Plate and binding of ACh to nicotinic receptors

- The nicotinic ACh receptor is also a Na+ and K+ ion channel.

- Binding of ACh to a subunits of the receptor causes a conformational change that opens the central core of the channel and increases its conductance to Na+ and K+. These are examples of ligand-gated channels.

Table 1-2. Agents Affecting Neuromuscular Transmission


Botulinus toxin



Blocks release of ACh from presynaptic terminals

Competes with ACh for receptors on motor end plate

Effect on Neuromuscular Transmission

Total blockade

Decreases size of EPP; maximal doses produce paralysis of respiratory muscles and death

Hemicholinium Blocks reuptake of choline into presynaptic terminal



Prolongs and enhances action of ACh at muscle end plate

Depletes ACh stores from presynaptic terminal

ACh = acetylcholine; EPP = end plate potential.

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