Tetanus toxin act by

The tetanus toxin specifically blocks synaptic inhibition in the spinal cord, presumably at inhibitory terminals that use glycine and GABA as neurotransmitters. The toxin acts pre-synaptically. The abolition of spinal inhibition causes uncontrolled spread pf impulses initiated anywhere in the central nervous system. This results in muscle rigidity and spasms due to the simultaneous contraction of agonists and antagonists, in the absence of reciprocal inhibition. Reference: Textbook of Microbiology; Anathanarayan and paniker's; 10th edition; Page no: 265