CEREBRAL TRACTS

Categories of Tracts Association: Confined to a given hemisphere. Connect regions of the same hemisphere. Commissural: Interconnect the two hemispheres.

Categories of Tracts Projection Tracts: Form internal capsule. Make up ascending and descending tracts. Connect hemispheres to other parts of brain and spinal cord.

Association Tracts: Examples Arcuate Cingulum Superior longitudinal fasciculus Superior occipitofrontal fasciculus Inferior occipitofrontal fasciculus Uncinate fasciculus

Arcuate Tracts Interconnect adjacent gyri.

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

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

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.

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

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.

Commissural Tracts: Examples Corpus callosum Anterior commissure Posterior commissure Hippocampal commissure

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.

Corpus Callosum: Subdivisions Splenium = Wide caudal part. Body = Large midportion. Genu = Anterior part. Rostrum is continuous with lamina terminalis.

Anterior Commissure Interconnects areas within the two temporal lobes.

Posterior Commissure Connects cerebral hemispheres with superior colliculi.

Hippocampal Commissure Interconnects two hippocampal formations.

Projection Tracts: Types Corticopetal: To cerebral cortex. Corticofugal: From cerebral cortex.

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

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.

Projection Tract Examples Thalamic radiation Corticopontine Corticobulbar Corticospinal Corticoreticular Optic radiation Fornix

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

Corticopontine Projections Corticopontine fibers projects to pontine nuclei in the pons. Pontine nuclei project to cerebrellum.

Corticobulbar Projections Part of pyramidal tracts. Originate mostly in motor cortex. Project to cranial nerve nuclei in brainstem.

Corticospinal Projections Part of pyramidal tracts. Originate mostly in motor cortex. Project to cell groups throughout all parts of spinal cord.

Corticoreticular Projections Originate in motor and somatosensory cortex. Project to brainstem reticular formations.

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.

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

Building a Cerebral Hemisphere