Download The Mandibular Nerve_c revised HO

The Fifth Cranial Nerve “The Trigeminal”
By
Prof. Dr. Muhammad Imran Qureshi
The Mandibular Nerve - Vc or VIII
This is the third and largest division of the trigeminal nerve.
It is formed by the junction of the slender motor root of the nerve with the most lateral
branch of the trigeminal ganglion, which is predominantly sensory.
These two nerve bundles leave the
cranial cavity through the foramen
ovale and unite immediately to form
the trunk of the mixed mandibular
nerve that passes into the
infratemporal fossa.
Here, it is sandwiched between
superior head of lateral pterygoid
and tensor vali palati muscles,
anterior to the middle meningeal
artery.
After a short course during which a
meningeal branch to the dura
mater, and the nerve to part of the
medial pterygoid muscle (and the
tensor tympani and tensor palati
muscles) are given off, the
mandibular trunk divides into a
smaller anterior and a larger
posterior division.
The anterior division receives most
of the fibres from the motor root
and distributes them
to the other muscles
of mastication i.e. the
lateral pterygoid,
medial pterygoid,
temporalis and
masseter muscles.
The sensory fibres that
it receives are
distributed as the
buccal nerve, to the
skin in the region of
the angle of the month and to a corresponding area of the mucous membrane lining the
cheek.
The posterior division is mostly
sensory and gives origin to the
inferior alveolar, lingual and
auriculotemporal nerves.
It receives only a few motor
fibres that are distributed, by
the mylohyoid branch of the
inferior alveolar nerve to the
mylohyoid and the anterior belly
of digastric muscles.
The Inferior Alveolar Nerve
This is the largest branch of the
mandibular nerve.
From its origin it passes
downwards behind the lingual
nerve, on the outer surface of
the medial pterygoid muscle and
deep to the lateral pterygoid
muscle, and then between the
mandibular ramus and the
sphenomandibular ligament to
enter the mandibular canal.
Immediately before entering
this canal it gives off its
mylohyoid branch.
The inferior alveolar nerve
passes forwards in the
mandibular canal, in company
with the inferior alveolar
artery, and distributes
branches to the lower molar
and premolar teeth and the
adjacent parts of the gingiva.
At the level of mental
foramen it divides into an
incisive branch, which
continues forwards in the mandible
to supply the canine and incisor
teeth, and the larger mental branch,
which passes out of the bony canal
by the mental foramen and is
distributed to the skin and
subcutaneous tissues of the chin region and the lower lip.
The Lingual Nerve
This nerve passes downwards and forwards anterior to the inferior alveolar nerve and
between the lateral and medial
pterygoid muscles.
Near its origin, the chorda
tympani nerve, which is a
branch of the facial nerve, joins
it from behind. The lingual nerve
inclines obliquely to the side of
the tongue, passing over the
mandibular attachment of the
superior constrictor muscle of
the pharynx.
Here the nerve lies against the
deep surface of the mandible on
the medial side of the roots of
the third lower molar tooth and
above the deep part of the
submandibular gland.
The nerve then passes forwards
on the upper aspect of the
mylohyoid muscle and lateral to
the hyoglossus muscle. The
lingual nerve then passes
laterally and hooks below the
submandibular duct. Here it
gives branches to the mucous membrane of the floor of the mouth and the gingivae.
At the anterior border of the hyoglossus muscle, the lingual nerve enters the substance
of the tongue where it distributes branches of the common sensation to the mucous
membrane of its anterior two thirds.
The fibres of the chorda tympani are of two types. The majority of the fibers are
sensory, with cell bodies in the geniculate ganglion; they are distributed with the lingual
nerve and sub serve taste sensibility in the anterior two thirds of a tongue, excluding
circumvallate papillae.
The others are preganglionic parasympathetic fibres, which relay in the submandibular
ganglion. The postganglionic fibres are secretomotor to the submandibular and
sublingual glands.
AURICULOTEMPORAL NERVE
This nerve arises from the posterior trunk of the mandibular nerve by two roots, which
surround the middle meningeal artery, and is at first directed posteriorly, deep to the
lateral pterygoid muscle, to the medial aspect of the neck of the mandible.
From here it passes upwards and outwards, between the temporomandibular joint and
the cartilage of the external auditory meatus, and in the substance of the parotid gland.
It finally emerges from the gland and ascends over the zygomatic arch with the
superficial temporal artery to terminate by supplying the skin of the temporal region
and the lateral part of the
scalp
In its course the
auriculotemporal nerve gives
cutaneous branches to the
external auditory meatus, the
anterior part of the tympanic
membrane, the tragus of the
pinna and a variable, but
usually small area of the
anterior and upper part of the
pinna itself.
It also supplies twigs to the
temporomandibular joint, and carries secretomotor fibres from the otic ganglion to the
parotid gland.
Clinical Considerations For The Trigeminal Nerve
Damage to the ophthalmic nerve is revealed by disturbances of sensation from the skin
supplied by this nerve and from the eye.
It is tested by determining the responsiveness of the skin of the forehead (frontal nerve)
to touch and pin prick.
A second test involves the corneal reflex. When the cornea is touched, the sensation
travels via VI back to the trigeminal nerve and thence to the brain.
Here fibers synapse with facial neurons innervating the palpebral portion of orbicularis
oculi, which is caused to contract, producing a blink.
Like the pupillary light reflex, the corneal reflex is consensual, i.e., both eyelids blink
when either cornea is touched.
Obviously, disturbances of the corneal reflex will occur if either the sensory or motor
limb is damaged.
If the sensory limb is damaged, neither eyelid will blink when the affected cornea is
touched.
On the other hand, if touching the cornea of one eye produces a blink in the opposite
eye, the examiner knows that VI is working and that the defect is in the facial nerve.
Damage to the maxillary nerve leads to disturbance of sensation over its region of
distribution.
Usually this is only tested by assessing the responsiveness of the skin over the front of
the cheek (infraorbital nerve) to touch and pain.
Nasal, palatal and upper dental sensations are affected by damage to maxillary nerve,
but these are not tested for routinely.
Damage of the sensory fibers that run in VIII leads to disturbances in sensation in its
region of supply.
This is very broad, but during a routine examination the test is usually confined to the
skin over the chin (mental nerve) and side of the cheek (buccal nerve).
General sensation to the front of the tongue (lingual nerve) may also be tested.
Obviously, a thorough neurological examination can involve tests over other regions
(e.g., temple, ear).
Damage to the motor fibers within VIII leads to severe disturbances in chewing.
Wasting of the temporalis and masseter can be seen.
There is also an obvious symptom due to paralysis of the lateral pterygoid.
As we know, this muscle is the main depressor of the mandible. When both lateral
pterygoids work properly, the jaw moves straight down during voluntary opening of the
mouth.
If only the right lateral pterygoid is working the right side of the jaw will be pulled
forward during opening and the chin will deviate to the left.
If only the left lateral pterygoid is working, the chin deviates to the right upon opening
of the mouth.
Tests for strength of the temporalis, masseter, and pterygoids are made in all routine
examinations.
The examiner places one hand over the left temporalis and the other hand over the
right temporalis and then asks the patient to clench his or her teeth.
An assessment is made about the degree to which one side may be contracting less
strongly than the other.
The test is repeated with the examiner's fingers placed over each masseter.
If the patient has a complete molar dentition, a tongue depressor may be placed
sideways in the mouth between the upper and lower teeth.
The patient is asked to bite down and relax.
The examiner removes the tongue depressor and assesses if the impressions made by
the teeth are equally deep on both right and left sides.
The lateral pterygoid, medial pterygoid, and superficial masseter, when acting together
on one side, protract that side and cause the jaw to deviate toward the opposite side.
The left protractors push the chin toward the right; the right protractors push the chin
to the left.
If the examiner places a hand on the right side of the chin and attempts to push the jaw
to the left, the patient must use the left protractors to resist this.
If the examiner places a hand on the left side of the chin and attempts to push the jaw
to the right, the right muscles must be used to resist this.
By asking the patient to resist such pushes on the jaw, an assessment of strength of the
jaw protractors on one side compared with those on the other may be made.
Trigeminal neuralgia (TN) Also known as Tic Douloureux, is considered to be one of the
most painful afflictions known to medical practice. It is a disorder of the fifth cranial
(trigeminal) nerve. The typical or “classic” form of the disorder (called TN1) causes
extreme, intermittent, sudden burning facial pain in the areas of distribution of the
trigeminal nerve – lips, eyes, nose, scalp, forehead, upper jaw, and lower jaw. The pain
episodes last from a few seconds to as long as two minutes. These attacks can occur in
quick succession, in cascades lasting as long as two hours. The “atypical” form of the
disorder (called TN2), is characterized by constant aching, burning, stabbing pain of
somewhat lower intensity than TN1. Both forms of pain may occur in the same person,
sometimes at the same time.