VII: Anatomy of Cranial Nerve 7
What is the difference between facial nerve palsy and bells palsy
Facial Nerve Palsy • Usually permanent, known nerve damage • Loss of facial expression and symmetry • Unable to lacrimate • Loss of function of obicularis muscles (Sphincters) - Obicularis ocul i→ ptosis - Obicularis oris → drooling • Bilateral damage less common • May be mistaken for stroke Bell's Palsy • Usually temporary - 6 weeks • Loss of facial expression and symmetry • Unable to lacrimate • Loss function of obicularis muscles (Sphincters) - Obicularis oculi→ptosis - Obicularis oris→drooling • Bilateral damage less common Normally the nerve gets damaged to due an infection, once this dies down the nerve recovers
What is the test for the facial nerve
Facial nerve tests - raise eyebrows, - wrinkle forehead (frontalis), - close the eyes tightly (orbicularis oculi), - broad smile for several muscles for symmetry, - puffing out the cheeks (buccinator) tests orbicularis oris as well
Describe the secretomotor fibres of CNVII
The Secretomotor Fibres of CNVII · Secretomotor fibres of cranial nerve VII innervate the sublingual and submaxillary glands. Pre-ganglionic fibres originate from the salivatory nucleus, which is located in the pons, near the motor nucleus · These fibres supply the following salivary glands - Sublingual glands -& - Submaxillary glands. • The submandibular ganglion
What is facial nerve palsy caused by
What is it caused by? • Usually permanent • Loss of facial expression • Facial asymmetry • Loss of naso-labial fold to affected side • Loss of lacrimation • Loss of secretomotor function in oral & nasal mucosa • Loss of actions of sphincter muscles - Orbicularis oculi: Complete opening of upper eyelid, Loss of blink reflex, Stasis of tears - Orbicularis oris: Oral incompetence, Drooling of saliva • Frowning of brow still possible - in unilateral nerve damage • Bilateral damage is only seen in - Parkinson's Disease - A side effect of certain medications - Bilateral damage to nerves (rare)
Describe the sensory root of CNVII chorda tympani
1. The Sensory Root of CNVII Chorda Tympani o It is the nerve for Special Sense of Taste for CNVII o Responds to taste input from the taste buds of the tongue. o The cell bodies of its fibers are in a sensory ganglion located near the inner ear (called the geniculate ganglion). o Rather than entering the skull with the facial nerve, the chorda tympani travels separately. o It passes between the malleus and the incus bones of the ear and enters from the skull separately, which is why taste is sometimes spared even though other branches of the facial nerve are affected in Bell's palsy.
Describe Bogorad's syndrome
Bogorad's Syndrome Aka: Syndrome of Crocodile Tears • History of damage to the facial nerve • Presents with lacrimation whilst eating or smelling food • May also be salivation on lacrimation due to connection • Less common presentation may be facial tic, increased facial muscle tone and impaired sense of taste • As the autonomic (gustatory) fibres to the salivary glands regenerate after damage to facial nerve - Facial nerve palsy - Bell's palsy • Some fibres are directed incorrectly to the lacrimal gland • Causes an incorrect connection between lacrimal and salivary glands
What are the motor branches
Branches of the facial nerve are responsible for innervating many of the muscles of the head and neck. All these muscles are derivatives of the second pharyngeal arch. The first motor branch arises within the facial canal; the nerve to stapedius. The nerve passes through the pyramidal eminence to supply the stapedius muscle in the middle ear. Between the stylomastoid foramen, and the parotid gland, three more motor branches are given off: Posterior auricular nerve - Ascends in front of the mastoid process, and innervates the intrinsic and extrinsic muscles of the outer ear. It also supplies the occipital part of the occipitofrontalis muscle. Nerve to the posterior belly of the digastric muscle - Innervates the posterior belly of the digastric muscle (a suprahyoid muscle of the neck). It is responsible for raising the hyoid bone. Nerve to the stylohyoid muscle - Innervates the stylohyoid muscle (a suprahyoid muscle of the neck). It is responsible for raising the hyoid bone. Within the parotid gland, the facial nerve terminates by bifurcating into five motor branches. These innervate the muscles of facial expression: Temporal branch - Innervates the frontalis, orbicularis oculi and corrugator supercilii Zygomatic branch - Innervates the orbicularis oculi. Buccal branch - Innervates the orbicularis oris, buccinator and zygomaticus muscles. Marginal Mandibular branch - Innervates the mentalis muscle. Cervical branch - Innervates the platysma.
What are the names of all the cranial nerves
CNI Olfactory CNII Optic CNIII Oculomotor CNIV Trochlear CNV Trigeminal CNVI Abducens CNVII Facial CNVIII Vestibulocochlear CNIX Glossopharyngeal CNX Vagus CNXI Accessory CNXII Hypoglossal
Describe facial nerve palsy
Complete Palsy of CNVII • It leads to denervation of CNVII effector organs • Palsy of the facial nerve or Bell's palsy would result • Need to distinguish between facial nerve palsy versus belly palsy • Facial symmetry will be lost • The face will be drawn towards the normal side and away from the lesion side
What are the motor, sensory and Parasympathetic supplies of the faciaal nerve
Motor - muscles of facial expression, posterior belly of the digastric, stylohyoid and stapedius muscles. Sensory - a small area around the concha of the external ear. Special Sensory - provides special taste sensation to the anterior 2/3 of the tongue via the chorda tympani Parasympathetic - supplies many of the glands of the head and neck, including: Submandibular and sublingual salivary glands. Nasal, palatine and pharyngeal mucous glands. Lacrimal glands. The facial nerve (CN VII) is the seventh paired cranial nerve.
Describe the motor division of the CNVII
Motor Division • Its motor supply to muscles of facial expression has three separate arrangements • It supplies the majority of muscles on the same side of the body as that of location of cell bodies of neurones of the facial motor nucleus (ipsilateral) • Muscles of expression of the forehead receive bilateral innervation from both motor divisions of cranial nerve VII (contralateral and ipsilateral). If they cant frown-> LMN isn't working. • Some of its muscle targets are not muscles of facial expression (e.g. Stapedius Muscle & Digastric Post) • This fact of anatomy has clinical significance when it comes to delineating the locations of neuronal lesions that paralyse muscles of facial expression • To note: Forehead Sparing: muscles of the face are DE innervated due to damage but this is spared in the forehead. • To Note: Bell's Palsy vs Facial Nerve Palsy
Describe the special visceral efferent of the facial nerve
Origin Begins in the motor nucleus of the facial n Termination Innervates the muscles of facial expression, stylohyoid, posterior digastric, and stapedius mm Summary SVE fibers are carried in the motor root of the facial n. SVE fibers are responsible for innervating the muscles of the 2nd pharyngeal arch Comment In Bell's palsy, the easiest symptom to observe is that the muscles innervated by the SVE fibers are paralyzed
Describe the general somatic afferent function of the facial nerve
Origin of Fibers Afferent fibers begin in the various receptors (nociceptors, mechanoceptors, proprioceptors) of the skin of the external ear and tympanic membrane Termination of Fibers Pain and temperature fibers terminate in the spinal nucleus of V Summary GSA fibers are carried in the nervus intermedius portion of the facial n. GSA fibers are responsible for providing sensory innervation to a portion of the external ear and tympanic membrane GSA fibers of the facial n. utilize the trigeminothalamic lemniscus to carry their sensory impulses to consciousness Comment Facial nerve provides a very small area of GSA distribution Nerve cell bodies for the primary fibers are located in the geniculate ganglion
Describe the special visceral afferent function of the facial nerve
Origin of Fibres Afferent fibers begin in the taste receptors of the anterior 2/3 of the tongue Termination of Fibres Primary afferent fibers travel in the tractus solitarius and terminate in the nucleus solitarius Summary SVA fibers are carried in the nervus intermedius portion of the facial n. SVA fibers are responsible for carrying the taste fibers from the taste buds on the anterior 2/3 of the tongue Comment Nerve cell bodies for the primary fibers are located in the geniculate ganglion
Describe the general visceral afferent component of the facial nerve
Origin of Fibres Afferent fibers begin in the various receptors (such as nociceptors) of the mucous membranes of the nasopharynx Termination of fibres Primary afferent fibers travel in the tractus solitarius and terminate in the nucleus solitarius Summary GVA fibers are carried in the nervus intermedius portion of the facial n. GVA fibers utilize the same pathway as the SVA fibers Comment Nerve cell bodies for the primary fibers are located in the geniculate ganglion
Describe the general visceral efferent component of the facial nerve
Origin of Fibres Preganglionic parasympathetic fibers begin in the superior salivatory nucleus Termination of Fibres Postganglionic parasympathetic fibers innervate the lacrimal, nasal, submandibular, and sublingual glands Summary GVE fibers are carried in the nervus intermedius portion of the facial n. Comment GVE fibers utilize 2 ganglia: •Pterygopalatine •Submandibular
What are the special sensory functions
The chorda tympani branch of the facial nerve is responsible for innervating the anterior 2/3 of the tongue with the special sense of taste. The nerve arises in the facial canal, and travels across the bones of the middle ear, exiting via the petrotympanic fissure, and entering the infratemporal fossa. Here, the chorda tympani 'hitchhikes' with the lingual nerve. The parasympathetic fibres of the chorda tympani stay with the lingual nerve, but the main body of the nerve leaves to innervate the anterior 2/3 of the tongue.
What is the course of the facial nerve
The nerve arises in the pons, an area of the brainstem. It begins as two roots; a large motor root, and a small sensory root (the part of the facial nerve that arises from the sensory root is sometimes known as the intermediate nerve). The two roots travel through the internal acoustic meatus, a 1cm long opening in the petrous part of the temporal bone. Here, they are in very close proximity to the inner ear. Still within the temporal bone, the roots leave the internal acoustic meatus, and enter into the facial canal. The canal is a 'Z' shaped structure. Within the facial canal, three important events occur: Firstly the two roots fuse to form the facial nerve. Next, the nerve forms the geniculate ganglion (a ganglion is a collection of nerve cell bodies). Lastly, the nerve gives rise to: Greater petrosal nerve - parasympathetic fibres to mucous glands and lacrimal gland. Nerve to stapedius - motor fibres to stapedius muscle of the middle ear. Chorda tympani - special sensory fibres to the anterior 2/3 tongue and parasympathetic fibres to the submandibular and sublingual glands. The facial nerve then exits the facial canal (and the cranium) via the stylomastoid foramen. This is an exit located just posterior to the styloid process of the temporal bone. Extracranial After exiting the skull, the facial nerve turns superiorly to run just anterior to the outer ear. The first extracranial branch to arise is the posterior auricular nerve. It provides motor innervation to the some of the muscles around the ear. Immediately distal to this, motor branches are sent to the posterior belly of the digastric muscle and to the stylohyoid muscle. The main trunk of the nerve, now termed the motor root of the facial nerve, continues anteriorly and inferiorly into the parotid gland (note - the facial nerve does not contribute towards the innervation of the parotid gland, which is innervated by the glossopharyngeal nerve). Within the parotid gland, the nerve terminates by splitting into five branches: Temporal branch Zygomatic branch Buccal branch Marginal mandibular branch Cervical branch These branches are responsible for innervating the muscles of facial expression.
What are the parasympathetic functions
The parasympathetic fibres of the facial nerve are carried by the greater petrosal and chorda tympani branches. Greater Petrosal Nerve The greater petrosal nerve arises immediately distal to the geniculate ganglion within the facial canal. It then moves in anteromedial direction, exiting the temporal bone into the middle cranial fossa. From here, its travels across (but not through) the foramen lacerum, combining with the deep petrosal nerve to form the nerve of the pterygoid canal. The nerve of pterygoid canal then passes through the pterygoid canal (Vidian canal) to enter the pterygopalatine fossa, and synapses with the pterygopalatine ganglion. Branches from this ganglion then go on to provide parasympathetic innervation to the mucous glands of the oral cavity, nose and pharynx, and the lacrimal gland. Chorda Tympani The chorda tympani also carries some parasympathetic fibres. These combine with the lingual nerve (a branch of the trigeminal nerve) in the infratemporal fossa and form the submandibular ganglion. Branches from this ganglion travel to the submandibular and sublingual salivary glands.
What are the nerve names for the modalities
The somatic motor component, Innervates somatic muscles It circles around cranial nerve VII Known as the Facial Nerve The visceral motor component Innervates the lacrimal, submaxillary, and submandibular glands, Known as the Greater Petrosal Nerve The somatic sensory component of cranial nerve VII Innervates external ear sensation Forms part of Nervus Intermedius The visceral sensory component Innervates special sense of taste for the anterior two thirds of the tongue Known as Chorda Tympani
Describe the chorda tympani
This has both visceral sensory fibres (start off in the cell bodies of the geniculate ganglion) and distributes to the anterior 2/3s of the tongue and the taste buds of the soft palate It also carries sectromotor fibres from the superior salivary nucleus to the submandibular and sublingual glands. This is issues in the facial canal which separates from the rest of the nerves. This abuts the window of the ear. The CNVII can be damaged in the facial canal but will not affect taste sensation as a the chorda tympani takes a different root • The sensory fibers of the facial nerve, called the chorda tympani nerve, respond to taste input from the taste buds of the tongue. • The cell bodies of these fibers are in a sensory ganglion located near the inner ear (called the geniculate ganglion). • Rather than entering the skull with the facial nerve, the chorda tympani travels separately. • It passes between the malleus and the incus bones of the ear and enters from the skull separately, which is why taste is sometimes spared even though other branches of the facial nerve are affected in Bell's palsy. • The chorda tympani has its own nucleus of cell bodies in the medulla, called the nucleus solitarius. • Secretomotor fibers of cranial nerve VII innervate the sublingual and submaxillary glands. These fibers originate from the salivary nucleus, which is located in the pons, near the motor nucleus • This goes through the petrotympanic fissure
How is Bogorad's syndrome treated
Treatment of Bogorad's Syndrome • Injection of Botulinum toxin into the lacrimal gland - Paralysis of lacrimal gland - Stops the tears - Does not reverse pathological cause • Resect palpebral lobe of lacrimal gland - Stops the tears - Irreversible
What do the 4 nucelli supply
What these nucelli supply · The Facial Nucleus of The Pons · It is motor to somatic muscles - Forms facial colliculus around cranial nerve VI · Superior Salivatory Nucleus of The Pons · It supplies the visceral motor component (Parasympathetic) · Spinal nucleus of cranial nerve V from the Medulla · It supplies somatic sensory component of cranial nerve VII · solitary tract nucleus of The Medulla · Supplies Special Sense of Taste of part of the tongue (Anterior 2/3 of Tongue) · Also known as The visceral sensory component
Describe the sensory root of CNVII
· The sensory Root of CNVII is by definition also known as part of The Nervus Intermedius · Sensations carried via CNVII will be either · Somatic Sensory (minor) (Carried by CNV) · Skin of the ear (minor) · Anterior two-thirds of the tongue (Major) · When we talk of the sensory branch of CNVII, we would normally be referring to its Special Sense of Taste · Special Sense of Taste is carried through the Chorda Tympani Branch of CNVII • The chorda tympani projects its axons centrally to cell bodies of the solitary nucleus in the medulla
Describe the sensory root
• Also known as part of Nervus Intermedius, supplies general sensation of the concha of the auricle and behind the ear • Special sensory - taste in anterior 2/3 via chorda tympani
What are the roots of the CNVII
• It has 3 separate roots of fibres with separate origins in the brainstem • 3 brain nuclei from which CNVII nerve roots arise are: - Facial Motor Nucleus - Nucleus Solitarius (sensory fibres from soft palate and anterior 2/3s, and to salivary glands - Superior Salivatory Nucleus - Geniculate ganglion (not in brain but in middle cranial fossa)
Describe the modalities of CNVII
• It has A Motor Division - Referred to as the facial nerve • Sensory Division (General sensation i.e. the oracle of the ear) - Forms part of Nervus Intermedius/ intermediate nerve • Autonomic Division - It is also a part of Nervus Intermedius - The Greater Petrosal Nerve is its largest branch • Visceral Sensory Division - Via Its Special Sense of Taste Division - Chorda Tympani is the main nerve: anterior 2/3s of the tongue (taste only)
What are the origins of the facial nerve
• Axons of CNVII originate in four nuclei in the pons and medulla The Facial Nucleus of The Pons • It is motor to somatic muscles, largest of the pontine nucelli • Its axons fibres circle around cranial nerve VI- Facial Colliculus (axons issue out and travel centrally over the abducens nucleus) Superior Salivatory Nucleus of the Pontine Tegmentum • It supplies the visceral motor component (Parasympathetic that travel with CNVII) • Chorda Tympani partly made from fibres arising here to salivary glands (autonomic ganglion also) • This is the nerve for salivation, located superiorly to the inferior salivary nucleus Spinal nucleus of cranial nerve V from the Medulla • Sensory nucleus • Some of the sensory fibres of CNVII are processed here to interact with each other • It is supplied by somatic sensory component of cranial nerve VII Solitary tract nucleus of The Medulla • Sensory nucleus, receives imputs from afferents and Supplies Special Sense of Taste of part of the tongue (anterior 2/3s) • Also known as The visceral sensory component • Chorda Tympani made partly from axons arising here. This presents twice (carries some of the secretomotor fibres with their cell bodies in the superior salivary nucleus and afferent fibres from the anterior 2/3s of the tongue for taste) to the solitary tract nucleus
Where can damage of CNVII occur
• Damage to facial nerve (outside the facial canal) -> paralysis of muscles of facial expression • Damage within posterior wall of the tympanic cavity (chorda tympani) affects taste to anterior 2/3rd of the tongue & on salivation and lacrimation • Surgery on the middle ear may damage the facial nerve within the labyrinthine wall of the tympanic cavity especially the chorda tympani • Tumours within the petrous part of the temporal bone will affect the facial nerve
What is the facial nerve at risk of damage
• Forceps delivery of babies: lack of protections the leaves the stylomastoid foramen as there is not a developed mastoid bone • Tumours of parotid gland • Parotitis • Parotidectomy • Inflammation of the facial nerve - Within the facial canal • Incision of the facial nerve • Tympanectomy: infections of the eye and sucking out the tympanic membrane • Surgical procedures of the infratemporal fossa
What are anatomical landmarks of the facial nerve
• Internal Acoustic Meatus • Petrous portion of the Temporal Bone • Facial Canal • Internal jugular vein • Stylomastoid Foramen • Parotid Sheath • Parotid Gland • Maxillary Vein
Describe the facial nerve in the facial canal
• It has a short and yet complex course through the petrous portion of the temporal bone • It then emerges through the stylomastoid foramen, large intraosseous course • This is a Z shaped canal, tight travel so if it needs to expand if it holds water due to inflammation = compressed.
Describe the facial nerve
• It is a purely somatic motor nerve • It supplies all muscles of facial expression on the same side of the body as itself • It has the widest distribution of any motor nerve of the head region • Frontalis muscles (forehead) receive bilateral innervation The Motor Root of The Facial Nerve • Leaves the cranium along a course in the facial canal that ends as the stylomastoid foramen • Immediately pierces the parotid sheath as it enters the parotid gland where it divides into 5 terminal branches • Any tumours of the parotid gland will lead to congestion within the parotid sheath leading to palsy of the motor branches of the facial nerve -> irreversible.
What does the motor component supply
• Motor to - Muscles of facial expression - Posterior Belly of Digastric Muscle - Stapedius Muscle • Damage Leads to - Loss of facial expression - Loss of sphincter function (orbicularis oris/oculi) - Loss of Naso-labial Fold - Hyperacusis= increased sensitivity of sounds
What does the sensory root supply
• Supplies the following glands - Lacrimal - Submandibular - Sublingual • Mucous Membranes of - Nasopharynx - Paranasal Sinuses - Hard Palate - Soft Palate
What do cranial nerves supply
• Their Head & Neck Targets are: - Muscles (somatic efferent) - Viscera (afferent & efferent) - General Sensation (afferent) - Special Sense Organs (afferent) • Some also supply viscera of the body outside of the Head & Neck Region
Describe the general features of cranial nerves
• There are 12 pairs of cranial nerves • They are largely bilaterally symmetrical • They exit the brain from its inferior surface apart from 1 (trochlear leaves through the superior part of the brain) • Short sections attaching the nerve to the brain are found within the cranium • They leave the cranium via foramina Most are typical of "peripheral nerves" • 2 are atypical in that they are true brain tracts and not peripheral nerves
What are the central origins of the nerve and what is the pathway
• These nuclei all combine their axons to leave the brainstem at the inferior border of the pons • They leave the brain at the level of the Ponto- medullary Junction • The nerve they give rise to is CNVII • CNVII Axons constitute two unequal roots • Larger motor root • Smaller sensory root • The nerve roots then enter the petrous portion of the temporal bone (most dense bone In the body + has ear ossicles) via the internal acoustic meatus • They enter the internal acoustic meatus together with Vestibulocochlear nerve (CNVIII) and labyrinth artery Within the petrous part the nerve forms 5 branches in the facial canal i.e. greater petrosal (foramen lacerum and joins with the deep petrosal Sym nerve), facial nerve, chorda tympani, nervus to stapedius, lesser petrosal nerve and is where the geniculate ganglion is
Diagram of the branches of the CNVII nerve
• This shows the facial motor nucleus where the axons go upwards and look over the abducens = facial coniculus. These are somatic motor fibres for CNVII supplying the muscles of facial expression • The superior salivary nucleus gives rise to two sets of fibres: one set is preganglionic efferent which terminate in the submandibular ganglion which then have post ganglionic fibres to submandibular and sublingual salivary glands. There is also lacrimal part which goes to the pterygopalatine ganglion. There the post ganglion fibres supply the lacrimal gland and small glands of the nose • The geniculate ganglion = is sitting on the genu of the facial nerve (bent knee). These have cell bodies of sensory neurone and where the sensory neurones have their origins. The top nerve goes from the cell body to the spinal trigeminal nucleus (somatic sensory). This senses the skin around the ear. Another variant of sensation is where the cell bodies start from the geniculate ganglion which has sensory innervation from the soft palate and taste in the anterior 2/3s of the tongue. Axons come and travel through the chorda tympani forming the nerve and terminating in the solitary tract of the medulla. The 2 nerves from the nervous intermedius.
Describe the terminology of CNVII
• We need to be aware of a potential source of difficulties with usage of terminology around this nerve • CNVII refers to the nerve when it is 'mixed' in terms of all its functional modalities • The term 'Facial Nerve' refers specifically to the purely motor branch of CNVII where no other modalities are represented - Purest in Stylomastoid Foramen
