Figure 20 LEARN HOW TO DRAW THIS DIAGRAM
- The three peripheral divisions of V supply common sensation (i.e. touch, temperature, pressure, pain) to the sin of the face and scalp.
- V1 supplies the skin in the anterior portion of the scalp, forehead, upper eyelid and the front of the nose down to the tip.
- V2 supplies the skin at the sides of the nose, lower eyelid and upper parts of the cheek and lip.
- V3 supplies the chin, lower lip, skin in front of the ear and on the side of the head up to where V1
supplies it.
- Note from the image above that the angle of the mandible is not innervated by the Trigeminal Nerve but by the Cervical Plexus along with the back of the head and neck
Page | 93 13.1.2. Central Connections
- The unipolar somatic sensory cells in the Trigeminal nerve cannot have their cell bodies and are instead, found in the Trigeminal Ganglion
o They then terminate in the spinal nucleus/nucleus of the spinal tract and chief sensory nucleus
Nuclei for General Sensation in brainstem
- Proprioceptive Fibres involved in the Proprioceptive Reflexes controlling the jaw and because of the speed in which they need to act, they are the only Peripheral Sensory Neurons where the cell bodies are located in the CNS.
o They lie in the Mesencephalic Nucleus.
- Motor cells of the Trigeminal Nerve originate in the Trigeminal Motor Nucleus
Figure 21 The Brainstem. This image will be revisited in the last topic.
Trigeminal: Chief Sensory Nucleus Trigeminal:
Mesencephalic Nucleus
Spinal Nucleus/Nucleus of the Spinal Tract Trigeminal Motor Nucleus
Page | 94
13.2. V
1: The Ophthalmic Division
- Purely sensory
13.2.1. Course
- It originates from the Trigeminal Ganglion and passes forward along the lateral wall of the Cavernous Sinus alongside III, IV and VI.
o Link this to symptoms of cavernous sinus thrombosis
- It enters the orbit by passing through the Superior Orbital Fissure (which separates the great and lesser wings of the Sphenoid bone).
- At this point, it divides into Three Branches:
o Lacrimal o Frontal o Nasociliary
Trigeminal Ganglion Ophthalmic Division
Maxillary Division Mandibular Division
Lacrimal Nerve Frontal Nerve
Nasociliary Nerve
Supraorbital Nerve Supratrochlear Nerve
Page | 95 13.2.2. Frontal Nerve
- Runs across the top of the orbit. As it approaches the face, it divides into two major branches o Supraorbital Nerve
Emerges onto the face through the Supraorbital Foramen
Runs up onto the forehead to supply the forehead and scalp.
o Supratrochlear Nerves
Runs medially and emerges from the orbit at the medial edge.
Runs up to supply:
Medial Portion of the Upper eyelid, skin of the forehead and scalp towards the medial aspect and the skin above the root of the nose.
13.2.3. Lacrimal Nerve
- Supplies the conjunctiva, the skin of the lateral upper eyelid and the lacrimal gland with common sensation
- V2 supplies the secretomotor for the lacrimal gland.
13.2.3. Nasociliary Nerve
- Supplies the medial structures of the orbit.
o Lining membranes of the Sphenoidal and Ethmoidal sinuses o Tissues of the roof of the nose
o Skin over the front of the nose down to the tip.
Page | 96
13.3. The Maxillary Division (V
2)
- Also purely sensory 13.3.1. Course
- Emerges as the intermediate branch of the Trigeminal Ganglion
- Runs forward in the middle cranial fossa along the lateral wall of the Cavernous Sinus - Exits the cranium via Foramen Rotundum
o Before it passes through the foramen, it gives off a small branch to supply the dura mater of the middle cranial fossa called the Middle Meningeal Nerve
- After exiting through Foramen Rotundum, it emerges into the Pterygopalatine Fossa superior to the Pterygopalatine Ganglion. At this point it gives off a number of branches.
o Two branches travel into the ganglion
o The main trunk continues anteriorly to run through the Inferior Orbital Fissure and runs along the floor of the orbit in the Infraorbital Groove and becomes the
Infraorbital Nerve. It then travels through the Infraorbital Canal before emerging on the facial surface of the maxilla through the Infraorbital foramen.
As it moves anteriorly it also gives off several branches.
The Infraorbital Groove forms the roof of the Infraorbital Canal
Infraorbital Nerve gives off the Anterior Superior Dental Nerve as it passes through the canal.
o Anterior Superior Dental Nerve runs through Canaliculus Sinosus
- Once on the maxilla, the Infraorbital Nerve gives off branches to the upper lip, lower eyelid and sides of the nose.
13.3.2. The Branches
- The branches include:
o Those in the pterygopalatine Fossa
Posterior Superior Dental
Palatine
Sphenopalatine
Pharyngeal
Zygomatic o Infraorbital
Anterior and Middle Superior Dental
- Palatine and Sphenopalatine come from the Pterygopalatine Ganglion whilst Zygomatic receives fibres from it without going through it.
Page | 97 13.3.2.1. Posterior Superior Dental Nerves
- Contribute to the nerve supply of the upper teeth.
o Targeted in a Superior Dental Block
- They run downwards on the back of the maxilla and pass into the bone through a series of foramina around the maxillary tuberosity.
- They run into the body of the maxilla and reach the lining of the Maxillary Sinus to supply sensory nerve endings.
- From here, the fibres are then distributed even further to form the Molar Part of the nerve plexus that supplies the upper teeth called the Superior Dental Nerve Plexus
- They also supply small endings to the Buccal gingivae of the molars and superior portion of the cheek in this area.
- Because the Molars and Maxillary Sinus share the same nervous supply, pain from the Maxillary Sinus can be referred to the upper teeth.
13.3.2.2. The Palatine Nerves
- Provides somatic sensory nervous supply to the palate and parasympathetic secretomotor fibres to the minor salivary glands in the palatal mucosa.
o The somatic fibres come from the branches of V2 that extend into the Pterygopalatine Ganglion
They emerge from the ganglion WITHOUT HAVING SYNAPSED.
o Some postganglionic PS secretomotor fibres from the ganglion hitch a ride and run with the somatic fibres to be distributed to the minor salivary glands.
Also contain some taste fibres.
- The branch travels from the Ganglion inferiorly, branching into Greater and Lesser Palatine Nerves.
o Lesser Palatine Nerves emerge through the Lesser Palatine Foramina in the palatine bones
Provide taste, secretomotor and somatosensory fibres to the tissues of the Soft Palate
o Greater palatine nerves pass through the Greater Palatine Foramen and run forwards in the palate up to the canine where they meet and anastamose with fibres from the Sphenopalatine Nerve
Recall that the palate has separate innervations at different points - These two also need to be targeted in a Superior Dental Block
Page | 98 13.3.2.3. Sphenopalatine Nerve
- From the Pterygopaatine Ganglion, it passes medially through the Sphenopalatine Foramen which lies in the deepest part of the Fossa.
- After passing through the foramen, it gives off some small lateral branches which are distributed over the lateral wall of the nasal cavity.
- The Long Sphenopalatine or Nasopalatine Nerve then crosses the roof of the nasal cavity and descends on the nasal septum to supply the mucous membrane
- It then continues through the Incisive Canal to communicate with the Greater Palatine Nerves o Small terminal branches help to supply the palatine supporting structures of the
central and lateral incisors.
13.3.2.4. The Pharyngeal Nerves
- Supply the mucous membrane of the upper nasopharynx
- They reach this by running posteriorly through the Pharyngeal Canal 13.3.2.5. The Zygomatic Nerve
- Runs into the orbit through the inferior orbital fissure alongside the Infraorbital Nerve
- Instead of running across the floor like the infraorbital nerve, it runs along the lateral wall of the zygomatic bone
- Whilst not running through the Pterygopalatine Ganglion, it does receive parasympathetic secretomotor fibres from it.
- Eventually, it divides into two branches:
o Zygomaticotemporal Nerve o Zygomaticofacial Nerve
- Both branches run into the zygomatic bone and via two small foramina which are named according to the branch it carries.
- The parasympathetic secretomotor fibres from the Ganglion don’t actually travel with the zygomatic nerve all the way.
o A branch from the Zygomaticotemporal Nerve called the Lacrimal Branch joins onto the Lacrimal Nerve from V1 and travels with it to reach the lacrimal glands.
13.3.2.6. The Infraorbital Nerve
- Discussed in detail before.
- Most important branches it gives off whilst still in the orbit are the middle superior and anterior superior dental nerves which contribute to the superior dental plexus.
Page | 99 13.3.3. Branches of the Maxillary Nerve from a Lateral View and Associated Structures
Trigeminal Ganglion
Maxillary Nerve (V2) Zygomatic Nerve
Pterygopalatine Ganglion
Greater and Lesser Palatine Nerves
Infraorbital Nerve entering the Infraorbital Canal Posterior Superior Dental Nerve
Lacrimal Branch
Middle Superior Dental Nerve
Anterior Superior Dental Nerve Lacrimal Nerve (from V1)
Maxillary Sinus Foramen Rotundum
Page | 100
13.4. Nerve Supply of the Upper Teeth
- When looking at the nervous supply of the upper teeth, it is important to take note of several things; namely:
o Nerve supply for the upper teeth (especially the molars) are closely related to the nerve supply of the maxillary sinus.
o The Superior Dental Plexus is made up of twiglets from the Posterior Superior, Anterior Superior and – when it’s present – Middle Superior Dental Nerves
NOTE THAT THE PRESENCE OF THE MIDDLE SUPERIOR DENTAL NERVES DO NOT MEAN THE AREA IS MORE SENSITIVE.
- When the Middle Superior Dental Nerve is present:
o Posterior Superior supplies the Molars and a twig to the Second Premolar
o Middle Superior supplies MB root of 6, Premolars and may jointly supply the Canines.
o Anterior Superior supply the anterior teeth and some of 4 o So:
P and M jointly supply 5 and 6
M and A jointly supply 3 and 4 - If it is present:
o Posterior Superior supplies the molars and 5
o Anterior Superior does Anterior teeth and 4 and some of 5 Clinically:
- If anaesthesia is required for a restoration, only the nerve to the teeth need to be hit.
- Anaesthesia for extractions need to get the nerve supply of the palatal tissues as well.
Page | 101
14. The Mandibular Division of the Trigeminal Nerve (V
3)
- Recall from the section above the areas that are supplied with Sensory Innervation from V3
14.1. Course
- V3 is the only branch of the Trigeminal Nerve that contains both Sensory and Motor.
o The Sensory component of the nerve passes into the ganglion and then to the brainstem alongside the sensory fibres from the other divisions.
o The Motor fibres leave from the pons as a separate motor root which joins the main trunk of the nerve just after the main trunk leaves the cranium.
- The Mandibular Nerve then exits the cranium through Foramen Ovale
- The trunk of the nerve then gives off its first branch called the Recurrent Meningeal Nerve o Known to cause many headaches
o It is a small branch containing sensory fibres that re-enters the cranium alongside the Middle Meningeal Artery through Foramen Spinosum to supply the dura mater with sensation.
- The main trunk then gives off several small muscular branches containing motor fibres to the tensor palate and tensor tympani muscles as well as the Medial Pterygoid Muscle.
o Tensor Tympani is a muscle that adjusts the tympanic membrane to change the sensitivity of hearing.
Pain from lower jaw can be reffered to the ear via this nerve.
- It also receives some communicating branches from the Otic Ganglion without actually passing through it.
o These communicating branches allow parasympathetic fibres to run with the nerve.
- After the main trunk runs past the Otic Ganglion, it divides into Posterior and Anterior Divisions.
Page | 102
14.2. Branches of the Posterior Division
- Auriculotemporal Nerve (Sensory and Parasympathetic) - Inferior Dental Nerve (Sensory)
- Lingual Nerve (Sensory and Parasympathetic)
- Nerve to Mylohyoid Muscle and Anterior Belly of Digastric Muscle (Sensory and Motor) 14.2.1. Auriculotemporal Nerve
- IMPORTANT as it provides sensory innervation to the TMJ and carries parasympathetic secretomotor fibres from the Otic Ganglion to the Parotid Gland
- It is BAD PRACTICE to anaesthetise it.
- It branches from the main trunk of the Mandibular Nerve shortly after the motor root joins on.
- It runs posteriorly toward the Middle Meningeal Artery, at which point it splits into two
branches which pass around the artery in a circle before joining back up to form a single branch.
- It continues to run posteriorly, running between the medial aspect of the neck of the mandibular condyle and sphenomandibular ligament
- It then curves around the TMJ which it supplies with sensory fibres and runs into the Parotid Gland.
- It gives off sensory and parasympathetic fibres to the gland.
- It then runs superiorly and terminates with the Superior Temporal Branches which supply common sensation to the skin and underlying structures in the posterior temple area and side of the scalp.
14.2.2. Inferior Dental Nerve (VERY IMPORTANT)
- I repeat. VERY IMPORTANT.
- It provides the sensory supply to the pulps of the lower teeth and does so by entering the body of the mandible.
o It also supplies the PDL fibres, the mandible itself as well as the labial gingivae and Buccal gingivae as far back as the second premolar.
- It does this by entering the Mandibular Foramen found on the medial surface of the Ramus of the mandible and then runs in the Mandibular Canal
- Initially it travels as a single trunk but soon gives off smaller branches which form a plexus in the body of the mandible.
- The nerve then splits into two branches
o The first branch is called the Incisive Plexus and continues forward in the body of the mandible to supply:
Labial Gingivae and the pulps of the anterior teeth
The second branch is called the Mental Nerve and exits the mandible via the Mental Foramen.
Page | 103
The position of this foramen can vary but it is generally between the roots of 4 and 5 .
BEWARE the position of the Mental Nerve when designing a periodontal flap.
o NEVER make an incision near the premolars. You are better off making the flap larger and exposing the nerve.
o The Mental Nerve supplies common sensation to the lower lip and the front of the chin.
14.2.3. Nerve to the Mylohyoid
- This nerve supplies motor function to the Mylohyoid and Anterior Belly of the Digastric Muscle o It was recently found however that it has a sensory component as well.
- It branches off from the Inferior Dental Nerve just before it passes into the Mandibular Foramen.
o At times, it can branch off quite high up from the inferior dental nerve to the point that it can avoid being bathed in anaesthetic when attempting an inferior dental block.
Therefore some patients, despite being successfully anaesthetised still showed sensitivity due to this nerve.
14.2.4. The Lingual Nerve
- Carries parasympathetic fibres after Chorda Tympani from VII joins onto it.
- Branches from the Posterior Division anteriorly to the Inferior Dental Nerve and runs parallel with it for some time without entering the body of the mandible.
- Instead, it curves above the mylohyoid muscle passing between the body of the mandible and the duct of the Submandibular gland.
- It rises again medially to terminate in the anterior part of the tongue.
- It is the major sensory nerve of the Anterior 2/3 of the tongue for common sensation and taste.
- The parasympathetic fibres acquired from Chorda Tympani are distributed to the Submandibular, sublingual and minor salivary glands.
o The preganglionic fibres synapse in the Submandibular ganglion which is located inferiorly to the lingual nerve, close to the gland where the postganglionic fibres exit and travel.
- It also supplies common sensation to the floor of the mouth, lingual gingival tissues and sometimes an accessory nerve supply to the lower anteriors must therefore be anaesthetised during an extraction of a lower tooth along with the inferior dental nerve.
Page | 104
14.3. Branches of the Anterior Division
- Masseteric Nerve (M) o Masseter Muscle
- Anterior and Posterior Deep Temporal Nerves (M) o Temporalis Muscle
- Medial Pterygoid Nerve (M)
o Medial Pterygoid Muscle - Lateral Pterygoid Nerve (M)
o Lateral Pterygoid Muscle - Buccal Nerve (S)
- You only need to know the names and destinations of the nerves to the muscles of mastication 14.3.1. The Buccal Nerve (aka Long Buccal Nerve)
- Provides common sensation to most of the cheek and the Buccal gingivae of the lower posterior teeth.
o Therefore, it also needs to be anaesthetised if a lower posterior tooth is to be extracted.
14.4. A Nice Visual Summary of the Branches
Page | 105
15. Brainstem and Nuclei
- The brainstem represents the union between the brain and the spinal cord. It is made up of three main parts:
o Midbrain o Pons
o Medulla Oblongata
- It transmits all sensory and motor pathways and information between the brain and the spinal cord. Also in the brainstem, we find the central connections of the Cranial Nerves and their associated nuclei.
15.1. The Reticular Formation
- Scattered deeply through the brain stem are loosely organised groups of tissue, collectively known as the Reticular Formation.
- It has the important task of controlling our level of awareness or consciousness to certain things o It directs you to changes in your environment like loud noises
- It also has a role in respiratory and cardiac functions Midbrain
Pons Cerebellum Medulla Oblongata
Page | 106
15.2. The Midbrain
- Forms the most superior part of the brainstem.
- It also contains a channel that connects the Third and Fourth Ventricles, the two most inferior of four cavities that contain Cerebrospinal Fluid, by the Cerebral Aqueduct, which is continuous with the central canals of the spinal cord.
o All part of circulation of CSF
- The part of the midbrain posterior to the Cerebral Aqueduct is called the Tectum and on its surface are four small elevations called the Colliculi, which are arranged in pairs.
o Inferior and Superior Colliculi
- These structures are important in reflex activity.
o The Superior Colliculi are associated with Vision
o The Inferior Colliculi are associated with Hearing and Balance Third Ventricle
Superior Colliculi
Inferior Colliculi
Page | 107 - The part of the midbrain anterior to the Cerebral Aqueduct is formed by the Cerebral Peduncles
which enter the cerebral hemispheres
- The Cerebral peduncles are tracts of white matter entering and exiting the brain. They are a destination of ascending and descending fibres.
15.3. The Pons
- It is the part of the brainstem located between the midbrain and the medulla.
- It lies anteriorly to the connections of the cerebellum and much of its structure is made up of fibres passing the midline and connecting the two cerebral hemispheres
o i.e. It provides communication between the left and right halves of the cerebellum.
- The pons is joined to the cerebellum via the Cerebellar peduncles
o In diagrams, these peduncles are usually only visible if the cerebellum has been removed and appear as ovoid masses.
- Dorsally, the pons contains sensory and motor tracts as well as the nuclei of Cranial Nerves V, VI and VII
- Ventrally, it contains fibres that connect the two hemispheres of the cerebellum.
- Cranial Nerves V – VIII all leave the brain stem from the pons. Many of the cranial nuclei associated with V are found here too.
- It was also found that within the pons, the motor nuclei tend to be more medially situated than the sensory nuclei.
- Furthermore, nuclei that have similar or related functions tended to be grouped fairly closely to
- Furthermore, nuclei that have similar or related functions tended to be grouped fairly closely to