Trigeminal nerve

5) Trigeminal nerve 1) TGN is the largest cranial nerve 2) TGN nuclei Main sensory nuclei Lies in the posterio...

5) Trigeminal nerve





1) TGN is the largest cranial nerve
2) TGN nuclei

Main sensory nuclei	Lies in the posterior part of the pons It’s lateral to the motor nucleus Continuous below with the spinal nucleus
Spinal nucleus	Continuous superiorly with the main sensory nucleus in the pons Extends inferiorly through the MO to the C2 spinal segment
Mesencephalic nucleus	Most medial nucleus (Close to cerebral aqueduct) Extends inferiorly into the pons
Motor nucleus	Situated in the pons medial to the main sensory nucleus

Sensory component of the TGN

1. About ½ of the fibers divide into ascending & descending branches when they enter the pons
2. Remainder ascends or descends without division
3. Ascending branches terminate in the main sensory nucleus
4. Descending fibers terminate in the spinal nucleus
5. Sensations of pain, temperature, touch & pressure travel along the axons, whose cell bodies are situated in the trigeminal sensory ganglion
6. Sensation of touch & pressure : Fibers in the main sensory nucleus
7. Sensation of pain & temperature : Pass to the spinal nucleus
8. Sensory fibers from the ophthalmic division : Terminate in the inferior part of the spinal nucleus
9. Sensory fibers from the maxillary division : Terminate in the middle part of the spinal nucleus
10. Sensory fibers from the mandibular division : Terminate in the superior part of the spinal nucleus
11.  Proprioceptive impulses from the muscle of mastication, facial and extra ocular muscles are carried out by fibers in the sensory root of the TGN that have by passed trigeminal ganglion (Origin of the fibers are the Unipolar cells of the Mesencephalic nucleus)
12. Pathway to the cerebral cortex
    
    1. The axons of the neurons of the main sensory nucleus, spinal nucleus & central processes of the cells of the Mesencephalic nucleus cross the median plane & ascend as the trigeminal lemniscus
    2. Trigeminal lemniscus terminates in the VPM nucleus of the thalamus
    3. The axons of these cells travel through the internal capsule to the post central gyrus (Area 3, 2 & 1) of the cerebral cortex

• Angle of the jaw is supplied by the great auricular nerve – C2 & C3 and not by branches of the TGN)

Motor component of the TGN

• Motor nucleus receives fibers from:
  
  1. Both cerebral hemispheres (Corticonuclear fibers)
  2. Reticular formation red nucleus
  3. Tectum
  4. Medial longitudinal fasciculus
  5. Mesencephalic nucleus
• Motor nucleus supplies:
  
  1. Muscles of mastication
  2. Tensor tympani
  3. Tensor veli palatine
  4. Mylohyoid
  5. Anterior belly of the digastrics muscle

The innervations of the TGN

Division	Innervations
Ophthalmic (V1)	Upper face, nose, cornea & eye lid Scalp to vertex Lacrimal glands
Maxillary (V2)	Middle face Nasal mucosa Upper teeth Pharynx Tonsils Inner quadrant of cornea
Mandibular (V3) – Sensory	Lower face (Not the angle of the jaw), Lip & Teeth Tongue (Lingual nerve – a branch of V3 carries the corda tympani nerve of the facial nerve) Part of the external ear PS fibers the parotid gland
Mandibular (V3) – Motor	Muscles of mastication (Masseter, Digastric, Pterygoid & Temporalis)

Examination of the TGN



Facial sensation

• Loss of sensation
  
  • Tested by using a pin
  • Check each 3 divisions separately
  • Check the symmetry of intensity on both sides
• Light touch : Use a piece of cotton wool
• The corneal reflexes (Normal – Brisk bilateral blink response)
  
  • Use a piece of cotton wool
  • Touch the cornea at its margin with the conjunctiva

Motor function

• Masseter muscles : Ask to clench teeth & palpate both masseters
• Temporalis muscles : While clenching the teeth, palpate over the temples
• Pterygoid muscles : Forceful opening of the jaws against the resistance (With unilateral Pterygoid weakness, jaw deviates to the ipsilateral side as it opens)
• The jaw jerk
  
  • 5^th nerve reflex
  • Patient should keep the jaw half open & relax
  • Reflex is increased in corticobulbar tract (UMN lesion) disease