The Cerebrum (The Cerebral Hemispheres) NEUROANATOMY Lecture : 2 The Cerebrum (The Cerebral Hemispheres) Prepared and presented by: Dr. Iyad Mousa Hussein, MD, Ph.D in Neurology Head of Neurology Department Nasser Hospital

LECTURE OBJECTIVES: Morphological subdivisions of the brain. Lobes and sulci of each cerebral hemisphere. The Important sulci, gyri, and functional areas of the frontal Lobe. The Important Sulci, gyri, and functional areas of the parietal lobe. The Important sulci, gyri, and functional areas of the temporal lobe. The Important sulci, gyri, and functional areas of the occipital lobe. The Internal structures of the cerebral hemispheres. The layers of the cerebral cortex. The white mater of the cerebral hemisphere.

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 medulla oblongata.

Morphological Subdivisions of the Brain The brain is the intracranial part of the CNS and formed of: 1. The Cerebrum: formed of right and left cerebral hemisphere. 2. The Cerebellum: below the posterior part of the cerebrum. 3. The Brain Stem: formed of the following parts (from downward): Medulla oblongata. Pons. Midbrain.

The Cerebrum (Cerebral Hemisphere)

The Cerebrum (Cerebral Hemisphere) Site: occupies most of cranial cavity and it is the larges part of the brain. The cerebrum formed of two cerebral hemispheres, connected to each other by: The corpus callosum. Right and left cerebral peduncles: connected to upper part of the brain stem.

The Cerebrum (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.

Lobes of Each Cerebral Hemisphere

Lobes of Each Cerebral Hemisphere

Sulci of Each Cerebral Hemisphere The longitudinal fissure: divides the cerebrum into two hemispheres. 2. The central sulcus (Roland sulcus): it separates the frontal lobe (infront of it) from parietal lobe (behind it). 3. The lateral sulcus (Sylvian sulcus): between frontal and parietal lobes (above) and temporal lobe (below). 4. The parieto-occipital sulcus: it found mainly on the medial surface of the hemisphere between parietal and occipital lobes.

Sulci of the Cerebral Hemisphere

Sulci of the Cerebral Hemisphere

Sulci of the Cerebral Hemisphere

Sulci of the Cerebral Hemisphere

A. The Frontal Lobe The Important Sulci of the Frontal Lobe: The precentral sulcus. The superior frontal sulcus. The inferior frontal sulcus.

Sulci or Fissures of the Frontal Lobe

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

The Important Gyri of the Frontal Lobe

The Important Functional Areas of the Frontal Lobe Lesion Function Site Areas Irritative: contralateral motor Jaksonian fit Destructive: contralateral motor paresis usually affecting one limb (monoplegia) Voluntary motor activity of opposite 1/2 of the body Precentral gyrus Primary motor area (4) Contralateral muscle hypertonia & exaggerated deep reflexes +ve pathological reflex Gives extrapyramidal fibers Anterior part of precentral gyrus Secondary motor (Premotor) area (6) Irritative: conjugate deviation of eyes to the opposite side Destructive: conjugate deviation of eyes to the same side. Voluntary conjugate deviation of eyes to opposite side Middle frontal gyrus Frontal eye field (8) Agraphia: the pt. is unable to express ideas in written words Motor center of writing. In dominant hemisphere. Inferior frontal gyrus in dominant hemisphere Area (45) Motor (expressive or Brocca's or verbal) aphasia: the pt. unable to express idea in spoken words Motor center of speech. In dominant hemisphere Brocca's area (44) Amnesia (impaired of memory); Dementia; Sphencteric dysfunction; Loss of personal hygiene Higher center of memory, orientation, thinking and intelligence Anterior pole Prefrontal Areas(9, 10, 11 & 12)

Areas of the Frontal lobe

Areas of the Frontal lobe

Cortical Somatotopy

Cortical Somatotopy

B. The Parietal Lobe The Important Sulci of the Parietal Lobe: The postcentral sulcus. The intraparietal sulcus.

Important Gyri of the Parietal Lobe The postcentral gyrus: its the main gyrus of parietal lobe, lies between the central and postcentral sulci. The superior parietal gyrus: lies above the intraparietal sulcus. The inferior parietal gyrus: lies 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 temporal sulcus.

Sulci of the parietal lobe

The Important Gyri of the Parietal Lobe

The Important Functional Areas of the Parietal Lobe Lesion Function Site Areas Irritative: contralateral sensory Jaksonian fit (numbness, paresthesia) Destructive: contralateral sensory loss of cortical sensation usually affecting one limb (monoanesthesia) Perception of cortical sensation from opposite 1/2 of the body Post central gyrus Primary sensory area (1,2,3) Asteriognosis: inability to recognize the felt objects Knowing the meaning of the sensations felt (by associating the visual, auditory and tactile sensation) Superior parietal gyrus Areas 5& 7 Visual aphasia (alexia): the pt. can not read because he does not understand letter & number (word blindness) Visual psychic area for speech (recognition of letters & numbers). In dominant hemisphere. Surround the upper end of superior temporal sulcus in dominant hemisphere Angular gyrus, area (39) Apraxia: inability to perform complex motor activity in absence of paresis and sensory loss or incoordination Center for complex movement. In dominant hemisphere Surround the upper end of lateral sulcus Supramarginal gyrus, area (40)

Areas of the Parietal lobe

Areas of the Parietal lobe

C. The Temporal Lobe The Important Sulci of the Temporal Lobe: The superior temporal sulcus. The middle temporal sulcus.

Important Gyri of the 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 middle temporal sulcus. The inferior temporal gyrus: lies below the middle temporal sulcus.

The Important Gyri of the Temporal Lobe

The Important Gyri of the Temporal Lobe

The Important Functional Areas of the Temporal Lobe Lesion Function Site Areas Irritative: auditory hallucination Destructive: Unilateral lesion of temporal lobe does not cause deafness as the sense of hearing is bilaterally represented Auditory sensory area In the middle part of the superior temporal gyrus Primary (area 41,42) and secondary (area 22) auditory center Auditory agnosia (sensory or Wernicke's aphasia): the pt. hears but does not understand sound Auditory association area (recognition & recall of sounds). In dominant hemisphere. In the superior temporal lobe of dominant hemisphere Sensory speech area or Wernicke's center Uncus: Irritative: olfactory hallucination Destructive: Unilateral lesion of temporal lobe does not cause anosmia as the sense of smell is bilaterally represented b. Hipocampus: Temporal epilepsy and amnesia to recent events Uncus: sense of smell Hipocampus: mood & memory Uncus and hypocampus in the medial and inferior surface of the temporal lobe Limbic system

Areas of the Temporal lobe

Areas of the Temporal lobe

D. The Occipital Lobe The main part of the occipital lobe lies on the medial surface. Only a small part appears on the lateral surface and presents one sulcus called the transverse occipital (calcarine) sulcus.

The Occipital Lobe

The Occipital lobe

The Occipital lobe

The Important Functional Areas of the Occipital Lobe Lesion Function Site Areas Irritative: visual hallucination Destructive: contralateral homonymous hemianopia with macular sparing Visual sensory area (perception of visual impulses) Posterior medial part of occipital lobe (surrounds calcarine sulcus) Primary visual sensory area (17) Visual agnosia: patient can see but does not recognize objects Visual association area (Recognition & recall of image). In dominant hemisphere Anterior to area 17 in dominant hemisphere Secondary (psychic) visual area (18, 19)

Areas of the Occipital Lobe

Areas of the Occipital Lobe

Internal Structures of the Cerebral Hemispheres 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 Ganglia: 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 layer. Multiform layer.

The Layers of the Cerebral Cortex

The White Mater of the Cerebral Hemisphere Consists of myelinated nerve fibers . There are three types of fibers in the white mater: Projection fibers. Commissural fibers. Association fibers.

The Projection Fibers Definition: they are afferent and efferent fibers of the cerebral cortex which pass through the internal capsule and connect the cerebral cortex with lower centers. 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 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: The corpus callosum: connect the two cerebral hemisphere. The anterior commissure: connect the two cerebral hemisphere. The posterior commissure: between the two side of the midbrain. The habenular commissure: between the right and left habenular nuclei and epithalamus.

The Commissural Fibers

The Association Fibers Definition: they are fibers which connect the different cortical areas in the same hemisphere. Function: they interrelate the functions of the different areas of the cortex and integrate the activities of cortex as a whole. 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.

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