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CEREBRAL TRACTS
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Categories of Tracts Association: Confined to a given hemisphere.
Connect regions of the same hemisphere. Commissural: Interconnect the two hemispheres.
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Categories of Tracts Projection Tracts: Form internal capsule.
Make up ascending and descending tracts. Connect hemispheres to other parts of brain and spinal cord.
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Association Tracts: Examples
Arcuate Cingulum Superior longitudinal fasciculus Superior occipitofrontal fasciculus Inferior occipitofrontal fasciculus Uncinate fasciculus
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Arcuate Tracts Interconnect adjacent gyri.
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Cingulum Connects frontal, parietal and temporal cortical areas on the medial side of each hemisphere.
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Superior Longitudinal Fasciculus
Interconnects areas within the frontal, parietal, occipital, and temporal lobes.
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Superior Occipitofrontal Fasciculus
Located in medial part of hemisphere underneath lateral extension of corpus callosum. Interconnects the frontal lobe with more posterior parts of hemisphere.
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Inferior Occipitofrontal Fasciculus
Runs between the occipital and frontal lobes in the lateral part of each hemisphere under the insula.
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Uncinate Fasciculus Makes a sharp bend around the lateral fissure.
Interconnects the orbital surface of the frontal lobe with the rostral part of the temporal lobe.
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Commissural Tracts: Examples
Corpus callosum Anterior commissure Posterior commissure Hippocampal commissure
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Corpus Callosum Contains about 300 million fibers.
Interconnects neocortical areas in all lobes. Unifies awareness and attention between the two lobes. Permits a sharing of learning and memory.
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Corpus Callosum: Subdivisions
Splenium = Wide caudal part. Body = Large midportion. Genu = Anterior part. Rostrum is continuous with lamina terminalis.
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Anterior Commissure Interconnects areas within the two temporal lobes.
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Posterior Commissure Connects cerebral hemispheres with superior colliculi.
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Hippocampal Commissure
Interconnects two hippocampal formations.
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Projection Tracts: Types
Corticopetal: To cerebral cortex. Corticofugal: From cerebral cortex.
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Corticopetal Projection Fibers
Mostly from thalamus. Form part of internal capsule. Diverge toward cerebral cortex. Form part of corona radiata.
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Corticofugal Projection Fibers
Originate in different parts of cerebral cortex. Converge toward: Basal nuclei. Thalamus. Form part of corona radiata. Form part of internal capsule.
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Projection Tract Examples
Thalamic radiation Corticopontine Corticobulbar Corticospinal Corticoreticular Optic radiation Fornix
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Thalamic Radiation Corticothalamic fibers project within internal capsule from cerebral cortex to thalamus. Thalamocortical fibers project within internal capsule from thalamus to cerebral cortex.
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Corticopontine Projections
Corticopontine fibers projects to pontine nuclei in the pons. Pontine nuclei project to cerebrellum.
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Corticobulbar Projections
Part of pyramidal tracts. Originate mostly in motor cortex. Project to cranial nerve nuclei in brainstem.
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Corticospinal Projections
Part of pyramidal tracts. Originate mostly in motor cortex. Project to cell groups throughout all parts of spinal cord.
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Corticoreticular Projections
Originate in motor and somatosensory cortex. Project to brainstem reticular formations.
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Optic Radiation = Geniculocalcarine tract.
Originates in lateral geniculate body. Runs in lateral direction in the internal capsule. Makes a sharp bend (= Meyer’s loop). Runs in caudal direction toward calcarine fissure in occipital lobe.
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Fornix Major projection system between the hippocampus in temporal lobe and the diencephalon.
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