How strychnine removes the spinal cord’s brake
The spinal cord does more than relay commands from the brain. It also sorts and limits incoming signals, helping keep routine sensory input from triggering excessive movement. Glycine is one of the chemical messengers used by inhibitory nerve cells—cells that dampen activity in nearby neurons.
When glycine attaches to its receptors, it makes certain nerve cells less likely to fire. Strychnine binds to those same receptors and prevents glycine from working. The result is not a new command to contract; it is a loss of the restraint that normally keeps motor circuits from becoming overactive.
Why small stimuli can set off a seizure-like response
With that inhibition weakened, ordinary signals such as touch or sound can provoke an exaggerated burst of activity through spinal motor pathways. Muscles contract forcefully, and the usual coordination between contraction and relaxation breaks down. The spasms can affect many muscles at once, including those involved in breathing.
This is why the reaction can look dramatically disproportionate to the trigger: the signal itself may be ordinary, but the circuit handling it has lost an important control. Strychnine turns down inhibition, not up a dedicated “spasm” command.
The distinction explains the poison’s danger. When the nervous system’s braking signals are blocked, the body cannot reliably settle the activity that would normally follow a stimulus, leaving muscles locked in repeated, exhausting contractions.
