Human Anatomy Lesson 13
Lesson 13 - Superficial Tissues of the Head
We are now moving on to the head and neck. The lessons on the head are organized such that we will be investigating structures from superficial to deep - in this lesson, we will cover the most superficial structures, including the muscles of facial expression; parotid gland; arteries, veins, and nerves in the subcutaneous fascia; and structures associated with the eyelids, external nose, and pinnae of the ear. In lesson #14 we will "peel" this layer back and take a look at the set-up and bones of the skull. In lesson #15 we will look inside the skull at the 12 cranial nerves, and in lesson #16 we will cover the gross structure of the brain, meninges, sinuses, and arterial supply of the brain. Lessons #17 to #20 will be on different parts of the craniofacial region.
Learning Objectives - By the end of this lesson, you should be able to ...
- List the muscles of facial expression, including their origins, insertions, and actions
- Understand that the facial nerve innervates all of these muscles
- List and describe the structures running through the parotid gland
- List the nerves that innervate the face, and understand which are branches of cranial nerve V and which of CN VII
- List and describe the arteries, veins, and lymph nodes in the face
- List and describe the layers, innervation, vasculature, and lymphatic drainage of the scalp
Muscles of Facial Expression
Humans have a surprisingly large number of muscles that can be used to make facial expressions. New research shows that humans have roughly twice the number of muscles dedicated to facial expression (and about twice the number of facial expressions) as do chimpanzees and other non-human primates. Muscles of facial expression receive their innervation from branches of the facial nerve (CN VII). The muscles of facial expression can be organized into four groups: an orbital group (orbicularis oculi, corrugator supercilii), nasal group (nasalis, procerus, depressor septi nasi), oral group (orbicularis oris, buccinator, depressor anguli oris, depressor labii inferioris, mentalis, risorius, zygomaticus major and minor, levator labii superioris, levator labii superioris alaeque nasi, levator anguli oris), and auricular group (anterior, superior, and posterior auricular muscles), in addition to two "extra" muscles, platysma and occipitofrontalis. Students in my fall 2019 Human Anatomy course at Benedictine University should focus on the following muscles: occipitofrontalis, orbicularis oculi, nasalis, procerus, orbicularis oris, buccinator, depressor anguli oris, depressor labii inferioris, mentalis, zygomaticus major and minor, levator labii superioris, levator labii superioris alaeque nasi, and platysma.
- Occipitofrontalis: on the anterior aspect of the head, two frontalis muscles originate around the eyebrows and skin above the root of the nose and course back over the forehead to insert onto a flat tendinous sheath called the epicranial aponeurosis somewhere anterior to the coronal suture. The epicranial aponeurosis inserts onto the external occipital protuberance and superior nuchal line at the back of the cranium, and more laterally, ends in the occipitalis muscles which insert onto the lateral-most aspects of the superior nuchal line. Contraction of the occipitofrontalis muscles pulls the skin of the eyebrows upward, as in an expression of surprise or incredulity. The epicranial aponeurosis is important from a clinical standpoint since three layers - the skin, subcutaneous tissue, and epicranial aponeurosis - are tightly bound to each other, so that no movement is possible between skin and aponeurosis. Transverse or coronal scalp wounds will gape open since the frontalis and occipitalis muscles are pulling at two opposite sides of the epicranial aponeurosis.
- Orbicularis oculi: this circular muscle surrounds each orbital orifice, with an orbital part that extends beyond the orbital rim and a palpebral part that runs from medial to lateral in each eyelid. The orbital part closes the eyelid gently and the palpebral part closes it more forcefully.
- Corrugator supercilii: this muscle is deep to the eyebrows and the orbicularis oculi muscle and is active during frowning, drawing the eyebrows toward the midline so there are vertical wrinkles above the nose (think of the corrugations in a cardboard box to help you remember this). It passes upward from its origin on the medial aspect of the superciliary arch to insert into the skin of the medial half of the eyebrow.
- Nasalis: consists of a transverse part, the compressor naris, and an alar part, the dilator naris. Fibers of the transverse part run superiorly and medially to insert on an aponeurosis across the dorsum of the nose, and compress the nares. The alar part runs from the maxilla below the nose to the alar cartilage, and opens the nares.
- Procerus: small muscle that runs from the nasal bone and upper part of the lateral nasal cartilage to insert into the skin between the eyebrows. This muscle draws the medial border of the eyebrows downward to produce transverse wrinkles over the bridge of the nose when an individual frowns.
- Depressor septi nasi: runs from the maxilla above the central incisors to insert in the lower part of the nasal septum. This muscle pulls the nose inferiorly, thereby assisting the alar part of nasalis in widening the nares.
- Orbicularis oris: largely circular muscle that originates from the midline maxilla and other muscles in the cheek, including the buccinator, and inserts into the skin and mucous membrane of the lips. It narrows the mouth and closes the lips, as when "pursing" the mouth during whistling.
- Buccinator: runs from the posterior part of the maxilla and mandible and the pterygomandibular raphe (a tendinous band between the pterygoid hamulus superiorly and mandible inferiorly) to the lips, blending with fibers of the orbicularis oris muscle. This muscle forms the structure of the cheek and is active when air is forcefully expelled from the cheeks, and it also presses the cheek against the teeth.
- Depressor anguli oris: runs from the mandible below the canine, premolar, and first molar to skin and orbicularis oris muscle fibers near the corner of the mouth, and depresses the corner of the mouth during frowning.
- Depressor labii inferioris: runs from the front of the mandible deep to depressor anguli oris and runs in a superior and medial direction to the lower lip; it depresses the lower lip and moves it laterally.
- Mentalis: runs ffrom the mandible inferior to the incisor teeth in an inferior direction to insert into the skin of the chin, and raises and protrudes the lower lip and wrinkles the skin of the chin (as occurs in pouting or drinking from a water fountain). Its fibers run deep to the fibers of orbicularis oris and depressor labii inferioris.
- Risorius: runs in a slight anteroinferior direction from fascia over the parotid gland to insert into the corner of the mouth, and pulls the corner of mouth laterally and superiorly during grinning. Risorius is one of the most superficial muscles of facial expression, passing superficial to platysma even.
- Zygomaticus major and minor: zygomaticus major runs along the posterior part of the lateral surface of the zygomatic bone deep to orbicularis oris in an anteroinferior direction to insert into the corner of the mouth; zygomatic minor is positioned superior and medial to this, and runs from the zygomatic bone to the upper lip medial to the corner of the mouth. Both muscles raise the corner of the mouth and move it laterally to help produce a smile.
- Levator labii superioris: runs in an inferomedial direction from the maxilla superior to the infraorbital foramen to blend with fibers of the orbicularis oris muscle and insert into the skin of the upper lip.
- Levator labii superioris alaeque nasi: runs from the maxilla next to the nose to the alar cartilage of the nose and skin of the upper lip, medial to the levator labii superioris; assists in flaring the nares.
- Levator anguli oris: runs from the maxilla just inferior to the infraorbital foramen to the skin at the corner of the mouth, deep to the two levator and zygomaticus muscles; it elevates the corner of the mouth and deepens the furrow between the nose and corner of the mouth during a sad expression.
- Anterior, superior, and posterior auricular muscles: these three muscles are named in a perfectly logical fashion - anterior muscle is anterolateral and pulls the ear superiorly and anteriorly; the superior muscle is superior and elevates the ear; and the posterior muscle is posterior and retracts and elevates the ear.
- Platysma: a large, thin sheet of muscle in the superficial fascia of the neck that runs from below the clavicle superiorly to the mandible, joining the muscles around the mouth; tenses the skin of the neck.
The parotid gland is positioned posterior to the mandibular ramus, in the retromandibular (parotid) region, although it is important to note that glandular tissue extends anteriorly onto the lateral surface of the mandible, masseter muscle, and zygomatic arch. The parotid gland creates serous (watery) saliva and releases it through the parotid duct into the oral cavity (see below). The parotid gland forms a sort of nexus through which nerves, arteries and veins course. We will discuss the course of these superficial vessels here.
- Parotid duct: runs from the anterior margin of the parotid gland midway between the zygomatic arch and corner of the mouth, crossing the medial border of the masseter muscle, dives into the buccal fat pad, and pierces the buccinator muscle to enter the mouth near the second upper molar.
- Facial nerve: runs from the stylomastoid foramen into the parotid gland, where it divides into upper and lower trunks and terminates in five branches: temporal, zygomatic, buccal, marginal mandibular, and cervical - that emerge from the parotid gland to provide sensory innervation to the face.
- Branches of the external carotid artery: runs into the inferior border of the parotid gland, gives off the posterior auricular artery and divides into two terminal branches near the lower border of the ear: the maxillary artery, which runs in a horizontal direction deep to the mandible; and the superficial temporal artery, which continues in a superior direction and emerges from the superior border of the parotid gland after giving off the transverse facial artery, which runs parallel to the zygomatic arch.
- Tributaries of the retromandibular vein: the superficial temporal vein and maxillary vein join together just inferior to the level of the ear lobe within the parotid gland, and superficial structures in the side of the head and the parotid gland.
- Auriculotemporal nerve: this branch of V3 carries somatic sensory innervation to the parotid gland, in addition to preganglionic parasympathetic fibers running to the otic ganglion from the glossopharyngeal nerve and postganglionic parasympathetic fibers associated with V3 that run from the otic ganglion to the gland.
Innervation of the Face
The face is innervated by branches of cranial nerve V, the trigeminal nerve and cranial nerve VII, the facial nerve. The skin over the face is innervated by branches of CN V, except for a small area covering the angle and lower border of the mandibular ramus and parts of the ear, which are innervated by cervical nerves.
- Ophthalmic nerve (CN V1): enters the orbit through the superior orbital fissure via the following five nerves - (1) supraorbital nerves and (2) supratrochlear nerves, which run through the orbit to innervate the upper eyelid, forehead, and scalp; (3) infratrochlear nerve, which innervates the medial half of the upper eyelid, skin in the area of the medial angle and side of the nose; (4) lacrimal nerve, which innervates the lateral half of the upper eyelid and skin in the area of the lateral angle; (5) external nasal nerve, which supplies the anterior part of the nose.
- Maxillary nerve (CN V2): exits the skull through the foramen rotundum, sending off a small (1) zygomaticotemporal branch, which supplies a small area of the anterior temple above the zygomatic arch, a small (2) zygomaticofacial branch, which supplies a small area of skin over the zygomatic bone, and a large infraorbital nerve, which divides into numerous branches on the maxilla after exiting the infraorbital foramen, and supplies the lower eyelid, cheek, side of the nose, and upper lip.
- Mandibular nerve: after exiting the skull through the foramen ovale, CN V3 gives off the following sensory branches: (1) auriculotemporal nerve, which we discussed above and which innervates the external acoustic meatus, surface of the tympanic membrane, and a large area of the temple; (2) buccal nerve, which runs on the surface of the buccinator muscle and innervates the skin of the cheek; and (3) mental nerve, which supplies the skin and mucous membrane of the lower lip and skin of the chin.
- Facial nerve: passes through the temporal bone, giving off several branches, and emerges from the stylomastoid foramen, giving off the following nerves: (1) posterior auricular nerve, which supplies the occipital belly of the occipitofrontalis muscle and posterior auricular muscle; (2) a main branch, which innervates the posterior belly of the digastric muscle and the stylohyoid muscle, and then enters the deep surface of the parotid gland to end in (3) five terminal branches, which supply all the other muscles in the face.
Vasculature and Lymphatic Drainage of the Face
Arterial supply is mostly from branches of the external carotid artery, and venous drainage is mostly back to the internal jugular vein.
- Facial artery: this branch off the external carotid artery passes posterior to the submandibular gland at the border of the mandible, curves around the mandible's inferior border anterior to the masseter, then runs superomedially to supply the face, passing just lateral to the nose to end in the angular artery at the medial corner of the eye. The facial artery gives off superior and inferior labial branches and a lateral nasal branch.
- Transverse facial artery: this branch of the superficial temporal artery passes through the parotid gland, crossing the face in a transverse direction on the superficial surface of the masseter muscle between the zygomatic arch and parotid duct.
- Maxillary artery: this large branch of the external carotid artery gives off several smaller branches, including the infraorbital artery, which supplies the face from the lower eyelid to upper lip; buccal artery, which supplies the face near the buccinator muscle; and mental artery, which supplies the chin. The maxillary artery runs deep to the condyle and ramus of the mandible in the infratemporal region, and so we will discuss it in greater detail in lesson #17. The mental artery runs along the inner border of the mandible before passing through the mental foramen to appear on the external part of the face . The infraorbital artery appears on the outer surface of the face after running through the infraorbital foramen. The buccal artery runs deep to the coronoid process before appearing on the external surface of the maxilla.
- Ophthalmic artery: this artery is a branch of the internal carotid artery; after it enters the orbit, it gives off the zygomaticofacial artery, which supplies the face over the zygomatic bone, and the dorsal nasal artery, which supplies the dorsum of the nose.
- Facial vein: the supratrochlear vein and supraorbital vein come together at the medial corner of the orbit to form the angular vein, which becomes the facial vein as it assumes a position posterior to the facial artery. It descends to the posterior border of the mandible and passes superior to the submandibular gland to enter the internal jugular vein. It drains the majority of the face.
- Transverse facial vein: this small vein accompanies the transverse facial artery in its path across the face, emptying into the superficial temporal vein within the parotid gland, or just above its superior border.
- Intracranial veins: the facial vein meets up with several veins running into the cranial cavity, including ophthalmic veins near the medial corner of the orbit, the infraorbital vein that passes through the infraorbital foramen, and the deep facial vein, which connects to the pterygoid plexus of veins in the pterygomandibular region. All of these veins have connections with the cavernous sinus inside the cranial cavity.
- Lymphatic drainage: there are three groups of lymph nodes in the face - (1) submental nodes, which drain lymph from the medial part of the lower lip and chin; (2) submandibular nodes, which drain the medial wall of the orbit, external nose, cheek, upper lip, and lateral part of the lower lip; (3) pre-auricular and parotid nodes, which drain the eyelids, part of the external nose, and lateral part of the cheek.
The scalp extends from the superciliary arches to the external occipital protuberance front to back, and to the superior nuchal lines and zygomatic arches laterally.
- Layers: Layers of the scalp can be listed as the word "scalp" itself - S - skin, C - connective tissue (dense), A - aponeurosis, L - loose connective tissue, P - pericranium.
- Innervation: as noted above, the occipitofrontalis muscle is innervated by branches of the facial nerve. Otherwise, branches of the trigeminal nerve provide sensory innervation anterior to the ears and vertex (via supratrochlear, supraorbital, zygomaticotemporal, and auriculotemporal nerves), whereas cervical nerves provide sensory innervation posterior to the ears and vertex (via C2 and C3 anterior rami fibers of the great auricular nerve, C2 anterior ramus fibers from the lesser occipital nerve, C2 posterior ramus fibers from the greater occipital nerve, and C3 posterior ramus fibers of the third occipital nerve.)
- Arterial supply: arterial supply is from the external carotid artery and the ophthalmic artery, itself a branch of the internal carotid artery. The supratrochlear and supraorbital arteries, which branch off of the ophthalmic artery in the orbit, supply the anterior and superior parts of the scalp as far posteriorly as the vertex of the head. Three branches of the external carotid artery - the superficial temporal artery, posterior auricular artery, and occipital artery - supply the lateral and posterior aspects of the scalp.
- Venous drainage: the pattern of venous drainage parallels the arterial supply - the supratrochlear and supraorbital veins drain the anterior part of the scalp, and the superficial temporal vein, posterior auricular vein, and occipital vein drain the posterior part of the scalp.
- Lymphatic drainage: lymph in the occipital region drains into occipital nodes near the attachment of the trapezius at the base of the skull, and from there into upper deep cervical nodes; lymph from the upper parts of the scalp drains either into mastoid nodes or into preauricular and parotid nodes in the parotid gland.
Starting with this lesson, the next 6 lessons cover the head.
- Human Anatomy Lesson 14
Lesson #14 covers the skull
- Human Anatomy Lesson 15
Lesson #15 covers the cranial nerves
- Human Anatomy Lesson 16
Lesson #16 covers the brain, meninges, and vasculature
- Human Anatomy Lesson 17
Lesson #17 covers the TMJ, temporal and infratemporal fossae
- Human Anatomy Lesson 18
Lesson #18 covers the orbit, eye, and ear
© 2014 Robert McCarthy