Contents

Search

entorhinal cortex (Brodmann's area 28)

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: 1) subiculum 2) CA1 region of the hippocampus 3) cortical (see hippocampal afferents, cortical) a) perirhinal cortex (areas 35 & 36) b) parahippocampal gyrus (areas TF & TH) c) cingulate cortex d) piriform cortex e) temporal polar cortex f) superior temporal gyrus g) ventral insular cortex h) orbitofrontal cortex Efferents: 1) hippocampal formation a) dentate gyrus* b) subiculum c) cornu ammonis CA1# d) cornu ammonis CA3 2) subcortical (see hippocampal efferents, subcortical) a) claustrum b) amygdala c) septal nuclei d) nucleus accumbens e) striatum (caudate & putamen) f) hypothalamus g) anterior thalamic nucleus h) mammillary bodies 3) cortical a) perirhinal cortex b) parahippocampal gyrus c) 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]

Related

alvear pathway Alzheimer's disease (AD) hippocampal afferents, cortical hippocampal efferents, subcortical perforant pathway

General

brain structure

References

  1. The Human Nervous System, George Paxinos, Academic Press, San Diego CA 1990
  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: 4090943

Component-of

hippocampus (hippocampal formation)

Images

images related to entorhinal cortex (Brodmann's area 28)