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. 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. 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. 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. Two types of dendrites present on pyramidal cells are apical and basal dendrites. Apical dendrites are the most distal along the ascending trunk, and reside in layer 1. These distal apical dendrites receive synaptic input from related cortical as well as globally modulatory subcortical projections. Basal dendrites include shorter radially distributed dendrites which receive input from local pyramidal cells and interneurons. Pyramidal neurons segregate their inputs using proximal and apical dendrites. 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. 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. The hippocampus contains pyramidal neurons in three areas: CA1, CA2, and CA3. The pyramidal neurons of each area have different properties. However, in all areas, dendritic synthesis of proteins is necessary for late long-term potentials in the hippocampal neurons. Neurons throughout the limbic system are known to have 'burst' properties. These cells undergo synchronous and paroxysmal depolarizations, firing short sequences of action potentials called bursts. The stratum oriens is the location between layers containing basal dendrites. The stratum lucidum, stratum radiatum, and the stratum moleculare-lacunosum are layers of apical dendrites and are ordered from least distant to most distant from the soma of the neuron. CA3 projects Schaffer collaterals to apical dendrites in CA1. Individual pyramidal cells in the CA3 region have burst properties due to high densities of calcium channels in their proximal dendrites. Depolarization of the membrane may also trigger these bursts. Calcium entry into the cell causes more prolonged depolarization and increased action potentials. Usually curtailed by the hyperpolarizing local inhibition (due to the excitatory collateral system), this can lead to gradual recruitment of CA3 neurons and result in synchronized burst discharges. After hyperpolarization by calcium-dependent potassium conductance is also used as a method of controlling these bursts.