Brain Internal Structure PDF

Brain (Internal structure)  The cross section of the brain shows the internal features of it It consists gray and white mater Gray mater is cell bodies while the white mater is mylenated fibers Gray mater is found in the cortex of the brain (mainly) and some of collection o...

Brain (Internal structure)  The cross section of the brain shows the internal features of it It consists gray and white mater Gray mater is cell bodies while the white mater is mylenated fibers Gray mater is found in the cortex of the brain (mainly) and some of collection of cell bodies below the cortex is called nuclei or ganglia  This gray mater includes Cuadate nucleus Lentiform nucleus Thalamus Between these run white fiber is called internal capsule Cerebrum White Matter (Medulla)  White Matter Underlies the cortex Contains: Nerve fibers (predominantly myelinated) Neuroglia Blood vessels The nerve fibers originate, terminate or sometimes both, within the cortex White matter White matter = myelinated axons that form bundles of fibers between different nuclear masses  Depending on their origin & termination, these nerve fibers are classified into three types: A. Association B. Projection C. Commissural  Association Fibers Unite different parts of the same hemisphere Are of two kinds: Short association fibers: those connecting adjacent gyri, Long association fibers: those connecting more distant gyri  Short Association Fibers Lie immediately beneath the gray substance of the cortex Connect together the adjacent gyri.  Legend: Short Association Fibers Pia gyrus Cerebral cortex sulcus (grey matter) Short arcuate / U-shaped fibers White matter Coronal section of cerebral cortex  Long Association Fibers Long fibers travel through white matter to connect distant areas of cerebral cortex Link the primary sensory areas in parietal, temporal and occipital lobes to the association areas of the cerebral cortex, and to each other  Legend: Long aAssociation Fibers Approximate location of Corona radiata posterior commissure Superior longitudinal fasciculus Corpus callosum Internal capsule * Anterior commissure Uncinate fasciculus Optic radiations Arcuate Fasciculus = white matter fasciculus Meyer’s loop + external and extreme capsules Mid-sagittal section through one hemisphere Superior longitudinal fasciculus: connects the frontal, parietal, temporal and occipital lobes Uncinate fasciculus: Broca’s Arcuate connects frontal Area Fasciculus Arcuate fasciculus: to temporal lobe, connect gyri in contributing to the frontal to temporal regulation of lobes, important for behavior Wernicke’s Area language function Cingulum: connects frontal & parietal lobes to the para- hippocampal gyrus and adjacent temporal gyri Inferior longitudinal fasciculus: connects occipital to temporal pole & contributes to visual recognition Brocas and Wenickes areas The speech centers in our brains are Broca's area and Wernicke's area. Broca's area in the left frontal cortex controls language production Wernicke's in the posterior temporal lobe analyzes the words you see and hear and also places those words in the correct order before you speak. How language centres work: an example Imagine that someone asks, "How are you?" Once that message travels through the ear, the electrical impulse from the vibration enters the primary auditory cortex, which figures out that the source is a human voice. Then, the information moves to Wernicke's area for interpretation, followed by Broca's area where you select the words for a response. That message then goes to the primary motor cortex that signals your larynx and mouth to vocalize, "I'm fine, thanks"  Commissural Fibers Corpus Callosum Connect the corresponding regions of the two hemispheres Include: F Corpus callosum Anterior commissure P Hippocampal commissure (commissure of fornix) *(Posterior commissure, not a cerebral commissure) Commissural Fibers  Corpus Callosum Is a fibrous bridge located in the depth of the median longitudinal fissure Connects the two cerebral hemispheres together Shorter craniocaudally than is the hemisphere Cranial end is nearer to the frontal pole of hemisphere as compared to caudal end to the occipital pole  The fibers in the corpus callosum connect the corresponding regions of the two C hemispheres with C each other (except the inferior part of the temporal lobes)  Fibers linking the two frontal poles Anterior with each other, forceps curve forward & F form u-shaped anterior forceps (forceps minor) C P C Fibers linking the two occipital poles with each other, Posterior curve backward & forceps O form u-shaped posterior forceps (forceps major)  Parts of Corpus Callosum Genu Body Splenium Rostrum Anterior commissure Anterior commissure: crosses midline rostral to the columns of the fornix has a «bicycle handlebars» shape connects the olfactory bulbs in each hemisphere interconnects frontal lobes as well as parietal lobes in each hemisphere Anterior Commissure fornix Bundle of fibers IVF runs transversely in front of the anterior Anterior columns of fornix column of fornix Connects the inferior and middle temporal gyri & the olfactory regions of the two hemispheres  Hippocampal Commissure Bundle of fibers runs transversely between the crura of the fornix Connect the two hippocampi with each other (note that hippocampo- mamillary fibers do not cross) Hippocampal Commissure Posterior commissure Posterior commissure: crosses midline within the caudal part of the 3rd ventricle Connects midbrain visual relay nuclei from both sides (Edinger-Westphal nuclei)  Posterior Commissure Rounded band of white fibers Crossing the midline on the dorsal aspect of the upper end of the cerebral aqueduct (located between superior P colliculus & pineal body) SC Connects the left and IC right midbrain. Plays Cerebral important role in the aqueduct bilateral pupillary reflex  Projection Fibers Fibers running vertically through the hemispheres Consist of: Cortical afferent fibers conveying impulses to the cerebral cortex: (mainly thalamo-cortical fibers) Cortical efferent fibers carrying impulses away from the cortex to the lower centers: (corticostriate, corticobulbar, corticopontine, corticospinal, & descending autonomic fibers)  Deeper to the cortex, these fibers are arranged radially as the corona radiata corona Then the fibers converge to radiata form a sheath, called the internal capsule, that passes between the thalamus and the basal ganglia Continue in the: Crus of the midbrain Basilar part of pons Pyramid of medulla oblongata Continue in the spinal cord as the corticospinal tracts Commissural fibers of Projection fibers of the corpus callosum the internal capsule Internal Capsule BG Bundle of projection fibers, passes through the interval Th between the thalamus and the basal ganglia Projection Tracts Has 5 parts: 1. Anterior limb: between caudate (C) & lentiform (L) nuclei C 2. Genu 1 2 L 3. Posterior limb: between 3 thalamus (TH) & lentiform nucleus Th (L ) 4 4. Retrolenticular part: caudal to lentiform nucleus 5. Sublenticular part: below lentiform nucleus (can not be seen in this section)  Anterior limb contains: Thalamocortical projections that connect mediodorsal nucleus of thalamus with the prefrontal cortex Frontopontine fibers Genu contains: Corticobulbar fibers which connect the cortex with cranial nerve motor nuclei in the brainstem  Posterior limb contains: Corticospinal Corticobulbar Thalamocortical projections from: VPN to the primary somatosensory cortex VAN & VLN to motor regions of cortex  Retrolenticular part contains thalamocortical projections: Geniculocalcarine fibers (visual radiation), from the lateral geniculate nucleus of thalamus to the visual cortex in the occipital lobe & few Geniculotemporal fibers (auditory radiation) from the medial geniculate nucleus of thalamus to the auditory cortex in the temporal lobe  Sublenticular part contains thalamocortical projections: geniculo- temporal fibers (auditory radiation) from the medial geniculate nucleus of thalamus to the auditory cortex in the temporal lobe  Internal capsule Anterior limb Frontopontine fibers Genu Corticobulbar fibers Posterior limb Corticospinal Corticobulbar Thalamocortical projections Retrolenticular part visual radiation auditory radiation Sublenticular part auditory radiation Commissural fibers of Projection fibers of the corpus callosum the internal capsule  QUIZ The types of fibers in the corpus collosum is? Commissural fubers Long association Short association Projection  QUIZ The fibers which connect different gyri in same hemisphere Commissural fubers Long association Short association Projection  QUIZ The fibers that connect the cortex with subcortical areas is called Commissural fubers Long association Short association Projection  QUIZ What is type of fibers in the internal capsule Commissural fubers Long association Short association Projection  Which part of the internal capsule contains cortico-spinal fibers a) Anterior limb b) Genu c) Posterior limb d) Retrolenticular part e) Sublenticular part  The hippocampal commissure connect Two cerebral hemisphere Corpus collosum in both hemisphere Fornix in both hemisphere None of the above  Clinical Notes Bilateral lesion of the inferior longitudinal fasciculus (as in carbon monoxide poisoning), leads to: Loss of identification of the: Nature of objects (object agnosia) Individual faces (prosopagnosia) The elementary vision remains intact Damage to corpus callosum leads to split-brain syndrome. The two half of the brain behave relatively autonomously Damage to splenium of corpus callosum leads to posterior disconnection syndrome of alexia (cannot understand written material) without agraphia (can speak and write without difficulty) Thank You & Good Luck