Figure 4.6

Somatic voltage response to a single synaptic EPSP on a spine at a distance of 500 μm in the apical dendrites of a CA1 pyramidal cell model (blue dot on cell image). The voltage amplitude is reduced (black line) when 20,000 inactive spines are evenly distributed in the dendrites, compared to when no spines are included (blue dashed line). The somatic voltage response is corrected if R_m is decreased and C_m is increased in proportion with the additional membrane area due to spines
(blue dotted line). The CA1 pyramidal cell is n5038804, as used in Migliore et al. (2005); model has 455 compartments (with no spines); passive membrane throughout with R_m = 28 kΩ cm², R_a = 150 Ω cm, C_m = 1 μF cm⁻²; spine head: diameter 0.5 μm, length 0.5 μm; spine neck: diameter 0.2 μm, length 0.5 μm; 20,000 spines increase the total membrane area by 1.4 and reduce the somatic voltage response by around 30%. For a similar comparison see Holmes and Rall (1992b).