Cerebrum-Cerebral Hemispheres. Cuneyt Mirzanli Istanbul Gelisim University

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1 Cerebrum-Cerebral Hemispheres Cuneyt Mirzanli Istanbul Gelisim University

2 The largest part of the brain. Ovoid shape. Two incompletely separated cerebral hemispheres.

3 The outer surface of the cerebral hemisphere is covered with cortex, which is highly folded due to the presence of sulci and gyri.

4 The core of the hemisphere consists of white matter containing a group of nuclei called basal ganglia. The cavity inside each hemisphere is called the lateral ventricle.

5 The median longitudinal fissure of cerebrum intervenes between the medial surfaces of the right and left hemispheres. At the bottom of the fissure lies the corpus callosum, which is a connecting bond between the two hemispheres.

6 The surface of the cerebral hemisphere is covered by a thin layer of grey matter called the cerebral cortex. The cortex follows the irregular contour of the sulci and gyri of the hemisphere and extends into the depths of the sulci.

7 As a result of this folding of the cerebral surface, the cerebral cortex acquires a much larger surface area than the size of the hemispheres would otherwise allow.

8 The greater part of the cerebral hemisphere deep to the cortex is occupied by white matter, within which are embedded certain important masses of grey matter.

9 Borders A coronal section through the cerebral hemispheres shows that each hemisphere has three borders: superomedial, inferolateral, and inferomedial.

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11 Lobes There are four lobes, namely frontal, parietal, occipital, and temporal, which are well demarcated on the superolateral surface.

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13 Frontal Lobe Located at the front of both cerebral hemispheres Primary motor cortex Pre-motor cortex Broca s Area- motor production of speech Complex Functioning- personality, judgement, insight, reasoning, problem solving, abstract thinking and working memory.

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16 Parietal lobe Located behind frontal lobe. Somatosensory cortex. Spatial orientation, perception and comprehension of language function recognising object by touch. Links visual and somatosensory information together.

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19 Temporal Lobes Located at each side of the brain Involved in receiving and processing auditory information, higher order visual information, complex aspects of memory and language Wernicke s Area- comprehension of speech.

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23 Speech Werniche s area: concerned with understanding language, left cerebral hemisphere, temporal lobe. Broca s area: concerned with controlling the muscles that produce speech, left cerebrale hemisphere, frontal lobe.

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25 Occipital lobes Rearmost portion of the brain Visual processing area

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27 Visual Processing The visual sensory area is at the back of the brain in occipital lobes. Receives sensory input from the optic nerves The 2 hemispheres see slightly different images from the opposite of the visual field, these differences can be used to judge distance

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30 Structure of Cerebral Cortex The cerebral cortex contains the cell bodies of an innumerable number of neurons along with their processes, neuroglia and blood vessels.

31 Pyramidal Cells The most abundant type of cortical neurons. All other neurons in the cortex are referred to as nonpyramidal neurons. Their cell bodies are triangular, The axon arises from the base of the pyramid.

32 The axon of a pyramidal cell may terminate in one of the following ways: It may travel to other regions like the basal ganglia, the brainstem or the spinal cord. It may cross to the opposite side and reach the corresponding region of the opposite hemisphere.

33 It may enter the white matter to travel to another part of the cortex. It may be short and may terminate within the same area of the cortex. The neurotransmitter used by pyramidal cells is either glutamate or aspartate.

34 Stellate Cells The stellate neurons are relatively small and multipolar. They form about one-third of the total neuronal population of the cortex.

35 Fusiform cells The fusiform cells have their long axis vertical to the surface and are concentrated mainly in the deepest cortical layers.

36 Horizontal Cells The horizontal cells are small, fusiform, horizontally oriented cells found in the most superficial layers of the cortex.

37 Martinotti Cells The cells of Martinotti are small,multipolar cells that are present throughout the levels of the cortex.

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39 Functional Areas of Cerebral Cortex Some areas of the cerebral cortex can be assigned specific functions. These areas can be defined in terms of known sulci and gyri. However, some areas are commonly referred to by numbers. The best known scheme is that of Brodmann who represented different areas by numbers.

40 The human brain is the site of the major coordination in the nervous system. There are three areas for coordination: Sensory areas Motor areas Association areas

41 Sensory Areas Sensory areas of the cerebral hemispheres receive impulses from sense organs, and transmit them association areas.

42 Motor Areas The motor areas transmit impulses to the effectors. The size of the motor and sensory areas is related to the numbers of receptors in that area.

43 Association Areas The association areas of the cerebral hemispheres receive impulses, interpret them in the light of past experiences, and transmit impulses to the effectors. used to compare sensory input with previous experiences and make decisions

44 These areas are involved in speech, understanding and memory retrieval. The frontal lobes are large in humans and it is thought that they responsible for higher functions like thought, personality & emotion.

45 Sensory & Motor Maps The maps show that regions of the body with many sensory (or motor) neurones have corresponding large areas of the cerebrum linked to them. for example the lips occupy a larger region of the sensory cortex than the shoulder, because there are more sensory neurones in the lips.

46 s ho u ld er s ho u ld er Mapping of the sensory & motor areas to the body toes genitalia legs t ru n k h ip fot Sensory Cortex e lb ow fo r wr i e ar m s t h an d fin ge rs t hum b eye n ose face lip s gum s jaw tr un k h ip legs ankle toes M otor Cortex el bo w w ris t h a n d f ing ers th um b n ec k e ye fac e li ps j aw p haryn x to n gu e s w al owin g a bdo m en c hewing ton gu e

47 CORTICAL AREAS Different areas of the cerebral cortex are functionally specialized. The precise division of the cortex into different areas of specialization is simplified by Brodmann.

48 Korbinian Brodmann

49 Brodmann's areas of the cerebral cortex have unique architectural characteristics in terms of the thickness and layering of the cerebral cortex. His numbering of cortical areas is still used as a shorthand for describing the functional regions of the cortex, particularly those related to sensory functions.

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54 Frontal Lobe: The precentral area may be divided into posterior and anterior regions. The posterior region which is referred to as the motor area, primary motor area or Brodmann area 4, occupies the precentral gyrus extending over the superior border into the paracentral lobule.

55 The anterior region is known as the premotor area, secondary motor area or Brodmann area 6 and parts of areas 8, 44, and 45. It occupies the anterior part of the precentral gyrus.

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57 The primary motor area, if electrically stimulated, produces isolated movements on the opposite side of the body as well as contraction of muscle groups concerned with the performance of a specific movement.

58 The movement areas of the body are represented in inverted form in the precentral gyrus. This is called as motor homunculus.

59 Motor Homunculus Distorted human form, of the somatotopic organization of the motor cortex as originally mapped by U.S. born Canadian neurosurgeon Wilder Penfield ( ). Within this mapping, the size of the brain region associated with a body part reflects the complexity of the activities carried out with that part of the body rather than its actual size.

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63 The prefrontal area is concerned with the makeup of the individual s personality. As the result of the input from many cortical and subcortical sources, this area plays a role as a regulator of the person s depth of feeling. It also exerts its influence in determining the initiative and judgment of an individual.

64 Parietal Lobe The primary somesthetic area (primary somatic sensory cortex S1) occupies the postcentral gyrus.

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66 Occipital Lobe Consists the primary visual area (Brodmann area 17). The secondary visual area (Brodmann areas 18 and 19) surrounds the primary visual area on the medial and lateral surfaces of the hemisphere.

67 Temporal Lobe The primary auditory area (Brodmann areas 41 and 42) includes the gyrus of Heschl and is situated in the inferior wall of the lateral sulcus. The secondary auditory area (auditory association cortex) is situated posterior to the primary auditory area in the lateral sulcus and in the superior temporal gyrus (Brodmann area 22).

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69 CEREBRAL DOMINANCE An anatomical examination of the two cerebral hemispheres shows that the cortical gyri and fissures are almost identical. Nevertheless, certain nervous activity is predominantly performed by one of the two cerebral hemispheres.

70 Handedness, perception of language and speech are functional areas of behavior that in most individuals are controlled by the dominant hemisphere. By contrast, recognition of faces and music are interpreted by the nondominant hemisphere.

71 More than 90% of the adult population is right-handed and, Therefore left hemisphere dominant. About 96% of the adult population is left hemisphere dominant for speech.