Cerebral Cortex PDF

# Cerebral Cortex ## Learning outcomes: * Identify major sulci, gyri and lobes. * Identify and describe major cortical areas in terms of their pathway and function. * Explain signs and symptoms following a lesion to major cortical areas. * Identify and describe white matter (commissural, associati...

# Cerebral Cortex ## Learning outcomes: * Identify major sulci, gyri and lobes. * Identify and describe major cortical areas in terms of their pathway and function. * Explain signs and symptoms following a lesion to major cortical areas. * Identify and describe white matter (commissural, association and projection fibres) of the cerebral hemisphere. * Describe major layers (layer 3, 4 and 5) of the cerebral cortex and their significance. * Identify and describe major blood supply of the brain. * Describe the formation and significance of circle of Willis. ## Cerebral cortex: * Cortex is composed of grey matter. * It forms a complete covering of the cerebral hemisphere. * Sulci = grooves/depressions * Gyri = folds/convolutions | part | description | |---|---| | cortex | grey matter | | white matter | | * **Sulcus vs fissure:** * Fissure = deeper groove compared to a sulcus * Longitudinal fissure = separates the left + right cerebral hemispheres. ## Lobes: * **Central sulcus** * starts at the superior medial border of each hemisphere. * separates the frontal lobe from the parietal lobe. * **Lateral sulcus** aka sylvian fissure * separates the frontal lobe from the temporal lobe. * **Parietooccipital sulcus** * separates the parietal lobe from the occipital. * **Calcarine sulcus** * runs within the occipital lobe. * **Corpus collosum** * composed of nerve fibres that connect the cerebral hemispheres. **Image description:** A diagram showing a side (lateral) view of the brain, highlighting the frontal, parietal, temporal, and occipital lobes and the central sulcus, lateral sulcus, and parieto-occipital sulcus. ## Medial surface: * Above the corpus collosum = cingulate gyrus * The cingulate gyrus is involved in the limbic system which is involved in memory + emotion. * Paracentral lobule is divided into the anterior part and the posterior part using the central sulcus. * The paracentral lobule surrounds the central sulcus. * Anterior = precentral gyrus * Posterior = postcentral gyrus **Image description:** A diagram showing the medial surface of the brain, highlighting the cingulate gyrus. ## Lateral view: * **Primary motor area occupies:** * precentral gyrus & * anterior part of the paracentral lobule. * **Primary somaesthetic area occupies:** * postcentral gyrus & * posterior part of the paracentral lobule. * **Insula:** * lies deep within the area surrounded by the lateral sulcus, and cannot be seen unless that part of the brain is removed. **Image description:** A diagram showing the lateral surface of the brain, highlighting the precentral gyrus, the postcentral gyrus. ## Function of the cerebral cortex: * Left frontal lobe = involved in personality + behaviour ## Cortical areas: * **Precentral gyrus** - primary motor area * **Postcentral gyrus** - primary somesthetic (somatosensory) area **Image description:** A diagram showing the lateral surface of the brain, highlighting the precentral gyrus, the postcentral gyrus and the insula. * **Below the lateral sulcus = superior temporal gyrus.** * **Primary auditory area =** area that receives auditory impulses. * **Primary visual =** receives visual impulses. ** Image description:** A diagram showing the lateral surface of the brain, highlighting the lateral sulcus, the superior temporal gyrus, the primary auditory area, and the primary visual area. * **Primary visual cortex is surrounded by calcarine sulcus.** **Image description:** A diagram showing the medial surface of the brain, highlighting the primary visual area and the calcarine sulcus. ## Overview of cortical areas: * **Premotor area** * programming of and preparing for movement. * involved in the control of posture * **Prefrontal area (cortex)** * make up of the individual's personality. * has a role in cognitive function e.g. thinking, judgement and decision making. * **Taste area:** * At the lower end of the postcentral gyrus and the insula. * Insula = part of the cortex that hidden deeper than the lateral sulcus **Image description:** A diagram showing the lateral surface of the brain, highlighting the premotor area, the prefrontal area, the primary motor area, and the taste area. * **Somesthetic association area:** * occupies the superior parietal lobule. * allows to recognise general sensation with other sensory stuff along with past sensory experience. * be able to recognise the form, size, texture of an object by touch * known as 'stereognosis'. * Lesion = astereognosis. * Normal Sensory Exam ; Stereognosis * **Auditory association area:** * be able to recognise what causes the sound they are hearing. * **Visual association area:** * be able to recognise and appreciate what they are seeing. **Image description:** A diagram showing the lateral surface of the brain, highlighting the somesthetic association area the auditory association area, and the visual association area. ## Language areas: * Language areas are found in the dominance hemisphere * Most population – dominant hemisphere is the left hemisphere in right-handed persons. * **Broca's area:** * found in the inferior frontal gyrus of the frontal lobe (dominant hemisphere). * responsible for expressive aspects of language - permits us to be able to form words. * A lesion: Expressive aphasia = have difficulty in forming words or express/produce speech but understand their meaning. (aphasia = impairment of language) * **Wernicke's area:** * mainly located in the superior temporal gyrus and extends around the posterior end of lateral sulcus into the parietal region (dominant hemisphere). * responsible for comprehension of the spoken words. * allows use to be able to understand spoken & written language. * be able to read a sentence, understand it and say it out loud. * Lesion: Receptive aphasia = be able to speak but unable to understand spoken and written words. As a result, incorrect words and non-existent words are used. **Image description:** A diagram showing the lateral surface of the brain, highlighting the premotor area, the prefrontal area, the primary motor area, the somesthetic association area, the auditory association area, Broca's area, and Wernicke's area. ## The motor + sensory homunculi: **Image description:** A diagram showing a homunculus, with limbs represented in different sizes based on the amount of motor cortex and sensory cortex devoted to each limb. * A specific part of the body is associated with a distinct region in CNS. * The representation of the body is contralateral and inverted i.e. the left hemisphere controls movement of the right side of the body and the sensory from the right side projects to the left hemisphere. ## Plasticity: * an ability of the nervous system to change and adapt over time, structurally + functionally in response to experiences, diseases + injury. * Cerebral dominance is established early on after birth. * Sometimes if an area of the brain is damaged, it can pass on that task to another region of the brain – neuroplasticity in developing brains. ## White matters of the cerebral hemisphere: * **Commissural fibres:** connect regions of the 2 hemispheres. * **Association fibres:** connect cortical regions within the same hemisphere. * **Projection fibres:** afferent & efferent fibres. ## Commissural fibres - Corpus collosum: **Image description:** A diagram showing the corpus collosum, which connects the two hemispheres. * Largest commissural fibre that connects the two cerebral hemispheres together. * Made up of 4 parts: * Splenium * Body * Genu – bent region * Rostrum (runs downward and backward) **Image description:** A diagram showing a side view of the brain, highlighting the 4 parts of the corpus collosum and a horizontal section illustrating how the fibers of the genu and splenium curve. * **Forceps minor** – fibres of genu curve forward into the frontal lobe. * **Forceps major** – fibres of splenium curve backward into the occipital lobe. ## Commissural fibres – anterior commissure fibre: ** Image description:** A diagram showing the anterior commissure, which connects the two hemispheres. * Anterior commissure fibres – connects the two hemispheres via the temporal lobe ## Association fibres: * Connect cortical regions within the same hemisphere. * Divided into: * Short association fibres = lie beneath the cortex and connect adjacent gyri. * Long association fibres = connect lobes within the same hemisphere. ## Long association fibres: **Image description:** A diagram showing the long assocation fibers of the brain. * **Superior longitudinal fasciculus** * largest association fibre * connects frontal, parietal, occipital and temporal lobe. * **Inferior longitudinal fasciculus** * connects occipital lobe & temporal lobe. * **Uncinate fasciculus** * connects motor speech area & gyri of frontal lobe with the temporal lobe * **Cingulum** * found in the cingulate gyrus. * It connects the frontal lobe, parietal lobe, parahippocampal gyrus & temporal lobe. ## Examples of the involvement of multiple cortical regions in a sensory/cognitive process: * **Angular gyrus & supramarginal gyrus** * provide a functional interface between auditory and visual association areas. * important in naming, reading, writing, and calculation. **Image description:** A diagram showing the brain, highlighting the angular gyrus and supramarginal gyrus. * **Naming an object seen** * Shows how different cortical regions work together to decipher an object i.e. a chair. * Angular gyrus & supramarginal gyrus * provide a functional interface between auditory and visual association areas * important in naming, reading, writing, and calculation. * Pathway = primary visual area → higher order visual association area → angular gyrus → Wernicke's area → arcuate fasciclus → Broca's area → primary motor area ## Projection fibres: * Afferent fibres * Efferent fibres ## Internal capsule = superior to the brainstem * **Composed of the anterior limb, genu + posterior limb.** * **Caudate nucleus =** medial to internal capsule. * **Thalamus =** medial to internal capsule * **Lentiform nucleus =** lateral to internal capsule. * Consist of two nuclei = putamen and the globus pallidus. * **Corona radiata =** Superior to these nuclear masses of gray matter - these radiating projection fibres are known as the corona radiata. * Move in all directions from this region to the cortex. **Image description:** A diagram showing a horizontal section of the brain, highlighting the caudate nucleus, the thalamus, the lentiform nucleus, and anterior, genu, and posterior portions of the internal capsule. ## Layers of the cerebral cortex: * Consist of 6 layers. **Image description:** A labeled diagram showing the 6 layers of the cerebral cortex. * Layer 1 is a more superficial layer * Layer 3 neurons give rise association/commissural fibres * Layer 4 – termination site for thalamocortical afferents * Layer 5 - efferent fibres * P = pyramidal cells gives efferent fibres which project to extracortical targets i.e. thalamus, basal ganglia, spinal cord + brainstem * In the precentral gyrus/primary motor area – layer 5 contains Betz cell (very large pyramidal cells) which give off fibres that form the 'Pyramidal tract' ## Variation in cortical layers: **Image description:** A labeled diagram showing the 6 layers of the cerebral cortex for the primary motor cortex and the primary sensory cortex. * Different areas of the cortex have different thickness of layers depending on function. * In primary motor cortex – layer 5 is thicker as Betz cells give rise to form the pyramidal tract. * In the primary sensory cortex – layer 4 is thicker due to more termination of the thalamocortical afferents. ## Arterial supply – Circle of Willis: **Image description:** A diagram showing the circle of Willis and the major arteries that supply blood to the brain. * Ventral arteries are paired (left and right) – travel across the neck + enter the skull. * Ventral arteries join to make the basilar artery (lies on the basilar part of the pons) * Anterior spinal arteries branch off – supplies the spinal cord. * Posterior inferior cerebellar artery – supplies the cerebellum. * The basilar artery branches off into pontine arteries – supply the pons. * Basilar artery also supplies the cerebellum via the anterior inferior cerebellar artery + superior cerebellar artery. * Posterior arteries are paired (left and right) * Internal carotid arteries (left and right) – also enter the skull and three arteries branch off each internal carotid arteries: * Anterior cerebral artery * Middle cerebral artery * Posterior cerebral artery * Anterior communicating artery – provides lateral circulation which is beneficial as it allows brain supply to reach the brain even if there's a blockage. * Anterior cerebral artery + middle cerebral artery + posterior cerebral artery = supply the cortex. ## Arterial supply of the cortex: **Image description:** A diagram showing the arteries that supply blood to the cortex. * Medial surface is associated with lower limbs. * ACA = Anterior cerebral artery * Medial surface as far back as the parieto-occipital sulcus (Supply 'the leg area') * MCA = Middle cerebral artery * Most of the lateral surface of the cortex. * PCA = Posterior cerebral artery * inferolateral and medial surface of the temporal lobe. * medial & lateral surface of the occipital lobe (supply the visual cortex) **Image description:** A diagram showing the arteries supplying blood to each surface of the brain: lateral, medial, and inferior ## Loss of function **Image description:** A table showing the loss of function, the cerebral artery affected, and the region of brain damaged. | Loss of function | Cerebral artery affected | Region of brain damaged | |---|---|---| | Paralysis of the right leg | Right anterior cerebral artery | | | Inability to understand language | | | | Loss of sensation in the left arm | Middle cerebral hemisphere * | | | Inability to recognise faces but not blind (prosopagnosia) | | | | Drooping of the left side of the mouth | | | | Paralysis of the right side of the tongue | | | | Loss of sensation in the left foot | | | * = in the right cerebral hemisphere – usually people have dominance in their right cerebral hemisphere – right handed people. ## Stroke = a condition that occurs in resut of the blood supply **Two main causes:** * Haemorrhagic – rupture of a blood vessel (e.g high blood pressure, abnormal vascular structure) * Ischemic - Interruption of the blood supply to the brain (e.g blood clot blocking the artery)