Anatomy of the cerebral hemispheres Dr. Mohammed Abuelnour اسم ورقم المقرر – Course Name and No. 6/30/2019

At the end of the lecture, the students should be able to: Objectives: At the end of the lecture, the students should be able to: Describe the cerebral hemispheres: shape, surfaces and subdivision into lobes Identify the important sulci and gyri of each lobe Describe the internal structure of each hemisphere: cortex (grey matter), medulla (white matter), basal ganglia, lateral ventricle Describe the functional areas of the cerebral cortex. Describe different types of fibers in the hemisphere and their functions اسم ورقم المقرر – Course Name and No. 6/30/2019

Cerebrum Largest part of the forebrain Corpus callosum Cerebrum Largest part of the forebrain Divided into two halves, the cerebral hemipheres The two hemispheres are separated by a deep median longitudinal fissure . the hemispheres are connected by the corpus callosum Left hemisphere Right hemisphere Median longitudinal fissure اسم ورقم المقرر – Course Name and No. 6/30/2019

The surface of each hemisphere are numerous FOLDS. These folds are separated by grooves to increase the Surface Area of the Cerebrum. The folds are called GYRI, and the grooves are called SULCUS.

SURFACES Superolateral Surfaces: Medial Inferior Each hemisphere has 3 surfaces, 4 borders, 4 Lobes. Surfaces: Lateral or superolateral: Convex and related to the skull. Medial: Flat & vertical and related to the falx cerebri & median longitudinal fissure. Inferior: Divided into orbital and tentorial parts by the of lateral sulcus. Superolateral Medial Inferior اسم ورقم المقرر – Course Name and No. 6/30/2019

BORDERS Four borders: 1- Medial or Superomedial border: Between lateral & medial surfaces. 2- Inferolateral border: Between lateral & inferior surfaces. 3- Inferiomedial border: Between inferior & medial surfaces. اسم ورقم المقرر – Course Name and No. 6/30/2019

Three sulci, are used to divide each hemisphere into lobes. These include: Central sulcus & Lateral sulcus on the superolateral surface Parieto-occipital sulcus, on the medial surface

Central sulcus Separates the frontal lobe from parietal lobe Lateral sulcus Separates the temporal lobe from the frontal and parietal lobes Parieto-occipital sulcus Separates the occipital lobe from the parietal lobe on the medial surface F P T F P O

Medial Surface Sulci: Parietooccipital , Calcarine, Cingulate Gyri: Cingulate, Parahippocam pal اسم ورقم المقرر – Course Name and No. 6/30/2019

Each hemisphere is divide into FOUR lobes (named after overlying bones) motor function, motivation, aggression, smell and mood reception and evaluation of sensory information visual processing smell, hearing, memory and abstract thought

Frontal lobe: Precentral gyrus Superior & inferior frontal sulci divide the lobe into superior, middle & inferior frontal gyri Parietal lobe: Postcentral gyrus Intraparietal sulcus dividing the lobe into superior & inferior parietal lobules Superior , middle & inferior frontal gyri Precentral gyrus Postcentral gyrus sfs ifs Inferior parietal lobule Superior parietal lobule Intraparietal sulcus

The gyri in the depth of lateral fissure, Superior, middle & inferior temporal gyri Temporal lobe: Superior & inferior temporal sulci giving rise to superior, middle & inferior temporal gyri Insula: The gyri in the depth of lateral fissure, sts its insula

Frontal Lobe Functional Areas of the Cerebral Cortex Primary motor cortex Located in precentral gyrus (Brodmann area 4) Controls voluntary, skilled movements

Premotor cortex (Brodmann’s area 6) On the lateral surface, this includes the posterior parts of superior, middle and inferior frontal gyri On the medial surface, it includes region of supplementary motor cortex.

Frontal eye field Located in the middle frontal gyrus (Brodmann’s area 8) Controls voluntary conjugate deviation of the eyes . Damage to this area results in conjugate deviation of the eyes toward the side of lesion

Broca’s (motor speech) area Located in the inferior frontal gyrus of the dominant hemisphere (usually left) Brodmann’s area 44 & 45 Involved in language functions Interconnected with parts of ipsilateral temporal, parietal and occipital lobes

Prefrontal cortex Extensive region of the frontal lobe anterior to premotor area Has cognitive functions of high order e.g. intellectual, judgemental and the planning of behaviour

Parietal lobe Primary sensory cortex Located in postcentral gyrus (Brodmann’s area 1, 2, 3) It is the final relay station for general sensations to a conscious level اسم ورقم المقرر – Course Name and No. 6/30/2019

Parietal association cortex Located posterior to primary sensory cortex Superior parietal lobule responsible for: Interpretation of general sensory information Conscious Inferior parietal lobule between somatosensoryy cortex and the visual & auditory cortices (and speech area in dominant hemisphere)

Temporal Lobe Primary auditory cortex Located in the superior temporal gyrus (Brodmann’s area 41, 42) Responsible for perception of sound There is bilateral, representation of the cochlear duct اسم ورقم المقرر – Course Name and No. 6/30/2019

Auditory association cortex Located posterior to the primary auditory cortex It is called Wernick’s area in dominant hemisphere Plays major role in understanding of the spoken words.

Parahippocampal gyrus: Located in the inferomedial part of temporal lobe Deep to this gyrus lies the hippocampus and the amygdala, which are parts of limbic system

Responsible for visual perception Occipital Lobe Primary visual cortex Located on the medial, in the gyri surrounding the calcarine sulcus (Brodmann’s area 17) Responsible for visual perception Upper half of visual field represented below the calcarine sulcus, and the lower half above the sulcus

Visual association cortex Responsible for the interpretation of visual images Lesion results in deficits in visual interpretation and recognition

Organized around the lateral fissure Language Area Organized around the lateral fissure Broca’s area: concerned with expressive aspects of language Wernick’s area: responsible for comprehension of the spoken words

The structure of cerebral hemipheres includes: Superficial layer of grey matter, the cerebral cortex Deeper to the cortex, an extensive mass of white matter within the white matter lie a number of nuclear masses known as the basal ganglia Cortex Basal ganglia WM WM

White Matter Underlies the cortex Contains: Nerve fibers Neuroglia Blood vessels The nerve fibers originate, terminate or sometimes both, within the cortex

Depending on their origin & termination, these nerve fibers are classified into three types: Association B. Projection C. Commissural

Association Fibers connect different parts of the same hemisphere Are of two kinds: Short association fibers: those connecting adjacent gyri, Long association fibers: those connecting more distant gyri اسم ورقم المقرر – Course Name and No. 6/30/2019

Connect the corresponding regions of the two hemispheres Commissural Fibers Connect the corresponding regions of the two hemispheres Include: Corpus callosum Anterior commissure Hippocampal commissure (commissure of fornix) *(Posterior commissure, not a cerebral commissure) Corpus Callosum F P اسم ورقم المقرر – Course Name and No. 6/30/2019

Projection Fibers Fibers running vertically through the hemispheres Consist of: Cortical afferent fibers conveying impulses to the cerebral cortex: (mainly thalamo-cortical fibers) Cortical efferent fibers carrying impulses away from the cortex to the lower centers:, corticobulbar, corticopontine, corticospinal, & descending autonomic fibers) اسم ورقم المقرر – Course Name and No. 6/30/2019

Internal Capsule BG Bundle of projection fibers, passes through the interval between the thalamus and the basal ganglia Th 6/30/2019

References Clinical Neuroanatomy for Medical Students, Richard S. Snell-6th Edition. Clinical Neuroanatomy and related neuroscience. M.J.T. FitzGerald, Jean Folan-Curran, Fourth Edition.