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Gall and phrenology
Described pyramidal decussation, cerebral peduncles, and performed great study on
cranial nerves and optic tract. Noticed the brain indents in the skull (major gyri and
sulci). Associated mental capacity with cerebral cortex
Broca (history of cerebral cortex)
Identified inferior frontal convolutions and pars triangularis and opercularis (locus of
patient Tan's stroke)
- regions were important for language
Six layers (lamina) of cortex
Layer 1 -> plexiform (acellular) layer
Layer 2 -> outer (external) granular layer
Layer 3 -> Outer (external) pyramidal layer
Layer 4 -> Inner granular layer
Layer 5 -> inner pyramidal layer
Layer 6 -> Multiform layer
Layer 1 (plexiform/acelllular layer)
Layer closest to the pia, contains dendritees and axons from other layers
Layer 2 (outer granular layer)
, Relatively small cells, cortical-cortical connections (back and forth within cortex)
- gives rise to rather short association pathways that link gyri together
Layer 3 (outer pyramidal layer)
Large cells with large apical dendrite, cortical-cortical connections
- commissural connections are mediated by axons that arise from layer 3,
interhemispheric (corpus callosum, anterior commissure)
- give rise to cortical association axons or axons that connect various part of crotex
together
Layer 4 (inner granular layer)
Relatively small cells, very few pyramidal cells seen here
- receives inputs from thalamus
Layer 5 (inner pyramidal layer)
Largest cells in cerebral cortex, sends outputs to subcortical structures (other than
thalamus)
- gives rise to cortical association axons or axons that connect various part of cortex
together
Layer 6 (multiform layer)
Many different cell shapes and sizes, primarily gives rise to corticothalamic projections
- sends outputs to thalamus
Other connections of cerebral cortex axons include...
Corticofugal axons to subcortical brain structures and spinal cord. Corticopetal
connections from other subcortical nuclei
When does a fetus develop neurons?