Cerebral Structure and Function PDF

SHS 479 Neuroanatomy Cerebral Structure and Function What does “cerebral” mean? Refers to the cortical hemispheres Distinguished from cerebellum and subcortical structures Thalamus Basal Ganglia Brainstem Etc… Cerebellum is smaller than cerebral. At least 4 lobes Insular c...

SHS 479 Neuroanatomy Cerebral Structure and Function What does “cerebral” mean? Refers to the cortical hemispheres Distinguished from cerebellum and subcortical structures Thalamus Basal Ganglia Brainstem Etc… Cerebellum is smaller than cerebral. At least 4 lobes Insular cortex (fissure between frontal and parietal from temporal lobe)  White matter - White and gray matter Relays information from one place to another Grey matter - Information processing Layers and pathways Most superficial Not all gray matter are uniform, there are different layers Least superficial Callosal fiber - Connect the left and right hemispheres of the brain, enabling communication between them. Projection fiber –Connect the cerebral cortex with lower brain regions and the spinal cord, transmitting motor and sensory information. Thalamocortical fiber- Connect the thalamus to the cerebral cortex, relaying sensory and motor signals. Association fiber (corticocortical fiber) - Connect different areas within the same hemisphere, enabling communication and information integration.  Cortical layers Layer I: glia and axons Layer II: small pyramidal cells Layer III: large pyramidal cells Layer IV: nonpyramidal cells Layer V: Betz cells Layer VI: various cells  Cerebral Cortex Features Cortex means “bark” Features include: Gyri (peaks) Sulci (valleys) Fissures (deep sulci): Longitudinal (between left and right hemisphere = corpus callosum) Central (between frontal and parietal lobe) Lateral (between frontal and parietal from temporal lobe) For protection and increases surface area for necessary gyri and sulci  Cortical Landmarks Dorsolateral surface Central sulcus (fissure of Rolando) = Central fissure Separation of primary motor from sensory cortex Lateral fissure (sylvian fissure) Separation of frontal from temporal lobe Parietooccipital sulcus Separation of parietal from occipital lobe Brodmann Areas Subdivisions of cortex based on Gross anatomy of the brain cytoarchitecture (cell structure) An alternative way to refer to specific brain regions Often abbreviated as BA – # 4- precentral gyrus (primary motor cortex) 3, 1, 2 – postcentral gyrus (somatosensory cortex) 6, 8 – premotor cortex 9 – 11 – prefrontal cortex 44, 45 – Broca’s Area inferior frontal lobule 22 - Wernicke’s area? 41, 42 – Primary Auditory Cortex Study parts, not memorize BA. Frontal Lobe Largest of the lobes Vertical precentral gyrus 3 horizontal frontal gyri Superior Middle Inferior Know 1, 2 and 3 too Precentral gyrus Important Frontal Lobe Regions Prefrontal cortex (BA – 9-12, 45-47) Broca’s Area (BA – 44, 45) Premotor cortex (BA – 6) Primary motor cortex (BA – 4) Prefrontal Cortex Occupies BA 9, 10, 11, 12, 45, 46, 47 Functionally involved with: Cognition (executive control) Personality Decision making Social behavior Restraint Impulse control Phineas Gage…  Prefrontal Cortex DLPF C Clinical considerations: OPFC VLPF C Dorsolateral PFC Deficits in thinking, planning, reasoning Ventrolateral PFC Involved in working memory Damage impairs comprehension of abstract, but not concrete words Orbitofrontal PFC Personality disorders Emotional disinhibition Abnormal impulsive social behaviors MPFC Medial PFC Reduced attention, motivation, and decisiveness  Broca’s Area Found on inferior frontal gyrus BA 45 Pars triangularis, involved in Interpretation of syntax and planning/programming of verbal responses (understanding of syntax formation and planning what to say) BA 44 Pars opercularis Coordinates and initiates speech effectors for language production(responsible for coordination and speech movements) E.g Broca’s Aphasia – difficulty in producing speech, caused by stroke Broca’s Area Damage may lead to Broca’s aphasia Language deficit Often leads to agrammatic speech Depending on extent of lesion, may also have apraxia (difficulty in controlling movements for speech)  Premotor Cortex (PMC) Occupies BA 6 Selecting, planning, and sequencing voluntary movements Supplementary motor area (SMA) Top of BA 6 Sequencing and Initiating Bi-manual tasks Damage to PMC may lead to apraxia Coordination issue does not algin what the brain tells you Possible to have both apraxia and Broca's aphasia Types of Apraxia Primary Motor Cortex Precentral gyrus – BA 4 Relays motor plans from BA 6 to the contralateral musculature Left hemisphere controls right primary motor cortex Damage may cause hemiparesis (weakness of one side of body) / hemiplegia (paralysis of one side of body) Dysarthria (speech disorder due to muscle weakness) Homunculus Motor Homunculus Motor Homunculus Function: Controls voluntary muscle movements. Representation: Emphasizes body parts requiring fine motor skills, like hands and face. Location: Primary motor cortex (precentral gyrus). Sensory Homunculus Function: Processes sensory information from the body. Representation: Emphasizes body parts with high sensory receptor density, like lips and fingertips. Location: Primary somatosensory cortex (postcentral gyrus). Paracentral Lobule Found in medial surface of the brain Controls contralateral motor and sensory functions of the lower limbs Spans both frontal and parietal lobes Paracentral Lobule Paracentral sulcus Central sulcusMarginal sulcus Precentral sulcus Parieto-Occipital Sulcu Important Parietal Lobe Regions Primary sensory cortex (BA 1-3) Somatosensory association cortex (BA 5, 7) Angular gyrus (BA 39) Supramarginal gyrus (BA 40)  Primary Sensory Cortex Postcentral gyrus – BA 1-3 Receives sensory information relayed from thalamus Touch Temperature Vibration Proprioception (awareness of where the limbs are located at) Damage causes reduced sensation Motor function may be impacted Homunculus Somatosensory Association Cortex Superior parietal lobule (BA 5, 7) Integrates information from primary sensory cortex Damage may cause astereognosis (hard to identify by touch) Can refine motor movements, especially during speech  Inferior Parietal Lobule Ventral portion of parietal lobe Inferior to superior parietal lobule Posterior (caudal) to primary sensory cortex Contains two distinct gyri Angular gyrus Supramarginal gyrus  Angular Gyrus Posterior IPL (BA 39) Dominant (Left) Language Visual word form processing Non-dominant (Right) Body and spatial orientation Damage may cause hemispatial neglect (individual ignore one side of the visual or body) & spatial intellect Spatial orientation (Body's lack of awareness) Supramarginal Gyrus Anterior IPL (BA 40) Auditory decoding of written words (Dominant hemisphere = left) Damage impairs decoding of novel, but not known words Role in language processing- Taking mental representation into articulatory representation Damage to non-dominant hemisphere also causes issues with body schema and spatial attention… Parietal Lobe (cont.) Clinical information (if parietal lobe is damaged...) Contralateral sensory loss (loss of sensation on opposite side of body from the damaged hemisphere) Perceptual/conceptual disorders of tactile recognition (difficulty recognizing objects by touch) Impaired constructional (drawing/designing) skills Impaired spatial orientation (no sense of direction & position to surroundings) Visual–spatial memory loss Tactile agnosia (Inability to recognize objects by touch affects 1 hand) Astereognosis (Inability to recognize objects by touch affects both hands)  Visual Processing Pathways Dorsal stream (18, 19, 7, and 39?) Where of vision Analyzes motion and spatial relationships Where are you looking at? Projecting parietal lobe (top arrow) Ventral stream (18, 19, and 37) What of vision; Analyzes forms, colors, and faces What are you looking at? (below arrow)  Occipital Lobe Primary visual cortex (BA 17) Visual perception Association visual cortex (BA 18, 19) Visual recognition Parieto-occipital sulcus Calcarine sulcus Primary visual cortex? Occipital Lobe Lateral and midsagittal surfaces Parietooccipital sulcus to occipital notch Calcarine sulcus (primary cortex, area 17) Visual perception Association visual cortex (area 18, 19) Visual recognition Occipital Lobe Clinical Info Primary visual cortex Blindness (homonymous hemianopsia) Loss of vision in both eyes Overlap of the visual field with a shadow or missing area in between Association visual cortex bilateral (secondary cortex) Visual and color agnosia - inability to recognize objects and colors despite having normal vision Alexia – word blindness, inability to recognize written words Cortical blindness- eyes are functioning but the brain cannot process vision No overlap of visual field so there is a possibility of being partially blind. Temporal Lobe Structures Lateral surface (gyrus) Superior Middle Inferior Medial surface Parahippocampal gyrus Colateral suclus Fusiform gyrus Auditory Cortex Heschl’s gyrus (BA 41, 42) Receives information from CN VIII and auditory pathway Processes for intensity and frequency Conscious perception of sound From low to high frequency Tonotopically organized Wernicke’s Area BA 22 (posterior portion) Maps sound to meaning Ventral stream Damage may cause Wernicke’s aphasia Fluent Jargon filled Has grammar and syntax (sounds choppy) idea to convey Both language comprehension and speech production issue Compare from Broca's area Parahippocampal Gyrus Medial surface of temporal lobe Entorhinal cortex (BA 28, 34) Interface between cortex and hippocampus Declarative memory Memory filing system Story pieces of information to share Fusiform Gyrus Spans temporal and occipital lobes (BA 37) Also includes part of inferior temporal gyrus Many proposed functions Visual recognition (e.g. identifying parts of faces) Reading (e.g. object identification) Prosopagnosia (face blindness)  “Hidden” Regions Cingulate Cortex (memory) Cognitive control Pain Autobiographical memory (memory system that involves recalling from personal experiences and events) Emotional processing Insular Cortex Sensorimotor function Emotional processing Possible language functions?  Back to pathways… Interhemispheric Corpus callosum is a band of fibers that connects the right and left hemispheres together Connects homologous region (identical left and right sides) Intrahemispheric Connections Numerous connections within the cerebral hemispheres Two examples: Superior longitudinal fasciculus Subcomponents Arcuate fasciculus Hemispheric Specialization Most people are left hemisphere language dominant 96% of right handers 85% of ambidextrous 73% of left handers