Neuromuscular junctions in fast-twitch muscle fibres

A confocal micrograph of living nerve terminals on rat skeletal muscle fibre. It shows mature (18 weeks after birth) neuromuscular junctions on extensor digitorum longus (EDL, fast -twitch and non-postural) rat muscle fibres. Fluorescently labelled alpha-bungarotoxin, a snake toxin, has been used to visualise the regions of highly concentrated receptor proteins on the musce fibre surface. These align precisely with branches of the overlying motor nerve terminal. When activated, the terminal releases chemicals which bind onto the receptors, making the muscle fibre contract.