- Cutaneous Innervation and Vasculature of the Face
- Muscles, Innervation and Blood supply of the Face
- Parotid
Embryologic Derivation
The muscles are sometimes indistinct at their borders because they develop embryologically from a continuous sheet of musculature derived from the second branchial arch.
The muscles of facial expression arise from bones or fascia of the skull and insert into the skin, which enables a wide array of facial expression. The muscles of facial expression are located in the superficial fascia in the neck, face, and scalp. Each muscle is innervated by CN VII (except the muscles of mastication, which are innervated by CN V-3).
Muscles of the face.
Occipitofrontalis Muscle
The occipitofrontalis muscle, which lies in the scalp, extends from the superior nuchal line in the back to the skin of the eyebrows in the front. It allows for the movement of the scalp against the periosteum of the skull and also serves to raise the eyebrows.
Orbicularis Oculi Muscle
The orbicularis oculi muscle lies in the eyelids and also encircles the eyes. It helps to close the eye in the gentle movements of blinking or in more forceful movements, such as squinting. These movements help express tears and move them across the conjunctival sac to keep the cornea moist.
Orbicularis Oris Muscle
The orbicularis oris muscle encircles the opening of the mouth and helps to bring the lips together to keep the mouth closed.
Buccinator Muscle
The buccinator muscle arises from the pterygomandibular raphe in the back and courses forward in the cheek to blend into the orbicularis oris muscle in the lips. It helps to compress the cheek against the teeth and thus empties food from the vestibule of the mouth during chewing. In addition, it is used while playing musical instruments and performing other actions that require the controlled expression of air from the mouth.
Platysma Muscle
The platysma muscle extends from the skin over the mandible through the superficial fascia of the neck into the skin of the upper chest, helping to tighten this skin and also to depress the angles of the mouth. Although lying primarily in the neck, it is grouped with the muscles of facial expression.
The muscles of facial expression are innervated by the facial nerve (CN VII).
The muscles of facial expression can be organized into the following groups:
- Scalp and forehead
- Frontalis. Connects with the occipitalis muscle by a cranial aponeurosis (galea aponeurotica); and wrinkles the forehead.
- Muscles of the orbit
- Orbicularis oculi. Consists of orbital and palpebral portions, forming a sphincter muscle that closes the eyelids.
- Corrugator supercilii. Located deep to the orbicularis oculi; draws the eyebrows medially.
- Muscles of the nose
- Procerus. Wrinkles the skin over the root of the nose.
- Nasalis and levator labii superioris alaquae nasi. Flare the nostrils.
- Muscles of the mouth
- Orbicularis oris. Originates from the bones or fascia of the skull and inserts in the substance of the lips, forming an oral sphincter.
- Levator labii superioris and levator anguli oris. Raise the upper lip.
- Zygomaticus major and minor. Raise the corners of the mouth (smile).
- Risorius. Draws the corners of the lips laterally.
- Depressor labii inferioris and depressor anguli oris. Lower the bottom lip.
- Buccinator. Compresses the cheek when whistling, blowing, or sucking; holds food between the teeth during chewing.
- Neck
- Platysma. Tenses the skin of the neck and lowers the mandible. Primarily located in the neck, although it does have attachments in the lower mandible and corners of the mouth.
The corneal blink reflex is tested by touching the cornea with a piece of cotton, which should cause bilateral contraction of the orbicularis occuli muscles. The afferent limb is the nasociliary nerve of CN V-1, and the efferent limb of the reflex arch is CN VII.
Motor Nerve Supply to the Face
CN VII provides motor innervation to the muscles of facial expression (Figure 20-2B). The facial nerve exits the skull through the stylomastoid foramen and immediately gives off the posterior auricular nerve and other branches that supply the occipitalis, stylohyoid, and posterior digastricus muscles and the posterior auricular muscle. CN VII courses superficial to the external carotid artery and the retromandibular vein, enters the parotid gland, and divides into the following five terminal branches: temporal, zygomatic, buccal, mandibular, and cervical nerves, which in turn supply the muscles of facial expression. Other muscles of the face include muscles of mastication (temporalis, masseter, and the medial pterygoid and lateral pterygoid muscles), which are innervated by the motor division of CN V-3.
One of the most common problems involving CN VII occurs in the facial canal, just above the stylomastoid foramen. Here, an inflammatory disease of unknown etiology causes a condition known as Bell's palsy, where all of the facial muscles on one side of the face are paralyzed. Bell's palsy is characterized by facial drooping on the affected side, typified by the inability to close the eye, a sagging lower eyelid, and tearing. In addition, the patient has difficulty smiling, and saliva may dribble from the corner of the mouth. If the inflammation spreads, the chorda tympani and nerve to the stapedius muscle may be involved.
Arteries
The blood supply of the face is through branches of the facial artery
After arising from the external carotid artery in the neck, the facial artery passes deep to the submandibular gland and crosses the mandible in front of the attachment of the masseter muscle. It takes a tortuous course across the face and travels up to the medial angle of the eye, where it anastomoses with branches of the ophthalmic artery. It gives labial branches to the lips, of which the superior labial artery enters the nostril to supply the vestibule of the nose.
The occipital, posterior auricular, and superficial temporal arteries supply blood to the scalp. They all arise from the external carotid artery. The superficial temporal artery gives a branch, the transverse facial artery, which courses through the face parallel to the parotid duct.
Veins
The superficial temporal and maxillary veins join within the substance of the parotid gland to form the retromandibular vein
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(Figure 1–3). The facial vein joins the anterior division of the retromandibular vein to drain into the internal jugular vein. Additional details about the venous drainage pattern of the scalp and face are provided in the discussion of the veins of the neck. The facial vein communicates with both the pterygoid venous plexus and the veins in the orbit. Each of these has connections to the cavernous sinus, thus allowing infections to spread from the face into the cranium.
Parotid Gland
The parotid gland is situated in the lateral part of the face on the surface of the masseter muscle, anterior to the sternocleidomastoid muscle. A dense fascia covers the gland. The parotid gland produces and secretes saliva into the oral cavity and is innervated by visceral motor parasympathetic fibers from the glossopharyngeal nerve (CN IX).
Parotid Duct
The parotid duct crosses the masseter muscle, pierces the buccinator muscle, and opens into the oral cavity adjacent to the second upper molar (Figure 20-3A).
A. Topography of the parotid gland. B. Horizontal section through the parotid gland. C. Glossopharyngeal nerve (CN IX) and its innervation of the parotid gland.
Structures Associated with the Parotid Gland
- Motor branches of CN VII. CN VII exits the stylomastoid foramen, enters the posterior surface of the parotid gland, and courses through the gland en route to innervate the muscles of facial expression. CN VII also provides visceral motor innervation to all glands of the head, with the only exception being the parotid gland, the gland that you would think CN VII would innervate (Figure 20-3A and B).
- Retromandibular vein. The superficial temporal vein and the maxillary vein join to form the retromandibular vein within the parotid gland and exit its inferior border, where the retromandibular vein bifurcates into anterior and posterior divisions. The anterior division joins with the facial vein to become the common facial vein, which enters the internal jugular vein. The posterior division joins with the posterior auricular vein, forming the external jugular vein.
- External carotid artery. The common carotid artery bifurcates at the level of the thyroid cartilage into the external and internal carotid arteries. The external carotid artery enters the inferior border of the parotid gland and within the gland divides into the superficial temporal artery and the maxillary artery. Both arteries emerge from the anterosuperior border and provide vascular supply to the temporal fossa and scalp (superficial temporal artery) and the deep face (maxillary artery).
The parotid gland is innervated by visceral motor neurons from CN IX (Figure 20-3C).
- Preganglionic parasympathetic neurons from CN IX originate in the inferior salivatory nucleus of the medulla and exit the jugular foramen along with the vagus nerve (CN X) and the spinal accessory nerve (CN XI).
- A branch of CN IX, the tympanic nerve, re-enters the skull via the tympanic canaliculus, enters the middle ear, and forms the tympanic plexus.
- CN IX gives rise to the lesser petrosal nerve, which exits the middle ear and the skull via the foramen ovale to synapse in the otic ganglion.
- Postganglionic parasympathetic neurons exit the otic ganglion and then “hitch-hike” along the auriculotemporal nerve en route to the parotid gland.
Mumps is a viral infection characterized by inflammation and swelling of the parotid gland, resulting in pain within the tight parotid fascia that covers the gland. Symptoms include discomfort in swallowing and chewing. The disease will usually run its course, with analgesics given to treat the pain and fever that is associated with the infection.