Why does strychnine cause violent muscle spasms? · Grey Matter

In the spinal cord and brainstem, inhibitory interneurons release glycine onto motor neurons, opening glycine receptors (chloride channels) that keep the motor neurons from responding to every input and let opposing muscles relax in turn.

Why does strychnine cause violent muscle spasms?

In the spinal cord and brainstem, inhibitory interneurons release glycine onto motor neurons, opening glycine receptors (chloride channels) that keep the motor neurons from responding to every input and let opposing muscles relax in turn. Strychnine binds the glycine receptor at the glycine site and blocks it. With that inhibition gone, any sensory input (a touch, a sound) drives motor neurons unchecked, and whole groups of muscles contract together in painful spasms. The brain stays largely unaffected at first, since forebrain inhibition relies mostly on GABA, which is why consciousness is usually preserved.