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apical dendrite
An apical dendrite is a dendrite that emerges from the apex of a pyramidal cell.〔 Apical dendrites are one of two primary categories of dendrites, and they distinguish the pyramidal cells from spiny stellate cells in the cortices. Pyramidal cells are found in the prefrontal cortex, the hippocampus, the entorhinal cortex, the olfactory cortex, and other areas.〔 Dendrite arbors formed by apical dendrites are the means by which synaptic inputs into a cell are integrated.〔Cline HT. Dendritic arbor development and synaptogenesis. ''Current Opinion in Neurobiology'' 2001; 11: 118-126〕 The apical dendrites in these regions contribute significantly to memory, learning, and sensory associations by modulating the excitatory and inhibitory signals received by the pyramidal cells.
== Background ==
Two types of dendrites present on pyramidal cells are apical and basal dendrites. Apical dendrites can be divided into two categories: distal and proximal. The longer distal apical dendrites project from the pyramidal cell body (soma) opposite from the axon. Distal apical dendrites form non-local synapses. Shorter proximal apical dendrites project radially to local pyramidal cells and interneurons.〔Henze DA CW, Barrioneuvo G. Dendritic Morphology and its effects on the amplitude and rise-time of synaptic signals in hippocampal CA3 pyramidal cells. ''Journal of Comparative Neurology''. 1996;369:331-344.〕 Pyramidal neurons segregate their inputs using proximal and apical dendrites.〔CL W. Dendritic Reorganization in Pyramidal Neurons in Medial Prefrontal Cortex after Chronic Corticosterone Administration. ''Journal of Neurobiology''. 2001;49:245-253.〕
Apical dendrites are studied in many ways. In cellular analysis, the electrical properties of the dendrite are studied using stimulus responses. A single surface shock of the cerebral cortex induces a 10-20 ms negative potential, a manifestation of the summed excitatory post-synaptic potentials
(EPSPs) evoked in the distal portions of the apical dendrite.〔Jibiki I MK, Ohtani T, et al. Dendritic Potential in Direct Cortical Responses and Seizure Activity. ''Folia Psychiatrica et Neurologica''. 1978;32(3):329-337〕 This has been called the Dendritic Potential (DP). This is identical with Adrian's Superficial Response in direct cortical responses.〔 At higher intensities the DP is followed by slow positive waves (Adrian's Deep Response) or by a prolonged negative wave lasting for more than 200 ms (Chang’s second component).〔 The highest amplitude of DPs is found on the cortical surface, with the polarity shifted from negative to positive within the superficial layer.〔
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