Main site of action of tetanus toxin:
**Core Concept**
Tetanus toxin is a potent neurotoxin produced by the bacterium *Clostridium tetani*. The toxin acts by inhibiting neurotransmitter release at the neuromuscular junction, leading to muscle rigidity and spasms. The main site of action of tetanus toxin is the central nervous system, specifically the spinal cord and brainstem.
**Why the Correct Answer is Right**
Tetanus toxin binds to gangliosides on the surface of neurons, particularly in the spinal cord and brainstem. Once bound, the toxin is internalized and cleaved into two fragments, which inhibit the release of neurotransmitters such as glycine and GABA. This results in an increase in excitatory neurotransmitter release, leading to muscle rigidity and spasms. The toxin's action on the central nervous system disrupts the balance between excitation and inhibition, causing the characteristic symptoms of tetanus.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because tetanus toxin does not primarily act on the peripheral nervous system.
**Option B:** This option is incorrect because tetanus toxin does not primarily act on the skeletal muscle itself, but rather on the neurons that innervate the muscle.
**Option C:** This option is incorrect because while tetanus toxin does bind to gangliosides, its primary site of action is not the peripheral nerves.
**Clinical Pearl / High-Yield Fact**
Tetanus toxin's action on the central nervous system can be remembered using the mnemonic "GABA-GONE," which stands for "Glycine, GABA, and other neurotransmitters are Obstructed by Neurotoxin's Effects."
**Correct Answer: C. spinal cord**