L15 Anatomy of Cerebrum PDF

L 15 ANATOMY OF CEREBRUM ILOs By the end of this session, the student should be able to: 1. Relate the different parts of cerebrum to its position inside the cranial cavity. 2. Describe general features of the cerebral hemisphere: surfaces, borders and lobes. 3. Correlate the...

L 15 ANATOMY OF CEREBRUM ILOs By the end of this session, the student should be able to: 1. Relate the different parts of cerebrum to its position inside the cranial cavity. 2. Describe general features of the cerebral hemisphere: surfaces, borders and lobes. 3. Correlate the different sulci and gyri of the cerebral cortex to their function. 4. Appraise the different cortical areas relevant to their clinical application Cortical lobes: There are four lobes of the brain: the occipital (vision), temporal (hearing), parietal (sensory) and frontal (motor) lobes. There is one other lobe that can’t be seen from the outside of the brain: the limbic lobe. The corpus callosum connects the two cortical hemispheres. Lobes of the cerebrum General features: Each cerebral hemispheres has three surfaces, and three poles. The surfaces are superolateral, medial and inferior. The poles are frontal, occipital and temporal. Page 1 of 5  Different surfaces of cerebrum Surface features: sulci and gyri: The surface of the cortex is highly convoluted and is subdivided into fissures (deep grooves), gyri (elevated folds; and sulci ; shallow grooves between folds). The longitudinal fissure separates the two cortical hemispheres. The lateral fissure (of Sylvius) separates the temporal lobe from the parietal and frontal lobes. The central sulcus separates the frontal and parietal lobes. The parieto-occipital sulcus separates parietal and occipital lobes. Cerebral lobes and main sulci separating them Page 2 of 5  On the lateral surface of the hemispheres, the boundaries between parietal, occipital and temporal lobes are established by continuing the line of the parieto-occipital sulcus downwards and the line of the posterior ramus of lateral fissure backwards to meet this line. Superolateral surface of the cerebrum: Central sulcus The central sulcus marks the position of two important functional areas: primary somatosensory cortex posterior in the postcentral gyrus and primary motor cortex anterior to this sulcus in the precentral gyrus. Both areas control the opposite side of the body. It lies between two parallel sulci (pre- and post- central sulci). Lateral Sulcus The stem appears on the inferior surface and runs to the lateral surface where it gives; anterior horizontal, anterior ascending (or superior) and posterior rami. It is a deep sulcus, where the cortex invaginates the lateral surface to give deep gray matter called the “insula” which is hidden inside. Motor speech centre (Broca’s area) lies around the ascending and horizontal rami of lateral sulcus. Central and lateral sulcus on inferior and superolateral surfaces of cerebrum Broca’s area between ascending and horizontal rami of lateral sulcus Page 3 of 5 Medial surface of the cerebrum: Cingulate gyrus: The cingulate sulcus follows the curvature of the corpus callosum, extending through both the frontal and parietal lobes. Below this sulcus is the cingulate gyrus (functionally associated with the limbic lobe). This cingulate sulcus terminates by passing upwards to form a sulcus that continues onto the lateral surface as the postcentral sulcus. The central sulcus is the sulcus anterior to this sulcus (on the lateral surface). The gyrus in between these two sulci is the postcentral gyrus, which contains the primary somatosensory cortex which control the opposite side of the body. Para central lobule: Anterior to the point where the cingulate sulcus crosses (to the lateral surface of the brain) is the paracentral lobule, which contains the lower limb, perineum primary motor and somatosensory cortical function regions controlling the opposite side of the body. Medial surface of cerebrum Calcarine sulcus: The calcarine sulcus is located at the caudal end of the medial surface of the brain. It separates the occipital lobe into two parts associated with vision: 1) lingual gyrus (inferior part) 2) cuneus (superior part) which lies posterior to parieto-occipital sulcus. Medial frontal gyrus: Medial frontal gyrus is a part of the frontal lobe that lies in front of the cingulate sulcus. Functionally, it is considered as part of the prefrontal area responsible for behavior, attention and concentration. Inferior surface of the cerebrum: The inferior surface of the cerebral hemisphere is divided by the stem of lateral sulcus into an orbital part and a tentorial part. On the inferior surface of the temporal lobe, the most medial gyrus is the parahippocampal gyrus, which expands at its anterior end to form the uncus. They are medial to collateral sulcus. These are concerned with the olfactory (smell) system and memory. Page 4 of 5  Inferior surface of cerebrum In the orbitofrontal cortex (the part that sits above the orbit in the skull) is located the olfactory gyrus. These structures form part of the limbic system, which is involved in emotional processing and perception ‫ادراك‬. Clinical notes: Lesions of the primary motor cortex in one hemisphere result in paralysis of the contralateral extremities. Lesions involving the calcarine sulcus result in a loss of vision in the opposite visual field. Page 5 of 5