Cerebrum (General Features) PDF

The base of the brain Central region of the base of the brain Anterior part of the base of the brain Position of the Cerebral Hemisphere Position of the Cerebral Hemisphere The Cerebral Hemisphere  The Cerebral Hemisphere Position: - The 2 cerebral hemispheres are sepa...

The base of the brain Central region of the base of the brain Anterior part of the base of the brain Position of the Cerebral Hemisphere Position of the Cerebral Hemisphere The Cerebral Hemisphere  The Cerebral Hemisphere Position: - The 2 cerebral hemispheres are separated from each other by a median longitudinal cerebral fissure into which the falx cerebri projects down from the vault of the skull. At the floor of this fissure lies the corpus callosum which connects the 2 cerebral hemispheres together.  The Cerebral Hemisphere Position: - The frontal lobe occupies the anterior cranial fossa. - The temporal lobe occupies the lateral part of the middle cranial fossa. - The occipital lobe occupies the upper part of the posterior cranial fossa above the cerebellum with the tentorium cerebelli In between.  Surfaces of Cerebral Hemisphere Surfaces: Each cerebral hemisphere has 3 surfaces: i. Lateral (supero-lateral) surface: convex. ii. Medial surface: flat. iii. Inferior surface: irregular. Divided into orbital and tentorial parts. Orbital Tentorial  Surfaces and borders of Cerebral Hemisphere Borders: i. An arched superior (supero-medial) border: separates the lateral from the medial surfaces. ii. A curved superciliary border: separates the lateral from the inferior surfaces in the anterior cranial fossa. iii. The inferior (infero-lateral) borders: separates the lateral from the inferior surfaces in the middle and posterior cranial fossae. A slight depression called the preoccipital notch is seen on this border about 2 inches in front of the occipital pole.  4. Division of the hemisphere into lobes A- The sulci which divide the hemisphere into lobes: 3 major sulci or fissures: i. The central sulcus: - It runs obliquely downwards and forwards across the lateral surface of the hemisphere. - It extends from a point in the middle of the superior border down to a point immediately above the middle of the posterior ramus of lateral fissure. - Its upper end usually cuts the upper border of the hemisphere and turns down a little on the medial surface of the hemisphere (Paracentral lobule). - It separates the motor area (in the frontal lobe) from the sensory area (in the parietal lobe).  4. Division of the hemisphere into lobes ii. The lateral fissure: - It extends laterally between the temporal and the frontal lobes to reach the lateral surface of the hemisphere where it divides into 3 rami: a. The posterior ramus: Is the longest; runs backwards on the lateral surface almost parallel to the inferior border. Its posterior end turns upwards cutting into the parietal lobe. b. The anterior horizontal ramus: 2 cm runs forwards in the frontal lobe. c. The anterior ascending ramus: 2 cm runs upwards in the frontal lobe.  4. Division of the hemisphere into lobes iii. The parieto-occipital sulcus: - It is a deep sulcus found on the medial surface of the hemisphere, it extends for short distance on the lateral surface between the parietal and occipital lobes. Lobes of the hemisphere into lobes F P O T  Lobes of the hemisphere into lobes Each hemisphere is divided into 4 lobes and the insula. They are: i. The frontal lobe: Is bounded by: - The central sulcus…………….. (behind). - The superior border…………. (above). - The superciliary border……. (below). - Frontal pole…………………….. (in front). ii. The parietal lobe: Is a quadrilateral area bounded by: - The central sulcus……………… (in front). - The upper border……………… (above). - The upper 1/2 of the line joining the parieto-occipital sulcus and the pre- occipital notch………………… (behind). - The posterior ramus of lateral fissure and a line joining the posterior ramus with the middle of the line between the parieto-occipital sulcus and the preoccipital notch……………… (below).  Lobes of the hemisphere into lobes iii. The occipital lobe: Forms the posterior extremity of the lateral surface of the hemisphere; it lies behind an imaginary line drawn from the upper end of the parieto-occipital sulcus down to the preoccipital notch. It is bounded posteriorly by the occipital pole. iv. The temporal lobe: Is bounded by: - The inferior border……………………. (below). - The posterior ramus of the lateral fissure……………………………………… (above). - The lower 1/2 of the line joining the parieto-occipital sulcus and the pre- occipital notch……………………… (behind). - Temporal pole……………………….. (in front). v. The insula: Is a submerged part of the cortex which lies in the bottom of the posterior ramus of the lateral fissure. Lobes of the hemisphere into lobes F P O T