Scalp,+Face,+and+Parotid+Regions

=**Objectives**=


 * 1. List the layers of the scalp. Give the importance of each of these layers.**

The layers of the scalp consists of 5 layers: the skin, connective tissue, aponeurosis, loose areolar connective tissue, and pericranium. An easy way to remember these layers is that the first letter each layer in spells SCALP.

The skin is the thin skin epidermis and dermis that is covered with hair, sweat and sebaceous glands.

The connective tissue layer contains the hypodermis and is a dense connective tissue with lots of fibrous septae with vascular supply running through them. Wounds to the scalp typically bleed profusely and require stitches because the connective tissue layer tends to keep blood vessels patent.

Aponeurosis layer is the galea aponeurotica formed from two muscles of facial expression, the frontalis and ocipitalis.

The skin, connective tissue layer, and aponeurousis layer are fused tightly together and can be easily removed all together. This causes wounds to the scalp to gap open, but also has significance for surgery to easily reflect back the scalp. Native Americans take advantage of this anatomy during the scalping of their enemies.

The loose areolar connective tissue layer contains a potential space where stuff can collect and spread.

The pericranium is the layer just superficial to the skull. It has strong attachments throughout the skull but are especially strong at suture junctions.


 * 2. Describe the blood supply and innervation to the scalp. What is the clinical significance of the arrangement?**

Blood to the scalp is supplied primarily by the internal and external carotid arteries. The internal carotid gives off a othphalmic artery branch which, in turn, gives rise to the supratrochlear artery and supraorbital artery. The supratrochlear and supraorbital arteries arise from the superior orbit and travel superiorly up the scalp, supplying the anterior portion. The external carotid gives off three branches: the superficial temportal artery, posterior auricular artery, and occipital artery. The superfical temporal artery travels superiorly from the lateral side of the head to supply the middle portion of the scalp. The posterior auricular and occipital arteries supply the posterior scalp, traveling superiorly from behind the ear and the posterior head, respectively. These five arteries anastomose with each other to supply the scalp.

The primary venous drainage of the scalp is done by companion veins to the arteries: the supratrochlear vein, supraorbital vein, superficial temporal vein, posterior auricular vein, and occipital vein. Additionally, small emissary veins also help drain some blood from the scalp into a dural sinus, penetrating flat bones along the way. These veins are also valveless and can provide a conduit from the scalp to the dural sinuses.

The scalp receives innervation from the three branches of the trigeminal nerve (CN V1-3) and from ventral and dorsal rami. The ophthalmic and maxillary branches of the trigeminal nerve (CN V1-2) innervate the anterior portion of the scalp. The mandibular branch of the trigeminal nerve (CN V3) and the lesser occipital nerve (ventral rami of C2, C3) innervate the lateral portion of the scalp. Lastly, the greater occipital nerve (ventral rami of C2) and third occipital nerve (dorsal rami of C3) innervate the posterior portion.


 * 3. Review on your own the major bones of the face.**

See Skull and Cranial Vault.

The skin of the face is very pliable and movable because of the need for expressions and eating. There is //no// deep fascia of the skin; in fact, the skin is only attached at the chin and the bridge of the nose to deeper structures. All the muscles of facial expression are in the superficial fascia. However, this means that it is very easy to have edema of the face and for edema to spread. Fortunately, because the skin is so highly vascularized, it repairs very well, which is the reason why plastic surgery is so successful.

There are eight major facial bones that make up the facial skeleton: nasal bones, maxilla, mandible, zygomatic bones, lacrimal bones (in the orbit), vomer bones (in the nasal cavity), inferior nasal concha (in the nasal cavity) and palatine bone (in the hard palate).


 * 4. Describe the sensory innervation and blood supply to the skin of the face.**

The sensory innervation of the skin of face is provided mostly by the three branches of the trigeminal nerve (CN V), the ophthalmic nerve (CN V1), maxillary nerve (CN V2), and mandibular nerve (CN V3).

The ophthalmic nerve (CN V1) has five major branches: the infratrochlear nerve, external nasal nerve, supratrochlear nerve, supraorbital nerve, and lacrimal nerve. The infratrochlear nerve supplies the area of the medial corner of the eye and the superior lateral part of the nose. The external nasal supplies the medial region of the nose. The supratrochlear nerve supplies from the medial region of the eyelid and superiorly all the way up to the scalp. The supraorbital nerve exits the supraorbital foramen and parallels the supratrochlear nerve but more lateral. Lastly, the lacrimal nerve supplies a small region paralleling but lateral to the supraorbital nerve but does not extend far beyond the eyebrow.

The maxillary nerve (CN V2) has three major branches: the infraorbital nerve, zygomaticotemporal nerve, and zygamaticofacial nerve. The infraorbital nerve exits out of the infraorbital foramen and supplies the cheek region below the eye, lateral part of the inferior nose (nares) and the upper lip. The zygomaticotemporal nerve supplies the region lateral to the eye and superiorly over the eyebrow region. The zygomaticofacial nerve supplies the region of the face lateral to the infraorbital nerve and inferior to the zygomaticotemporal nerve.

The mandibular nerve (CN V3) has three major branches: the mental nerve, buccal branch of the mandibular nerve, and the auricular temporal nerve. The mental nerve exits the mental foramen and supplies the region of the chin, and lower lip. The buccal branch of the mandibular nerve supplies the region of the inferiolateral cheek. Lastly, the auricular temporal nerve supplies the lateral side of the face all moving superiorly to supply part of the scalp.

The main artery of the face is the facial artery, a branch of the external carotid artery. The face also receives arterial supply from the superficial temporal artery, transverse cervical artery, and supraorbital and supratrochlear arteries.

The facial artery branches off of the external carotid artery and runs near the edge of the mandible before ascending up the face towards the medial corner of the eye where it becomes the angular artery. This artery has a tortuous path because of it must accommodate the movement of the face during expression, eating, etc. As it ascends, the facial artery gives off the superior and inferior labial arteries to the upper and lower lips. The submental artery branches off the facial artery before it begins to ascend and courses under the edge of the mandible.

The superficial temporal artery branches off the external carotid and ascends on the lateral side of the face, anterior to the ear, and goes superiorly into the scalp. As it ascends, it dives deep and gives off the maxillary artery which courses inferioanteriorly. When it resurfaces at the inferior border of the ear, it gives off a transverse facial artery that course anteriorly.

Lastly, the supratrochlear and supraorbital arteries exit course superiorly from the superior border of the orbit to supply the temple and the scalp. The supraorbital artery exists from the supraorbital foramen.

Blood typically drains from the face following companion veins to the arteries. That is, the face is drained by the facial vein, supraficial temporal vein, supratrochlear vein, and supraorbital vein which parallel the course of their respective arteries. Unlike the facial artery, the facial vein is straight and not coiled. The facial vein drains toward the pteryoid plexus which drains to the maxillary vein as it drains to the retromandibular vein with the superficial temporal vein. The retromandibular vein then drains into the internal jugular and external jugular veins. See Vessels and Nerves of the Neck.

The facial vein can also drain to the angular vein and into the inferior ophthalmic vein in the orbit, ultimately draining into the cavernous sinus, of the dural sinuses. Similarly, the supratrochlear and supraorbital veins drain into the eye via the superior ophthalmic vein which also drains into the cavernous sinus.


 * 5. Explain the clinical significance of the "danger zone" of the face.**

The danger zone of the face is a bilateral triangle that extends from the boundaries of the facial and angular veins laterally, and lateral side of the nose medially with the base of the triangle at the upper lip and the apex at the medial corner of the eye where the angular vein drains into the orbit.

The facial and angular vein can drain not only to the pterygoid plexus, but also into the inferior ophthalmic vein. The superior and inferior ophthalmic veins actually drain into the cavernosus sinus, one of the dural sinuses. Because these are all valveless veins, this provides a route for which infections in the danger zone of the face to travel from the face and into the dural sinuses and the brain. See Skull and Cranial Vault.


 * 6. Describe the organization of the skin of the face; list the major muscles and give their action and innervation.**

All the muscles of facial expression are embedded in the subcutaneous tissue and originate from the second pharyngeal arch. There is no deep fasica of the face. They originate from subcutaneous tissue or bone and insert into the skin.

//All muscles of facial expression are innervated by the facial nerve (CN VII). However, it does not supply the skin overlying them.// The facial nerve exits the brainstem and passes through the inner acoustic meatus and into the skull. The motor component goes over the superior boundary of the middle ear and exits the skull via the stylomastoid foramen on the temporal bone. It comes out behind the ear and gives off a branch to the muscles of the auricle and occipitalis muscle, and a branch to the stylohyoid and posterior belly of the digastric muscles. It then turns anteriorly, going through the parotid gland before dividing into its 5 main branches: temporal branch, zygomatic branch, buccal branch, mandibular branch, and cervical branch.

The platysma muscle originates from the superficial fascia of the neck and covers parts of the anterior and posterior triangles before it inserts by blending with the muscles of facial expression in the mandible. Its action is to wrinkle the skin of the neck and can help depress the mandible.

The occipitalis originates over the superior part of the ears and becomes part of the galea aponeurotica that covers the scalp like a helmet. The frontalis muscle originates from the galea aponeurotica and inserts over the skin of forehead and eyebrows. It acts to elevate the eyebrows and skin of forehead.

The orbicularis oculi is a sphincter-like muscle that surrounds the orbit and acts to squint or close the eyes tightly.

The orbicularis oris is another sphincter-like muscle that surrounds the mouth and acts to purse the lips.

Zygomaticus major originates by the cheek and inferiomedially inserts to the corner of the mouth, acting to help smile.

Levator labii superioris originates from the frontal process of the maxilla and the infraorbital region and attaches to the upper lip. It acts to elevate the upper lip. A long tendon of the levator labii superioris called the levator labii superioris alaque nasi reaches up around the nose towards the region just inferior to the medial corner of the eye. This tendon helps raise the lip in a snear or flare the nose.

Levator anguli oris originates superiolaterally and attaches inferiomedially to the corner of the mouth. This muscles helps lift the corner of the mouth.

Depressor anguli oris is triangular muscle that attaches from the skin around the chin towards the corner of the mouth. This mucle is used to lower the corner of the mouth.

Depressor labii inferioris attaches along the inferior border of the mouth and is used to lower the lower lip.

Buccinator is originates laterally and attaches medially to the lateral sides of the mouth and is the muscle used for drinking from a straw or for playing the horn.

Interrupting CN V innervation to the face would result in a lost of sensation of the face, depending of which branch(s) are interrupted.
 * 7. Discuss the consequences of interrupting CN V or CN VII innervation to the face.**

Interrupting CN VII innervation to the face would result in the loss of function to the muscles of facial expression, causing Bell’s palsy. Patients with Bell’s palsy may need to wear an eye patch over the eye of the affected side to keep the eyelid closed and prevent the eye from ulcerating. Because the muscles attaching to the mouth, such as buccinator, is not functioning on the affected side, the patient can experience difficulty eating, speaking, or drinking, depending on the severity of the palsy.


 * 8. Describe the location of the parotid gland.**

The parotid gland is the largest of the salivary glands. It is found in the subcutaneous tissue of the face, overlying the mandibular ramus and anterior and inferior to the external ear.


 * 9. Give the relationships of the parotid gland to the surrounding structures.**

Structures which transverse or lie deep to the parotid gland include:

(1) Parotid duct, piercing the buccinators to deliver saliva to the oral cavity. (2) Facial nerve, passing through and dividing up into its 5 branches: the temporal branch, zygomatic branch, buccal branch, mandibular branch, and cervical branch. (3) External carotid artery and superficial temporal artery (4) Retromandibular vein (5) Auricular temporal nerve, a branch of the mandibular branch of the trigeminal nerve (CN V3)


 * 10. Describe the nerve and vascular supply to the gland.**

Presynaptic parasympathetic fibers derived from the glossopharyngeal nerve (CN IX) travel a branch of CN IX, the lesser petrosal nerve. The lesser petrosal nerve hitchikes (//but does not join//) along the mandibular nerve (CN V3) to reach the otic ganglion. There, the parasympathetic fibers synapse and join the auriculotemporal nerve. The parasympathetic fibers travel the auriculotemporal nerve and jump off at the parotid gland to supply secretomotor parasympathetic innervation. Stimulation of these fibers produces thin, watery saliva.

Sympathetic fibers are derived from cervical ganglia through the external carotid nerve plexus on the external carotid artery. Sensory nerve fibers pass to the gland through the great auricular and auriculotemporal nerves. The great auricular nerve (C2, C3) off the cervical pelxus innervates the parotid sheath.

Branches of the external carotid artery, which traverses the glandular tissue supply the parotid gland with oxygenated blood, whereas numerous local veins drain the organ. These veins drain into tributaries of external and internal jugular veins.