The neuromuscular junction (motor end plate) is a specialised cholinergic synapse. Which feature is UNIQUE to the motor end plate compared to a central cholinergic synapse?

• A Presynaptic calcium-triggered ACh vesicle release
• B Junctional folds of the postsynaptic membrane greatly increasing the surface area for nAChR clustering ✓
• C Acetylcholinesterase in the synaptic cleft
• D Nicotinic acetylcholine receptors on the postsynaptic membrane

Explanation

The motor end plate has several structural specialisations not found in central synapses: the postsynaptic membrane is deeply infolded into junctional folds (secondary synaptic clefts) that hugely amplify the surface area for nicotinic ACh receptor (nAChR) clustering at the crests of the folds, while voltage-gated Na+ channels are concentrated at the depths. This architecture is unique to skeletal NMJs and accounts for the high reliability of neuromuscular transmission. Both central and peripheral cholinergic synapses use calcium-triggered vesicle release and have acetylcholinesterase, but junctional folds are the NMJ-specific feature targeted by Lambert-Eaton syndrome antibodies and by alpha-bungarotoxin.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.