CEREBRAL TRACTSCEREBRAL TRACTS

Categories of TractsCategories of Tracts

Association:Association:

Confined to a given hemisphere.Confined to a given hemisphere.

Connect regions of the same hemisphere.Connect regions of the same hemisphere.

Commissural:Commissural:Interconnect the two hemispheres.Interconnect the two hemispheres.

Categories of TractsCategories of Tracts

Projection Tracts:Projection Tracts:

Form internal capsule.Form internal capsule.

Make up ascending and descending tracts.Make up ascending and descending tracts.

Connect hemispheres to other parts of Connect hemispheres to other parts of brain brain and spinal cord.and spinal cord.

Association Tracts: ExamplesAssociation Tracts: Examples

ArcuateArcuateCingulumCingulumSuperior longitudinal fasciculusSuperior longitudinal fasciculusSuperior occipitofrontal fasciculusSuperior occipitofrontal fasciculus Inferior occipitofrontal fasciculusInferior occipitofrontal fasciculusUncinate fasciculusUncinate fasciculus

Arcuate TractsArcuate Tracts

Interconnect adjacent gyri.Interconnect adjacent gyri.

CingulumCingulum

Connects frontal, parietal and temporal Connects frontal, parietal and temporal cortical areas on the medial side of each cortical areas on the medial side of each hemisphere.hemisphere.

Superior Longitudinal Superior Longitudinal FasciculusFasciculus

Interconnects areas within the frontal, Interconnects areas within the frontal, parietal, occipital, and temporal lobes.parietal, occipital, and temporal lobes.

Superior Occipitofrontal Superior Occipitofrontal FasciculusFasciculus

Located in medial part of hemisphere Located in medial part of hemisphere underneath lateral extension of corpus underneath lateral extension of corpus callosum.callosum.

Interconnects the frontal lobe with more Interconnects the frontal lobe with more posterior parts of hemisphere.posterior parts of hemisphere.

Inferior Occipitofrontal Inferior Occipitofrontal FasciculusFasciculus

Runs between the occipital and frontal Runs between the occipital and frontal lobes in the lateral part of each lobes in the lateral part of each hemisphere under the insula.hemisphere under the insula.

Uncinate FasciculusUncinate Fasciculus

Makes a sharp bend around the lateral Makes a sharp bend around the lateral fissure.fissure.

Interconnects the orbital surface of the Interconnects the orbital surface of the frontal lobe with the rostral part of the frontal lobe with the rostral part of the temporal lobe.temporal lobe.

Commissural Tracts: ExamplesCommissural Tracts: Examples

Corpus callosumCorpus callosumAnterior commissureAnterior commissurePosterior commissurePosterior commissureHippocampal commissureHippocampal commissure

Corpus CallosumCorpus Callosum

Contains about 300 million fibers.Contains about 300 million fibers. Interconnects neocortical areas in all Interconnects neocortical areas in all

lobes.lobes.Unifies awareness and attention between Unifies awareness and attention between

the two lobes.the two lobes.Permits a sharing of learning and memory.Permits a sharing of learning and memory.

Corpus Callosum: SubdivisionsCorpus Callosum: Subdivisions

Splenium = Wide caudal part.Splenium = Wide caudal part.Body = Large midportion.Body = Large midportion.Genu = Anterior part.Genu = Anterior part.Rostrum is continuous with lamina Rostrum is continuous with lamina

terminalis.terminalis.

Anterior CommissureAnterior Commissure

Interconnects areas within the two Interconnects areas within the two temporal lobes.temporal lobes.

Posterior CommissurePosterior Commissure

Connects cerebral hemispheres with Connects cerebral hemispheres with superior colliculi.superior colliculi.

Hippocampal CommissureHippocampal Commissure

Interconnects two hippocampal Interconnects two hippocampal formations.formations.

Projection Tracts: TypesProjection Tracts: Types

Corticopetal:Corticopetal:To cerebral cortex.To cerebral cortex.

Corticofugal:Corticofugal:From cerebral cortex.From cerebral cortex.

Corticopetal Projection FibersCorticopetal Projection Fibers

Mostly from thalamus.Mostly from thalamus.Form part of internal capsule.Form part of internal capsule.Diverge toward cerebral cortex.Diverge toward cerebral cortex.Form part of corona radiata.Form part of corona radiata.

Corticofugal Projection FibersCorticofugal Projection Fibers

Originate in different parts of cerebral Originate in different parts of cerebral cortex.cortex.

Converge toward:Converge toward:

Basal nuclei.Basal nuclei.

Thalamus.Thalamus.Form part of corona radiata.Form part of corona radiata.Form part of internal capsule.Form part of internal capsule.

Projection Tract ExamplesProjection Tract Examples

Thalamic radiationThalamic radiationCorticopontineCorticopontineCorticobulbarCorticobulbarCorticospinalCorticospinalCorticoreticularCorticoreticularOptic radiationOptic radiationFornixFornix

Thalamic RadiationThalamic Radiation

Corticothalamic fibers project within Corticothalamic fibers project within internal capsule from cerebral cortex to internal capsule from cerebral cortex to thalamus.thalamus.

Thalamocortical fibers project within Thalamocortical fibers project within internal capsule from thalamus to cerebral internal capsule from thalamus to cerebral cortex.cortex.

Corticopontine ProjectionsCorticopontine Projections

Corticopontine fibers projects to pontine Corticopontine fibers projects to pontine nuclei in the pons.nuclei in the pons.

Pontine nuclei project to cerebrellum.Pontine nuclei project to cerebrellum.

Corticobulbar ProjectionsCorticobulbar Projections

Part of pyramidal tracts.Part of pyramidal tracts.

Originate mostly in motor cortex.Originate mostly in motor cortex.

Project to cranial nerve nuclei in Project to cranial nerve nuclei in brainstem.brainstem.

Corticospinal ProjectionsCorticospinal Projections

Part of pyramidal tracts.Part of pyramidal tracts.

Originate mostly in motor cortex.Originate mostly in motor cortex.

Project to cell groups throughout all parts Project to cell groups throughout all parts of spinal cord.of spinal cord.

Corticoreticular ProjectionsCorticoreticular Projections

Originate in motor and somatosensory Originate in motor and somatosensory cortex.cortex.

Project to brainstem reticular formations.Project to brainstem reticular formations.

Optic RadiationOptic Radiation

= Geniculocalcarine tract.= Geniculocalcarine tract.Originates in lateral geniculate body.Originates in lateral geniculate body.Runs in lateral direction in the internal Runs in lateral direction in the internal

capsule.capsule.Makes a sharp bend (= Meyer’s loop).Makes a sharp bend (= Meyer’s loop).Runs in caudal direction toward calcarine Runs in caudal direction toward calcarine

fissure in occipital lobe.fissure in occipital lobe.

FornixFornix

Major projection system between the Major projection system between the hippocampus in temporal lobe and the hippocampus in temporal lobe and the diencephalon.diencephalon.