Trigeminal Nerve

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Original Editor - Saumya Srivastava

Top Contributors - Saumya Srivastava, Riccardo Ugrin, Wendy Walker, Kim Jackson, Vidya Acharya and Ahmed M Diab

Trigeminal Nerve 

Description

The Trigeminal Nerve (TNr) is the fifth cranial nerve. It is also represented as CN V. It is the largest of all the cranial nerves. It is also the most complex of all the cranial nerves as it has an extensive anatomic course. Knowing its course further helps in understanding the relationship between the brainstem, skull base, and facial area.

Trigeminal nerve is a mixed nerve - having both sensory and motor fibres. The origin of the trigeminal nerve is the annular protuberance at the limit of the cerebellar peduncles. It originates from three sensory nuclei (mesencephalic, principal sensory, spinal nuclei of trigeminal nerve) and one motor nucleus (motor nucleus of the trigeminal nerve) extending from the midbrain to the medulla.

Distal Roots -

• The sensory nuclei merge to form the sensory root at the level of the pons and the motor nucleus continues to form the motor root.

• As a result the sensory root is large (made up of about 50 fascicles), while the motor root is more slender (composed of six or seven fascicles).These roots are analogous to the dorsal and ventral roots of the spinal cord

• The sensory root then expands into the trigeminal ganglion, in the middle of the cranial fossa. The trigeminal ganglion is located lateral to the cavernous sinus, in a depression of the temporal bone, known as the trigeminal cave.

Trigeminal Branches

Peripheral Divisons of The TNr into Branches-

The TNr divides into 3 nerves distal to the trigeminal ganglion -

1. The Ophthalmic nerve, passes forward in the lateral wall to the cavernous sinus. It then enters the orbit via the superior orbital fissure.
2. The Mandibular nerve, runs laterally along the skull base then exits the cranium by descending through the foramen ovale into the masticator space. The motor root of the trigeminal nerve bypasses the trigeminal ganglion and reunites with the mandibular nerve in the foramen ovale basis cranii
3. The Maxillary nerve, leaves the skull base through the foramen rotundum ossis sphenoidalis, inferolateral to the cavernous sinus. It then enters the pterygopalatine fossa, giving off several branches. The main trunk then continues anteriorly in the orbital floor and emerges onto the face as the infraorbital nerve

Function

It is a mixed nerve - the sensory part of the nerve supplies the face and the motor for muscles of mastication

Motor -

• The motor root of the trigeminal nerve bypasses the trigeminal ganglion and reunites with the mandibular nerve in the foramen ovale basis cranii.
• The motor root of the mandibular nerve innervates the four muscles of mastication:

1. the mylohyoid,
2. the anterior belly of digastric,
3. the tensor muscle of the tympanic membranes, and
4. tensor muscle of valum palatinum

References

Original Editor - Saumya Srivastava

Top Contributors - Saumya Srivastava, Riccardo Ugrin, Wendy Walker, Kim Jackson, Vidya Acharya and Ahmed M Diab