Neuromuscular junction Flashcards
What is the speed of conduction down a motor nerve?
Why is conduction so fast?
Very fast, around 50-100 m/s, which is much faster than would be expected from the diameter of the nerve: a squid giant axon with a diameter of 500 μm still only conducts impulses at 25 m/s.
The myelin insulates parts of the fibre so that conduction jumps between the gaps between adjacent Schwann cells - these bare areas are about 1 μm long and are known as nodes of Ranvier. There is a concentration of voltage-gated sodium channels at the nodes of Ranvier so that depolarization occurs then ‘jumps’ to the next node. This known as saltatory conduction.
What are the precursors for ACh synthesis and where do they come from?
As the name suggests, ACh (Fig 1a) requires a source of choline (Fig 1b) and acetyl groups (Fig 1c). Choline is an essential nutrient found particularly in meat and eggs: some is present in vegetables, although at a much lower concentration. Acetyl-CoA, produced during aerobic decarboxylation of pyruvate, donates the acetyl group.
The enzyme responsible for synthesis of ACh is choline acetyltransferase. This is a product of the CHAT gene on the long arm of chromosome 10 (location 10q11.2).
