As the name implies, local anaesthetics are painkillers that act locally. This they do by blocking the transmission of impulses along the nerve fibre – or, in medical language, by blocking “nerve conduction”.
Most people know local anaesthetics from dentistry. When the dentist injects a local anaesthetic into your gums, all the conduction in the relevant nerve is blocked. As a result you don’t have any sensation in the area supplied by the blocked nerve (in this case your lips, gums, teeth, part of your tongue, etc.).
Nerves not only conduct pain, but also supply (innervate) muscles and transmit sensations such as pressure, temperature and touch. The local anaesthetic therefore renders the whole innervated area insensitive. For instance, you can bite down hard on your tongue without feeling it, and you won’t feel heat or coldness in the area. When your tooth is pulled, pain is also eliminated.
The downside is that you lose control over the movement of your tongue and lips, so your speech becomes slurred.
Obviously, local anaesthetics are not employed by dentists only. They are widely used to conquer pain during and after surgery, labour pain (epidural anaesthesia and pain relief) and pain from trauma.
Reviewed by Prof CL Odendal, senior specialist at the department of anaesthesiology at the University of the Free State, April 2010.