Face, Parotid Region, and Extracranial Facial Nerve Flashcards
Do not burden your memory with attachments of muscles of facial expression!
What explains the partial innervation of the face by the 2nd cervical nerve (C2)?
The territories of cutaneous innervation of ophthalmic, maxillary, and mandibular nerves are not horizontal, but curved in the posterosuperior direction, indicating the direction of growth of brain and head. Thus the original beard area has been drawn up to the temple and necessarily the neck skin is drawn up to overlap the angle of the mandible.
[Diagram: Surface anatomy of the face]
[Diagram: Well labelled skull]
[Diagram: Well labelled skull (2)]
[Diagram: cutaneous innervation of the face]
Use your atlas too!
Further notes:
Temple: The area on the side of the skull between the superior temporal line and zygomatic arch is popularly known as temple. The name temple is supposedly derived from the fact that with age (i.e., time) greying of hair occur first in this area (tempus = time).
~ There are six layers of soft tissue in the region of temple. From superficial to deep, these are:
1. Skin.
2. Connective tissue.
3. Extension of epicranial aponeurosis.
4. Temporal fascia.
5. Temporalis muscle.
6. Pericranium.
State the cutaneous branches of each of the 3 divisions of the trigeminal nerve involved in sensory innervation to the face.
From V1:
Supraorbital
Supratrochlear
Infratrochlear
External nasal branch of anterior ethmoidal nerve
Palpebral branch of lacrimal nerve
From V2:
Infraorbital
Zygomaticofacial
Zygomaticotemporal
From V3:
Mental
Buccal
Auriculotemporal
[Diagram]
Describe the motor innervation of the face.
~ The motor nerve supply of the face is derived from the facial nerve.
~ After coming out of cranial cavity through stylomastoid foramen, the facial nerve wind around the lateral aspect of styloid process and then enters the parotid gland.
~ Here it divides into 5 terminal branches (viz. temporal, zygomatic, buccal, marginal mandibular, and cervical), which emerge in the face radiating through the anterior border of the parotid gland and supply the muscles of facial expression.
~ These 5 sets of terminal branches form the goose-foot pattern (pes anserinus) on the face.
Briefly discuss the following with regard to clinical anatomy of sensory innervation of the face:
a) Trigeminal neuralgia (tic douloureux)
b) Herpes zoster ophthalmicus
a) Trigeminal neuralgia (tic douloureux): It is a clinical condition characterized by sudden paroxysmal attacks of lancinating pain lasting from few hours to several days, confined to distribution of one or more divisions of trigeminal nerve. It commonly starts in the maxillary territory and more frequently on the right side. [Click here for a diagram showing more information.]
b) Herpes zoster ophthalmicus: It is a viral infection involving the ophthalmic nerve. It presents as severe pain and edema in the ophthalmic territory and is characterized by the appearance of vesicles along the course of cutaneous branches of the ophthalmic nerve.
Further notes:
Lancinating pain: pain that feels as if you were cut or pierced by a sharp object.
The skin of the face is thick, elastic, and very vascular. It contains large number of sweat and sebaceous glands. The sweat glands help to regulate the body temperature whereas sebaceous glands keep the face oily by their secretion. The skin of face is lax except on the nose where it is firmly attached to the underlying cartilages and provides insertion to the muscles of facial expression.
State the clinical correlation regarding the skin of the face.
~ Since the blood supply to the skin of the face is profuse, therefore it is rare in plastic surgery for skin flaps to necrose in this region.
~ The laxity of greater part of skin facilitates rapid spread of edema in the region of the face.
~ Face is also the common site for acne due to the presence of a large number of sebaceous glands in this region.
Further notes:
“A skin flap is a type of wound closure. A local skin flap consists of skin taken from an adjacent area and moved to fill the surgical defect often created from the removal of a skin lesion such as skin cancer. Flaps differ from skin grafts in that a flap is transferred with an intact blood supply and remains connected to its origin, while a graft is a transfer of tissue which has been completely removed from its origin and therefore relies entirely on the recipient site for its blood supply.”
a) What does the superficial fascia contain?
b) Why is deep fascia absent in most parts of the face? Which gland and muscle have this fascia?
a) It contains muscles of facial expression, vessels and nerves, and variable amount of fat. The fat is absent in the eyelids but is well-developed in cheeks forming buccal pad of fat, which provides rounded contour to cheeks. The buccal pads of fat are very prominent in infants in whom they help in suckling milk and are called suctorial pad of fat.
b) The deep fascia is absent in the region of face except over the parotid gland and masseter muscle, which are covered by parotidomasseteric fascia. The absence of deep fascia in the face is essential for the facial expression.
The muscles of facial expression are embedded in the superficial fascia. Most of them arise from bones of the skull and are inserted into the skin. They bring about different types of facial expressions, hence the name muscles of facial expression, the actions of many of them are implied by their names.
State the characteristic features of the muscles of facial expression.
- They lie in superficial fascia and inserted into the skin.
- Morphologically, they represent the specialized members of the subcutaneous muscle (panniculus carnosus), of lower animals.
- Embryologically, they develop from mesoderm of 2nd pharyngeal arch, hence supplied by facial nerve, the nerve of 2nd arch.
- Functionally, they perform all important functions of
non-verbal communication in addition to closing and opening the orifices in the region of the face.
The face refers to the front part of the human head, in front of the ears and anteroinferior to the classical scalp hairline. It houses the orbit, nose and mouth which in turn house some of the special sensory organs.
Describe the sensory innervation of the face.
- CN V is the main sensory nerve of the face because it supplies the whole of the face, except skin over the angle of the mandible, which is supplied by great auricular nerve derived from ventral rami of C2 and C3.
- Upper 1/3 of the face (developing from frontonasal process): CN V1
- Middle 1/3 of the face (developing from maxillary processes): CN V2
- Lower 1/3 of the face (developing from mandibular processes): CN V3
- [Diagram]
State the clinical relevance of the facial muscles around the orifice of the eye with regards to:
a) Crow’s feet
b) Ectropion
a) Crow’s feet: The contraction of entire orbicularis oculi draws the skin of forehead, temple, and cheek towards the lateral angle of the eye, producing radiating skin folds from the lateral angle of the eye, which may be a permanent feature in some old people forming the so called crow’s feet.
b) Ectropion: The paralysis of orbicularis oculi results in drooping of the lower eyelid (ectropion) causing spilling of tears on the cheek (epiphora).
State the facial muscles around the nasal cavity and their functions. Note that these muscles are poorly developed because anterior nares are open.
- Procerus: produces transverse wrinkles across the bridge (root) of the nose as in frowning.
-
Nasalis:
a) transverse part called compressor naris: compresses the nasal aperture
b) alar part called dilator naris:
- dilates the anterior nasal apertures as in deep inspiration.
- involved in expression of anger - Depressor septi nasi: fixes the nasal septum to allow dilation of anterior nasal aperture by dilator naris.
The muscles around the mouth are responsible for the movement of lips and cheek. These include:
1. Orbicularis oris: acts as sphincter
2. Nine muscles converging around the mouth act as
dilators.
Discuss the orbicularis oris.
1. Extrinsic and intrinsic portions (this is to understand the anatomy of this complex muscle)
2. Nerve supply
3. Actions
- Extrinsic and intrinsic portions:
Major extrinsic (or superficial) portion: composed of interlacing fibres of the muscles which converge around the mouth for their insertion into the lips, viz. levator anguli oris, depressor anguli oris, buccinator, etc. Most of the fibres come from buccinator. The fibres of buccinator converge towards the modiolus. At modiolus they form chiasma. The uppermost and lowermost fibres pass straight into their respective lips, whereas the middle fibres decussate, so that the upper fibres pass into the lower lip, and lower into the upper lip.
Intrinsic portion: consists of fibres running obliquely between the skin and mucus membrane of the lips, and incisive slips, which pass laterally into the lips from the jaws adjacent to the incisor teeth and interlace with the fibres of peripheral part of orbicularis oris as they approach the modiolus.
[Diagram: Orbicularis oris muscle]
[Diagram: Arrangement of fibres of orbicularis oris muscle]
[Diagram: Formation of modiolus] - Buccal branch of the facial nerve
- Because of its complex nature, orbicularis oris is capable of producing wide variety of movements of lips such as closing, pouting, pursing, twisting, etc.
State the ten muscles converging around the mouth, and their functions.
- Levator labii superioris alaeque nasi: elevates the upper lip and helps to dilate the nostril.
- Levator labii superioris: elevates the upper lip.
- Levator anguli oris: raises the angle of the mouth.
- Zygomaticus minor: elevates the upper lip.
- Zygomaticus major: draws the angle of the mouth upward and laterally.
- Depressor labii inferioris: draws the lower lip downwards and somewhat laterally.
- Depressor anguli oris: draws the angle of the mouth downwards and laterally.
- Risorius: retracts the angle of the mouth gently.
-
Buccinator:
a. It flattens the cheek against the gum and teeth, and thus prevents the accumulation of food in the vestibule of mouth during mastication.
b. It expels air from distended cheeks as when playing wind instruments (hence the name trumpeter’s muscle). - Mentalis: It puckers the chin and protrudes the lower lip
- [Diagram: muscles of the face] [Diagram: muscles of the face (2)] [Diagram: muscles of the face (3)]
Further notes:
The vestibule of the mouth refers to the space between the soft tissue (lips and cheeks), and the teeth and gums.
a) What is the modiolus?
b) The modiolus is formed due to interlacing of fibres of muscles which converge towards the angle of the mouth. Name these muscles.
a) It is a dense, compact, mobile, fibromuscular mass situated about 1.25 cm lateral to the angle of the mouth.
b) muscles of the modiolus
- oribicularis oris
- levator anguli oris
- zygomaticus major
- buccinator
- depressor anguli oris
- risorius
- platysma pars modiolaris
- mentalis
- depressor labii inferioris
[Diagram: muscles of the face] [Diagram: muscles of the face (2)] [Diagram: muscles of the face (3)]
NOTE:
~ The modiolus an be easily palpated by using opposed thumb and index finger to compress the skin and mucosa simultaneously. The pulsations of facial artery can be felt just lateral to the modiolus. The inadvertent damage of modiolus during plastic surgery leads to unacceptable facial asymmetry.
The facial muscles are arranged in groups around the orifices of mouth, eye and nose as sphincters and dilators of these orifices. The muscles of facial expression also include the muscles of scalp, auricle and the subcutaneous muscle of the neck—the platysma. State the muscles around the orifice of the eye together with their functions. Appreciate their locations using an atlas and linked images.
- Orbicularis oculi:
Orbital part:
- closes the eye tightly to protect the eye from intense light and dust particles.
- winking.
Palpebral part:
- closes the eyelids gently as in sleep or in blinking.
Lacrimal part:
- dilates the lacrimal sac by exerting traction on the lacrimal fascia, thus helping in the drainage of lacrimal fluid
- [Diagram 1] [Diagram 2] - Corrugator supercilii:
- drags the eyebrow medially and downwards producing vertical wrinkles on the forehead as in frowning, an expression of annoyance - Frontalis:
- elevates the eyebrows and produces transverse wrinkles on the forehead as an expression of surprise, horror or fright
NOTE: Around the orifice of the eye, we also have levator palpebrae superioris muscle. It is not a muscle of the face, but it elevates the upper lid.
Outline the course of the transverse facial artery.
For each emotional expression below, state the presenting features and the facial muscles involved.
1. Laughing
2. Sadness/sorrow/grief
3. Grinning
- Laughing:
Angle of mouth drawn upwards and laterally - Zygomaticus major. - Sadness/sorrow/grief:
a) Accentuation of nasolabial fold: Levator labii superioris.
b) Elevation and eversion of the upper lip: Levator anguli oris and zygomaticus minor.
c) Angle of mouth drawn downwards and laterally: Depressor anguli oris. - Grinning:
Retraction of angle of the mouth laterally: Risorius. - [Diagram: muscles of the face] [Diagram: muscles of the face (2)] [Diagram: muscles of the face (3)]
For each emotional expression below, state the presenting features and the facial muscles involved.
1. Surprise/horror/fright
2. Frowning
3. Anger
- Surprise/horror/fright:
Transverse wrinkles of the forehead - Frontalis. - Frowning:
a) Vertical wrinkles of the forehead - Corrugator supercilii. [Diagram: demonstration]
b) Transverse wrinkle across the root of nose - Procerus. [Diagram: demonstration] - Anger:
a) Dilation of the anterior nasal aperture - Dilator naris. [Diagram: demonstration]
b) Depression of lower mobile part of the nasal septum - Depressor septi nasi. - [Diagram: muscles of the face] [Diagram: muscles of the face (2)] [Diagram: muscles of the face (3)]
For each emotional expression below, state the presenting features and the facial muscles involved.
1. Disdain/doubt
2. Worry
3. Irony
- Disdain/doubt: Puckering of the chin, protrusion of lower lip: Mentalis.
- Worry: Skin folds radiating laterally from lateral angle of the eye: Orbicularis oculi.
- Irony: Angle of the mouth drawn downwards and somewhat laterally: Depressor labii inferioris.
- [Diagram: muscles of the face] [Diagram: muscles of the face (2)] [Diagram: muscles of the face (3)]
Discuss the following functional components of the facial nerve:
(a) Special Visceral Efferent
(b) General Visceral Efferent [briefly discuss preganglionic and postanglionic fibres]
The facial nerve has several functional components, each arising from a different nucleus:
(a) Special Visceral Efferent fibres: these arise from the motor nucleus and supply the muscles derived from the mesoderm of the 2nd pharyngeal arch i.e. muscles of facial expression.
(b) General Visceral Efferent fibres: these fibres arise from the lacrimatory and superior salivatory nuclei for lacrimation and salivation respectively.
~ The preganglionic fibres arising from the lacrimatory nucleus terminate in the pterygopalatine ganglion (greater petrosal nerve being one of the fibres terminating in the pterygopalatine ganglion; it does not synapse in the geniculate ganglion), from which postganglionic fibres arise and supply the lacrimal gland through zygomatic branch of maxillary nerve.
~ The preganglionic fibres arising from superior salivatory nucleus relay in the submandibular ganglion (chorda tympani being one of the preganglionic fibres), from which postganglionic fibres arise and supply the submandibular and sublingual salivary glands.
NOTE:
~The greater petrosal nerve (or greater superficial petrosal nerve) is a nerve of the head mainly containing pre-ganglionic parasympathetic fibres which ultimately synapse in the pterygopalatine ganglion.
~ It branches from the facial nerve (CN VII) and is derived from the parasympathetic part of the nervus intermedius component of CN VII, with its cell bodies located in the superior salivary nucleus.
~ In the connective tissue substance of the foramen lacerum, the greater petrosal nerve unites with the (sympathetic) deep petrosal nerve to form the nerve of the pterygoid canal (vidian nerve) which proceeds to the pterygopalatine ganglion.
~ It forms part of a chain of nerves that provide secretomotor innervation to the lacrimal gland and mucosal glands of nasal cavity and palate.
Define the “danger area” of the face and state its anatomical basis.
“Danger area” of the face comprises the triangular area formed by the corners of the mouth to the bridge of the nose. [Diagram]
Anatomical basis:
The facial vein and its communications are devoid of valves in their lumens. Since facial vein rests directly on the muscles of facial expression, the movements of these muscles may facilitate the spread of septic emboli from the “danger area” in retrograde direction through deep facial vein, pterygoid venous plexus, and emissary vein [of Vesalius] into the cavernous sinus leading to meningitis and cavernous sinus thrombosis. [Diagram]
Discuss the following functional components of the facial nerve:
(a) Special Visceral Afferent
(b) General Somatic Afferent
(a) Special Visceral Afferent fibres: these are concerned with taste sensations. The cell bodies of these fibres lie in the geniculate ganglion. The peripheral processes of ganglion cells carry taste sensations from the taste buds on the anterior two-third of the tongue except vallate papillae. The central processes of ganglion cells carry these sensations to the upper part of the nucleus of tractus solitarius (gustatory nucleus).
(b) General Somatic Afferent fibres: these fibres have their cell bodies in the geniculate ganglion. The peripheral processes of these cells innervate part of the skin of the external ear, while their central processes terminate in the spinal nucleus of trigeminal nerve. [Which general sensations do these fibres carry?]
Further notes:
In the context of “Special Visceral Afferent” (SVA) fibers, the term “visceral” refers to sensory nerves that develop in association with the gastrointestinal tract. These specialized afferent fibers carry the special sense of taste (gustation) from specific regions of the oral cavity and pharynx.
Discuss the intracranial course of the facial nerve.
~ The facial nerve arises from as two roots: a large motor root (medial) and a smaller sensory and parasympathetic root (nervus intermedius/intermediate nerve of Wrisberg) (lateral).
~ The two roots arise from the pontomedullary junction lateral to the superior end of the olive of the medulla. The sensory root lies between the motor root of facial medially and the vestibulocochlear nerve laterally.
~ After emerging from the brainstem, the roots of the facial nerve pass laterally and forward in the cerebellopontine angle, along with the vestibulocochlear nerve and labyrinthine artery.
~ All these structures then enter the internal acoustic meatus, a 1 cm long opening in the petrous part of the temporal bone.
~ Still within the temporal bone, the roots leave the internal acoustic meatus and enter into the faclal canal. The canal is a ‘Z’ shaped structure. Within the facial canal, three important events occur:
(a) the two roots fuse to form the facial nerve
(b) the nerve forms the geniculate ganglion. Note that the geniculate ganglion of facial nerve houses the cell bodies of sensory nerve fibers of facial nerve.
(c) Lastly, the nerve gives rise to (in the following order): (Acronym: GSC)
(i) the greater petrosal nerve: parasympathetic fibres to mucous glands and lacrimal gland
(ii) nerve to stapedius: motor fibres to stapedius muscle of the middle ear
(iii) chorda tympani (joins the lingual nerve of V3): special sensory fibres to the anterior 2/3 tongue and parasympathetic fibres to the submandibular and sublingual glands
~ The facial nerve exits the facial canal (and the cranium) via the stylomastoid foramen.
~ [Diagram 1] [Diagram 2] [Diagram 3]
Further notes:
~ The stapedius dampens vibrations of the stapes, protecting the hearing apparatus when exposed to loud sounds.
Discuss the extracranial course of the facial nerve.
~ After exiting through the stylomastoid foramen, the facial nerve turns forwards, making a curve around the lateral side of the base of the styloid process.
~ The first extracranial branch to arise is the posterior auricular nerve. It supplies the occipital belly of occipitofrontalis, auricularis posterior, and auricularis superior.
~ Immediately distal to this, motor branches are sent to the posterior belly of the digastric muscle and to the stylohyoid muscle. [Acronym: PDS i.e. posterior auricular nerve, then nerve to digastric, then nerve to stylohyoid muscle]
~ The main trunk of the nerve, now termed the motor root of the facial nerve, continues anteriorly and inferiorly into the parotid gland (note – the facial nerve does not contribute towards the innervation of the parotid gland, which is innervated by the glossopharyngeal nerve).
~ Within the parotid gland, the nerve terminates by splitting into five branches responsible for innervating the muscles of facial expression [Diagram]:
(i) Temporal branch
(ii) Zygomatic branch
(iii) Buccal branches
(iv) Marginal mandibular branch
(v) Cervical branch
(TZBMC: from superior to inferior)
Name the muscles supplied by the temporal branch of the motor root of the facial nerve and state their functions. (3 muscles)
(a) Frontalis: Responsible for raising the eyebrows and wrinkling the forehead.
(b) Orbicularis Oculi (upper part): Controls eyelid closure and blinking.
(c) Corrugator Supercilii: Creates vertical wrinkles between the eyebrows as in frowning.
