Cranial nerves/ dental implant courses by Indian dental academy

CRANIAL NERVES

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INTRODUCTION • Nerves are a collection of axons contained within the peripheral nervous system whereas tracts are a collection of axons in the central nervous system (i.e. the brain and spinal cord). Therefore, when we talk about the cranial nerves we are really referring to part of the peripheral nervous system. • What makes the cranial nerves so special, after all we have hundreds of nerves throughout the body? The answer is that the cranial nerves are nerves that come directly off of the brain

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INTRODUCTION • Modality is unit of the nervous system that performs a certain type of action: sensation, movement, constriction, etc.

• There are two general modalities in the peripheral nervous system: motor (efferent) and sensory (afferent).

• Efferent impulses • Afferent impulses

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INTRODUCTION • There are 12 pairs of cranial nerves that supply structures in the head, neck, thorax and abdomen.

• A cranial nerve can be made up of a mixture of functions which are called modalities or may be made up of a single modality.

• A modality is sensory, motor, special sensory, etc. www.indiandentalacademy.com

EMBRYOLOGY • INTRODUCTION: • The Neural tube and its Subdivisions: - Apart from its blood vessels and some neuroglial elements, the whole of the nervous system is derived from Ectoderm.

- The part of the ectoderm that is destined to give origin to the brain and spinal cord, can be distinguished while the embryo is still in the from of a three-layered embryonic disc. www.indiandentalacademy.com

- It soon becomes thickened to form the neural plate.

- The neural plate becomes depressed along the midline as as result of which the neural groove is formed.

- This groove becomes progressively deeper, at the same time the two edges of the neural plate come nearer each other, and eventually fuse, thus converting the neural groove into the neural tube.

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• THE NEURAL CREST: - At the time when the neural plate is being formed, some cells at the junction between the neural plate and the rest of the ectoderm become specialized to form the primordia of the neural crest.

- The spinal cord is developed from the caudal cylindrical part of the neural tube.

- The medulla oblongata develops from the Myelencephalon.

- The pons arises from the ventral part of the Metencephalon - The Mid brain is developed from the Mesencephalon www.indiandentalacademy.com

- The cerebellum develops from the dorsolateral part of the alar lamina of the Metencephalon.

- The Cerebral hemisphere is a derivative of the Prosencephalon.

- The Thalamus and Hypothalamus develop from the Diencephalon.

- The Corpus striatum is a derivative of the Telencephalon.

- The Cerebral cortex is fromed by migration of the cells from the mantle layer into the overlying marginal layer. www.indiandentalacademy.com

NAMES OF CRANIAL NERVES • • • • • • • • • • • •

Ⅰ Olfactory nerve Ⅱ Optic nerve Ⅲ Oculomotor nerve Ⅳ Trochlear nerve Ⅴ Trigeminal nerve Ⅵ Abducent nerve Ⅶ Facial nerve Ⅷ Vestibulocochlear nerve Ⅸ Glossopharyngeal nerve Ⅹ Vagus nerve Ⅺ Accessory nerve www.indiandentalacademy.com Ⅻ Hypoglossal nerve

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FUNCTIONAL COMPONENTS • GSE -- motor to skeletal muscles GVE -- motor to heart muscle, smooth muscle, glands. In the cranial nerves, these impulses are part of the parasympathetic nervous system.

SVE -- motor to skeletal muscles that develop in branchial arches of the embryo (pharynx, larynx, middle ear) GSA -- sensations of touch, pain, temperature SSA -- special sense from organs developing in ectoderm of embryo (vision, hearing) GVA -- sensory from sensory organs (heart, intestine) SVA -- special sense from organs developing in association of gastrointestinal tract (smell, taste)

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CLASSIFICATION OF CRANIAL NERVES •

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Sensory cranial nerves: contain only afferent (sensory) fibers – Ⅰ Olfactory nerve, – Ⅱ Optic nerve, – Ⅷ Vestibulocochlear nerve.

Motor cranial nerves: contain only efferent (motor) fibers – Ⅲ Oculomotor nerve, – Ⅳ Trochlear nerve, – Ⅵ Abducent nerve, – Ⅺ Accessory nerve, – Ⅻ Hypoglossal nerve.

Mixed nerves: contain both sensory and motor fibers--– Ⅴ Trigeminal nerve, – Ⅶ Facial nerve, – Ⅸ Glossopharyngeal nerve, – Ⅹ Vagus nerve.

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ORIGIN

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CONTENTS • • • • •

Type Origin Innervation Course Applied Anatomy www.indiandentalacademy.com

OLFACTORY NERVE

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OLFACTORY NERVE • It is the first cranial nerve and nerve of smell and form first order neuron of olfactory pathway.

• Type → Special Sensory type.

• Origin → From olfactory epithelium in the olfactory region of nasal cavity (superior nasal concha and opposed part of nasal septum). www.indiandentalacademy.com

• Course → After origin they pass through the cribriform plate of ethmoid bone and within the cranial cavity they end.

• Innervation → Nasal Mucous Membranes.

• Enter → Cribriform plate of the ethmoid bone. www.indiandentalacademy.com

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• Applied anatomy →  In case of fracture of anterior cranial fossa olfactory nerves may be separated from olfactory bulb and results in loss of smell (Anosmia).  It may tear the meningeal sheaths, so leakage of CSF from nose.  Infection from nose may spread through the meningeal sheaths to brain and intracranial complication and Meningitis and encephalitis may occur. www.indiandentalacademy.com

EXAMINATION OF THE CRANIAL NERVES • a) Introduce yourself, obtain consent, wash your hands.

• b) Position patient (they should be sitting in a chair or on the edge of a bed).

• c) General inspection.

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OLFACTORY NERVE • Ask “Have you noticed any change in your sense of smell or taste recently?”

• If yes, check that the problem is not due to a cold/blocked nose and say “I would like to formally examine the sense of smell”. This involves the use of bottles containing standard smells (rarely used) or the use of a substance with a strong aroma eg. coffee. Remember to test each nostril separately. www.indiandentalacademy.com

OPTIC NERVE

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OPTIC NERVE • It is the second cranial nerve and is nerve of vision.

• Type → Special Sensory Type

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• Origin → Its fibres origin from Ganglionic layer of retina and stratum opticum.

• Innervation → Optic Canals.

• Course → After emerging out of the eyeball it passes through the orbit for a short course and enters the cranial cavity by passing through the optic foramen. In the cranial cavity on the superior surface of body of sphenoid bone it ends.

• Intra cranial part → It runs backwards and www.indiandentalacademy.com medially from optic canal to optic chiasma.

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• Applied anatomy → Lesions of different parts of the pathways and effects  Retina – Scotoma (Blind spots in certain parts).  Optic nerve – Due to injury and effect is blindness.  Optic chiasma – a) Central part – Bitemporal hemianopia. b) Peripheral part (both side) – Binasal hemianopia. [ Hemianopia is loss of vision in one half of field of vision.] www.indiandentalacademy.com

OPTIC NERVE

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CRANIAL NERVE FUNCTION & MUSCLE INNERVATION RELATIVE TO EYE MOVEMENT Superior rectus CN III

Lateral rectus CN VI

Inferior rectus CN III

Inferior oblique CN III

Medial rectus CN III

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Superior oblique CN IV

OPTIC EXAMINATION • • • • • •

Remember APAFF: Acuity Pupils Accommodation Fields Fundoscopy

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Acuity •

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Ask “Do you usually wear glasses/contact lenses?” If yes, ask patient to put them on. Use a pocket Snellen chart. “Cover your left eye with your left hand and read down the chart from the top”. Repeat for right eye. Record visual acuity. If no Snellen chart available, test using a magazine/name badge and say “I would like to formally assess acuity using a Snellen chart at 6m”.

If unable to see letters, check if able to: count fingers, detect hand movement, detect light.

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Pupils • PERLA – are the Pupils Equal and Reactive to Light and Accommodation?

• Inspect size and symmetry of pupils. Tell the patient that you are going to shine a light in their eyes. Shine a pen torch twice into each eye checking first for a direct and then for a consensual response (both pupils should constrict in response to a light being shone in either one of them). Dimming background light makes this process easier. www.indiandentalacademy.com

Accommodation • Ask the patient to look at a point on the far side of the room. Then ask them to look at a point about 15cm from their face. The pupils should constrict as the patient focuses on the near object.

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Fields • Tested by confrontation. Sit in front of, and at the same level as, the patient, about 1m apart. “Cover your right eye with your right hand please and look straight into my eye” (you should cover your left eye with your left hand at the same time). Bring a target (ideally a red hat pin, otherwise the wiggling end of your finger) in diagonally from above and below on each side (you will need to swap hands halfway through), making sure that the target is equidistant between the two of you. Ask the patient when they first see the target. Repeat for the other eye. Compare your fields with those of the patient.

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Fundoscopy • Say “I would also like to examine the fundi with an ophthalmoscope”.

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OCCULOMOTOR NERVE • It is the third nerve supplying all the muscles of the eye ball except Lateral rectus and Superior oblique and also supplies sphincter pupillae and ciliaris muscle.

• Type → Motor www.indiandentalacademy.com

• Origin → ORIGIN (Deep origin or nucleus of origin) : Nucleus of the third nerve lies in the grey matter of upper part of floor of cerebral aqueduct of midbrain at the level of superior colliculi .

• Nucleus of third nerve: Segmental and consists of following components with function.

• Enter → Superior Orbital Fissure.

• Innervation → LPS,SR,IR,MR & IO. • Course → Intra neural part & Extra neural part www.indiandentalacademy.com

• I) Intracranial part: From the nucleus of origin the fibres pass through the tegmentum. Red nucleus and medial part of substantia nigra in a curved manner and finally emerges out of the brain from the medial side of the crus cerbri through oculomotor sulcus.

• Superficial origin: From the oculomotor sulcus on the medial side of crus cerebri.

• II) Extracranial part: The fibre of the oculomotor nerve after emerging out of the brain through oculomotor sulcus leaves the pial sheath and runs in the subarachnoid space. www.indiandentalacademy.com

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• Applied anatomy →  Complete optholmoplegia : loss of function of all three of these nerves, and can result from cavernous sinus thrombosis, superior orbital fissure fracture, or elevated ICP.  Traumatic mydriasis : damager to the third nerve _ dilatation and non-reactivity of the pupil.  Ptosis : Drooping of upper eyelid due to paralysis of levator palpebrae.  Lateral strabismus (squint) : due to unopposed action of lateral rectus.  Dilation of pupil : due to paralysis of sphincter pupillae and ciliaris muscle slight prominence of eyeball owing to most of the muscles of eyeball being relaxed.  The third nerve is usually affected due to syphilitic periarteritis of posterior cerebral and superior cerebellar arteries as the nerve www.indiandentalacademy.com passes between them.

TROCHLEAR NERVE

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TROCHLEAR NERVE • It is the fourth cranial nerve which supplies superior oblique muscle of eyeball.

• Type → Motor • Origin →Deep or Nucleus of origin : Nucleus of the trochlear nerve lies in the grey matter of lower part of the floor of cerebral aqueduct www.indiandentalacademy.com at the level of inferior colliculi.

• Course → Intraneural (part within the brain) –From the nucleus of origin the nerve runs downwards and laterally in the tegmentum and then turns backwards around the central grey matter towards the dorsal aspect of the brain stem. Here the two nerves cross each other before emergence.

• Superficial origin: It emerges out below inferior colliculus and on surface of superior medullary velum ends on each side of frenulum veli.

• Intracranial part: The trochlear nucleus gives rise to nerves that cross (decussate) to the other side of the brainstem just prior to exiting the brainstem. The trochlear nerve fibers curve forward and enter the duramater at the angle between the free and attached border of the tentorium cerebelli. The nerve travels in the lateral wall of the cavernous sinus and then enters the orbit via the www.indiandentalacademy.com superior orbital fissure.

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• Innervation → SOM

• Applied anatomy :  If the nerve is injured, downward and lateral movement of eyeball will not be possible and no difficulty so long the patient looks above the horizontal level.  Double vision will occur if he looks downward and the patient has a pathetic look and so this nerve is known as pathetic nerve.

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TRIGEMINAL NERVE

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TRIGEMINAL NERVE • Attached to the side of pons, very large.

Sensory from muscles of mastication, skin of face and scalp, mucous membranes of mouth and nasal cavity, cornea of eye, teeth, and duramater. Motor to muscles of mastication.

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TRIGEMINAL NERVE • It is the fifth cranial nerve and largest of all cranial nerves.

• Type → Mixed so both Motor & Sensory.

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• Origin → Deep origin or Nucleus of origin • I. Sensory nucleus (Principal): Situated within the pons lateral to the motor nucleus of nerve. It receives sensory fibres for touch sensation.

• II. Spinal nucleus of trigeminal nerve: An elongated nucleus extending from the sensory nucleus, cranially to second or third cervical spinal segments caudally. It receives pain and temperature from trigeminal area.

• III. Mesencephalic nucleus: Situated in the central grey matter of mid brain on either side of cerebral aqueduct. It receives proprioceptive sensations of the fifth nerve.

• IV. Motor nucleus: Situated within the pons, medial to sensory nucleus and the fibres from it form the motor root of the nerve.

This nucleus represents the special visceral afferent column. www.indiandentalacademy.com

• Superficial origin: Two roots: Motor and sensory emerge from the ventral aspect of the pons. Sensory root larger and motor root smaller and motor root lies ventrimedial to sensory root. • The sensory root passes forward from the posterior cranial fossa and joins the concave posterior margin of trigeminal ganglion. • The motor root passes forward and then passes below the sensory root and trigeminal ganglion in the trigeminal cave and finally joins with the sensory part of mandibular nerve in the foramen ovale and from trunk of mandibular nerve. www.indiandentalacademy.com

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Branches Ophthalmic Nerve (V1) → Purely Sensory Nerve.

Maxillary Nerve (V2) → Sensory.

Mandibular Nerve (V3) → Mixed and consisting of two roots.

• 1.OPTHALMIC NERVE: - It is one of the divisions of trigeminal nerve.

- It is purely a sensory nerve.

- Arises from the convex anterior margin of trigeminal ganglion.

- After origin it lies on the lateral wall of cavernous sinus below 4th cranial nerve and above maxillary division.

- In the anterior part of cavernous sinus it terminates by dividing into a) Frontal, b) Lacrimal, c) Nasociliary. www.indiandentalacademy.com

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FRONTAL NERVE: Largest branch of ophthalmic nerve.

It is a sensory nerve.

It enters the orbit through lateral part of sof outside the annulus tendinous communis (ring) lateral to trochlear nerve.

It terminates in the midway between base and apex of the orbit by dividing into two branches.

A. supratrochlear.

B. supraorbital.

LACRIMAL NERVE: Smallest of the branches of ophthalmic nerve and sensory nerve.

Receives few filaments from trochlear nerve and these filaments are those which pass from ophthalmic to trochlear nerve previously.

It passes to orbit through lateral compartment of superior orbital fissure outside annulus tendinous ring and lateral to frontal nerve.

It passes above lateral rectus accompanied by lacrimal artery and receives a twig from zygomatico-temporal branch which carries post ganglionic secretomotorwww.indiandentalacademy.com fibres of lacrimal gland.

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NASOCILIARY NERVE: 1) It is a sensory nerve and one of the three branches of ophthalmic nerve.

2) Origin: It arises from the ophthalmic nerve in the anterior part of cavernous sinus.

3) It enters the orbit by passing through the middle compartment of superior orbital fissure within the annulus tendinous communis and then the two heads of lateral rectus muscle.

4) Ultimately it passes through anterior ethmoidal foramen and terminates by continuing as anterior ethmoidal nerve.

5) Branches1)Branches of communication: Sympathetic plexus, 3rd nerve, ciliary ganglion.

2)Branches of distributioni. Long ciliary branches. ii. Posterior ethmoidal. iii. Infratrochlear. iv. Anterior ethmoidal a) Internal nasal branch. b) External nasal branch. www.indiandentalacademy.com

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2. MAXILLARY NERVE: It is the intermediate division of trigeminal nerve.

Origin: from the convex aspect of trigeminal ganglion.

Course: After origin it runs forwards along the lower part of lateral wall of cavernous sinus below the ophthalmic nerve.

Then it leaves the skull by passing through foramen rotundum and enters into the pterygopalatine fossa. From there it inclines to the posterior surface of maxilla and enters the orbit through inferior orbital fissure. It is then named infraorbital nerve It passes through infraorbital groove and canal on the floor of the orbit.

Branches: 1) Within cranium: Meningeal. It supplies duramater of middle and partly in the anterior cranial fossa.

2) In the pterygopalatine fossa: 1) Ganglionic: 2) Zygomatic: a. zygomaticotemporal b. zygomaticofacial.

3) Posterior superior alveolar.

3) In the infraorbital canal: i. Middle superior alveolar. ii. Anterior superior alveolar.

4) In the face: 1. Palpebral. www.indiandentalacademy.com 2. Nasal.

3. Superior labial.

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3. MANDIBULAR NERVE: It is the largest division of trigeminal nerve.

Origin: Larger sensory root arises from convex aspect of trigeminal ganglion and smaller motor root from motor nucleus of trigeminal nerve in the pons.

Course: The united trunk enters the infratemporal fossa by passing through foramen ovale and lies in between tensor veli palate-medially and lateral pterygoid laterally.

Branches: 1) From the trunk, i.e. before division: i) Nervous spinous or meningeal branch ii) Nerve to medial pterygoid.

2) From anterior divisions: Motor branches: i) Deep temporal ii) Nerve to lateral pterygoid iii) Massetric www.indiandentalacademy.com Sensory branch: Buccal nerve and skin

3) Posterior division: I) Auriculotemporal: a) Branches of communicationi) With otic ganglion and receives post Ganglionic secretomotor fibres for the parotid gland. ii) With seventh nerve. b) Branches of distributioni) Anterior auricular - to pinna. ii) External acoustic branch. iii) Articular branches to temporomandibular joint. iv) Parotid branches. v) Superficial temporal branches. www.indiandentalacademy.com

II) Lingual nerve: it is a sensory nerve for mucous membrane to anterior 2/3rd of tongue, floor of the mouth and gum.

ORIGIN: from the posterior trunk of mandibular nerve in the infratemporal fossa.

COURSE: after origin it passes between tensor palate and lateral pterygoid and in this part chorda tympani nerve joins it and also a branch from inferior alveolar nerve.

Distribution: branches supply: Mucous membrane of floor of mouth, Lingual surface of gum,Mucous membrane of anterior 2/3rd of tongue except vallate papilla, It also carries post Ganglionic fibres from submandibular ganglion for sublingual salivary and anterior lingual gland. www.indiandentalacademy.com

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• Inferior alveolar nerve: It is the branch of posterior trunk of mandibular nerve. • Course: it runs downward deep to lateral pterygoid and passes between sphenomandibular ligament and ramus of mandible upto mandibular foramen and enters the mandibular canal and runs below the teeth as far as mental foramen and terminates by dividing into mental and incisive branch. • Branches: 1) Nerve to myolohyoid 2) Mental 3) Incisive branch www.indiandentalacademy.com 4) Dental branch

• Applied anatomy:  The sensory root of this nerve is divided into three divisions, each division may be tested by light touch or pinprick on the skin overlying its respective area of distribution.  The motor root of trigeminal supplies the muscles of mastication and can be tested by palpating the temporalis and masseter during clenching movements.

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• Applied anatomy:  Lesion of whole of trigeminal nerve, 1) Anesthesia of the corresponding anterior half of scalp, face(except the area at the angle of mouth, because of supply by great auricular), cornea, conjunctiva, mucous membrane of nose, mouth, anterior 2/3rd of tongue.

2) Paralysis and atrophy of muscles supplied by the nerve and so when patient tries to open the mouth the mandible will thrust to the paralysed side.  Lesions of any divisions of nerve.  Lesion of lingual nerve below the point of joining of chorda tympani .  Pain or neuralgia is of very common.  In case of frontal or ethmoidal sinusitis or glaucoma severe supraorbital pain occurs. It is also a case of referred pain. www.indiandentalacademy.com

ďƒ˜ Trigeminal neuralgia (TN) : is a disorder of unilateral (usually right-sided) facial pain. While the exact cause is unknown, it is thought that TN results from irritation of the trigeminal nerve. This irritation results from damage due either to changes in the blood vessels or the presence of a tumor or other lesions that cause compression of the nerve. ďƒ˜ The pain quality is usually sharp, stabbing, lancinating (cutting or tearing), and burning. It may have an "electric shock"-like character. ďƒ˜ In some individuals the attacks may be initiated by non-painful physical stimulation of specific areas (trigger points or zones) that are located on the same side of the face as the pain. www.indiandentalacademy.com

ABDUCENT NERVE

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ABDUCENT NERVE • It is the sixth cranial nerve which supplies lateral rectus muscle.

• Type → Motor nerve.

• Origin → The fibres arise from a small nucleus situated in the dorsal aspect of the pons in the floor of the fourth ventricle close to the median plane and beneath the facial colliculus. www.indiandentalacademy.com

• Course → The abducent nerve after leaving the brain stem runs upwards laterally and forwards through cisterna pontis.As it proceeds forwards it will be crossed by anterior inferior cerebellar artery ventrally and then loses its dural sheath at the lateral side of dorsal sellae. Then it bends sharply forwards at the apex of petrous part of temporal bone to the lateral margin of dorsum sellae. After that enters into orbital cavity through middle part of superior orbital fissure within annulous tendinous communis. Finally it terminates in the orbit.

• Enter → Superior Orbital Fissure.

• APPLIED ANATOMY:  It is liable to be damaged during fracture of skull. When intracranial pressure increases, pons is pushed backwards and downwards and this nerve may get stretched and may lose its function.  Effects of paralysis: – Convergent squint due to unopposed action of medial rectus. www.indiandentalacademy.com – Often diplopia with convergent squint will be present.

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References • • • •

Gray’s Anatomy 2nd edition.

B D Chaurasia 3rd Vol 4th edition.

Human Anatomy Chakraborthy.

Hutchinson’s clinical manual.

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thank you

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Facial Nerve

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FACIAL • Origin → Lateral Surface of the Brainstem.

• Course • Enter

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Vestibulocochlear Nerve

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VESTIBULOCOCHLEAR • Origin → Lateral Surface of the Brainstem.

• Course → Pons & Medulla.

• Enter →

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Glossopharyngeal Nerve

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GLOSSOPHARYNGEAL • Origin • Course • Enter

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Vagus Nerve

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VAGUS • Origin • Course • Enter

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Spinal Accessory Nerve

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SPINAL ACCESSORY • Origin • Course • Enter

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Hypoglossal Nerve

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HYPOGLOSSAL • Origin • Course • Enter

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Under the Guidance of • • • • • • • •

Prof. L. Krishna Prasad Prof. Srinivas Chakravarthy Dr. Neelima Dr. M. Sridhar Dr. Raja Subhash Dr. Suprakash Dr. Giridhar Kumar Dr. Sumanth Krishna www.indiandentalacademy.com

Some Facts About The Cranial Nerves • • • • • • • •

Which cranial nerve is the largest?

CN V (Trigeminal) Which cranial nerve is the only one that exits the "posterior" side of the brainstem?

CN IV (Trochlear) How many cranial nerves are responsible for eye movements?

Three: CN III (Oculomotor), IV (Trochlear), and VI (Abducens).

What does "abducens" refer to?

The abducens nerve carries motor impulses to the lateral rectus eye muscle which moves the eye laterally causing abduction of the eye.

Which cranial nerves carry gustatory (taste) information?

CN VII (Facial), CN IX (Glossopharyngeal) and CN X (Vagus).

Which cranial nerve is the longest?

CN X (Vagus) which reaches from the medulla to the digestive and urinary organs.

What two cranial nerves carry sensory information about blood pressure to the brain?

CN IX (Glossopharyngeal) and CN X (Vagus).

Which cranial nerve is responsible for pupillary constriction?

CN III (Oculomotor).

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