WHY has this happened and WHY does it hurt?

Imagine a typical daily task such as brushing your teeth or putting on sunscreen.  Pretty uneventful, right?  Get it done, move on.  Well, now imagine having to do that task knowing that it was going to cause you excruciating pain that could last for minutes, hours, etc.  That is what those who have trigeminal neuralgia suffer from daily.  The most minimal of contact with the trigeminal nerve will change the course of their near future due to the pain that it is sure to cause them.  Here is how it works...

The trigeminal nerve is the fifth cranial nerve.  It is one pair of 12 different pairs of nerves that are attached directly to the brain.  Here is a list of the cranial nerves.  The cranial nerves are sensory only, which means that they relay information regarding the senses (smell, sight, touch, etc.) or both sensory and motor, which means that they relay sensation but also assist with movement.  The numbers are placed into the photo based on what information they carry.

1. Olfactory - smell
2. Optic - vision
3. Oculomotor - the muscles of the eye
4. Trochlear - the superior, oblique muscles of the eye
5. Trigeminal (sensory and motor) - sends sensory information from the face and mouth and motor information to the chewing muscles of the mouth (Notice how large the corresponding number is on the image!  If this nerve is the cause of pain, it unfortunately has a lot of reach.)
6. Abducens - the lacteral rectus muscles of the eye
7. Facial - muscles of facial expression, lacrimal glands (tear ducts!) and salivary glands
8. Vestibulocochlear (Acoustic) - equilibrium and hearing
9. Glossopharyngeal - throat for swallowing, posterior part of tongue, salivary glands
10. Vagus - internal organs
11. Spinal Accessory - the muscles that move head, neck and shoulders
12. Hypoglossal - muscles of the tongue

The trigeminal nerve splits into three different branches which carry information from three different areas of the face and mouth.  Here is an image of these three areas -

In a trigeminal neuralgic attack, pressure is applied directly to a part of the nerve that has lost its protective covering called its myelin sheath.  Nerves are composed of nerve cells called neurons which relay information by sending an electrical impulse up an axon, a long, thin cablelike projection.  Because the axon is sending electrical information, it is covered with a protective covering called the myelin sheath.  Myelin is only found in our nervous system and is basically insulation for the nerve cells to give protection and to allow information to travel quickly, like the protective covering of an electrical wire.

Something has damaged this protective covering in a case of trigeminal neuralgia and the nerve is exposed.  This can be caused by a number of different things.  The different causes of damage to the myelin sheath define the type of trigeminal neuralgia.  The different types of this disease are:

• TN1 (classic or tic douloureux) - This pain is caused by loss or damage to the myelin typically from pressure on the sheath from a surrounding blood vessel.  The pain occurs spontaneously and is temporary.

• TN2 - This is similar to TN1, however the pain is more chronic.

• STN (secondary symptomatic TN) - The loss of myelin sheath in this type of trigeminal neuralgia is caused by multiple sclerosis.

• PHN (post-herpetic neuralgia) - This pain is caused by a shingles outbreak on the trigeminal nerve.

• TNP (trigeminal neuropathic pain) - Neuropathic pain differs from neuralgic pain in that it is caused by damage to the nerve itself...not just the myelin sheath.  The injured nerve will send random painful signals to the brain.  It could be a result of facial trauma, ear, nose or throat surgery, a stroke, etc.

• TDP (trigeminal deafferentation pain) - This type of trigeminal pain results from a loss of the nerve, but continued pain signals...sort of like phantom limb pain.

The bottom line is that damage to the myelin sheath and exposure of the trigeminal nerve can result in an excruciating pain whenever pressure is applied to that nerve.  The pain and suffering that this disease causes to the person can be debilitating.

References:

http://www.brainfacts.org/brain-basics/neuroanatomy/articles/2012/the-neuron/

http://fpa-support.org/trigeminal-neuralgia/