The Front Cover (80k JPEG)
CURRENT GENERATION WHERE NERVE MEETS MUSCLE
An MCell simulation of ionic current generation at a neuromuscular junction in a rat diaphragm muscle shows the neurotransmitter acetylcholine (ACh, cyan spheres) 300 microseconds after release of 6,200 ACh molecules. The highly convoluted membrane of the junction is covered with acetylcholine receptors (cup-shaped objects on the membrane). After release, ACh molecules diffuse away from their release point and bind to receptors and acetylcholinesterase (AChE). The image shows bound AChE (black spheres), unbound AChE (gray spheres), and receptors--unbound (purple), singly bound (red), doubly bound closed (green), and doubly bound open (yellow). Doubly bound open receptors conduct an ionic current that initiates a cascade of events leading to muscle fiber contraction. AChE breaks down ACh and prevents prolongation of the current.