Trigeminal Nerve/CN 5

The trigeminal nerve, also known as cranial nerve V (CN V), is a large and complex nerve responsible for a variety of functions, primarily in the face. Here's a breakdown of its key aspects:   

Basic Information:     It is the largest of the 12 cranial nerves.  

There are two trigeminal nerves, one on each side of the face.   

• It is a mixed nerve, meaning it has both sensory and motor functions.   
   
• Its name "trigeminal" refers to its three major branches.   
   

Anatomy and Branches:

The trigeminal nerve originates in the brainstem (pons) and has three main branches that extend to different parts of the face:   

1. Ophthalmic nerve (V1): This is a sensory branch that provides sensation to:   

    
   • The skin of the forehead, upper eyelid, and the front part of the scalp.   
      
   • The cornea and conjunctiva of the eye.   
      
   • Parts of the nasal cavity and sinuses.
   • The lacrimal gland.   
      

2. Maxillary nerve (V2): This is also a sensory branch responsible for sensation in:   

    
   • The skin of the lower eyelid, cheek, and upper lip.   
      
   • The teeth of the upper jaw.   
      
   • The mucous membrane of the nose, upper mouth (palate), and maxillary sinus.

3. Mandibular nerve (V3): This is the largest branch and has both sensory and motor functions:  

    
   • Sensory: It carries sensation from the skin of the lower face, chin, and side of the head, the teeth of the lower jaw, the mucous membrane of the lower mouth and part of the tongue (general sensation, not taste).
   • Motor: It controls the muscles of mastication (chewing), including the masseter, temporalis, and pterygoid muscles. It also innervates other muscles like the mylohyoid, anterior belly of the digastric, tensor veli palatini, and tensor tympani.   
      

      

These three branches originate from the trigeminal ganglion, a cluster of nerve cell bodies located in the middle cranial fossa.  

Functions:

The trigeminal nerve has several crucial functions:

• Sensory innervation of the face: It transmits sensations of touch, pain, temperature, and pressure from most of the face, scalp, oral cavity, and nasal cavity to the brain.   
   
• Motor control of chewing: The mandibular branch controls the muscles necessary for chewing, biting, and other movements of the jaw.   
   
• Proprioception: It carries proprioceptive information (awareness of body position) from the jaw, teeth, and muscles of mastication.
• Reflexes: It plays a role in reflexes such as the corneal reflex (blinking when the cornea is touched).  
   

Clinical Significance:

The trigeminal nerve can be affected by various conditions, most notably:

• Trigeminal Neuralgia: This is a chronic pain condition characterized by sudden, severe facial pain, often described as sharp, shooting, or electric shock-like. It is often triggered by light touch or everyday activities like eating, speaking, or brushing teeth. It's often caused by a blood vessel pressing on the trigeminal nerve.   
   

   
• Trigeminal nerve damage: Injury to the trigeminal nerve due to trauma, surgery, tumors, or infections can lead to facial numbness, pain, weakness of the chewing muscles, or altered reflexes.   
   

Understanding the anatomy and function of the trigeminal nerve is essential in diagnosing and treating various neurological and dental conditions affecting the face.

Author

Paddy Kalish OD, JD and B.Arch