To my understanding, a monosynaptic reflex is the simplest reflex arc, containing only a primary afferent and an effector neuron. Efferent motor pathways are monosynaptic, meaning that there is only a single synapse between the CNS and the skeletal muscle. This means that efferent motor neurons can be very long.
On the other hand, autonomic pathways are polysynaptic. Synapse morphology is different between autonomic and motor pathways. At the neuromuscular junction, a motor neuron splits into a cluster of axon terminals that branch out over the motor end plate. Autonomic neurons have several synaptic varicosities arranged in series like a string of beads.
(1). Yes, with certain drugs anything is possible. Simply block the neurotransmitters and the twitch or reflex is blocked.
http://jp.physoc.org/content/206/2/345.short(2) Monosynaptic reflex are faster than polysynaptic reflexes as there is generally a prolonged output. In a monosynaptic reflexes, it is like me speaking to you over a telephone. I am the only talker and you are the only listener. The phone line only has to connect to 2 people. If I am the one talking, I would be the sensory neuron, and if you are listening you would be the motor neuron. I can tell you what to do really fast because it is only 1 person I have to give instructions to. An example of this is the patellar reflex. The doc hits the patella and your leg kicks. This is becuse the sensory neuron gets hit and he quickly tells the motor neuron to kick. It happens really, really fast. Another example is touching a hot stove, what happens? Before you can even think to yourself that the stove is hot, your hand will pull away. Monosynaptic reflexes are made for very quick responses to stimuli that will not need to be stopped or thought about in order to react.
(3). distracting task slows down reaction time, where consistent warning increases your reaction time