Cerebrum external features
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The document provides a detailed overview of the gross anatomy of the cerebral hemispheres, including their lobes, surfaces, borders, poles, sulci, gyri, and functional areas. Key points include: 1. The cerebral hemispheres are separated by the median longitudinal fissure and connected by the corpus callosum. They are divided into lobes named according to the overlying cranial bones. 2. The hemispheres have four surfaces - superolateral, medial, inferior (orbital and tentorial), and borders that divide the surfaces. 3. Functional areas include the primary motor, sensory, and association cortices in the frontal, parietal and temporal lobes that control voluntary movement, process
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Cerebrum external features
- 1. Gross Anatomy of Cerebral Hemisphere Dr. Prabhakar Yadav Asociate Professor Department of Human Anatomy BPKIHS, Dharan, Nepal
- 2. Cerebrum: largest part of the brain Location: anterior and middle cranial fossae and occupy whole concavity the vault Cerebral hemispheres: separated by median longitudianal fissure ( longitudinal cerebral fissure ) Corpus callosum, connects the hemispheres across the midline Fissure contains: falx cerebri & anterior cerebral arteries. Tentorium cerebelli: Fold of dura mater that separates the cerebral hemispheres from the cerebellum.
- 3. Surfaces: superolateral surface: convex & related to cranialvault medial surface is flat and vertical. It presents corpus callosum. inferior surface is irregular to adopt the floors of anterior and middle cranial fossae. It is divided into two parts by stem of lateral sulcus (a) small anterior part, orbital surface (b) large posterior part, tentorial surface.
- 4. Borders: inferolateral border: separates superolateral surface from tentorial surface superciliary border: separates superolateral surface from orbital surfaces medial orbital border: separates medial surface from orbital surface. medial occipital border: separates medial surface from tentorial surface. inferomedial/hippocampal border surrounds the cerebral peduncle superomedial border: separates superolateral surface from medial surface
- 5. POLES: Frontal pole :at the anterior end ,is more rounded than occipital pole. occipital pole at the posterior end, is more pointed than frontal pole. temporal pole: at the anterior end of temporal lobe
- 6. Hemisphere - divide into lobes, named according to cranial bones under which they lie. Central, lateral , Parieto-occipital sulci & calcarine sulci
- 7. Central sulcus: • Indents superior medial border about 1 cm behind the midpoint. • Runs oblique downward & forward ly on the superolateral surface . • lower end is separated from posterior ramus of the lateral sulcus by a narrow bridge of cortex.
- 8. • Central sulcus is the only sulcus on lateral surafce that indents the superomedial border and lies between two parallel gyri • Precentra gyrus –primary motor area (4)- motor cells that initiate movements of opposite side of body • Postcentra gyrus- primary somesthetic area (3,2,1)-receives sensory information frome opposite side of the body.
- 9. Lateral sulcus: is a deep cleft found mainly on inferior & lateral surfaces of cerebral hemisphere. Consists of: a short stem that divides into three rami. Stem arises on the inferior surface, on reaching the lateral surface, it divides into anterior horizontal ramus, anterior ascending ramus and continues as the posterior ramus. Insula: An area of cortex that lies at the bottom of the deep lateral sulcus.
- 10. Parieto-occipital sulcus: • Begins on the superior medial border about 2 inches (5 cm) anterior to occipital pole • passes downward and forward on the medial surface to meet the calcarine sulcus calcarine sulcus: • Begins below the spleium and arches upward & backward to reach the occipital pole. • Calcarine sulcus is joined by the parieto-occipital sulcus about halfway along its length.
- 11. Lobes of Cerebral Hemisphere Superolateral Surface : Frontal lobe: area anterior to central sulcus & superior to the lateral sulcus. divided by 3 sulci into 4 gyri. precentral sulcus: runs parallel to the central sulcus precentral gyrus: lies between central & precentral sulcus
- 12. superior frontal sulcs and inferior frontal sulcus - extend anteriorly from the precentral sulcus superior frontal gyrus - lies superior to superior frontal sulcus Middle frontal gyrus - lies between superior and inferior frontal sulci inferior frontal gyrus - lies inferior to inferior frontal sulcus Inferior frontal gyrus is invaded by : Anterior & Ascending rami of lateral sulcus.
- 13. Parietal lobe : area posterior to the central sulcus & superior to lateral sulcus; extends posteriorly as far as the parieto-occipital sulcus. Divided by 2 sulci into 3 gyri. postcentral sulcus: runs parallel to the central sulcus postcentral gyrus: lies between central & postcentral sucus. Intraparietal sulcus : Run posteriorly from middle of the postcentral sulcus. superior parietal lobule (gyrus): lies superior to the intraparietal sulcus Inferior parietal lobule (gyrus): lies inferior to the intraparietal sulcus
- 14. Inferior perial gyrus: is invaded by * upturned ends posterior ramus of the lateral sulcus, and ** superior and inferior temporal gyri. They divide the inferior parietal gyrus into anterior, middle and posterior parts. Anterior part is called supramarginal gyrus, and the middle part is called angular gyrus.
- 15. Temporal lobe: occupies area inferior to lateral sulcus. divided into 3 gyri by 2 sulci. Superior temporal & middle temporal sulci: run parallel to posterior ramus of lateral sulcus Superior, Middle & inferior temporal gyri Inferior temporal gyrus is continued onto the inferior surface of the hemisphere
- 16. occipital lobe: lie behind the parieto-occipital sulcus occipital lobe is further subdivided by (a) Lateral occipital sulcus: into superior and inferior occipital gyri. (b) lunate sulcus separates these gyri from occipital pole.
- 17. Medial & Inferior Surfaces : Corpus callosum: largest commissure of the brain. callosum is divisible into the genu, body & splenium. Below the corpus callosum there are: septum pellucidum, fomix & thalamus. Cingulate gyrus: begins beneath the anterior end of corpus callosum & continues above corpus callosum until it reaches its posterior end. Cingulate gyrus: is separated from the corpus callosum by the callosal sulcus.
- 18. cingulate sulcus: separates cingulate gyrus from the superior (medial) frontal gyrus . Its posterior end reaches superomedial border a little behind the upper end of central sulcus Supraspenial sulcus: lies above & behind the splenium
- 19. Paracentral lobule: U shaped area of cerebral cortex that surrounds the indentation produced by central sulcus on the superior border. • Anterior part of this lobule is a continuation of the precentral gyrus on the superior lateral surface • Posterior part of the lobule is a continuation of the postcentral gyrus on the superior lateral surface Precuneus: area of cortex bounded; Anteriorly by: upturned posterior end of cingulate sulcus. Posteriorly by: parieto-occipital sulcus.. Cuneus: triangular area of cortex bounded Above by: Parieto-occipital sulcus Inferiorly by : Calcarine sulcus Posteriorly by: superior medial border
- 20. Inferior Surface Tentorial surface: collateral sulcus: runs anteriorly below the calcarine sulcus. Lingual gyrus: between collateral sulcus & calcarine sulcus. parahippocampal gyrus: Anterior to the lingual gyrus.it terminates in front as the hooklike- uncus parahippocampal gyrus is joined to singulate gyrus through isthmus
- 21. Medial occipitotemporal gyrus: Extends from occipital pole to temporal pole. Bounded Medially by: collateral sulcus; laterally by : occipitotemporal sulcus. Lateral Occipitotemporal gyrus: lies lateral to occipitotemporal sulcus sulcus and is continuous with inferior temporal gyrus .
- 22. Inferior surface ( Orbital Suraface): olfactory bulb and tract lie in olfactory sulcus. Gyrus rectus: lies medial to olfactory sulcus. Lateral to olfactory sulcus orbital surface is divided by H- shaped sulcus into Anterior, posterior, medial & Lateral gyri.
- 23. Occipital lobe: lateral occipital sulcus: divide occipital lobe into superior & inferior occipital gyri Lunate sulcus: separate superior & inferior occipital gyri from occipital pole
- 24. types of sulci: 1.Limiting sulcus: separates two areas which are different functionally and structurally. Example-central sulcus between motor & sensory areas. 2.Axial sulcus: develops in the long axis of a rapidly growing homogeneous area. An example- postcalcarine sulcus in the long axis of the striate area (Fig. 28.3B). 3.Operculated sulcus: separates by its lips two areas, and contains a third area in the walls of the sulcus. An example is the lunate sulcus. 4.Secondary sulcus: is produced by factors other than the exuberant growth in the adjoining areas of the cortex. Examples are the lateral and parieto-occipital sulci. 5.Complete sulcus: is very deep so as to cause elevation in the walls of the lateral ventricle. Examples are the collateral and calcarine sulci.
- 25. Structural and Functional Type of the Cortex archicortex and paleocortex together constitute the allocortex Archicortex: Phylogenetically it is the oldest and in man is represented by hippocampus & parts of rhinencephalic regions (pyriform area and hippocampal formation). Structurally it is simple and made up of three layers. • Paleocortex: Phylogenetically it is intermediate in development and in man is represented by the cingulate gyrus. • Neocortex: Phylogenetically it is most recent in development and in man it comprises about 90% of the total area of the cerebral cortex. Structurally it is thick and consists of six layers. It is subdivided into a. Granular cortex: It is basically a sensory cortex. b. Agranular cortex. This is the motor cortex.
- 26. Functional Areas of the Cerebral Cortex Types of cortical areas: 1. Motor areas: concerned with motor functions; give origin to fibres of corticospinal & corticonuclear tracts. 2. Sensory areas: concerned with the sensory functions and receive fibres from thalamic nuclei 3. Association areas: have associative, integrative & cognitive functions Functional areas in the frontal lobe Primary motor area (area 4 of Brodmann) - located in the precentral gyrus on the superolateral surface & extends to the anterior part of paracentral lobule on the medial surface. - controls voluntary motor activities of the opposite half of the body.
- 27. Although the primary motor area control contralateral musculature of body, the muscles of the upper part of the face, tongue (genioglossus), mandible, larynx, pharynx and axial musculatur has significant bilateral control Lesions of primary motor area in one hemisphere produce flaccid paralysis of the extremities of the opposite half of the body (hemiplegia). The upper facial, extraocular, masticatory, laryngeal& pharyngeal muscles are spared for being represented bilaterally
- 28. Specific regions within the area of cerebral cortex are responsible for movements in the specific parts of the body Human body is represented in an upside down manner in the precentral gyrus (inverted homunculus) as shown in Figure 12.13. The pharyngeal region and tongue are represented in the lowermost part, followed by face, hand, trunk and thigh. The legs, feet and perineum are represented on the medial surface of the hemisphere in the paracentral lobule. The area of cortex controlling a particular movement is proportional to the skill involved in performing that movement and not to the bulk of muscle participating in the movement. Thus, face especially the lips, tongue, larynx and hand have disproportionately larger areas while the trunk and lower limb have smaller areas.
- 29. Premotor area (area 6 of Brodmann): -Located anterior to primary motor area in the posterior parts of superior, middle& inferior frontal gyri and extends on to the medial surface of the hemisphere. -Main site for the cortical origin of extrapyramidal (corticorubral, corticoolivary, corticonigral, etc.) fibres. -Receives inputs from the sensory cortex, thalamus and basal ganglia. - Stores the programmes of motor activity assembled as a result of past experience. - Responsible for programming the intended movements of the primary motor area, and controlling the movements in progress. Lesions of premotor (secondary motor) area produce difficulty in performance of skilled movements.
- 30. Frontal eye field (area 8 of Brodmann) Located in the posterior part of the middle frontal gyrus Electrical stimulation of this region causes deviation of both eyes especially to the opposite side (conjugate movements of the eyes). Frontal eye field controls voluntary scanning movements of the eyes and is independent of the visual stimuli. Frontal eye field is connected to the visual area of occipital cortex by association fibres. Involuntary following of moving objects by the eyes involves the visual area of the occipital cortex.
- 31. Clinical Correlation Lesions of the frontal eye field of one hemisphere cause the two eyes to deviate to the side of lesion and an inability to turn the eyes to the opposite side. The involuntary tracking movement of the eyes when following moving objects is unaffected since the lesion does not involve the visual cortex of the occipital lobe.
- 32. Motor speech area of Broca (areas 44 and 45 of Brodmann) Located in pars triangularis(45) and pars opercularis (44) of inferior frontal gyrus of frontal lobe of left hemisphere (dominant hemisphere) in most of the individuals, and the persons are right handed. However, in 30% cases it is present in the right hemisphere and persons are left handed. Broca's area is responsible for the production of expressive speech/vocalization. It brings about the formation of words by its connections with the adjacent primary motor area, which in turn appropriately stimulate the muscles of the larynx, mouth, tongue, soft palate, and the respiratory muscles.
- 33. Clinical Correlation The lesions of motor speech area of Broca result in loss of ability to produce speech, i.e. expressive aphasia (also called motor aphasia). The patients, however, retain the ability to think about the words they wish to say, they can write the words, and they can understand their meaning when they see or hear them.
- 34. Primary sensory area (areas 3, 1 and 2 of Brodmann) located in the postcentral gyrus and extends into posterior part of the paracentral lobule Opposite half of the body is represented up-side down exactly in same fashion as in the primary motor area. Similarly, the area of cortex assigned for a particular part is not proportional to the size of that part but to its functional significance (i.e. to the intricacies of sensations received from it). Thus, the thumb, fingers, lips and tongue have a disproportionately large representation. Primary sensory area is concerned with the perception of extero-ceptive (pain, touch and temperature) and proprioceptive (vibration, muscle and joint sense) sensations from the opposite half of the body. However, sensations from pharynx, larynx and perineum go to both sides. primary sensory area receives projection fibres from ventral posterolateral (VPL) and ventral posteromedial (VPM) nuclei of the thalamus.
- 35. Clinical Correlation Lesions of primary sensory area lead to the loss of appreciation of exteroceptive and proprioceptive sensations from the opposite half of the body. The crude pain, temperature and touch sensations oen return, but this is believed to be due to functions of the thalamus.
- 36. Sensory association area (Fig. 12.11) Sensory association area occupies the superior parietal lobule corresponding to the Areas 5 and 7 of Brodmann. It is concerned with the perception of shape, size, roughness, and texture of the objects. Thus, it enables the individual to recognize the objects placed inhis/her hand without seeing. Such ability is referred to as stereognosis. Clinical Correlation Lesions of this area result in inability to recognize or identify an object by its feel. This condition is called tactile agnosia or astereognosis.
- 37. Sensory speech area of Wernicke (Fig. 12.11) Sensory speech area is located in the le dominant hemisphere occupying the posterior part of the superior temporal gyrus of temporal lobe and angular (area 39) and supramarginal (area 40) gyri of the inferior parietal lobule. The Wernicke's area is concerned with the interpretation of language through visual and auditory input. It is also an essential zone for constant availability of the learned word patterns. N.B. The sensory and motor speech areas exist together in one hemisphere only. The Wernicke's area is connected to the Broca's area by a bundle of nerve fibres called arcuate fasciculus.
- 38. Clinical Correlation Lesions of Wernicke's area in the dominant hemisphere produce loss of ability to understand the spoken and wrien speech. This condition is called receptive sensory aphasia. Since Broca's area is unaffected, the expressive speech is unimpaired and the individual can produce a fluent speech. However, he is unaware of the meaning of the words he uses consequently he uses, incorrect words or even non-existent words. The person is unaware of his mistakes. To the others his speech sounds like an incomprehensive foreign language Lesions involving both Broca's and Wernicke's speech areas result in loss of the production of speech as well as loss of understanding of the spoken and wrien speech. This condition is called global aphasia.
- 39. Primary auditory area (Brodmann's areas 41 and 42) Primary auditory area is located in the inferior wall of the lateral sulcus, and to be very specific on the superior surface of the superior temporal gyrus occupying the anterior transverse temporal gyrus (Heschl's gyrus) and extends slightly to the adjacent part of the superior temporal gyrus (Fig. 12.11). The primary auditory area receives input from the medial geniculate body through auditory radiations. The medial geniculate body receives input from organ of Corti in the cochlea of inner ear of both the sides but mainly from the opposite side. This area is concerned with the reception of isolated impressions of loudness, quality and pitch of the sound. In addition it also picks up the source of the sound. Clinical Correlation Unilateral lesions of the primary auditory area result in slight loss of hearing because it receives auditory input from the cochleae of both sides, but loss will be greater in the opposite ear. Bilateral lesions of the primary auditory areas cause complete cortical deafness. Secondary auditory area/auditory association area (Brodmann's area 22) Secondary auditory area is situated on the lateral surface of the superior temporal gyrus slightly posterior to the primary auditory area which it surrounds (Fig. 12.9). It receives auditory impulses from primary auditory area and correlates them with the past auditory experiences. Thus, this area is necessary for the interpretation of the sound heard.
- 40. Clinical Correlation The lesions of secondary auditory area result in an inability to interpret the meaning of the sounds heard, and the patient may experience word deafness (auditory verbal agnosia).
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