Neuroscience LC4B The Cerebrum PDF

COURSE OUTLINE The cerebral cortex is important for: ○ Thought I. Introduction ○ Memory II. Frontal Lobe...

COURSE OUTLINE The cerebral cortex is important for: ○ Thought I. Introduction ○ Memory II. Frontal Lobe ○ Intellect A. Primary Motor Cortex ○ Conscious awareness B. Premotor Cortex Most sensory modalities ascend to the cortex C. Supplementary Motor Cortex from the thalamus, perceived and interpreted D. Frontal Eye Field in the light of the previous experience. E. Motor Speech Area/Broca’s Area ✔ Consciousness requires an individual to fulfill the F. Prefrontal Cortex following conditions: III. Parietal Lobe A. Must be awake (wakefulness is contributed A. Primary Somatosensory Cortex by the brainstem) IV. Temporal Lobe B. Must be aware of what is happening to its A. Primary Auditory Cortex body or environment (awareness is B. Auditory Association Area contributed by the cerebral cortex) V. Occipital Lobe The posterior part of the cerebrum receives A. Primary Visual Cortex sensory information in the: B. Visual Association Area Parietal lobe - Somatosensory VI. Fibers in the subcortical region Occipital lobe - Vision Temporal Lobe - Hearing A. Commissural fibers 1. Corpus Callosum 2. Anterior Commissure II. FRONTAL LOBE 3. Posterior Commissure A. PRIMARY MOTOR CORTEX B. Projection fibers PRIMARY MOTOR CORTEX 1. Descending Pathway PRECENTRAL GYRUS 2. Ascending Pathway Brodmann’s Area 4 C. Association fibers Gives rise to the corticospinal tract. 1. Uncinate Fasciculus If damaged: 2. Arcuate Fasciculus ○ Hemiplegia Complete paralysis (plegia); total absence 3. Cingulum Fasciculus of strength. 4. Superior Longitudinal Fasciculus ○ Hemiparesis 5. Inferior Longitudinal Fasciculus Weakness (paresis); not a complete VII. Cerebral Cortical Layers absence of strength. A. Types of Cortex B. PREMOTOR CORTEX B. Three Major Fissures Premotor Cortex VIII. Brodmann’s Area Summary Brodmann’s Area 6 A. Frontal Lobe For programming and planning actions B. Parietal Lobe ○ Area 4 will aid in executing the action. Area 6 C. Temporal Lobe plans on how the action will proceed in detail. D. Occipital Lobe If damaged: IX. Blood Supply ○ Apraxia Lack the ability to perform or plan an action. I. INTRODUCTION C. SUPPLEMENTARY MOTOR CORTEX On the medial surface of the premotor cortex. The principal subcortical input to premotor and supplementary motor cortex is the ventral anterior nucleus of the thalamus. This nucleus receives its afferent from the globus pallidus & substantia nigra. —------------------------------------------------------------------ Figure 1. Identified functions of the Cerebrum in their specific part of the gyrus BATCH 2028 1F 1 NEUROSCIENCE LC 2 Figure 2. Location of the supplementary motor cortex indicated in light yellow, just anterior to the primary motor cortex. Figure 3. Location of the Motor Speech Area/Broca's Area indicated in the red box. D. FRONTAL EYE FIELD Language entails that a person should be able It lies in the posterior part of the middle frontal to understand what others are saying, gyrus. formulate thoughts, and express himself. It is corresponding to Brodmann’s Area 8 Brodmann's area 44 and 45 is the motor It controls conjugate movement of the eyes. language center. Unilateral damage to Area 8 causes conjugate deviation of the eyes to the side of the lesion. F. PREFRONTAL CORTEX Globus pallidus & substantia nigra Lies anterior to premotor area It has rich connections with the parietal, temporal, and occipital cortex. Functions: ○ Intellect ○ Judgment ○ Prediction ○ Motivation ○ Planning of Behaviour The prefrontal cortex separates us from the rest of the animal kingdom. Humans do not act instinctively like the rest of the animals. Figure. Location of the frontal eye field (area 8) indicated inside the circle In the cerebrum, everything is opposite. Area 8 is responsible for your horizontal gaze. It will make you look at the opposite side. Example: What will happen if the right area 8 is destroyed? The person will not be able to look to the left side. Both her eyeballs deviated to the right (the patient looks to the lesion) side but the weakness is on the left. Figure 4. Brodmann Areas E. MOTOR SPEECH AREA / BROCA’S AREA In the inferior frontal gyrus in the dominant III. PARIETAL LOBE (usually left) hemisphere. Brodmann’s Areas 44 & 45 A. PRIMARY SOMATOSENSORY CORTEX It has connections with ipsilateral temporal, parietal, occipital lobes that share in language function. Lesion: Left middle cerebral artery Expressive or Brocas or nonfluent motor aphasia (inability to express thought, answer or writing in spite of a normal comprehension) globus pallidus & substantia nigra. Figure 5. Location of the Primary Somatosensory Cortex (color red) BATCH 2028 1F 2 NEUROSCIENCE LC 2 BRODMANN’S AREA 1,2,3 ○ 1: Medial Lemniscus (Fine In the postcentral gyrus & posterior part of touch, vibration & Proprioception) paracentral lobule ○ 2: Anterior Spinothalamic Tract It corresponds to Brodmann’s Areas 1, 2 and 3 (Coarse touch & Pressure) Here thalamocortical neurons terminate (3rd ○ 3: Lateral Spinothalamic Tract order neurons) (Pain & Temperature) Input comes from ventral posterior nucleus ○ 4. Trigeminothalamic Tract (VPN) of the thalamus (General sensation from head) Within the somatosensory cortex the ○ VPL (Body; L for limbs) contralateral half of the body is represented ○ VPM (head) upside down. (Homunculus) IV. TEMPORAL LOBE Anterior part of the postcentral gyrus borders the central sulcus (area 3), is granular in type, A. PRIMARY AUDITORY CORTEX and contains only scattered pyramidal cells. The outer layer of Baillarger is broad and very Lies in the superior bank of the middle of the obvious. superior temporal gyrus. The posterior part of the postcentral gyrus Hidden within the lateral fissure. (areas 1 and 2) possesses fewer granular cells. Brodmann’s Area 41, 42 Primary Hearing Center Its precise location is marked by small transverse temporal gyri (Heschl’s Convolutions). Input to the primary auditory cortex is from the medial geniculate nucleus (MGN) of the thalamus. Figure 7. Location of the Primary Auditory Cortex (Brodmann’s Figure 6. Location of the Medial Lemniscus, Spinal Area 41, 42) indicated in the red box. Lemiscus, Spinothalamic tract & Trigeminothalamic tract The primary auditory cortex will just receive VL - Primary Motor Cortex noise or sounds, but for you to be able to interpret VA - Premotor Cortex/ Supplementary the sounds that you’re hearing, it’s actually because Motor Cortex of the associated area known as the Wernicke’s Medial Geniculate Nucleus - Primary Area. Auditory B. SECONDARY AUDITORY CORTEX OR Lateral Geniculate Nucleus - Vision AUDITORY ASSOCIATION CORTEX VP (Ventral Posterior) - Sensory Lies behind the primary auditory cortex. VPL (Ventral Posterior Lateral) upper Continuous posteriorly with the second speech extremity (body); lower extremity) (Wernicke’s Area 21, 22) area. ○ Pain and temperature, vibration Here the heard sounds or words are from the body interpreted. ○ Projects to Brodmann’s area Lesion: Sensory/Receptive/Wernicke’s/fluent 1,2,3 (meaning they could talk but they talk VPM (Ventral Posterior Medial) nonsense)/aphasia; inability to recognize the ○ Pain and temperature coming meaning of sounds or words with hearing from the head/face unimpaired. ○ Projects to area 1,2,3 Ventral Posterior Nucleus (VPN) receives: BATCH 2028 1F 3 NEUROSCIENCE LC 2 B. VISUAL ASSOCIATION CORTEX Figure 8. Location of the Wernicke’s Area indicated in the red box. Figure 10. Visual Association Cortex Arcuate Fasciculus - a type of association fiber Brodmann’s Area 18 and 19 are called that connects Wernicke’s Area to Broca’s Area VISION ASSOCIATION CORTEX. They are interpretive to the visual image. CONDUCTION APHASIA ○ Lesion: Visual Agnosia - inability to Unable to conduct impulses coming from the recognize a seen object Wernicke’s to the Broca’s Lateral Occipital Lobe - facial recognition Problem with repetition (the problem is in the Prosopagnosia - unable to recognize faces Arcuate Fasciculus) V. OCCIPITAL LOBE A. PRIMARY VISUAL CORTEX Figure 11. The Limbic Lobe Lies on the Medial Wall of the Cerebral Hemisphere VI. FIBERS IN THE SUBCORTICAL WHITE MATTER Figure 9. Location of the Primary Visual Cortex ( Brodmann’s Area 17) Lies on medial surface of the occipital lobe In close relation to the calcarine sulcus It extends to the occipital pole Brodmann’s Area 17 ○ It receives optic radiation from the lateral geniculate nucleus (LGN) of the thalamus. ○ Each lateral half of the visual field is represented in the visual cortex of the contralateral hemisphere. ○ Lesion: Figure 12. Fibers in the subcortical white matter Homonymous Hemianopia: a visual field defect involving either the two right or the two left halves of the visual fields of both eyes. BATCH 2028 1F 4 NEUROSCIENCE LC 2 A. COMMISSURAL FIBERS interconnect the two hemispheres L-R and R-L Figure 16. Normal corpus callosum and with ACC 2. Anterior commissure Small bundle fibers that crosses the midline in the lamina terminalis 3. Posterior commissure Bundle of nerve fibers that crosses the Figure 13. Commissural fibers midline immediately above the opening of the cerebral aqueduct into the third 1. CORPUS CALLOSUM ventricle. largest commissure of the brain, connects the two cerebral hemisphere B. PROJECTION FIBERS Leave the hemisphere for subcortical targets Afferent and efferent fibers passing to and from the brainstem to the entire cerebral cortex and to the large nuclear masses of gray matter within the cerebral hemisphere. Internal capsule contains a lot of projection fibers that are destined to either go to the face, or to the upper and lower extremities. 1. Motor Neurons - Descending Pathways Figure 14. Transverse view of the corpus callosum Figure 15. Sagittal view of the corpus callosum Agenesis of the Corpus Callosum Birth defect that has a full or partially missing corpus callosum. Depending on the missing amount, a person with this defect might be symptomatic or have no connection between the left and right hemispheres leading to seizures, difficulty in learning, and neurological impairment. Figure 17. Pathway of the cortIcospinal tract BATCH 2028 1F 5 NEUROSCIENCE LC 2 frontal to occipital and temporal lobes 2. Sensory Neurons - Ascending Pathway (frontal to parietal and occipital). 5. Inferior Longitudinal Fasciculus temporal to occipital lobe VII. CEREBRAL CORTICAL LAYERS Cerebrum is the most specialized of all the different structures in the nervous system that is why it has six (6) layers: Molecular layer - very few cells mostly dendrites External granular layer - lot of stellate cells (star-shaped) External pyramidal layer Internal granular layer Internal pyramidal layer Multiform layer Cerebellum - 3 layers Three most important cells to remember: Stellate cells Figure 18. Pathway of the spinothalamic tract Fusiform cells Pyramidal cells C. ASSOCIATION FIBERS ○ Giant pyramidal cells of Betz Interhemispheric connections, L-L,and R-R These are the fibers connecting different cortical areas of the same side to one another. Short association fibers connect adjacent gyri. Long association fibers connect distant parts of the cerebral cortex on the same side. Figure 19. Association fibers connecting different cortical areas Figure 20. Cells and layers of the cerebral cortex of the same side. NOTE: Layers 1, 2 and 3 - mostly association fibers 1. Uncinate Fasciculus Layer 4: major sensory layer. All the nuclei temporal pole to motor speech area and from the thalamus (VA, VL, VPM, VPL, medial orbital cortex (frontal to anterior temporal). geniculate) will be received in layer 4. Primary 2. Arcuate fasciculus sensory cortex will have a well developed frontal to superior temporal (Wernicke’s layer 4. area to Brocca’s area) Layer 5 - major motor layer. Corticospinal tract Conduction Aphasia - happens when there will mostly arise from layer 5. Primary motor is a lesion in the arcuate fasciculus cortex will have a well developed layer 5. 3. Cingulum Fasciculus ○ Giant pyramidal cell of betz - most cingulum gyrus to parahippocampal gyrus. important cell for motor. 4. Superior Longitudinal Fasciculus Layer 6 - also motor but sends impulses to the thalamus BATCH 2028 1F 6 NEUROSCIENCE LC 2 Figure 21. The cerebral cortex layers and their components Destructive lesions cause eyes to look at lesion A. TYPES OF CORTEX Irritative lesions causes the eye to look away from lesion 1. Isocortex or Neocortex - six layers AREA 44, 45 2. Mesocortex - three to six layers like insula Broca’s area and cingulate 3. Allocortex Inferior frontal (opercularis, some triangularis) 4. Archicortex - three layers like limbic and AREAS 9 to 14, 46, 47 hippocampus Prefrontal cortex 5. Paleocortex - three to five layers like B. PARIETAL LOBE parahippocampus, uncus, and lateral olfactory gyrus AREA 1, 2, 3 Primary somatosensory cortex B. THREE MAJOR FISSURES Postcentral gyrus Touch, pain, temperature, vibration, 1. Median Longitudinal Fissure - separate left proprioception from face and body and right hemispheres VPM from the face 2. Central Sulcus of Rolando - separate frontal VPL from the body from parietal lobe AREA 5, 7 3. Lateral Sulcus or Sylvian fissure - separate Somatosensory association cortex temporal lobe from the upper frontal and Superior parietal lobule parietal Interpret whatever touch, vibration, proprioception you will receive VIII. BRODMANN’S AREA SUMMARY Sensory Agnosia (inability to interpret sensations) A. FRONTAL LOBE ○ Astereognosis – Impaired sensory for object perception AREA 4 ○ Abarognosia – Impaired sensory for Primary motor cortex weight perception Precentral gyrus lesion causes: ○ Agraphesthesia – impaired sensory for ○ contralateral hemiplegia (total paralysis) numbers and letters perception ○ Hemiparesis (weakness of half of the You can feel pain but cannot body) identify objects Parietal association cortex Receives projections from ventrolateral nucleus Contralateral neglect of thalamus AREA 39 AREA 6 Angular and are 40 supramarginal gyrus = both Premotor Cortex, lateral frontal form a part of the Wernicke’s area Supplementary motor cortex, medial superior frontal C. TEMPORAL LOBE For planning and programming AREA 41, 42 Lesion causes apraxia Primary auditory cortex Ventral-anterior nucleus from thalamus Superior temporal lobe (Hescl’s convoluted AREA 8 transverse temporal gyrus) Medial geniculate body Frontal eye field BATCH 2028 1F 7 NEUROSCIENCE LC 2 AREA 21, 22 Auditory association area Wernicke’s aphasia Inferotemporal lobe Memory (hippocampus) Emotions (amygdala) D. OCCIPITAL LOBE AREA 17 Primary visual cortex Cortical blindness Contralateral hemianopia LGB AREA 8, 19 Visual association area Visual agnosia Figure 24. Blood supply of the brain, inferior view. Vertebral artery will ascend posteriorly inside the vertebrae Common carotid artery is palpable. If you palpate both you will lose consciousness Common carotid artery location: at the angle of the mandible, it will separate into right external and left external common carotid, which enters foramen lacerum Figure 22. Brodmann’s area Vertebral arteries will supply the medulla, and will unite to become the basilar artery in the pons then terminate with the posterior cerebral IX. BLOOD SUPPLY artery which supplies the occipital lobe. Collectively those are actually known as your Circle of Willie’s Figure 23. Blood supply of the brain, posterior view Figure 25. Blood supply of the brain BATCH 2028 1F 8