Membranes, Ions, and Impulses

Volume 5 of the series Faseb Monographs pp 171-189

Motoneuron dendrites: role in synaptic integration

  • John N. BarrettAffiliated withDivision of Neurobiology, Department of Physiology and Biophysics, University of IowaDepartment of Physiology and Biophysics, University of Miami

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Dendrites constitute over 80% of the receptive surface area in cat motoneurons. Calculations based on matched electrical and geometrical measurements in these neurons indicate that the specific resistance of dendritic membranes in resting motoneurons is at least 2,000 ohm-cm2. When the specific membrane resistance is this high, even the most distal dendritic synapses can contribute significantly to the depolarization of the soma, and hence influence the rate of action potential generation. However, dendritic membrane resistance depends strongly on the level of background synaptic activity. The conductance changes associated with excitatory synaptic activity on a dendrite can be great enough to reduce significantly both the excitatory synaptic driving potential and the effective membrane resistance on that dendrite, and thus greatly reduce the effectiveness of synapses on that dendrite. Inhibitory synaptic activity produces an even greater reduction in dendritic membrane resistance. Thus the relative effectiveness of dendritic synapses depends on the type, distribution, and intensity of background synaptic activity, as well as on dendritic geometry and resting membrane properties. —Barrett, J. N. Motoneuron dendrites: role in synaptic integration. Federation Proc. 34: 1398–1407, 1975.