Figure 3. Bladder smooth muscle cells (SMCs) have a membrane oscillator that generates the periodic action potentials that initiate the process of excitation–contraction coupling.

Neurotransmitters such as ATP and acetylcholine (ACh), which are released from parasympathetic axonal varicosities that innervate the bladder, activate or accelerate the oscillator by inducing membrane depolarization (ΔV) through two separate pathways. Reproduced from Berridge (2008), with permission.