What will be the pathologic effect of Clostridium tetani on the muscles?

Answer 1

Clostridium tetani is a bacterium that produces and secretes a toxin -- the tetanus toxin -- that paralyzes muscles. Tetanus is characterized by a specific type of paralysis wherein the muscles are continuously flexed. The toxin achieves this by selectively altering the activity of the neurons that control muscle (called motor neurons). Motor neurons are controlled through connections from many other cells. Some connections are stimulatory and would tend to increase the likelihood that the motor neuron stimulates muscle contraction; other connections are inhibitory and decrease the likelihood of motor neuron activity.

The stimulatory and inhibitory connections are constantly in a tug-of-war over control of the motor neurons. It is the regulation of these connections that controls whether a muscle will contract or not. At rest, input from the inhibitory neurons predominates, and the motor neuron is quiet; when contraction is desired, the stimulatory neurons increase their activity and activate the motor neuron. Tetanus toxin selectively knocks out these inhibitory connections so that motor neurons are excited continuously. The result is that motor neurons cannot be controlled in the usual way, by increasing and decreasing the stimulatory and inhibitory inputs. Since this is the only way to control muscle contraction, the ultimate result is paralysis -- the inability to consciously control the muscles. The specific type of paralysis caused by tetanus is called spastic paralysis. This is different from the flaccid paralysis seen in other diseases (eg, Clostridium botulinum).