Scalp Anatomy and Facial Nerves

Learning Outcomes

• Layers of the scalp, its blood supply, and bleeding from the scalp should be listed
• Superficial temporal artery and the facial artery should be described
• Veins of the face and temporal region should be described
• Major muscles of the face and jaw should be identified
• The seventh cranial nerve, its relations, lesions, and testing should be described
• The parotid gland and its duct, their relations and clinical conditions and its secretomotor innervation should be described
• Anatomy of the ophthalmic division of the trigeminal nerve, including how their integrity is tested clinically should be described

Layers of the Scalp

• Skin is the outermost layer
• Connective tissue layer, also known as the sub-cutaneous tissue
• Aponeurosis is a broad, flat tendon
• Loose connective tissue is a layer allowing for movement
• Periosteum is the innermost layer, covering the skull bone

Scalp Layers in Detail

• Skin is thin, with the exception of the occipital region
• There is an abundance of sweat and sebaceous glands, along with hair follicles
• An abundant arterial supply and good venous & lymphatic drainage are found in the scalp layers
• Connective tissue layer or sub-Cutaneous tissue consists of numerous blood vessels & nerves
• Wounds bleed profusely because blood vessels are prevented from retraction by fibrous tissue
• Aponeurosis is the tendinous sheet of occipitofrontalis
• Loose connective tissue is a dangerous layer of the scalp
• Periosteum is the outermost layer of bone
• Cephalhaematoma is a collection of blood between the periosteum and skull bone

Clinical Application

• Internal scalp bleeding can occur
• Subaponeurotic haemorrhage is bleeding beneath the aponeurosis layer
• A sub-periosteal haematoma, also called Cephalhaematoma, is a collection of blood under the periosteum
• Black eye, also known as Periorbital hematoma, can result secondary to trauma to the scalp

Arterial Supply to the Scalp

• Includes the supratrochlear artery and vein
• Includes the supra-orbital artery and vein
• Includes the superficial temporal artery and vein
• Includes the posterior auricular artery
• Includes the occipital artery
• All arteries listed branch from the external carotid artery except the supratrochlear and supraorbital arteries

Venous Drainage

• Veins of the scalp freely anastomose with one another
• Connected to the diploic veins of skull bones
• Drains into the internal and external jugular veins
• Connected to intracranial venous sinuses by emissary veins

Lymphatic Drainage

• The anterior scalp drains to the parotid glands
• The posterior scalp drains to the retroauricular lymph nodes

Nerve Supply to the Scalp

• Anterior to the ears/vertex:
  • Supratrochlear and Supraorbital nerves (V1)
  • Zygomaticotemporal nerve (V2)
  • Auriculotemporal nerve (V3)
• Posterior to the ears/vertex:
  • Great auricular nerve (C2/3)
  • Lesser occipital nerve (C2)
  • Greater occipital nerve (C2)
  • Third occipital nerve (C3)

Face General Anatomy

• Anterior aspect of head from forehead to chin and from one ear to the other
• Skin of the face is elastic, vascular, and contains sweat and sebaceous glands
• Skin of the face bleeds profusely however heals rapidly
• Connected to underlying bones by loose connective tissue
• Superficial fascia contains facial muscles, blood vessels & nerves, and fat tissues, except in the eyelids
• No deep fascia in the face except over certain areas

Muscles of the Face

• Called muscles of facial expression
• Lie in the superficial fascia
• Take origin from the facial bones & are inserted into the skin
• Develop embryologically from mesoderm of the 2nd pharyngeal arch
• Facial nerve supplies motor function to muscles of facial expression
• Facial muscles serve as sphincters or dilators of orifices of face, namely the orbit, nose and mouth

Muscles Around the Orbit

• Orbicularis oculi
• Levator palpebrae superioris
• Corrugator supercilii

Muscles Around the Nose

• Compressor naris
• Dilator naris
• Procerus
• Levator labii superioris alaeque nasi

Muscles Around the Mouth

• Orbicularis oris
• Levator labii superioris
• Zygomaticus minor and major
• Levator anguli oris (deep to zygomatic muscles)
• Risorius
• Depressor anguli oris
• Depressor labii inferioris
• Mentalis
• Buccinator is the muscle of cheek

Platysma Muscle

• Muscle lies in the SUPERFICIAL FASCIA
• Located just deep to the skin
• Largest of the MUSCLES OF FACIAL EXPRESSION
• Supplied with motor innervation by the FACIAL NERVE (Cranial Nerve VII)
• Contraction of the platysma tightens the skin of the neck
• Pulls the corners of the mouth down, and lifts the skin over the upper thorax
• Facial expression it conveys is one of mixed shock, disbelief and horror

Facial Muscles Table

• Frontalis muscle, innervated by the Temporal Branch, raises the eyebrows
• Orbicularis oculi muscle, innervated by the Zygomatic Branch, closes the eyelids
• Buccinator muscle, innervated by the Buccal Branch, pushes food from the vestibule of the mouth into the oral cavity proper
• Orbicularis oris muscle, innervated by the Marginal Mandibular Branch, closes the lips
• Platysma muscle, innervated by the Cervical Branch, assists with shaving

Branches of Facial Nerve Supplying Facial Muscles

• Includes Temporal branches
• Includes Zygomatic branches
• Includes Buccal branches
• Includes Marginal mandibular branches
• Includes Cervical branches

Lymphatic Drainage of the Face

• Depicted by nodes concentrated around the parotid region and along the jawline

Jaw Muscles

• Move the lower jaw or mandible
• Upper jaw or maxilla is fixed to the base of the skull
• There are four principal muscles, all innervated by motor fibres from the TRIGEMINAL NERVE:
  • Masseter
  • Temporalis
  • Medial Pterygoid
  • Lateral Pterygoid
• Some authorities add the Digastric muscle as a fifth

Parotid Gland

• Largest of the salivary glands
• Composed mostly of serous acini
• Enclosed by thick parotid fascia derived from investing layer of deep cervical fascia
• Secretes 25% of saliva
• Secretes serous (watery) secretions

Parotid Salivary Gland

• Covered by a thin capsule of fibrous tissue
• Opening the mouth presses the ramus against the gland
• If the gland is swollen and tender, as it is in the infectious disease MUMPS, attempting to open the mouth is quite painful

Structures within the Parotid Gland

• The EXTERNAL CAROTID ARTERY lies deep within the gland
• The external carotid artery divides into its two terminal branches, the MAXILLARY and SUPERFICIAL TEMPORAL arteries
• Superficial to the artery lies the RETROMANDIBULAR VEIN which is formed by the union of the MAXILLARY and SUPERFICIAL TEMPORAL veins, and divides into ANTERIOR and POSTERIOR DIVISIONS within the gland
• Superficial to the vein lies the FACIAL NERVE, which runs forwards and divides into its five terminal branches: TEMPORAL, ZYGOMATIC, BUCCAL, MANDIBULAR and CERVICAL
• A few PAROTID LYMPH NODES, usually classified as SUPERFICIAL and DEEP, also lie within the gland

Parotid Duct

• Thick-walled duct, about 5 cm long, emerges from middle of anterior border of the gland (Stensen Duct)
• Runs forward on masseter with transverse facial artery & upper buccal above and lower buccal branch of facial nerve below
• Opens into vestibule of mouth opposite the crown of upper 2nd molar tooth

Parasympathetic Innervation to the Gland

• Parasympathetics from the inferior salivatory nucleus leave the brain with the glossopharyngeal nerve (IX)
• IX leaves the skull by the jugular foramen
• The tympanic nerve from IX ascends into the inferior tympanic canaliculus and joins the tympanic plexus
• The lesser petrosal nerve comes out from the tympanic plexus and leaves the petrous temporal bone via the foramen for the lesser petrosal nerve
• The lesser petrosal nerve leaves the middle cranial fossa via the foramen ovale
• Synapses in the otic ganglion just under the foramen ovale
• The post synaptic parasympathetic fibres then hitch hike with the auriculotemporal nerve to the parotid

Clinical Application of Parotid Gland

• Parotitis indicates inflammation of the parotid gland, note swelling, pain, and lumps (tumors)
• Inflammatory conditions
• Infections like stones, bacterial infections, mumps virus
• Frey's Syndrome is a rare condition following trauma or surgery to the auriculotemporal nerve in the parotid area
• Patient complains of redness & sweating in the cheek & temporal area on the affected side when eating/thinking of food

Branches of the External Carotid Artery

• From the anterior surface: SUPERIOR THYROID, LINGUAL, FACIAL
• From the posterior surface: OCCIPITAL, POSTERIOR AURICULAR
• From the deep surface: ASCENDING PHARYNGEAL
• At the level of the neck of the mandible: TERMINAL BRANCHES -- MAXILLARY, SUPERFICIAL TEMPORAL

Facial Artery

• Arises just below the angle of the mandible
• Loops upwards, deep to the mandible
• Gives off the TONSILLAR ARTERY which supplies the palatine tonsil
• Turns downwards, giving off the SUBMENTAL ARTERY
• The submental artery runs forwards supplying the muscles in the floor of the mouth, the overlying skin, the chin and lower lip
• Crosses the lower border of the mandible where it can be readily palpated
• Follows a very sinuous course towards the inner angle of the eye
• Gives off the INFERIOR LABIAL ARTERY which supplies the lower lip
• Gives off the SUPERIOR LABIAL ARTERY which supplies the upper lip and nasal septum
• Gives off the LATERAL NASAL ARTERY which supplies the nose

Introduction to the Facial Nerve

• The 7th cranial nerve
• Mixed nerve – consists of both sensory and motor roots
• Has parasympathetic function which passes through the sensory root
• Attached to the lower border of the pons between the olive and inferior cerebellar peduncle

Course of the Facial Nerve

• Divided by the stylomastoid foramen into intracranial and extracranial parts

Branches of Facial Nerve

• The Greater petrosal nerve is located inside the facial canal
• Nerve to Stapedius supplies the Stapedius muscle
• Chorda tympani nerve arises about 6mm above the stylomastoid foramen
• Chorda tympani conveys the taste fibers from the anterior 2/3rd of the tongue
• Carries preganglionic secretomotor fibers for submandibular & sublingual glands
• Below the stylomastoid foramen:
  • Posterior auricular nerve supplies muscles around the auricle and occipital belly of Occipito-frontalis
  • Nerve to the posterior belly of digastric
  • Nerve to the stylohyoid muscle
• Branches in the face:
  • Temporal
  • Zygomatic
  • Buccal
  • Marginal mandibular
  • Cervical

Clinical Application of Facial Nerve

• Facial nerve paralysis: lesion at different levels
  • Supranuclear
  • Nuclear
  • Infra-nuclear: Bell’s palsy
  • Lesion in the internal acoustic meatus
  • Lesion at the genu (geniculate ganglion)
  • Lesion distal to the genu
  • Lesion below the stylomastoid foramen

Testing Motor Function of the Facial Nerve

• Examine the patient's face signs of paralysis or asymmetry
• Look for loss of wrinkling of the forehead, drooping of mouth corner, and labionasal fold reduction
• Tell the patient to:
  • Raise the eyebrows and wrinkle the forehead to test Temporal branches
  • Close the eyes tightly to test Zygomatic branches
  • Puff out the cheeks to test Buccal branch
  • Grin to show the teeth to test Buccal and Mandibular branches
  • Contract the platysma to test Cervical branch