Figure 1.

Spatial relationships in cortical cholinergic signaling. When cholinergic axons (blue, ACh) make synapses in the cortex (Synaptic), the postsynaptic element is usually a dendrite. Nicotinic and muscarinic cholinergic receptors (nAChR and mAChR, respectively) are observed on dendritic branches (Dendrite) and spines (Spine), and are also observed on noncholinergic axons (GABA, glutamate) where they regulate transmitter release. Cholinergic receptors can be activated synaptically or via volume transmission. The latter mode includes both diffusion outside the cleft after synaptic release (Spillover) or in the absence of a synapse (Non-synaptic).