Motor Innervation of The Head & Neck Mind Map
Motor Innervation of the Head and Neck
Motor innervation of the head and neck is primarily supplied by the facial nerve, which exits the stylomastoid foramen and divides within the parotid gland into its terminal branches. These branches are arranged from superior to inferior as temporal, zygomatic, buccal, marginal mandibular, and cervical. The temporal branch innervates the frontalis and orbicularis oculi in the upper face, while the zygomatic branch supplies the orbicularis oculi and other muscles around the zygomatic arch. The buccal branch provides motor supply to the buccinator, orbicularis oris, and levator muscles of the upper lip. The marginal mandibular branch innervates the depressor anguli oris, depressor labii inferioris, and mentalis muscles of the lower lip and chin. The cervical branch supplies the platysma in the neck. This superior-to-inferior organization allows for efficient innervation of the muscles of facial expression and is clinically relevant during parotid surgery and in the evaluation of facial nerve palsy.
Facial Nerve Branches
- Facial spa sponsor = Facial nerve branches
- High tempo = Temporal branch
- Zanzibar’s automatic cars = Zygomatic branch
- Buckled up for safety = Buccal branch
- At the margin of the racetrack = Marginal mandibular branch
- Servers = Cervical branch
Temporal Branch
Temporal Branch of the Facial Nerve
The temporal branch of the facial nerve innervates several muscles of the upper face that are critical for eyebrow and eyelid movement. The frontalis muscle elevates the eyebrows and creates horizontal forehead wrinkles, while injury to its innervation causes inability to raise the eyebrows and eyebrow ptosis. The corrugator supercilii pulls the eyebrows inferomedially, generating vertical glabellar lines that contribute to the scowling appearance. The upper orbicularis oculi enables tight eyelid closure and blinking, and dysfunction leads to impaired eyelid closure. Chronic contraction of this muscle produces crow’s feet at the lateral canthus. Clinically, the temporal branch is especially vulnerable to injury as it courses superficially across the zygomatic arch, making the frontalis particularly at risk. Unilateral paralysis of the frontalis results in asymmetry with flattening of forehead wrinkles on the affected side.
Temporal Branch of the Facial Nerve
- Front bumper = Frontalis
- Raising eyebrows = Eyebrow elevation
- Horizontal grill = Causes horizontal forehead wrinkles
- Toaster toasted the front = Nerve injury → inability to elevate eyebrows → eyebrow ptosis
- Super core battery pack = Corrugator supercilii
- Angry = Pulls eyebrows inferomedially (vertical glabellar lines, scowling appearance)
- On upper platform with orbit-helmet = Upper orbicularis oculi
- Eyes closed = Tight closure of eyelids, blinking
- Crow = Causes crow’s feet
- Arch of Zanzibar = Most susceptible to injury as it crosses over the zygomatic arch
- Half of a front bumper smashed = Unilateral frontalis paralysis can result from injury
Zygomatic Branch
Zygomatic Branch of the Facial Nerve
The zygomatic branch of the facial nerve primarily innervates muscles involved in periorbital, nasal, and upper lip movements. The orbicularis oculi enables eyelid closure, and weakness can result in inability to fully shut the eye. The procerus pulls the eyebrows downward and generates horizontal glabellar lines, while the nasalis contributes to nasal wrinkling and nostril flaring, producing bunny lines. The levator labii superioris alaeque nasi elevates the upper lip and flares the nostril, whereas the levator labii superioris elevates and everts the upper lip, with overactivity sometimes producing a gummy smile. The zygomaticus major and minor are the main elevators and retractors of the mouth angles, critical for smiling. Injury to the zygomatic branch produces deficits most apparent lateral to an imaginary line drawn from the lateral canthus to the oral commissure. Clinically, loss of function may result in inability to close the eye, flare the nostril, or elevate the upper lip. However, extensive cross innervation between the zygomatic and buccal branches often mitigates complete paralysis.
Zygomatic Branch of the Facial Nerve
- Orbiting clouds = Orbicularis oculi
- Pro racer = Procerus
- Low eyebrows = Pulls eyebrows down
- Holding globe with horizontal lines = Responsible for horizontal glabellar lines
- Racer inhaling nasal spray = Nasalis
- Flared nostril = Causes wrinkle in the nose, flares nostrils
- Bunny = Responsible for bunny lines
Lip Elevators
- Levitating aqua car with nose = Levator labii superioris alaeque nasi
- Driver with large upper lip touching nose = Elevates upper lip and flares nostril
- Levitating car = Levator labii superioris
- Racer making a kissy face = Elevates and everts upper lip
- Large gums in teeth = Responsible for gummy smile
- Zanzibar major and child = Zygomaticus major and minor
- Smiling = Main muscles responsible for smiling (mouth angle retractors/elevators)
Clinical Deficits
- Eyes wide open = Inability to shut eyes
- Pinching nose = Inability to flare nostrils
- Sad face = Inability to elevate upper lip
- Racer with open helmet shield = Most deficits occur lateral to an imaginary line from lateral canthus to oral commissure
- Buckled up = Zygomatic and buccal branches have extensive cross innervation
Buccal Branch
Buccal Branch of the Facial Nerve
The buccal branch of the facial nerve innervates key muscles required for cheek, lip, and mouth movements that are essential for mastication, speech, and facial expression. The buccinator flattens the cheek against the teeth, prevents food accumulation during chewing, and allows high-pressure blowing, such as extinguishing candles. The orbicularis oris encircles the mouth and is critical for lip puckering, pursing, and articulation during speech. Multiple lip elevators including the levator labii superioris alaeque nasi, levator labii superioris, zygomaticus major and minor, and levator anguli oris elevate the upper lip or mouth angle and contribute to smiling. The risorius acts as a weaker mouth angle retractor with a lesser role in smiling. Damage to the buccal branch produces food accumulation between the teeth and cheek, impaired lip puckering and pursing, drooling due to poor lip seal, muffled speech from orbicularis oris weakness, and asymmetry such as a drooping smile. However, due to significant cross innervation with the zygomatic branch, these deficits are often partial and temporary unless there is extensive injury.
Buccal Branch of the Facial Nerve
- Buckled up in safety simulator = Buccal branch
- Big buckle = Buccinator
- Pushing cheek = Flattens cheek against teeth
- Throwing out food in the trash = Prevents food accumulation
- Blowing out birthday candles = High-pressure blowing
- Tongue circling in an orbit = Orbicularis oris
- Giving a speech = Required for clear speech
Lip Elevators
- Elevated cars in Zanzibar = Lip elevators can have variable innervation with zygomatic or buccal branch
- Levitating aqua car with nose = Levator labii superioris alaeque nasi
- Levitating car = Levator labii superioris
- Zanzibar major and child = Zygomaticus major and minor
- Levitating racer measuring angle of his own mouth = Levator anguli oris (mouth angle retractor/elevator)
- Rising star = Risorius
- Smiling = Lesser role in smiling
- Next to angle-measuring racer = Mouth angle retractor
Signs of Damage
- Food all over racer = Food accumulation between cheek and teeth
- Open mouth = Inability to pucker/purse lips
- Drooling = Drooling from decreased lip sealing ability
- Race dog wearing a muzzle = Muffled speech
- Droopy one-sided smile = Uneven facial expression at rest and with smiling
- Poster of Zanzibar = Extensive cross innervation with zygomatic branches, deficits often partial and temporary unless extensive damage
Marginal Mandibular and Cervical Branches
Marginal Mandibular Nerve & Cervical Nerve
The marginal mandibular branch of the facial nerve innervates the lower lip depressors including depressor anguli oris, depressor labii inferioris, and mentalis, which are primarily responsible for lower lip retraction and protrusion. Mentalis additionally contributes to lower lip protrusion, while lower lip elevation is achieved through synergistic action. Injury to this branch is clinically significant because the face often appears symmetric at rest but becomes asymmetric with smiling. Affected patients may also demonstrate inability to evert the lower lip. This branch is particularly vulnerable because it has only 1-2 rami and lies just beneath thin skin and platysma, creating a high risk of permanent motor deficit when injured. Common mechanisms of injury include procedures such as neck liposuction or submentoplasty, and trauma localized 2-3 cm inferolateral to the oral commissure where the nerve crosses the mandible. Its course is superficial to the facial artery, which helps in identifying its anatomical relationship. The cervical branch of the facial nerve supplies the platysma, which intercalates with the lip depressors, contributes to tensing of the neck skin, and is involved in grimacing. Injury to this region reduces the ability to grimace due to platysma dysfunction.
- At the margin of the racetrack = Marginal mandibular branch
- Lip depressors = Depressor muscles of the lip
- Depressed racer measuring angle of mouth = Depressor anguli oris is a lip depressor/retractor
- Depressed racer pulling down lips = Depressor labii inferioris is a lip depressor/retractor
- Going mental = Mentalis
- Protruding lower lip = Lower lip protrusion
- Lifting up a car = Lower lip elevation
Injury results in (shown by fans in the bleachers):
- Asymmetric smile = Face is normal at rest but asymmetric when smiling
- Taped lips = Inability to evert lower lip
Vulnerability and anatomical risk factors:
- Broken down motor car on the margin = Highest risk of causing permanent motor deficits because it only has 1-2 rami and is covered by thin skin/platysma
- 1 nerve antenna on racer = 1-2 rami
- Siphoning gasoline = Can be injured during neck liposuction or submentoplasty
- Man with large jaw injury = Most susceptible 2-3 cm inferolateral to oral commissure as it passes over the mandible
- Facial spa (with arterial design) = Passes superficially over facial artery
Cervical branch functions:
- Servers = Cervical branch
- Holding a large plate = Platysma
- Next to lip depressors = Intercalates with lip depressors
- Tight neck collar = Tenses neck skin
- Grimacing = Responsible for grimacing (injury results in decreased ability to grimace)