Anerve poison that blocked neurotransmitter receptors on the dendrites would

prevent transmission across the synaptic cleft

When the poison binds to the neurotransmitter receptors on the dendrites, it will block the receptors. The neurotransmitter cannot bind to the blocked receptors, making it unable to work. The poison should cause paralyzing effect because the signal cannot be sent. 
One of the toxins that work this way is curare.

only b