The cerebral cortex is well known for its complexity. At least 20 different cortical cell types can be classified with ease, and by many accounts this would represent a conservative estimate. Recent studies have used gene expression to identify cell types within the cortex and revealed a high degree of cell diversity (Sugino et al., 2006). It is not the purpose of this chapter to describe every nuance of cell type exhaustively, and indeed there are many excellent accounts elsewhere (Peters and Jones, 1984; Markram et al., 2004; Sugino et al., 2006). Instead, a brief summary of the salient features is given in the following sections as a prelude to describing their synaptic properties and some of the general features of cortical circuitry to emerge from studies in recent years. Neurons in the cortex are almost entirely glutamatergic and thus excitatory, or GABAergic and thus inhibitory (Section 3.3). The following two sections look at the excitatory and inhibitory cell types.

Excitatory cells

There are three main types of excitatory cell in the cortex: the spiny stellate, the star pyramid and the pyramidal cell. The star pyramid is intermediate in form between the stellate and pyramidal cell. The main features of the three cell types are described below, beginning with the spiny stellate and star pyramidal cells and ending with the diversity of pyramidal cell types in individual cortical layers.

Spiny stellate cells

Spiny stellate cells are characterized by, and indeed named after, their star-shaped dendritic pattern.