The location where strychnine mainly acts for its clinical presentation is:

Strychnine competitively antagonizes glycine, an inhibitory neurotransmitter released by postsynaptic inhibitory neurons in the anterior horn cells of the spinal cord. It binds to the chloride ion channel, causing increased neuronal excitability and exaggerated reflex arcs. This results in generalized seizure-like contraction of skeletal muscles. Simultaneous contraction of opposing flexor and extensor muscles causes severe muscle injury, with rhabdomyolysis, myoglobinuria, and acute renal failure. Ref: Nordt S.P. (2012). Chapter 145. Strychnine. In K.R. Olson (Ed), Poisoning & Drug Overdose, 6e.