Muscles Of Facial Expression And Parotid Gland Flashcards
Course and distribution of CN VII
The motor root of CN VII emerges from the pons with the nervus intermedius (sensory root).
The two roots travel and enter the petrosal temporal bone at the internal acoustic meatus with CN VIII.
They leave the internal acoustic meatus and enter facial canal where they fuse to form the facial nerve and give off
- greater petrosal nerve
- nerve to stapedius
- chorda tympani
Then they exit via the stylomastoid foramen and gives off
- posterior auricular
- digastric nerve (posterior belly and stylohyoid)
Main trunk is now called motor root of facial nerve enters parotid gland where 5 terminal branches arise from a plexus within this gland.
Clinical note for CN VII
Intracranial lesions
- occur during intracranial course
- risk of compression from proximal injury means muscles of FE will be paralysed or weakened
- nerve to stapedius damage will result in ipsilateral hyperacusis (hypersensitive to sound)
Extracranial lesions
- motor function only affected
- at birth mastoid process isn’t formed so not complete protection of nerve so the CN VII at risk of compression during forceps delivery leading to paralysis of facial muscles
CN VII Branches from parotid gland
Temporal
Zygomatic
Buccal
Marginal mandibular
Cervical
CN VII injury
Nerve and it’s branches at risk during surgery on parotid gland or duct or following facial lacerations.
Marginal mandibular branch dips inferior to mandible overlying submandibular branch so susceptible to injury during surgery of this gland
Corneal reflex
Blink reflex protects cornea from foreign bodies
Afferent sensory fibres: ophthalmic division of trigeminal (senses stimulus)
Efferent motor fibres: facial nerve (initiates motor response in the orbicularis oris muscle)
Buccinator
Originates from posterior part of alveolar process of maxilla/mandible and from pterygomandibula raphe
Innervation: buccal branches of CN VII
Action: press the cheeks against molar teeth during chewing. Assists tongue to keep bolts of food central in oral cavity
Orbicularis oris
Originates from medial aspect of maxilla /mandible and surrounding muscles
Innervation: buccal and marginal mandibular branches of CN VII
Actions: close mouth and to protrude lips
Platysma
Originates from subcutaneous tissue of infra and supraclavicular regions
Innervation: cervical branch of CN VII
Actions: depresses mandible and angle of mouth and tense the skin of lower face and anterior neck
Occipitofrontalis
Frontal belly - originates from epicranial aponeurosis and inserts into skin of eyes and forehead
Occipital belly - origin is lateral 2/3 of superior nuchal line and inserts into epicranial aponeurosis
Innervation: temporal branch of CN VII (frontal) and posterior auricular (occipital)
Action: frontal - lifts eyebrows and wrinkles skin of forehead occipital - retracts scalp
Orbicularis oculi
Origin
Orbital from nasal part of frontal bone and inserts into skin around orbital region
Palpebral from medial Palpebral ligament and inserts into lateral palebral raphe
Actions
Orbital part - forceful closure of eye
Palpebral part - blink
Innervation by temporal and zygomatic branches of CN VII
Parotid gland anatomical relations
Retro mandibular vein
ECA (posterior auricular, maxillary and superficial temporal)
CN VII
Parotid lymph nodes
Vascular supply and drainage of parotid gland
Branches of ECA
- superficial temporal
- maxillary
- transverse facial
Retro mandibular vein
Innervation of parotid gland
Parasympathetic
- Preganglionic fibres travel from CN XI to otic ganglion in tympanic and lesser petrosal nerve (branches of CN IX). CN IX synapses with otic ganglion,
Secretomotor
- Post ganglionic secretomotor fibres pass from otic ganglion to reach parotid gland via auriculotemporal nerve (CN V3) that sends branches to parotid gland
Sympathetic
- from adjacent sympathetic plexus of carotid sheath
Tumours of parotid gland
Tumours
- 80% benign
- Most common is pleomorphic adenoma
- Presents with painless swelling of parotid gland and some weakness in surround muscles
- parotidectomy is required but can lead to CN VII injury
Ramsay hunt syndrome (Herpes zoster oticus)
Reactivation of dormant herpes zoster virus in geniculate ganglion (sensory ganglion of facial nerve) which is in close proximity to the facial nerve
Symptoms and signs
- ipsilateral peripheral facial palsy
- ear pain
- rash on auricle, external auditory meatus, hard palate and tongue
- hearing loss
- nausea
