<P> Snake venoms act as toxins at the neuromuscular junction and can induce weakness and paralysis . Venoms can act as both presynaptic and postsynaptic neurotoxins . </P> <P> Presynaptic neurotoxins, commonly known as β - neurotoxins, affect the presynaptic regions of the neuromuscular junction . The majority of these neurotoxins act by inhibiting the release of neurotransmitters, such as acetylcholine, into the synapse between neurons . However, some of these toxins have also been known to enhance neurotransmitter release . Those that inhibit neurotransmitter release create a neuromuscular blockade that prevents signaling molecules from reaching their postsynaptic target receptors . In doing so, the victim of these snake bite suffer from profound weakness . Such neurotoxins do not respond well to anti-venoms . After one hour of inoculation of these toxins, including notexin and taipoxin, many of the affected nerve terminals show signs of irreversible physical damage, leaving them devoid of any synaptic vesicles . </P> <P> Postsynaptic neurotoxins, otherwise known as α - neurotoxins, act oppositely to the presynaptic neurotoxins by binding to the postsynaptic acetylcholine receptors . This prevents interaction between the acetylcholine released by the presynaptic terminal and the receptors on the postsynaptic cell . In effect, the opening of sodium channels associated with these acetylcholine receptors is prohibited, resulting in a neuromuscular blockade, similar to the effects seen due to presynaptic neurotoxins . This causes paralysis in the muscles involved in the affected junctions . Unlike presynaptic neurotoxins, postsynaptic toxins are more easily affected by anti-venoms, which accelerate the dissociation of the toxin from the receptors, ultimately causing a reversal of paralysis . These neurotoxins experimentally and qualitatively aid in the study of acetylcholine receptor density and turnover, as well as in studies observing the direction of antibodies toward the affected acetylcholine receptors in patients diagnosed with myasthenia gravis . </P> <P> Any disorder that compromises the synaptic transmission between a motor neuron and a muscle cell is categorized under the umbrella term of neuromuscular diseases . These disorders can be inherited or acquired and can vary in their severity and mortality . In general, most of these disorders tend to be caused by mutations or autoimmune disorders . Autoimmune disorders, in the case of neuromuscular diseases, tend to be humoral mediated, B cell mediated, and result in an antibody improperly created against a motor neuron or muscle fiber protein that interferes with synaptic transmission or signaling . </P>

Explain what happens at the neuromuscular junction in order to initiate muscle contraction