Dendrites

Abstract Dendrites are highly branched neuronal structures that form the main synaptic target of other nerve cells. They are studded with small spines that are the contact points for excitatory inputs. Dendrites integrate these excitatory inputs, along with inhibitory inputs, in the form of brief depolarising or hyperpolarizing synaptic potentials, and generate the output of the neuron. This signal is usually in the form of an action potential initiated near the soma. Although early models assumed that the dendrites were passive, we now know that they have many voltage dependent conductances distributed heterogeneously over the surface of the arbours. These conductances lead to various forms of signal modulation and localised regenerative activity that greatly expand the computational complexity of CNS neurons. Key Concepts: Dendrites comprise approximately 95% of the neuronal surface and are the main place where synaptic contacts are made. Dendritic architecture is stereotypical for different neurons types and probably relates to the integrative function of these cells. Synaptic potentials originate in the dendrites and propagate decrementally to the axon hillock where the output sodium spike is usually generated. Dendrites contain voltage‐dependent channels distributed in ways characteristic to each cell type, which modulate the propagation of synaptic potentials. These voltage‐dependent channels can also support regenerative action potentials, which either back‐propagate over the dendrites from the somatic region, or are initiated locally in the dendrites. These dendritic action potentials are complex. They are primarily sodium dependent, calcium dependent, or, in some cases, involve the ligand‐gated NMDA receptor. The function of these dendritic action potentials is not always clear. One possibility is to control the calcium concentration in different parts of the cell, which can then regulate synaptic plasticity or other signalling mechanisms. Another possibility is to influence the integration of synaptic potentials and ultimately determine the output of the neuron.