Dendrites

William N Ross, New York Medical College, Valhalla, New York, USA
Matthew Larkum, Humboldt University, Berlin, Germany

Published online: July 2012

DOI: 10.1002/9780470015902.a0000092.pub3

Full Article on Wiley Online Library

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.

Keywords: synaptic potentials; action potentials; integration; initial segment; channels

Further Reading
	Johnston D, Magee JC, Colbert CM and Christie BR (1996) Active properties of neuronal dendrites. Annual Review of Neuroscience 19: 165–186.
	book Johnston D and Wu SM (1995) Foundations of Cellular Neurophysiology. Cambridge, MA: MIT Press.
	book Levitan IB and Kaczmarek LK (1997) The Neuron: Cell and Molecular Biology, 2nd edn. New York: Oxford University Press.
	book Stuart G, Spruston N and Häusser M (2008) Dendrites, 2nd edn. New York: Oxford University Press.
	Yuste R and Tank DW (1996) Dendritic integration in mammalian neurons, a century after Cajal. Neuron 16: 701–716.

Article Title:	Dendrites
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	Figure 1. Heterogeneity of dendritic shapes from a variety of vertebrate and invertebrate species: (a) cat motor neuron; (b) locust interneuron; (c) rat neocortical pyramidal cell; (d) cat retinal ganglion cell; (e) salamander amacrine cell; (f) human Purkinje cell; (g) rat thalamic relay neuron; (h) mouse olfactory granule cell; (i) rat striatal spiny projection neuron; (j) human cell from nucleus of Burdach; (k) Purkinje cell from mormyrid fish; (l) Golgi glial cell in mouse cerebellum; (m) axonal arborisation of turtle isthmotectal neuron. Adapted from Mel BW (1994) Neural Computation 6: 1031–1085. © 1994 by the Massachusetts Institute of Technology.
	Figure 2. Action potentials in a rat neocortical layer V pyramidal neuron initiated by distal synaptic stimulation. The traces show simultaneous whole‐cell recordings from the soma and from a location in the dendrites 525 m away. The positions of the recording and stimulating electrodes are shown schematically in the inset on the right. Following stimulation (arrow), a fast‐rising synaptic potential is recorded at the dendritic location. In the soma, this synaptic potential is smaller and slower. However, when the action potential is initiated it is recorded first in the soma and later in the dendrites. The dendritic action potential is smaller and slower, but still active. Adapted from Stuart GJ and Sakmann B (1994) Nature 367: 69–72.
	Figure 3. Pyramidal neuron from the somatosensory region of the rat cortex showing the regions of the dendritic tree and the kinds of spikes that are generated. Black designates the principal region for Na⁺ action potentials with the initiation region labelled. The region for the generation of dendritic calcium spikes indicated in blue and the regions for NMDA spike generation in thin dendrites indicated in red. The inset shows the high density of synaptic boutons that occurs on the thin dendrites. Reproduced with permission from Larkum ME et al. (2009) Science 325: 756–760.

Dendrites

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