Rule of 4 of the brainstem

Rule 1

There are 4 cranial nerves from above the pons (including 2 from the midbrain), 4 from the pons, and 4 from the medulla oblongata

Above the pons

1. CN I (Olfactory nerve): not from the midbrain, essentially a peripheral outpost of the CNS

2. CN II (Optic nerve): not from the midbrain, essentially a peripheral outpost of the CNS

3. CN III (Oculomotor nerve): From the midbrain

4. CN IV (Trochlear nerve): From the midbrain

From the pons

1. CN V (Trigeminal nerve)

2. CN VI (Abducens nerve)

3. CN VII (Facial nerve)

4. CN VIII (Vestibulocochlear nerve)

   • The vestibular nuclei are located in the lateral medulla, involvement of which leads to vertigo, vomiting and nystagmus. Intractable vomiting can also occur due to damage to the area postrema in the dorsomedial aspect of the medulla (Neuromyelitis Optica Syndrome is an example of this)

Below the pons - medulla

1. CNIX (Glossopharyngeal):

2. CNX (Vagus nerve):

3. CNXI (Accessory nerve):

4. CNXII (Hypoglossal nerve):