Nerves and the Nervous SystemOral Implications and Dental Considerations

Nerves and how they work

Overview of the different Nervous Systems

Cranial Nerves

Focus on Facial and Trigeminal Nerves

Nervous System Disorders

Clinical Considerations: Anesthesia

Case Study: Multiple Sclerosis

Nerves Neuron: A functional cell of the nervous system. The cell is composed of an axon,

cell body, and dendrite.

Nerve: A bundle of neurons.

Afferent Nerve: Sensory nerve that sends signals from the periphery of the

body to the CNS.

Efferent Nerve: Motor nerve that sends signals from the CNS to the periphery

of the body.

Ganglion (Ganglia): An accumulation of cell bodies outside the CNS.

Synapse: A junction between two neurons or between a neuron and an effector

organ.

Innervaition: A supply of nerves to a body part.

How Nerves Work1. There is an “equal” distribution of electrical charges and ions inside and

outside the neuron cell membrane. The outside of the cell is more positive (Na) and the inside cell is more negatively charged (K). The charge difference is called Resting potential. This balance of ions is maintained by Sodium-Potassium pumps.

2. An Action potential occurs when the cell membrane depolarizes allowing sodium ions to rush inside the cell. The action potential moves down the cell at an alarming rate. Sodium and potassium pumps work together to reestablish resting potential.

3. When a impulse reaches a synapse, the cell uses chemical agents called Neurotransmitters to relay the impulse to the next nerve or tissue.

Central Nervous System (CNS) Composed of brain and spinal cord.

Meninges: membrane that has three layers; Dura mater, arachnoid

mater. And pia mater.

Cerebrum – two cerebral hemispheres.

Cerebellum

Brainstem: Includes medulla, pons, midbrain.

Diencephalon: Thalamus and hypothalamus.

Surrounded and protected by bone.

Peripheral Nervous System (PNS)

Network of 43 pairs of

motor and sensory nerves

that connect the brain and

spinal cord to the rest of

their body

Control functions of

sensation, movement, and

motor coordination

Includes nerves such as the

femoral, radial, ulnar,

brachial plexus, and sciatic.

Autonomic Nervous System (ANS) Conveys sensory impulses from the blood vessels, the heart, and all of the

other organs in the chest, abdomen, and pelvis through nerves to other parts

of the brain

Impulses do not reach our consciousness, elicit mostly automatic or reflex

responses

Consists of sympathetic and parasympathetic divisions, either fight or flight

or rest and digest.

Overview of Cranial Nerves

12 pairs of nerves that go directly from the brain to specific areas of the head and neck

Some are involved in special senses

Some are involved in muscle movement and gland regulation

Nerves are named and numbered according to their location from the front of the brain to the back

Cranial Nerve I/Olfactory Nerve

Type of Nerve: Afferent – special sensory for smell.

Origin: Nerve enters the skull through the perforations in the cribriform plate of the ethmoid bone to join the olfactory bulb in the brain

Transmitting Foramen: Olfactory Foramina

Innervates: Transmits smell from the olfactory mucosa to the brain

Cranial Nerve II/Optic Nerve

Type of Nerve: Afferent – special

sense of vision

Origin: Nerve enters the skull

through the optic canal of the

sphenoid bone on its way to the

retina. Right and left optic nerves

join at the optic chiasma, many of

the fibers cross and continue into

the brain as the optic tracts.

Transmitting Foramen: Optic

Canal

Innervates: Transmits sight from

the retinal ganglionic layer to the

brain

Cranial Nerve III/Oculomotor Nerve

Type of Nerve: Efferent

Origin: Lateral wall of the cavernous sinus, carries preganglionic

parasympathetic fibers to the ciliary ganglion near the eyeball, and

postganglionic fibers to the small muscles inside the eyeball.

Transmitting Foramen: Superior Orbital Fissure

Innervates: Two components control muscles for precise eye movement

(Somatic Motor) and control pupillary light and accommodation reflexes

(Visceral Motor).

Cranial Nerve IV/Trochlear Nerve

Type of Nerve: Efferent

Origin: Runs in the wall of the cavernous sinus and goes to the orbit.

Transmitting Foramen: Superior Orbital Fissure

Innervates: The superior oblique muscle of the eye which is responsible

for eye movement, tracking, and fixation on an object

Cranial Nerve VI/Abducens Nerve

Type of Nerve: Efferent

Origin: Runs through the sinus, close to the internal carotid artery on its

way to the orbit

Transmitting Foramen: Superior Orbital Fissure

Innervates: The lateral rectus muscle which is also responsible for eye

movement, tracking, and fixation on an object

Cranial Nerve VIII / Vestibulocochlear Nerve

Type of nerve: Afferent Nerve – Sensory for hearing and balance.

Origin: The nerve attaches to the brain at the junction of the pons and

medulla oblongata, just lateral to the origin of the facial nerve.

Transmitting Foramen: Nerve enters cranial cavity through the internal

acoustic meatus of the temporal bone.

Innervates: Connects brain to inner ear.

Cranial Nerve IX / Glossopharyngeal Nerve Type of nerve: Efferent and afferent nerve

Origin: Arises from the anterior portion of the posterolateral sulcus of the

medulla oblongata.

Transmitting Foramen: Jugular foramen

• Innervates:

(Efferent) Innervates the pharyngeal muscle, the stylopharyngeus muscle, and the

preganglionic gland parasympathetic innervation for the parotid salivary gland.

(Afferent) Innervates the oropharynx and deals primarily with taste and general sensation

for base of the tongue and the gag reflex.

Additionally, the lesser petrosal nerve of IX, synapses with the otic ganglion.

Cranial Nerve X / Vagus Nerve Type of nerve: Afferent and Efferent nerve.

Origin: Arises from the lateral aspect of the medulla oblongata just below the ipsilateral glossopharyngeal nerve. It is the longest cranial nerve.

Transmitting Foramen: Jugular foramen.

Innervates:

(Afferent) Innervates parasympathetically to many organs in the thorax and abdomen such as the heart, thymus, and stomach. It also innervates the skin around the ear and taste sensation, and the epiglottis.

(Efferent) Innervates muscle of soft palate, pharynx, and larynx.

Cranial Nerve XI / Accessory Nerve Type of nerve: Efferent nerve.

Origin: Originates as two roots: one from the medulla oblongata adjacent

to the origin of the vagus nerve; the second from the cervical spinal cord.

Transmitting Foramen: Jugular foramen.

Innervates: Innervates the trapezius and sternocleidomastoideus muscles.

Additionally, it innervates muscles of the soft palate and pharynx.

Cranial Nerve XII / Hypoglossal Nerve Type of nerve: Efferent Nerve.

Origin: Arises as 10 to 15 rootlets from the anterolateral sulcus between

the olive and pyramid of the medulla oblongata.

Transmitting Foramen: The ipsilateral hypoglossal canal of the occipital

bone.

Innervates: Innervates muscles the intrinsic and extrinsic muscles of the

tongue.

Cranial Nerve VII/Facial Nerve

Type of Nerve: Afferent and Efferent components

Origin: The main trunk of the nerve emerges from the skull and gives off two

branches, the posterior auricular nerve and a branch to the posterior belly of the

digastric and stylohyoid muscles. It also sends off small efferent branches to

the stapedius muscle and two other branches to the ear. There are also a

multitude of smaller nerves that go off into the muscles of the face.

Transmitting Foramen: Mainly the Stylomastoid Foramen

Branches of the Facial Nerve:

Greater Petrosal Nerve

Chorda Tympani Nerve

Posterior Auricular, Stylohyoid, and Posterior Digastric Nerves

Temporal Branch

Zygomatic Branch

Mandibular Branch

Buccal Branch

Cervical Branch

Greater Petrosal Nerve

Type of Nerve: Afferent and Efferent

Origin: Branch off the facial nerve before it exits the skull, carries

preganglionic parasympathetic fibers

Innervates: Parasympathetic fibers go to the pterygopalatine ganglion and

then join with branches of the maxillary nerve which is carried to the

lacrimal gland, nasal cavity, and minor salivary glands of the hard and soft

palate. The afferent nerve fibers of the greater petrosal nerve go to the

palate for taste sensation.

Chorda Tympani Nerve

Type of Nerve: Afferent and Efferent

Origin: Branches off the facial nerve within the petrous portion of the

temporal bone and crosses the eardrum before exiting and traveling down

to the lingual nerve along the floor of the mouth

Transmitting Foramen: Petrotympanic Fissure (behind the TMJ)

Innervates: Parasympathetic efferent fibers innervate the submandibular

and sublingual salivary glands, afferent fibers are found in the body of the

tongue for taste sensation.

Posterior Auricular, Stylohyoid, and Posterior

Digastric Nerves Types of Nerves: All are Efferent nerves

Origins: Branches of the facial nerve after it exits the stylomastoid

foramen

Innervates: Posterior auricular nerve goes to the occipital belly of the

epicranial muscle. The stylohyoid innervates the stylohyoid muscle. The

posterior digastric nerve innervates the posterior belly of the digastric

muscle

Branches to the Muscles of Facial Expression

Types of Nerves: All five branches are efferent

Origins: These branches of the facial nerve originate in the parotid salivary

gland and then go to the muscles they supply

Innervates:

Temporal: Muscles anterior to the ear, frontal belly of epicranial muscle, superior

portion of orbicularis oculi, and corrugator supercili

Zygomatic: Inferior portion of orbicularis oculi and zygomatic minor and major muscles

Buccal: Muscles of upper lip and nose, buccinators, risorius, and orbicularis oris

Mandibular: Muscles of lower lip and mentalis muscle

Cervical: Runs inferior to the mandible to supply platysma

Cranial Nerve V / Trigeminal Nerve Type of nerve: Efferent and afferent nerve.

Afferent - The sensory component is thick.

Efferent - The motor component is thin.

Origin: Emerges from the inferolateral aspect of the pons. The trigeminal

nerve is the largest cranial nerve in diameter and is composed of a thin

efferent nerve and a thick afferent nerve. At the sight of the trigeminal

ganglion (located within the skull), the nerve divides into three anatomical

branches and exits through transmitting foramen.

Branches of the Trigeminal Nerve:

1. Ophthalmic Nerve (V1)

2. Maxillary Nerve (V2)

3. Mandibular Nerve (V3)

Ophthalmic Nerve (V1) Type of nerve: Afferent nerve. Is the smallest division.

Transmitting Foramen: Superior Orbital Fissure.

Innervates: Innervates the conjunctiva, cornea, eyeball, orbit, forehead, and ethmoidal and frontal sinsuses.

Three major nerves:

1. Frontal Nerve – Composed of supraorbital nerve and supratrochlear nerve. This nerve courses along the roof of the orbit.

2. Lacrimal Nerve – This nerve supplies the conjunctiva and the lacrimal gland. Additionally it also delivers the postganglionic parasympathetic nerve to the lacrimal gland.

3. Nasociliary Nerve – Composed of several nerves including the infratrochlear nerve, ciliary nerves, anterior ethmoidal nerve, external nasal nerve, and internal nasal nerves. These nerves innervates the skin of the eyelids, lacrimal sac, eyeball, and the nose.

Maxillary Nerve (V2) Type of nerve: Afferent Nerve.

Transmitting Foramen: Foramen rotundum of sphenoid bone.

Other nerve branches: within the pterygopalatine fossa the main maxillary trunk

diverges into many nerves, the largest being the infraorbital nerve. Other nerves include

the zygomatic, the anterior, middle, and posterior superior alveolar nerves, the greater

and lesser palatine nerves, and nasopalatine nerves. Additionally, within the

pterygopalatine fossa the pterygopalatine ganglion can be found. This ganglion caries

parasympathetic fibers from the facial nerve, and caries parasympathetic fibers to minor

salivary glands.

Innervates: Innervates the maxillae, overlying skin, maxillary sinuses, nasal cavity,

palate, and nasopharynx.

Maxillary Nerve (V2) Continued1. Zygomatic nerve – divides into the zygomaticofacial and zygomaticotemporal nerves. It

exits the pterygopalatine fossa through the inferior orbital fissure. These nerve innervate the

skin of the cheeks and the temporal regions.

2. Infraorbital Nerve – Branches into nerves that innervate the upper lip, medial part of the

cheek, lower eyelid, and side of the nose. Emerges from the Infraorbital foramen.

3. Anterior Superior Alveolar Nerve – Innervates maxillary central incisors, lateral incisors,

and canines, as well as the surrounding tissue.

4. Middle Superior Alveolar Nerve – Innervates maxillary premolar teeth and mesiobuccal

root of the maxillary first molar and their associated periodontium and buccal gingiva.

Maxillary Nerve (V2) Continued5. Posterior Superior Alveolar Nerve – Innervates most parts of maxillary teeth,

periodontium, buccal gingiva, and maxillary sinus.

6. Greater Palatine Nerve – Also known as the anterior palatine nerve, its located between

the mucoperiosteum and the bone of the posterior hard palate. Innervates the posterior hard

palate and posterior lingual gingiva.

7. Lesser Palatine Nerve – Also known as the posterior palatine nerve, it innervates the soft

palate and palatine tonsils.

8. Nasopalatine Nerve – Innervates the anterior hard palate, anterior lingual gingiva, and

nasal septum tissue.

Mandibular Nerve (V3) Type of nerve: Afferent and efferent nerve. This is the largest of the three

branches.

Transmitting Foramen: Foramen ovale of sphenoid bone.

Innervates:

(Efferent) innervates muscles of mastication.

Muscles of mastication include: Temporal, masseter, and lateral pterygoid muscles.

(Afferent) innervates skin, mucous membranes, gingiva, tongue, and periodontium.

Several nerve branches arise from the mandibular nerve (V3)

Mandibular Nerve (V3) Continued Meningeal branches – Afferent nerves for

parts of the dura mater.

Buccal nerve – Afferent nerve that

innervates the skin of the cheek, buccal

mucous membrane, and buccal gingiva near

mandibular posterior teeth.

Muscular branches – Efferent Nerves

Deep Temporal Nerves – two nerves

(anterior and posterior) .

Masseteric Nerve

Lateral Pterygoid Nerve

Medial Pterygoid Nerve – Efferent nerve

that innervates the medial pterygoid, tensor

tympani, and tensor veli palatini muscles.

Auriculotemporal Nerve – Afferent nerve

that innervates external ear and scalp. This

nerve also caries postganglionic

parasympathetic nerve fibers to the parotid

salivary gland.

Mandibular Nerve (V3) Continued Lingual Nerve – Afferent nerve that supplies general sensation for the body of the

tongue (anterior 2/3), floor of mouth, lingual gingiva, and mandibular teeth.

Inferior Alveolar Nerve – Afferent nerve that divides into the incisive and mental

nerves.

Mental Nerve – Afferent nerve that emerges from the mental foramen and supplies the

chin, lower lip, and labial mucosa.

Incisive Nerve – Afferent nerve which innervates mandibular premolars and anterior

teeth and periodontal tissue.

Mylohyoid Nerve – Efferent nerve that innervates the mylohyoid muscle and anterior

belly of the digastric muscle.

Disorders of the Nervous System

The nervous system can be damaged by

trauma, infection, genetic defects,

degeneration, tumors, autoimmune disease, and

blood flow disruption

Signs of a disorder can be loss of feeling,

tingling, persistent headaches, memory loss,

double vision, weakness, tremors, seizures,

lack of coordination, and change in mental

ability

Categories of Nervous System Disorders

Vascular Disorders: Stroke, transient ischemic attack (TIA), subarachnoid hemorrhage, subdural hemorrhage and hematoma, and extradural hemorrhage’

Infections: Meningitis, encephalitis, polio, and epidural abscess

Structural Disorders: Brain or spinal cord injury, Bell's palsy, cervical spondylosis, carpal tunnel syndrome, brain or spinal cord tumors, peripheral neuropathy, and Guillain-Barrésyndrome

Functional Disorders: Headache, epilepsy, dizziness, and neuralgia

Degeneration: Parkinson's disease, multiple sclerosis, amyotrophic lateral sclerosis (ALS), Huntington's chorea, and Alzheimer's disease

Case Study: Oral Implications of MS

Multiple Sclerosis is an autoimmune disorder

that affects about 400,000 people in the U.S.

Affects Central Nervous System by damaging

myelin sheath around the nerves

Symptoms may include numbness, tingling,

weakness, fatigue, dizziness, blurring vision

Oral manifestations commonly include

paresthesia and facial palsy

Case Study: Oral Implications of MS

54 year old Caucasian male with MS since the age of 19

Healthy gingival tissues with slight xerostomia (due to medications), slight bleeding on probing

Severe attrition and some hyperkeratinization due to bruxism from muscle spasticity

Plaque score of 57% with most of it found interproximally

Very motivated and educated patient who just needed slight adjustments for better oral care

Showed how to angle brush 45 degrees and floss in a C shape for improved plaque removal

Every patient is an individual and needs an individual treatment plan, help those who have chronic illnesses improve their oral health

Review

Nerves control what we feel, how we feel it, and how we respond

to it.

The nervous system has different divisions and each are

interrelated and have coordinating functions

We have 12 pairs of cranial nerves that have special sensory,

motor, and regulatory functions

The facial and trigeminal nerves are absolutely essential to

understand as dental professionals

It is important to understand nervous system disorders and nerve

damage when dealing with people who have chronic illnesses or

conditions or when administering anesthesia.

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References

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Reich, M., & Campbell, P. (2010, January 1). The Oral Implications of MS. Retrieved November 10, 2014, from http://www.dimensionsofdentalhygiene.com/ddhright.aspx?id=6992

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