine fissure divides the medial surface of the occipital lobe into the cuneus and the lingual gyrus. The wedge-shaped cuneus lies between the calcarine and parieto-occipital fissures, and the lingual (lateral occipitotemporal) gyrus is between the calcarine fissure and the posterior part of the collateral fissure.
The cortex on the banks of the calcarine fissure (termed the striate cortex) is the site of termination of visual afferents from the lateral geniculate body; this region of cortex thus functions as the primary visual cortex. The posterior part of the medial occipitotemporal gyrus is on the basal surface of the occipital lobe.
Temporal Lobe
The temporal lobe lies below the lateral cerebral fissure and extends back to the level of the parieto-occipital fissure on the medial surface of the hemisphere.
The lateral surface of the temporal lobe is divided into the parallel superior, middle, and inferior temporal gyri, which are separated by the superior and middle temporal sulci.
The hippocampal fissure extends along the inferomedial aspect of the lobe from the area of the splenium of the corpus callosum to the uncus. The parahippocampal gyrus lies between the hippocampal fissure and the anterior part of the collateral fissure. Its anterior part, the most medial portion of the temporal lobe, curves in the form of a hook; it is known as the uncus.
Insula
The insula is a sunken portion of the cerebral cortex. It lies deep within the lateral cerebral fissure and can be exposed by separating the upper and lower lips (opercula) of the lateral fissure.
Some of the features on the medial surface of cerebral hemisphere are:
Corpus Callosum
Lateral ventricle
Thalamus
Hypothalamus
Fornix
Septum pellucidum
Cortical features
Cingulate sulcus and gyrus
Medial frontal gyrus
Paracentral lobule
Parieto-occipital sulcus
Calcarine sulcus
Cuneus and precuneus
The arterial blood supply of the brain is mainly derived from two pairs of large vessels: the internal carotid arteries, branch of the common carotids, and the vertebral arteries, which arise from the subclavian arteries.
The vertebral arterial system supplies the brain stem, cerebellum, occipital lobe of cerebrum, and parts of the thalamus, and the carotids normally supply the remainder of the forebrain.
Blood supply to cerebrum
The blood supply to cerebrum (including cortex, white matters and deeper structures) are derived from the following three arteries:
Anterior cerebral artery:
Branches and supply:
Cortical branches supply all the medial surface of the cerebral cortex upto the parieto-occipital sulcus.
Also supply a strip of cortex about 1 inch wide on the adjoining lateral surface.
Middle cerebral artery:
The largest terminal branch of the carotid artery runs laterally from the medial end of the lateral sulcus.
Branches and supply
Cortical branches supply the entire lateral surface of the hemisphere, except for the narrow strip supplied by anterior cerebral artery, the occipital pole and the inferolateral surface of the hemisphere, which are supplied by the posterior cerebral artery.
Corpus Callosum
Lateral ventricle
Thalamus
Hypothalamus
Fornix
Septum pellucidum
Cortical features
Cingulate sulcus and gyrus
Medial frontal gyrus
Paracentral lobule
Parieto-occipital sulcus
Calcarine sulcus
Cuneus and precuneus
The arterial blood supply of the brain is mainly derived from two pairs of large vessels: the internal carotid arteries, branch of the common carotids, and the vertebral arteries, which arise from the subclavian arteries.
The vertebral arterial system supplies the brain stem, cerebellum, occipital lobe of cerebrum, and parts of the thalamus, and the carotids normally supply the remainder of the forebrain.
Blood supply to cerebrum
The blood supply to cerebrum (including cortex, white matters and deeper structures) are derived from the following three arteries:
- Anterior cerebral artery
- Middle cerebral artery
- Posteriors cerebral artery
The first two are the branches from the cerebral part of internal carotid artery where as the third one is the branch of basilar artery.
Anterior cerebral artery:
Anterior cerebral artery is the smaller terminal branch of internal carotid artery. It runs forward and medially superior to the optic nerve and enters the median longitudinal fissure of the cerebrum. It is joined to the anterior cerebral artery of opposite side by the anterior communicating artery. It arches backward above the corpus callosum, and finally anastomoses with the posterior cerebral artery.
Branches and supply:
Cortical branches supply all the medial surface of the cerebral cortex upto the parieto-occipital sulcus.
Also supply a strip of cortex about 1 inch wide on the adjoining lateral surface.
Central branches supply parts of the lentiform and caudate nuclei and the internal capsule.
Middle cerebral artery:
The largest terminal branch of the carotid artery runs laterally from the medial end of the lateral sulcus.
Branches and supply
Cortical branches supply the entire lateral surface of the hemisphere, except for the narrow strip supplied by anterior cerebral artery, the occipital pole and the inferolateral surface of the hemisphere, which are supplied by the posterior cerebral artery.
Thus, MCA supplies all the motor area except for the “leg area”
Central branches supply the lentiform and caudate nuclei and the internal capsule.
Posterior cerebral artery
It curves laterally and backward around the midbrain and is joined by the posterior communicating branch of internal carotid artery.
It curves laterally and backward around the midbrain and is joined by the posterior communicating branch of internal carotid artery.
Branches and supply
Cortical branches supply the inferolateral and medial surface of temporal lobe and the lateral and medial surface of the occipital lobe.
Cortical branches supply the inferolateral and medial surface of temporal lobe and the lateral and medial surface of the occipital lobe.
Central branches supply parts of the thalamus and the lentiform nucleus and the midbrain, the
pineal and the medial geniculate bodies.
pineal and the medial geniculate bodies.
Arterial Circle of Willis
It is the arterial circle at the base of the brain which is formed by the anastomosis between the arteries of internal carotid and vertebral arteries.
It is the arterial circle at the base of the brain which is formed by the anastomosis between the arteries of internal carotid and vertebral arteries.
The participating arteries in the formation of circle are as follows:
Anteriorly – anterior communicating artery
Anterolaterally – anterior cerebral arteries and internal carotid arteries
Posterolaterally – posterior communicating arteries
Posteriorly – posterior cerebral and basilar arteries
REFERENCES:
Gray’s Anatomy, 39th Edition
Snell’s Clinical Neuroanatomy 7th Edition
Lange Clinical Neuroanatomy 25th Edition
Anteriorly – anterior communicating artery
Anterolaterally – anterior cerebral arteries and internal carotid arteries
Posterolaterally – posterior communicating arteries
Posteriorly – posterior cerebral and basilar arteries
REFERENCES:
Gray’s Anatomy, 39th Edition
Snell’s Clinical Neuroanatomy 7th Edition
Lange Clinical Neuroanatomy 25th Edition