Lecture: 2 Dr. Eyad M. Hussein Cerebral Hemispheres Ph.D of Neurology Consultant in Neurology Department, Nasser Hospital, Assistant Professor, Faculty of Medicine, Islamic University Faculty of Dentistry, University of Palestine

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The Cranial Fossa The cranium is divided into three regions (fossa): 1. Anterior Cranial Fossa: house for frontal lobes. 2. Middle Cranial Fossa: house for temporal lobes. 3. Posterior Cranial Fossa: house for occipital lobes, cerebellum and brain stem.

Morphological Subdivisions of the Brain - It is contains about one trillion cells (100 billion neurons and 900 billion neuroglial cells). - The adult brain weight is about 1200 – 1500 g . - The brain reaches full size about 18 year age. - It is formed of: Cerebrum: - Is the largest part of the brain that located above the tentorium cerebelli and orbit. - It consists of two cerebral hemispheres connected together by the corpus callosum. 2. Cerebellum: - Is a large mass of brain tissue which located in the posterior cranial fossa below the tentorium cerebelli and behind brain stem.

3. Diencephalon: - Is located between the two cerebral hemispheres and above the midbrain. 4. Brain Stem: - Is the part of brain located below the diencephalon and in the front of the cerebellum. - Is connected the cerebellum by three pairs of cerebellar peduncles. - Connects the two cerebral hemispheres with the spinal cord. - It consists of three parts, from below upwards: a. Medulla oblongata b. Pons c. Midbrain

The Cerebrum (Cerebral Hemisphere) Site: occupies most of cranial cavity and it is the large part of the brain. The cerebrum formed of two cerebral hemispheres by a median longitudinal fissure, connected to each other by: The corpus callosum. Right and left cerebral peduncles: connected to upper part of the brain stem. Anterior, posterior & habenular commissures

The Commissural Fibers

The Cerebrum (Cerebral Hemisphere)

Integrative Function of the Cerebral Cortex Consciousness: (brain stem-reticular formation, frontal, temporal and deep structures of cerebrum). Use of language: speech center present in frontal and temporal lobes (in 90-95% of population the centre is present in the left hemisphere). Emotions: frontal and temporal lobes (limbic system). Memory: frontal and temporal lobes Orientation, thinking and intelligence: frontal lobe.

External Feature of the Cerebrum Each cerebral hemisphere has: Three surfaces. Three poles. Five borders.

Surfaces of Each Cerebral Hemisphere Each cerebral hemisphere has 3 surfaces: Lateral (superolateral) surface. Medial surface. Inferior surface.

Surfaces of Each Cerebral Hemisphere

Poles of Each Cerebral Hemisphere Each cerebral hemisphere has 3 poles: 1. Frontal pole: at the anterior end of the frontal lobe. 2. Temporal pole: at the anterior end of the temporal lobe. 3. Occipital pole: at the posterior end of the occipital lobe.

Poles of Each Cerebral Hemisphere

Lobes of Each Cerebral Hemisphere The surface of each cerebral hemisphere is divided by three main sulci or fissures into four lobes (which have been given the names of the skull bones under which they lie). These four lobes are: 1. The frontal. 2. The parietal. 3. The temporal. 4. The occipital. Each surface of lobes is divided by sulci into gyri.

The Important Sulci of Cerebral Hemisphere The longitudinal fissure divides the cerebrum into two hemispheres. Each cerebral hemisphere is divided by sulci (grooves) into gyri. 1. The central sulcus (Roland sulcus): it separates the frontal lobe (in front) from parietal lobe (behind). 2. The lateral sulcus (Sylvian sulcus): between frontal and parietal lobes (above) and temporal lobe (below). 3. The parieto-occipital sulcus: it found mainly on the medial surface of the hemisphere between parietal and occipital lobes.

Sulci of Each Cerebral Hemisphere

Cortical Somatotopy

Cortical Somatotopy

The Important Sulci of Frontal Lobe The important sulci of frontal lobe are: The precentral sulcus: it present in front of the central sulcus. The superior frontal sulcus: present in front of the precentral sulcus (superior part of the frontal lobe). The inferior frontal sulcus: present in front of the precentral sulcus (inferior part of the frontal lobe).

Sulci of Each Cerebral Hemisphere

The Important Gyri of Frontal Lobe 1. The precentral gyrus: between the central and precentral sulci. 2. The superior frontal gyrus: above the superior frontal sulcus. 3. The middle frontal gyrus: between the superior and inferior frontal sulci. 4. The inferior frontal gyrus: below the inferior frontal

Lobes of Each Cerebral Hemisphere

The Important Functional Areas of the Frontal Lobe Site Areas Voluntary motor activity of opposite 1/2 of the body Precentral gyrus Primary motor area (4) Gives extrapyramidal fibers Anterior part of precentral gyrus Secondary motor (Premotor) area (6) Voluntary conjugate deviation of eyes to opposite side Middle frontal gyrus Frontal eye conjugate (8) Motor center of writing. Inferior frontal gyrus in dominant hemisphere Area (45) Motor center of speech. Brocca's area (44) Higher center of memory, orientation, thinking and intelligence Anterior pole Prefrontal Areas(9, 10, 11 & 12)

Areas of Cerebral Cortex

The Important Sulci of Parietal Lobe The important sulci of parietal lobe are: The postcentral sulcus: it present behind the central sulcus. The intraparietal sulcus.

Sulci of Each Cerebral Hemisphere

Important Gyri of Parietal Lobe The postcentral gyrus: its the main gyrus of parietal lobe, between the central and postcentral sulci. The superior parietal gyrus: above the intraparietal sulcus. The inferior parietal gyrus: below the intraparietal sulcus. The supramarginal gyrus: small gyrus surrounding the upper end of lateral sulcus. The angular: small gyrus surrounding the upper end of the superior temporal sulcus.

Lobes of Each Cerebral Hemisphere

The Important Functional Areas of the Parietal Lobe Site Areas Perception of cortical sensation from opposite 1/2 of the body Post central gyrus Primary sensory area (1,2,3) Knowing the meaning of the sensations felt (steriognosis) in absence of sensory loss Superior parietal gyrus Areas 5& 7 Visual psychic area for speech (recognition of letters & numbers). Surround the upper end of superior temporal sulcus in dominant hemisphere Angular gyrus, area (39) Associative area and center for complex movement. Surround the upper end of lateral sulcus Supramarginal gyrus, area (40)

Areas of Cerebral Cortex

The Important Sulci of Temporal Lobe The superior temporal sulcus: below the lateral sulcus. The inferior temporal sulcus.

Important Gyri of Temporal Lobe The superior temporal gyrus: lies between the lateral sulcus and the superior temporal sulcus. The middle temporal gyrus: lies between the superior and inferior temporal sulcus. The inferior temporal gyrus: lies below the inferior temporal sulcus.

Lobes of Each Cerebral Hemisphere

The Important Functional Areas of the Temporal Lobe Site Areas Auditory sensory area In the superior temporal gyrus Primary auditory (area 41,42) Auditory association area (recognition & recall of sounds). In the superior temporal lobe of dominant hemisphere Sensory speech area or Wernicke's center (area 22) Uncus: sense of smell Hipocampus: mood & memory Uncus and hypocampus in the medial and inferior surface of the temporal lobe Limbic system

Areas of Cerebral Cortex

The Important Sulci of Occipital Lobe The calcarine sulcus: lies on the medial surface of the occipital lobe and extends backwards to the occipital pole. The lateral occipital sulcus: is a short horizontal sulcus running on the middle of the superolateral surface of the occipital lobe.

Sulci of the Cerebral Hemisphere

Important Gyri of Occipital Lobe The superior occipital gyrus: above the lateral occipital sulcus. The inferior occipital gyrus: below the lateral occipital sulcus.

Lobes of Each Cerebral Hemisphere

The Important Functional Areas of the Occipital Lobe Site Areas Visual sensory area (perception of visual impulses) Posterior medial part of occipital lobe (surrounds calcarine sulcus) Primary visual sensory area (17) Visual association area (Recognition & recall of image). Anterior to area 17 in dominant hemisphere Secondary (psychic) visual area (18, 19)

The Occipital Lobe

Areas of Cerebral Cortex

Areas of the Occipital Lobe

The Insula The insula is a part of the cerebral cortex which is hidden in the bottom of lateral sulcus. The insula is subdivided two long gyri (behind) and 3-4 short gyri (in front). Function of the insula: cortical taste center and some visceral activities (e.g. salivation).

Internal Structure of the Cerebrum The cerebral hemispheres consists of : Gray Mater (outer): composed of nerve cells (cerebral cortex). The cells of each area has specific functions. White Mater (inner): composed of nerve fibers conducting impulses to and from the cortex. Basal Nuclei: there are several groups of nuclei situated at various levels within the white mater. Lateral Ventricle: the cavity of the cerebral hemisphere.

Internal Structures of the Cerebral Hemispheres

The Layers of the Cerebral Cortex Molecular layer. External granular layer. External pyramidal layer. Internal granular layer. Internal pyramidal (ganglionic) layer. Multiform layer.

The Layers of the Cerebral Cortex Betz cells

The White Mater of the Cerebrum Consists of myelinated nerve fibers . There are three types of fibers in the white mater: Projection fibers: They connect the cerebral cortex with the lower subcortical centers. Association fibers: They connects different areas of the same cerebral hemisphere . Commissural fibers: They connect similar areas of both hemispheres.

The Projection Fibers Definition: they are afferent and efferent fibers (tracts) of the cerebral cortex which connect the cerebral cortex with the lower part of the brain and spinal cord (e.g. pyramidal tract). Types of the Projection Fibers: Ascending (afferent or sensory): to the cerebral cortex from the thalamus. Descending (efferent or motor): from the cerebral cortex to lower centers.

The Association Fibers Definition: they are fibers which connect the different cortical areas in the same hemisphere. Types of Association Fibers: Short association fibers: they connect adjacent gyri with one another. Long association fibers: connect the different lobes of the hemisphere together.

The Commissural Fibers Definition and function: is a band of white mater (nerve fibers) connecting and coordinating of activates of the right and left hemisphere. The Commissural Fibers Include: Corpus callosum. Anterior commissure. Posterior commissure. Habenular commissure. Hippocampal commissure.

The Commissural Fibers

Internal Capsule It is a thick lamina of white matter made up of projection fibers which pass to and from the cerebral cortex. It is continuous superiorly with the corona radiata, and inferiorly with pedunculi of midbrain. Parts of Internal Capsule: Anterior limb. Genu. Posterior limb.

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