entorhinal cortex (Brodmann's area 28)
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Structure
- temporal cortex closely associated, if not considered part of the ventral hippocampal formation
- it extends rostrally to about 5 mm short of the rostral end of the amygdala & caudally to the anterior edge of the lateral geniculate nucleus (about midway back through the hippocampus).
- rostrally, the entorhinal cortex borders the periamygdaloid cortex medially
- as the other fields of the hippocampal formation appear caudally, the entorhinal cortex merges medially with the subiculum (pre or para-subiculum)
- there is no easily identifiable lateral border of the entorhinal cortex; it merges with the perirhinal cortex on the banks of the collateral sulcus
- cytoarchitecturally, the entorhinal cortex transforms the 4 layers of the allocortex into the 6 layers of the neocortex
- the allocortical entorhinal region does not gradually transform into the temporal isocortex
- instead, there is an extended stretch of "transentorhinal" cortex with interdigitation of allocortical & isocortical laminae[2]
- stellate nerve cells of layer 2 (pre-alpha) are transformed into pyramidal cells with the transition of allocortex to isocortex
The transentorhinal region thus consists of 6 layers, distinct from other neocortical regions.
- Layer 1: acellular, plexiform layer
- Layer 2: islands of pyramidal & stellate* neurons
- Layer 3: medium sized pyramidal cells (homogenous population)
- Layer 4: often indistinct acellular region
- Layer 5: large pyramidal cells (5-6 cells deep)
- Layer 6: often indistinct
Afferents
- subiculum
- CA1 region of the hippocampus
- cortical (see hippocampal afferents, cortical)
- perirhinal cortex (areas 35 & 36)
- parahippocampal gyrus (areas TF & TH)
- cingulate cortex
- piriform cortex
- temporal polar cortex
- superior temporal gyrus
- ventral insular cortex
- orbitofrontal cortex
Efferents
- hippocampal formation
- dentate gyrus*
- subiculum
- cornu ammonis CA1#
- cornu ammonis CA3
- subcortical (see hippocampal efferents, subcortical)
- cortical
- perirhinal cortex
- parahippocampal gyrus
- orbitofrontal cortex
* Neurons of layers 2 & 3 of the lateral entorhinal cortex send axons into the dentate gyrus to synapse on granule cell dendrites in the outer 2/3 of the molecular layer in the perforant pathway of the trisynaptic circuit.
# Neurons of layers 2 & 3 of the medial entorhinal cortex send axons into the hippocampus to synapse on basilar dendrites of hippocampal CA1 pyramidal cells in the alvear pathway.
Pathology
- stellate neurons of layer 2 are among the most vulnerable & 1st injured in Alzheimer's disease; they are particularly prone to development of neurofibrillary tangles
- the isocortical pyramidal cells of layers 3 to 5 are far less inclined to develop neurofibrillary changes.[2]
More general terms
Additional terms
- alvear pathway
- Alzheimer's disease (AD)
- hippocampal afferents, cortical
- hippocampal efferents, subcortical
- perforant pathway
Component of
References
- ↑ The Human Nervous System, George Paxinos, Academic Press, San Diego CA 1990
- ↑ 2.0 2.1 2.2 Braak H, Braak E. On areas of transition between entorhinal allocortex and temporal isocortex in the human brain. Normal morphology and lamina-specific pathology in Alzheimer's disease. Acta Neuropathol (Berl). 1985;68(4):325-32. PMID: https://www.ncbi.nlm.nih.gov/pubmed/4090943