THE HEAD

Introduction to the skull

Superficial face; scalp

Parotid region and deep face

Intracranial cavity and meninges; cranial nerves

Eye and orbit

Nose, nasal cavities and paranasal sinuses

Oral cavity and contents

Ear and temporal bone

Lymphatics of the head and neck

INTRODUCTION TO THE SKULL

Development of the skull

• The base of the skull develops by endochondral ossification
• The brain and cranial nerves develop before the skull, so when the chondrocranium develops, its components form around the nerves and form foramina.
• The chondrocranium ossifies from a number of centers.
• The last piece of cartilage to ossify is between the body of the sphenoid bone and the occipital bone, just anterior to the foramen magnum: this is the spheno-occipital synchondrosis. Its epiphyseal plate exists for the growth in length of the base of the skull and it ossifies at age 25.

The bones of the calvarium ossify by intramembranous ossification

• The bones of the calvarium also ossify from separate centers and they meet to form sutures (Clemente plate 482 fig. 756; Grant p. 608-609; Netter 3e 2-11; 4e 2-12). The process is completed at about 3 years.

The bones of the face are partly basal and partly calvarial bones so they ossify both by intramembranous and endochondral ossification.

Calvalrial bones

The bones of the cranium and the underlying lobes of the brain have the same name (Clemente plate 481 fig. 754; Grant p. 610-615, 722-723; Netter 3e 2-7, 4e 4 &105):

• The frontal bone (which houses the frontal lobe of the brain) ossifies from 2 centers and there are right and left frontal bones at birth (Clemente plates 484-485; Grant p. 608-609; Netter 3e 11, 4e 12). The metopic suture separating the 2 frontal bones normally ossifies, leaving one large frontal bone.
• The parietal bones are separated from each other by the sagittal suture (Clemente plate 482 fig. 756; Grant p. 614-615; Netter 3e 7, 4e 7) and from the frontal bone by the coronal suture (Clemente plate 482 fig. 756; Grant p. 612-613; Netter 3e 4; 4e 4-7).

At birth, the anterior fontanelle (Clemente plate 485 fig. 762; Grant p. 608-609; Netter 3e 11, 4e 12) is a diamond-shaped area between the 2 frontal bones and the 2 parietal bones. It pulsates and bulges when the baby cries. It closes by 18 months to 2 years and is then known as the bregma (Clemente plate 482 fig. 756; Grant p. 614; Netter 3e 7, 4e 7).

• The parietal bones and the occipital bone meet at the posterior fontanelle (Clemente plate 485; Grant p. 609; Netter 3e 11; 4e 12) which becomes lambda, along the lambdoid suture in the adult (Clemente plate 482 fig. 756; Grant p. 614; Netter 3e 7, 4e 7).
• The side wall of the skull is completed by the squamous part of the temporal bone and the greater wing of the sphenoid bone, at the pterion (Clemente plate 481; Grant p. 612-613; Netter 3e 4, 4e 4).
  • This is located 4 cm above the midpoint of the zygomatic arch and is the site of surgical exploration for the middle meningeal artery (Grant p. 635, Netter 3e 6, 4e 6).
• The flat bones of the skull (frontal, parietal, temporal and occipital) are formed by a sandwich of diploë (cancellous bone containing red bone marrow) between 2 layers of compact bone (Clemente plate 486 fig. 765; Grant p. 634; Netter 3e 96, 4e 102).
• The bones are drained by diploic veins; there are usually 4 on each side:  frontal, anterior temporal, posterior temporal and occipital (Clemente plate 486 fig. 764; Grant p. 634; Netter 3e 94, 4e 99 & 102) which open into the nearest convenient venous sinus.
• The flat bones of the skull are also pierced by emissary foramina transmitting emissary veins connecting veins of the scalp with the dural venous sinuses inside the skull (this is a possible route for the spread of infection). They may be seen in the parietal bone or in the temporal bone posterior to the external auditory meatus (Grant 785; Netter 3e 94, 96; 4e 7, 99 & 102).

In an X-ray of the skull, it is necessary to differentiate the following normal structures from fractures (Grant p. 620-621; Netter 3, 5):

• the sutures (possible metopic suture),
• the diploic veins,
• and the middle meningeal artery.

The pineal gland near the center of the brain may contain corpora aranaceae (calcareous granules) and it can be used to detect displacement of the brain.

• The occipital bone (Clemente plate 482 fig. 757; Grant p. 614; Netter 3e 8, 4e 6 & 8):
  • The external occipital protuberance is located inferior to lambda.
  • The superior nuchal lines run lateral from the external occipital protuberance and the inferior nuchal lines are situated inferiorly.

The cranial fossae (Clemente plates 496-497; Grant p. 618-619; Netter 9):

From anterior to posterior, 3 fossae form 3 successive steps leading down to the foramen magnum.

1) Anterior cranial fossa:

• Orbital plate of the frontal bone
• Lesser wing of the sphenoid bone
• The cribriform plate of the ethmoid with the crista galli transmits olfactory nerves from the upper part of the nasal cavity; this is a possible route for infection or escape route for CSF in skull fractures.
• Optic canal for transmission of optic nerve.
• Anterior clinoid processes projecting posteriorly to the posterior clinoid processes of the sphenoid bone.

2) Middle cranial fossa

• is formed by the greater wing of the sphenoid bone and the temporal bone. It is occupied by the temporal lobe of the brain.
  • The greater wings and the body of the sphenoid bone form a butterfly shape.
• The most posterior tip of the greater wing contains the foramen spinosum.
• Anterior to the foramen spinosum is the foramen ovale and then the foramen rotundum. The foramen rotundum leads to the pterygopalatine fossa.
• The superior orbital fissure is a gap between the lesser wing and the greater wing of the sphenoid leading to the orbit, just lateral to and below the optic nerve.
• The body of the sphenoid bone contains the hypophyseal fossa for the pituitary gland. This fossa is also called the sella turcica and it is shaped like a 4-poster bed (clinoid processes; clinical = patient is in bed).
  • Its maximum length is 14 mm and its depth is 8 mm. Measurements are important because pituitary tumors cause ballooning of the sella.
• The foramen lacerum is located lateroposterior to the sella.

The middle meningeal artery enters the skull through the foramen spinosum and its groove can be traced laterally and anteriorly on the squamous portion of the temporal bone before dividing into anterior and posterior (frontal and parietal) branches.

• The anterior branch crosses the greater wing at the pterion and then breaks up into branches that run superiorly and posteriorly.
• The posterior branch runs posteriorly supplying bone and meninges.

3) Posterior cranial fossa

• is formed by the temporal bone and the occipital bones.
• houses the cerebellum.

The posterior cranial fossa contains:

• the foramen magnum for the lower end of the medulla.
• The clivus, anterior to the foramen magnum, which leads up to the body of the sphenoid bone.
• The transverse sinus
• The sigmoid sinus which ends at the jugular foramen.
• The hypoglossal canal (anterior condylar) canal and the posterior condylar canal.
• The internal auditory meatus on the posterior aspect of petrous temporal bone.
• The arcuate eminence on the petrous portion of the temporal bone, marking the position of the superior semicircular canal.

The superior sagittal sinus (Grant p. 613; Netter 97-98) is continuous with the right transverse sinus whereas the smaller straight sinus is continuous with the left transverse sinus. The right jugular foramen is thus usually larger than the left.

The exterior base of the skull (Clemente plate 498; Grant p. 616-617; Netter 8).

• Recognize the above- mentioned foramina from the exterior.
• The spine of the sphenoid bone is near the foramen spinosum.
• The jugular foramen is occupied by the jugular bulb (for expansion of the internal jugular vein) in life.
• The styloid process, the mastoid process and the stylomastoid foramen between the 2 processes.
• Anterior to the jugular foramen and in the petrous portion of the temporal bone lies the carotid canal.
• The spine of the sphenoid bone lies medial to the mandibular fossa. The mandibular fossa articulates with the head of the mandible to form the temporomandibular (TMJ) joint.
• The foramen ovale lies at the base of the lateral pterygoid plate.
• The medial pterygoid plate (with the pterygoid hamulus at its base) and the lateral pterygoid plate are parts of the sphenoid bone.
• The inferior orbital fissure leads anteriorly from the pterygoid region to the orbit.
• The hard palate is formed by the palatine process of the maxilla and by the horizontal plate of the palatine bone. There are 3 foramina in the horizontal plate, the larger being the greater palatine foramen.
• The vomer bone in the posterior opening (the choanae) of the nasal cavity is attached by a fibrous joint to the undersurface of the body of the sphenoid.

The internal carotid artery (Clemente plate 491 fig. 772, plate 497; Grant p. 644-645; Netter 3e 130, 4e 136):

• enters the carotid canal,
• runs anteromedially to the foramen lacerum
• and then runs superoanteriorly to enter the cranium through the internal orifice of the foramen lacerum.
• It then turns anteriorly and lies on the side of the sella turcica. It now lies in the cavernous sinus.
• It then turns superoposteriorly, medial to the anterior clinoid process and breaks up into 3 branches.

THE SKELETON OF THE FACE

The following structures are found in the orbit (Clemente plate 480; Grant p. 650; Netter 3e 2, 4e 2 &4):

• the superior orbital fissure
• the optic canal
• The greater and lesser wings of the sphenoid.
• The zygomatic bone and the (hollow) maxilla are in the lateral wall of the orbit.
• The ethmoid bone and the small fragile lacrimal bone are in the medial wall .

The supraorbital, infraorbital and mental foramina (Clemente plate 480; Grant p. 610-611; Netter 2) lie on a vertical line and transmit the ophthalmic, maxillary and mandibular divisions of the trigeminal (Vth cranial) nerve (Clemente plate 542; Grant p. 630-631; Netter 3e 116, 4e 122).

updated 10/20/2008

SUPERFICIAL FACE AND SCALP

FACIAL MUSCULATURE

2 main groups of muscle are located on the face:

• muscles of facial expression innervated by the facial nerve (cranial nerve VII)
• and muscles of mastication supplied by the mandibular division of the trigeminal nerve (cranial nerve V).

Muscles of facial expression (innervated by the facial nerve) are superficial muscles which can move skin and fascia in various directions. They are also dilators and sphincters for the various orifices in the face region. The 2 major groups are around the eye and the mouth.

Around the eye:

The sphincter is the orbicularis oculi (Clemente plate 462 fig. 728; Grant p. 626, 628-629; Netter 3e 22, 4e 26) which has:

• a palpebral part in the eye lid (closes eye gently)
• and an orbital part which surrounds the orbit and blends in with the anterior belly of occipitofrontalis (closing the eye forcibly). The orbital part causes radiating skin wrinkles from the lateral corner of the eye.

The dilator is the levator palpebrae superioris (Clemente plate 509 fig. 801; Grant p. 654--655; Netter 3e 77, 4e 84) innervated by the oculomotor nerve (cranial nerve III) and postganglionic sympathetic fibers from the superior cervical ganglion.

Around the mouth:

The sphincter is the orbicularis oris (Clemente plate 462 fig. 728; Grant p. 630; Netter 3e 22, 4e 26) which closes the lips but can also protrude the lips as in whistling, or kissing.

The dilators are:

• Levator labii superioris alaeque nasi ("Grace" muscle; Clemente plate 462 fig. 728; Grant p. 629; Netter 3e 22, 4e 26)
• Levator labii superioris
• Levator anguli oris
• Zygomaticus minor
• Zygomaticus major
• Platysma (risorius; Clemente plate 463 fig. 729; Grant p. 746; Netter 3e 22, 4e 26)
• Depressor anguli oris
• Depressor labii inferioris
• Mentalis

The buccinator (Clemente plates 466-467; Grant p. 666; Netter 3e 22, 50, 4e 26) is the main muscle of the cheek and it keeps the cheeks in contact with the gums so that food does not accumulate in the vestibule of the mouth.

*Bell's Palsy: lesions of the facial nerve (Cranial nerve VII)

• Drainage of tears and dribbling of saliva due to paralysis of the 2 main orbicularis muscles. Paralysis of buccinator will lead to accumulation of food in the vestibule.
• Test by asking patients to screw up the eye (loss of muscle tone causes the normal skin folds to disappear on the side of the lesion), to smile or to whistle.
• Muscles must be supported during recovery or they will stretch under gravity and cause a permanent asymmetry of the face.

Muscles of mastication (Grant p. 672-673; Netter 3e 50, 4e 54-55) developed from the first branchial arch and are innervated by branches from the anterior branch of the mandibular division of the trigeminal nerve (Grant p. 828-829, Netter 3e 116, 4e 122):

• The masseter (Clemente plate 466; Grant p. 626-627; Netter 3e 50, 4e 54) muscle attaches to the zygomatic arch and the outer surface of the mandible near the angle. It is composed of a superficial and deep part. The masseter closes the jaw and is innervated by the masseteric nerves passing through the mandibular notch.
• The temporalis muscle attaches from the lateral side of the skull below the temporal line to coronoid process and anterior border of the ramus of the mandible almost as far as the third molar tooth (Grant p. 666-667; Netter 3e 50, 4e 54). The temporalis muscle closes the jaw and is innervated by the deep temporal nerves.
• The lateral pterygoid muscle (Clemente plate 470; Grant p. 670; Netter 3e 51, 4e 55) attaches from the lateral surface of the lateral pterygoid plate to the neck of mandible and the intraarticular disc of the temporomandibular joint. It is the only muscle in this group to open the jaw.
• The medial pterygoid is attached from the medial surface of the lateral pterygoid plate to the deep surface of the mandible (at the angle of the mandible) opposite to the attachment of the masseter muscle. The angle of the mandible thus lies between these 2 muscles. The medial pterygoid muscle closes the jaw.
• Both pterygoid muscles are innervated by the pterygoid nerves.

Blood vessels:

The facial artery (Clemente 468, 474; Grant p. 632; Netter 3e 19, 4e 23):

• provides the main blood supply.
• passes over the lower border of mandible at the anterior border of the masseter (feel the pulse).
• has a tortuous course to allow for movement of the face, first to the angle of the mouth and then up at the side of the nose to the medial angle of the eye.
• gives off upper and lower labial branches as well as numerous other branches to the face. Free anastomoses on the same side as well as across the midline.

The facial vein has a straighter path and communicates with deeper veins such as veins of the orbit (leading to the cavernous sinus within the skull (Clemente plates 468, 475; Grant p. 633; Netter 3e 19, 81, 4e 23, 85) at the medial angle of the eye and the pterygoid venous plexus. The central face area is thus a "danger area" for an infection on the face to travel into the skull or into the deep face.

The superficial temporal artery (Clemente 468, 474; Grant p. 626-627, 632; Netter 3e 19, 4e 23) is a branch of the external carotid artery. Its pulse can be felt in front of the tragus of the ear. Above the ear it divides into anterior and posterior branches. It anastomoses with the facial artery.

Parotid gland (Grant p. 627; Netter 3e 19, 4e 25, 61)

• This major salivary gland becomes inflamed with the mumps. It is enclosed in a split layer of deep cervical fascia so that swelling of the gland leads to increase in pressure and pain. The medial thickening in this capsule forms the stylomandibular ligament (Clemente plate 468, plate 472 fig. 740; Grant p. 674; Netter 3e 12, 14, 4e 16).
• The duct (Clemente plate 466; Grant p. 627; Netter 3e 17, 4e 25) leaves the anterior border, crosses the masseter muscle, turns around the anterior border of the muscle and pierces the buccinator muscle to enter the mouth opposite the 2nd upper molar tooth. It can be rolled under the fingers when the masseter is contracted by clenching the teeth. It is in line with the tragus of the ear.
• The gland occupies the space between the sternocleidomastoid and the back of the mandible and molds itself to all adjacent structures.

3 important structures passes through the parotid gland from superficial to deep: the facial nerve, the retromandibular vein and the external carotid artery.

The facial nerve (Clemente plate 469; Grant p. 627, 830; Netter 3e 21, 4e 25):

• from the stylomastoid foramen,
• gives off a posterior auricular branch to the occipital belly of occipitofrontalis,
• divides within the parotid gland forming an intraglandular network,
• 5 branches emerge from the anterior border of the gland: temporal, zygomatic, buccal, marginal mandibular and cervical (Palm of hand on parotid gland with 5 fingers spread onto the face).
• *The marginal mandibular branch runs below the border of the mandible to supply the muscles of the chin. Incision should always be made a finger's width below it.

The retromandibular vein (Clemente plate 477; Grant p. 633; Netter 3e 66, 4e 61)

• is formed in the gland by the union of the maxillary and superficial temporal veins,
• emerges from the gland near the angle of the mandible
• divides into 2 with the anterior branch joining the facial vein and draining into the internal jugular vein,
• the posterior branch joins with the small posterior auricular vein to form the external jugular vein (Clemente plate 475; Grant p. 662; Netter 3e 66, 4e 61).

The external carotid artery (Clemente plate 477; Grant p. 632; Netter 3e 65, 4e 61 & 69)

• divides in the substance of the parotid gland into the maxillary and superficial temporal arteries,
• The maxillary artery runs deep to the neck of mandible to enter the infratemporal region,
• The superficial temporal artery lies in front of the ear and divides into anterior (frontal - side of forehead) and posterior (parietal - side of scalp) branches (Clemente plate 474; Grant p. 626-627; Netter 3e 19, 4e 23).

The scalp is attached to the zygomatic arch laterally (Clemente plate 466; Grant p. 626; Netter 3e 22, 4e 4 & 26).

• S = skin
• C = connective tissue
• A = aponeurosis referring to the Galea aponeurotica (epicranial aponeurosis). This aponeurosis belongs to the occipitofrontalis muscle located antero- and posteriorly. The posterior attachment of this muscle is to the occipital bone above the superior nuchal line.
• L = space, this is a plane of cleavage for injury and the spread of blood which can travel as far as the zygomatic arch and into the upper eyelids. The first 3 layers of scalp remain attached to each other in case of cleavage.
• P = periosteum

Blood vessels and nerves of the scalp.

Anastomoses in the scalp are formed by the following arteries from anterior to posterior (Clemente plates 468, 469; Grant p. 632; Netter 3e 19, 4e 23):

• Supratrochlear artery
• Supraorbital artery
• Superficial temporal artery
• Posterior auricular artery
• Occipital artery

The scalp is extremely vascular and bleeds profusely when cut. Due to anastomoses, there is no single vessel to compress but bleeding may stop by direct pressure on or around the wound.

Emissary veins (valveless) may spread infections from the scalp to the intracranial cavity. Normal blood flow is from inside to outside of the skull.

The following nerves innervate the scalp from anterior to posterior (Clemente plate 469; Grant p. 634; Netter 3e 20, 4e 24):

• 2 branches from the ophthalmic division of the trigeminal nerve (cranial nerve V): the supratrochlear and suprorbital nerves
• 1 branch from the maxillary division of the trigeminal nerve: the zygomaticotemporal nerve
• 1 branch from the mandibular division of the trigeminal nerve: the auriculotemporal nerve

Branches of the trigeminal nerve lie anterior to the external ear or auricle

Posterior to the auricle:

• The lesser occipital nerve (C2,3)
• The greater occipital nerve (C2)
• The third occipital nerve (C3)

updated 10/20/2008

THE PAROTID REGION AND THE DEEP FACE

The zygomatic bone has processes related to the frontal, maxillary and temporal bones (Clemente plates 480, 481; Grant p. 610-613; Netter 3e 2, 4e 4)

Bony landmarks on the mandible (Grant p. 664-665; Netter 3e 4, 13, 4e 15):

• The body is formed by the fusion of the right and left sides at 2 years (Clemente plate 484 fig. 760).
• 2 rami.
• Alveolar process for the teeth.
• Coronoid process.
• Condylar process with head (in temporomandibular joint) and neck (Clemente plates 481, 542, 543; Grant p. 664-665; Netter 3e 14, 4e 16).
• Mandibular notch.
• The mandibular foramen and canal lie medial to the mandibular angle. They contain the inferior alveolar nerve (V3) and vessels.
• The lingula serves as attachment point for the sphenomandibular ligament.

The PAROTID BED (Clemente plate 468; Grant p. 662-663; Netter 19) is defined:

• Posteriorly by the mastoid process with the origins of the sternocleidomastoideus and the posterior belly of the digastric (Clemente plate 476; Grant p. 662; Netter 3e 23, 4e 25);
• Medially by the styloid process of the temporal bone and the stylohyoid muscle (Clemente plates 472 fig. 740, plate 476; Grant p. 663; Netter 3e 23, 4e 27). Styloglossus (Clemente plate 538; Grant p. 788-789; Netter 3e 55, 4e 59) and stylopharyngeus are also medial to the parotid bed within the lateral pharyngeal space;
• Anteriorly by the sphenomandibular and stylomandibular ligaments (Clemente plate 472; Grant p. 674; Netter 3e 14, 4e 16) as well as the fasciae of the medial pterygoid (Clemente plates 470, 471; Grant p. 668; Netter 3e 51, 4e 55) and masseter muscles (Clemente plates 468, 469; Grant p. 666-667; Netter 3e 50, 4e 54);
• Superiorly by the zygomatic arch;
• Inferiorly by the posterior belly of the digastric.

*The deep cervical fascia (Clemente plate 446; Grant p. 747; Netter 3e 31, 4e 24, 35) envelops the parotid gland and is weakest between the styloid process and spine of the sphenoid:

• Infections may spread from the parotid fascia into the lateral pharyngeal space which communicates with the retropharyngeal space (Clemente plate 549; Grant p. 747; Netter 3e 31, 4e 35) between the pharynx and prevertebral musculature.
• Infections may track inferiorly through the neck and into the thorax, along the course of the carotid sheath, between visceral and prevertebral fasciae.

The parotid gland is innervated by the lesser petrosal branch (secretomotor) of the IXth (glossopharyngeal) nerve (Clemente plate 527 fig. 836; Grant p. 835; Netter 3e 119, 4e 125).

Preganglionic parasympathetic fibers from the tympanic plexus in the middle ear (Clemente plate 527; Grant p. 835; Netter 3e 89, 119, 4e 125, 134):

• enter the middle cranial fossa by a hiatus on the anterior aspect of the petrous bone,
• run through the periosteal dura
• and exit the middle cranial fossa through the foramen ovale with V3.
• The preganglionic fibers synapse in the otic ganglion on the medial aspect of V3.
• The postganglionic fibers join with the auriculotemporal nerve to run to the parotid gland.
• The auriculotemporal nerve thus carries secretomotor fibers of IXth and sensory fibers of V3 for pain in the gland.

The sympathetic innervation is from the superior cervical ganglion via the arteries and it controls the fluid content of the saliva.

The INFRATEMPORAL REGION (Clemente plates 478, 479; 481 fig. 755; Grant p. 664-665; Netter 3e 8, 4e 8, 10, 14) is:

• inferior to the temporal fossa and zygomatic arch
• and deep to the ramus of the mandible.
• It stretches from the parotid fascia posterior to the mandibular ramus to the tuberosity of the maxilla.

The lateral wall is formed by the medial aspect of ramus of the mandible

The anterior wall is formed by the:

• Body and tuberosity of the maxilla, deep to zygoma and zygomatic process of the maxilla.
• The pterygomaxillary fissure or sphenopalatine foramen (Clemente plate 481 fig. 755; Grant p. 665; Netter 3e 12, 4e 14) may be seen in the medial aspect of this anterior wall, opening into the more medial pterygopalatine fossa.
• The inferior orbital fissure may also be seen.
• Inferior to the pterygomaxillary fissure is the hamulus serving as attachment point for the pterygomandibular raphé. It serves as the common site of origin for the buccinator and the superior constrictor muscle and runs from the hamulus to the upper 1/5 of the mylohyoid line.

The medial wall is formed by the:

• lateral pterygoid plate,
• superior constrictor muscle,
• levator and tensor palati muscles.

The roof of the infratemporal fossa is formed by:

• the greater wing of the sphenoid anteriorly
• and the squamous portion of the temporal bone posteriorly.

The infratemporal crest is on the anterior aspect of the undersurface of the greater wing of the sphenoid and serves as an attachment site for the upper head of the lateral pterygoid. Posterior to this infratemporal crest are:

• The foramen ovale for transmission of V3 and the lesser petrosal nerve (from IXth) from the middle cranial fossa to the infratemporal fossa (Clemente plates 498, 499; Grant p. 669; Netter 8, 10);
• The foramen spinosum for transmission of the middle meningeal artery from the infratemporal fossa to the middle cranial fossa.

Contents of the infratemporal fossa

The key structure for orientation is the lateral pterygoid muscle (Clemente plate 478; Grant p. 668; Netter 3e 51, 4e 55).

This muscle has 2 heads (Clemente plate 470; Grantp. 668, 672; Netter 3e 51, 4e 55):

• from the infratemporal crest to the capsule of the interarticulating disc of the TMJ
• and from the lateral aspect of the lateral pterygoid plate to the neck of the mandible.

*Protrusive actions of the lateral pterygoid muscle are used to test V3: deviation is TOWARDS the side of the lesion.

The maxillary artery lies lateral to the lateral pterygoid muscle (Clemente plates 478, 479; Grant p. 668-670; Netter 3e 36, 4e 40).

• From the external carotid artery in the parotid gland, the artery enters the posterior aspect of the infratemporal fossa by passing deep to the neck of the mandibular condyle.
• It crosses the lateral side of the lateral pterygoid muscle and enters the pterygomaxillary fissure.
• It is divided into a first or mandibular part, second or pterygoid part and third or pterygopalatine part.
• The mandibular and pterygoid parts are associated with the infratemporal fossa
• and the pterygopalatine part is associated with the deep face and the nasal region.

The mandibular division of the maxillary artery has 5 branches, all entering a canal:

• The middle meningeal artery is the principal artery to periosteal dura of the cranial cavity.
• The inferior alveolar artery runs into the mandibular foramen and supplies the teeth and the mandible. The angle of the mandible is poorly supplied and may suffer from alveolar osteitis (dry socket).
• The deep auricular artery supplies the auditory meatus
• The anterior tympanic artery accompanies the chorda tympani through the petrotympanic fissure to reach the middle ear.
• The accessory meningeal branch (inconsistent) enters the foramen ovale and supplies the trigeminal ganglion and the surrounding dura.

The pterygoid portion of the maxillary artery has 5 branches supplying muscles of mastication in the infratemporal fossa:

• 2 deep temporal branches,
• a masseteric branch,
• a pterygoid branch,
• and a buccal branch.

The pterygoid plexus of veins (Clemente plate 477; Grant p. 613; Netter 3e 66, 4e 70) follows the maxillary artery in the infratemporal fossa, lying mostly lateral to the artery.

• This is a route for infection: the veins have connections with the cavernous sinus via the deep facial, inferior ophthalmic and emissary veins in the sphenoid bone.
• Veins of the head have NO valves.

Branches of V3 (Mandibular division of the trigeminal nerve)

I. Anterior division (Clemente plates 478, 479; Grant p. 667-669, 671; Netter 3e 42, 67, 4e 46, 71):

• Masseteric branches
• Posterior and anterior temporal branches to the temporalis muscle
• The nerve to the medial pterygoid
• The nerve to the lateral pterygoid
• The buccal nerve

The buccal nerve of V3 :

• passes between the 2 heads of the lateral pterygoid muscle.
• continues into the cheek on the lateral surface of the buccinator muscle.
• is the terminal branch of the anterior division
• is sensory to the mucosa of the inside of the cheek and the lower gums around the molar teeth.
• does not supply the motor innervation of the buccinator.

II. Posterior division:

Auriculotemporal nerve:

• leaves V3 just inferior to the foramen ovale and projects posteriorly in the infratemporal fossa parallel to the roof.
• The initial segment encircles the middle meningeal artery as the artery ascends to enter the foramen spinosum and receives postganglionic parasympathetic fibers from the otic ganglion which are secretomotor to the parotid gland.
• Passes medial to the head of the mandibular condyle and sends a sensory branch to the TMJ.
• Enters the deep portion of the parotid gland giving sensory branches as well as parasympathetic postganglionic fibers from the otic ganglion.
• Its terminal portion accompanies the superficial temporal artery and innervates the upper half of pinna of the ear and part of the temporal region (Pain and general sensation).

Inferior alveolar (dental) nerve (Clemente plate 542 fig. 866; Grant p. 828-829; Netter 3e 67, 4e 71)

• From the foramen ovale to the mandibular foramen on the medial aspect of the ramus of the mandible, lying between the medial and lateral pterygoid muscles and just posterior to the lingual nerve (Clemente plate 478; Grant p. 669, 671; Netter 3e 67, 4e 71).
• The branch to mylohyoid and to the anterior belly of the digastric is the only branch in the infratemporal fossa. It first lies in the mylohyoid groove, and then on the inferior aspect of the mylohyoid to reach the anterior belly of the digastric muscle (Clemente plate 479; Grant p. 681; Netter 3e 67, 4e 71).
• The portion of the inferior alveolar nerve in the ramus of the mandible is entirely sensory to lower teeth, lower gums and the mucosa of the lower lips.
• It exits the mandible as the mental nerve (Clemente plate 542; Grant p. 630, 671; Netter 3e 67, 4e 71) to innervate the mucosa and gum adjacent to the lower lip.

Lingual nerve (Clemente plate 479; Grant p. 668-669; Netter 3e 67, 4e 71)

• lies anterior to the inferior alveolar nerve and remains medial to mandible.
• receives the chorda tympani in the infratemporal fossa. The chorda tympani reaches the infratemporal fossa via the petrotympanic fissure (Clemente plate 527 fig. 835, plate 565 fig. 919; Grant p. 625; Netter 3e 42, 4e 46). The chorda tympani contains preganglionic parasympathetic secretomotor fibers of VII from the tympanic plexus and special sensory fibers for taste from the anterior 2/3 of the tongue. The taste fibers have their cell bodies in the geniculate ganglion of VII.
• Terminal distribution of the lingual nerve and associated fibers which mediate general sensation (pain, touch temperature and pressure) is to the floor of the mouth and the anterior 2/3 of the tongue.

Mandibular block technique:

• Injection of anesthetic is performed in the fascial compartment defined by the fascial covering of the medial pterygoid and the medial aspect of the ramus of the mandible (Clemente plate 477; Grant p. 678; Netter 3e 51, 4e 55).
• The anesthetic diffuses to the lingual and inferior alveolar nerves.

Temporomandibular joint (TMJ; Clemente plate 473; Grant p. 674-675; Netter 3e 14, 4e 16)

• Head of mandible
• Mandibular fossa and articular tubercle of the temporal bone
• Synovial joint with intraarticular disc dividing joint into a lower compartment (hinge rotation for mandibular head) and upper compartment (sliding joint for protrusion).

Minor supportive elements of the TMJ:

• Lateral temporomandibular ligament (thickening of the joint capsule; Clemente plate 472; Grant p. 674-675; Netter 3e 14, 4e 16)
• Stylomandibular ligament (between parotid and submandibular glands;
• Sphenomandibular ligament

Major supportive elements of the TMJ: MUSCLES OF MASTICATION

Movements of the mandible:

• Elevation
• Depression
• Protrusion
• Retraction

updated 10/26/2008

INTRACRANIAL CAVITY AND MENINGES; CRANIAL NERVES

The cranial cavity is a rigid box containing brain, important blood vessels and CSF. It communicates with the vertebral canal through the foramen magnum (Clemente plate 498; Grant p. 642; Netter 3e 5, 4e 5) and with tissues outside the cranium via foramina. Because it is a rigid box, extensive bleeding or a growing tumor inside the cranium has little room for expansion and an early rise in intracranial pressure will occur.

Structure of intracranial blood vessels:

• To avoid collapse of the veins during a rise in pressure (systole), the veins have rigid walls composed of dura and are called venous sinuses (Clemente plates 488, 489; Grant p. 639; Netter 3e 100, 4e 102-104).
• Intracranial arteries have thin walls because when the arteries are distended during systole, the effect is counteracted by a rise in intracranial pressure. However, the arteries are prone to localized distension (aneurysm) and when the vessel breaks, this may lead to a fatal hemorrhage.

Meninges

• Dura mater (pachymeninx)
• Arachnoid
• The subarachnoid space continues through the foramen magnum, around the spinal cord.
• Pia mater (closely adherent to the brain)

*Arachnoid and pia mater are also called leptomeninges.

Dura mater:

2 layers (Clemente plate 486 fig. 765; Grant p. 636; Netter 3e 96, 4e 102):

• An outer fibrous layer
• and an inner serous layer, which parts from the fibrous layer to form the venous sinuses.

The dura is supplied by small arteries and the middle meningeal artery (Clemente plate 487; Grant p. 635; Netter 3e 95, 4e 100). The vein runs with the artery.

Intracranial partitions of the dura mater:

• The falx cerebri (Clemente plate 488; Grant p. 638; Netter 3e 97, 4e 103) with the superior sagittal sinus, starts at the crista galli.
• The tentorium cerebelli incompletely roofs over the posterior cranial fossa.
• At this level, the midbrain runs superiorly through the opening to join with the diencephalon (Grant p. 640; Netter 3e 98, 100, 4e 104, 106). The sharp edges of dura may have fatal consequences when the brain is displaced by force or a space-occupying lesion.

The flow of the cerebrospinal fluid in the venous sinuses is from the superior sagittal sinus to the right transverse sinus to the sigmoid sinus to the internal jugular vein (Clemente plates 488, 489; Grant p. 639; Netter 3e 97, 98, 4e 103-104 ).

The arachnoid villi drain CSF from the subarachnoid space to the venous sinuses. With age, the arachnoid villi become clumped together to form the arachnoid granulations (Clemente plate 486 fig. 765, plate 487; Grant p. 637; Netter 3e 94 - 96, 4e 100, 102).

The inferior sagittal sinus is in the free edge of the falx cerebri and receives part of the drainage of the great cerebral vein (of Galen) and becomes the straight sinus (Grant p. 639; Netter 3e 97, 4e 103-104). This passes to the left and forms the left transverse sinus, left sigmoid sinus and left internal jugular vein.

*Because the flow from the larger superior sagittal sinus tends to go to the right transverse sinus, the right jugular foramen is usually bigger than the left (Clemente plate 498; Grant p. 615; Netter 3e 7, 4e 104). But, at other times, the ends of the superior sagittal sinus and the straight sinus join together to form the confluence of the sinuses and the jugular foramina will be even in size.

The cavernous sinuses, are found on either side of the sella turcica (pituitary gland; Clemente plates 489, 494; Grant p. 639; Netter 3e 98, 4e 104):

• Anteriorly, the superior and inferior opthalmic veins open into them.
• Posteriorly, minor venous sinuses (superior and inferior petrosal sinuses) also open into them. The inferior petrosal sinus communicates at its other end with the internal jugular vein at the jugular foramen.
• The cavernous sinuses are joined across the midline by intercavernous sinuses lying anterior and posterior to the pituitary gland. The pituitary fossa is roofed in by the diaphragma sellae through which runs the pituitary stalk (Clemente plate 492 fig. 773; Grant p. 640; Netter 3e 98, 4e 104). Superoanteriorly, lies the optic chiasma.
• Veins from the lower parts of the brain also drain into the cavernous sinuses.
• The cavernous sinus contains cranial nerves III, IV, V, and VI, and the internal carotid artery (Clemente plate 490 fig. 770; Grant p. 644; Netter 3e 98, 4e 104).

Blood supply of the brain

After passing through the cavernous sinus, the internal carotid artery turns superiorly (Clemente plate 458, plate 493; Grant p. 643-649; Netter 3e 130, 132, 133, 4e 136, 138, 140):

• it then gives out the opthalmic artery (which runs into the optic canal with the optic nerve),
• and terminates as the anterior and middle cerebral arteries and the posterior communicating artery.
• Before it breaks up into terminal branches, it gives out small branches to the pituitary gland and adjacent structures.

The vertebral artery (Grant 647; Netter 4e 138-139) goes through the foramen magnum and gives off:

• the anterior spinal artery
• the posterior spinal artery,
• the posterior inferior cerebellar artery
• and finally joins with the opposite artery to form the basilar artery.

The basilar artery lies ventral to the pons of the brainstem, on the clivus. The basilar artery sends out :

• branches to the brainstem,
• the anterior inferior cerebellar artery
• and terminates as the superior cerebellar and posterior cerebral arteries.

Terminal branches of the internal carotid and the vertebral arteries form the circle of Willis.

Cranial nerves within the cranium

The cranial nerves all leave the brain on its ventral surface except for the IVth cranial (trochlear) nerves (Clemente plate 495; Grant p. 642, 644; Netter 3e 112 4e 114-115).

Ist cranial (olfactory) nerve: The cell bodies from the olfactory epithelium lie in the olfactory mucosa and their axons travel upwards to reach the olfactory bulb through the cribrifrom plate (Clemente plate 524 fig. 830; Grant p. 813, 818; Netter 3e 113, 4e 119).

IInd cranial (optic) nerves (Clemente plate 495; Grant p. 819-820; Netter 3e 114, 4e 120) develop as optic stalks which are prolongations of the brain, surrounded by the meninges: The cerebrospinal fluid may extend as far as the back of the eyeball (Grant p. 647; Netter 83, 4e 87) and rise in intracranial pressure will affect the optic nerve and the optic disk (Clemente plate 520 fig. 822; Grant p. 651; Netter 3e 86, 4e 90).

• Nerve fibers of the optic nerve will not regenerate if cut.
• Optic nerves leave the eyeballs posteriorly, enter the cranium through the optic canal and form the optic chiasma.

Note (Grant p. 820; Netter 3e 114, 4e 120):

• the pattern of nerve fibers in the optic nerve, chiasma and optic tract.
• The difference between blindness, bitemporal hemianopia and homonymous hemianopia.

IIIrd, IVth and VIth cranial nerves innervate the muscles of the eyeball (LR6, SO4)3 (Clemente plate 510-512; Grant p. 821; Netter 3e 115, 4e 121)

• VIth cranial (abducens) nerve for the abductor muscle.
• IVth (trochlear) nerve for the superior oblique muscle.
• IIIrd cranial (oculomotor) nerve for all other muscles including the levator palpebrae superioris.

The IIIrd cranial nerve:

• passes between the superior cerebellar and posterior cerebral arteries (Clemente plate 493; Grant p. 644, 646; Netter 3e 136, 4e 143)
• pierces the dura posterior to the clinoid process
• travels high up in the lateral wall of the cavernous sinus (Clemente plate 490 fig. 770, plate 492 fig. 773; Grant p. 644; Netter 3e 98, 4e 104)
• enters the orbit via the superior orbital fissure
• divides into upper and lower branches (Clemente plates 511, 513; Grant p. 822-823; Netter 3e 115, 4e 121).

The IVth cranial nerve

• passes around the midbrain from its dorsal aspect (Clemente plate 495; Grant p. 644; Netter 3e 108, 4e 114),
• pierces the dura posterior to the IIIrd cranial nerve (Clemente plate 492 fig. 773; Grant p. 644; Netter 3e 98, 4e 104),
• lies in the lateral wall of the cavernous sinus below the IIIrd cranial nerve (Clemente plate 490 fig. 770; Grant p. 644; Netter 3e 98, 4e 104).
• However, the IVth cranial nerve enters the superior portion of the orbital fissure to reach the upper border of the superior oblique (Clemente plate 510; Grant p. 821; Netter 3e 98, 4e 86).

The VIth cranial nerve

• leaves the brain at the lower border of the pons in the posterior cranial fossa (Clemente plate 495; Grant p. 646, 812-813; Netter 3e 108, 115, 4e 104).
• pierces the dura on the clivus,
• runs over the ridge of the petrous portion of the temporal bone
• enters the cavernous sinus (Clemente plate 490; Grant p. 644; Netter 3e 98, 4e 104).
• It lies lateral to the internal carotid artery before entering the orbit via the lower part of the superior orbital fissure (Clemente plate 513; Grant p. 821; Netter 3e 115, 4e 83, 121).

The Vth cranial (trigeminal) nerve (Clemente plate 514; Grant p. 644-645, 824-829; Netter 3e 116, 4e 122)

• starts in the posterior cranial fossa,
• crosses the petrous temporal bone, carrying with it a diverticulum of dura (cavum trigeminale or Meckel's cave) from the posterior cranial fossa,
• enlarges to form the ganglion in the middle cranial fossa over the roof of the carotid canal.

Anteriorly, its 3 branches (ophthalmic, maxillary and mandibular) pierce the dura in the cavernous sinus.

• The ophthalmic division pierces the dura and enters the orbit via the superior orbital fissure and divides into frontal, lacrimal and nasociliary divisions (Clemente plates 510, 512; Grant p. 825; Netter 3e 81, 4e 86).
• The maxillary nerve leaves the cranium via the foramen rotundum (Clemente plate 510; Grant p. 826; Netter 3e 98, 4e 122).
• The mandibular nerve leaves the cranium via the foramen ovale accompanied by the lesser petrosal nerve (Clemente plate 511; Grant p. 828-829; Netter 3e 41, 4e 46).

The VIIth cranial (facial) nerve and the VIIIth cranial (vestibulocochlear) nerve run into the internal auditory meatus (Clemente plate 494; Grant p. 642, 813; Netter 3e 98, 4e 104). Parasympathetic fibers which will form the chorda tympani and the greater petrosal nerve travel in the nervus intermedius lying between VII and VIII (Clemente plate 574; Grant p. 813; Netter 3e 98, 118, 4e 104, 123).

The VIIIth cranial (vestibulocochlear) nerve enters the internal auditory meatus and divides into vestibular and cochlear branches (Grant 832; Netter 124).

The IXth cranial (glossopharyngeal) nerve arises from the medulla of the brain and immediately enters the jugular foramen to exit the cranium (Clemente plates 494, 495; Grant p. 642; Netter 98, 119, 125).

The Xth cranial (vagus) nerve passes through the jugular foramen accompanied by the cranial portion of the XIth cranial nerve.

The XIth cranial (accessory) nerve:

• The spinal portion arises from the side of the upper 5 segments of the spinal cord and enters the cranium via the foramen magnum.
• It joins with the cranial portion and X to pass through the jugular foramen and immediately leaves to supply sternocleidomastoideus and trapezius.
• The cranial portion joins with X to be distributed with its branches.

The XIIth cranial (hypoglossal) nerve (Clemente plate 495; Grant p. 839; Netter 3e 122, 4e 128) is a purely motor nerve arising from the side of the medulla to pass through the hypoglossal (anterior condylar) canal (Clemente plate 494; Grant p. 813; Netter 3e 7, 4e 8, 104).

updated 11/03/2008

---

EYE AND ORBIT

Text:  Gross Anatomy, K. W. Chung, 6^th edition: pp. 375-387

Reference:  Clinically Oriented Anatomy, K.L. Moore, A.F. Dalley, 5^th edition: pp. 957-977

Dissector:

Clemente’s Anatomy Dissector, 2nd edition:  pp. 366-379

Grant’s Dissector, P.W. Tank, 14^th edition:  pp. 227-233

Bony landmarks:

• The margin of the orbit is formed by the frontal, zygomatic and maxillary bones (Clemente plate 480; Grant p. 650; Netter 2).
• The medial wall of the orbit is formed by the lacrimal and ethmoid bones.
• The lateral wall of the orbit is formed by the zygomatic bone.
• The floor of the orbit is formed by the maxillary bone
• The roof of the orbit is formed by the orbital plate of the frontal bone.
• Deep in the orbit, the greater and lesser wings of the sphenoid bone are separated by the superior orbital fissure.
• The inferior orbital fissure is a gap between the maxillary bone and the greater wing of the sphenoid bone.
• The optic canal lies in the root of the lesser wing of the sphenoid bone.

The medial walls of the orbit are parallel, whereas the lateral walls diverge (Clemente plate 509 fig. 802; Grant p. 652-653; Netter 3e 79, 4e 83): the long axis of the orbit is at an angle to the long axis of the eyeball.

The fibromuscular cone:

• Except for the inferior oblique muscle, all the muscles of the eyeball originate from or near a fibrous ring that includes the lower part of the inferior orbital fissure and the optic canal (Clemente plate 517 fig. 815; Grant p. 656; Netter 3e 79, 4e 83-84).
• From the fibrous ring, the muscles spread out to attach around the periphery of the eyeball (Clemente plate 516; Grant p. 658; Netter 3e 80, 4e 84).
• A fascial sheath is continuous around and between the muscles, forming a fibromuscular cone.
• The interior of the cone is filled with fat and contains the optic nerve (Clemente plate 517 fig. 816; Grant p. 655; Netter 3e 79, 4e 83).

The levator palpebrae superioris muscle (Clemente plate 509 fig. 801; Grant p. 654-655; Netter 3e 77, 80, 4e 84):

• Superior to the cone, outside of it, lies the levator palpebrae superioris muscle attaching anteriorly to the upper eyelid.
• From the back of the orbit, above the fibrous ring, it lies under the roof of the orbit.
• It is supplied both by the IIIrd cranial nerve and sympathetic nerves (loss of either innervation will lead to ptosis).

Muscles of the eyeball (Clemente plate 516; Grant p. 658-659; Netter 3e 80, 4e 84):

The lateral rectus (LR) on the lateral wall of the orbit, is an abductor (Clemente plate 515 fig. 809; Grant p. 653; Netter 3e 79, 4e 84) and turns the pupil laterally.

The medial rectus (MR) lies along the medial wall of the orbit and turns the pupil medially. Left and right medial recti muscles contract simultaneously to cause convergence of the gaze (for focusing on a near object).

The superior rectus (SR) turns the pupil superiorly and medially (Clemente plate 514 fig. 808; Grant p. 659; Netter 3e 80, 4e 84).

The inferior rectus (IR) turns the pupil inferiorly and medially.

The superior oblique (SO) runs along the medial wall to reach the trochlea (Clemente plate 515 fig. 810; Grant p. 657; Netter 3e 81, 4e 84). It then loops posteriorly through a fascial sling before being attached to the eyeball. Its action are incyclotorsion (primary), depression (secondary) and abduction (tertiary).

The inferior oblique (IO) arises from the floor of the orbit and travels laterally below the eyeball, attaching to the eyeball laterally (Clemente plate 515 fig. 810; Grant p. 654, 656; Netter 3e 80, 4e 84). Its actions are excyclotorsion (primary), elevation (secondary) and abduction (tertiary).

The secondary actions of the superior and inferior oblique muscles are best demonstrated with the eye adducted.

Movements of the eyeball:

• Looking straight up: SR and IO
• Looking straight down: IR and SO
• Looking left: left LR and right MR

The movements of the eyeball are finely coordinated and may be easily disturbed (influence of alcohol).

BLOOD VESSELS

The ophthalmic artery arises from the internal carotid artery (Clemente plate 513; Grant p. 657; Netter 3e 81, 4e 85).

The ophthalmic artery gives out the central artery of the retina which:

• is an end artery.
• enters the optic nerve
• travels near its center towards the eyeball (Clemente plate 520, plate 521 fig. 824; Grant p. 657, 660-661; Netter 3e 83, 4e 90).
• divides within the eye into superior temporal and inferior temporal branches. These in turn give rise to nasal (medial) and temporal (lateral) branches accompanied by corresponding veins. These can be observed with an ophthalmoscope (Clemente plate 520 fig. 822; Grant p. 661; Netter 3e 86, 4e 90).

In the orbit, the ophthalmic artery crosses to the medial side, above the optic nerve (Clemente plate 512, 513; Grant p. 657; Netter 3e 81, 4e 85). It then travels anteriorly along the medial wall of the orbit and ends by dividing into dorsal nasal and supratrochlear arteries, emerging onto the face .

Other branches of the ophthalmic artery in the orbit are:

• The lacrimal artery, which follows the lateral wall of the orbit, supplies the lacrimal gland and ends on the face by supplying the eyelids.
• The long (2) and short (many) posterior ciliary arteries (Clemente plate 518 fig. 817; Grant p. 661; Netter 3e 86, 4e 91) which enter the eyeball to supply the choroid.
  • The short arteries supply the back of the eyeball.
  • The long arteries enter the back of the eyeball but will break up into branches only at the corneoscleral junction.
  • The long and/or short posterior ciliary arteries may give out an anterior ciliary artery to the front of the eyeball.
• The supraorbital artery lies below the roof of the orbit and runs out superiorly to supply the scalp (Clemente plate 512, plates 504-505; Grant p. 632, 652, 657; Netter 3e 19, 81, 4e 85).
• The anterior and posterior ethmoidal arteries enter canals in the ethmoid bone to supply the ethmoidal air cells and the posterior ethmoidal artery continues into the nasal cavity.

Veins accompany all the arteries but they drain into the superior and inferior ophthalmic veins (Clemente plates 475, 494; plate 514 fig. 807; Grant p. 656; Netter 3e 81, 4e 85), which communicate with the cavernous sinus and the pterygoid plexus of veins.

NERVES

Motor innervation

The IVth cranial nerve enters the orbit above the fibrous ring (Clemente plate 510; Grant p. 656; Netter 3e 79, 4e 83) and therefore lies outside of the muscular cone, crosses to the medial side and enters the upper border of the superior oblique muscle (Clemente plate 511; Grant p. 652-653; Netter 3e 82, 4e 86).

The VIth cranial nerve enters within the fibrous ring (Clemente plates 510-513; Grant p. 656; Netter 3e 79, 4e 85) and immediately turns laterally to enter the lateral rectus.

The IIIrd cranial nerve divides into 2 divisions lying above and below the nasociliary nerve within the cone:

• The superior branch travels upward to reach the superior rectus and the levator palpebrae superioris muscles (Clemente plate 511; Grant p. 822; Netter 3e 115, 4e 121).
• The inferior branch (Clemente plate 513; Grant p. 822; Netter 3e 115, 4e 121) breaks up to supply the medial rectus, the inferior rectus and the inferior oblique muscles.
  • The nerve to the inferior oblique carries parasympathetic fibers from the Edinger-Westphal nucleus in the midbrain. They travel in a branch to the ciliary ganglion where they synapse. The short ciliary nerves travel to the back of the eyeball. They supply the ciliaris muscle and the sphincter pupillae (Grant p. 650, 805; Clemente plate 823; Netter 3e 82, 83-85, 4e 86, 121).

Sensory innervation

Sensory nerves are all branches of the ophthalmic division of the trigeminal (Vth cranial) nerve: the frontal and lacrimal nerves enter the orbit above the fibrous ring and the nasociliary within it.

The frontal nerve (Clemente plate 510; Grant p. 652; Netter 3e 82, 4e 86) is directly below the roof of the orbit, lying on the levator palpebrae superioris. It divides into the supraorbital and supratrochlear nerves leaving the orbit at its upper border and supplies the scalp (Clemente plates 504-505; Grant p. 634; Netter 3e 20, 4e 24).

The lacrimal nerve travels along the lateral wall of the orbit to supply the skin of the eyelids (Clemente plate 507 fig. 797; Grant p. 652-653; Netter 3e 82, 4e 86) and it also carries parasympathetic secretomotor fibers to the lacrimal gland (Clemente plate 507 fig. 797; Grant p. 825; Netter 3e 116, 4e 122).

The nasociliary nerve has similar branches to the ophthalmic artery, except that:

• short ciliary nerves are derived from the ciliary ganglion, not the nasociliary nerve
• and the lacrimal nerve is a separate branch from the ophthalmic division.

The nasociliary nerve gives off 2 long ciliary nerves entering the back of the eyeball, which carry sympathetic fibers to the dilator pupillae (Clemente plate 512; Grant p. 823; Netter 3e 82, 4e 121) and sensory fibers to the cornea (Grant p. 823). Along the medial wall of the orbit, the nasociliary nerve gives out a posterior ethmoidal nerve and ends by turning into the anterior ethmoidal nerve, giving off a small infratrochlear nerve (Clemente plate 513; Grant p. 653; Netter 3e 82, 4e 86).

updated 11/03/2008

NOSE, NASAL CAVITIES AND PARANASAL SINUSES

Cutaneous innervation

• The nerve supply to the skin of the nose is by V1 (infratrochlear nerve) and V2 (infraorbital nerve; Clemente plate 504; Grant p. 630; Netter 3e 20, 4e 24).
• The innervation of the tip of the nose is by the external nasal nerve, an anterior ethmoidal branch of the nasociliary nerve (V1) running from the root of the nose to the tip of the nose.

Loss of sensation to the tip of the nose may be due to an intracranial, intraorbital or ethmoidal air sinus disorder affecting V1 pathway from the trigeminal ganglion.

Bony landmarks

• The paired nasal bones articulate with the frontal bone and frontal processes of the maxillary bones (Clemente plate 522 fig. 825; Grant p. 690; Netter 3e 32, 4e 36).
• The central septal cartilage connects with the superior lateral cartilages articulating with the nasal bones (Clemente plate 524 fig. 829; Grant p. 690; Netter 32, 4e 36).
• Alar cartilages are supported by the septal cartilage.

NASAL CAVITIES

• The nares (nostrils) open into the right and left nasal cavities separated by the septum.
• The choanae are the posterior apertures leading to the nasopharynx (Clemente plate 552; Grant p. 616, 790-791; Netter 3e 33, 4e 37).

Floor of nasal cavity:

• palatine processes of the maxilla
• and horizontal plates of the palatine bone.

Roof of nasal cavity is composed of (Clemente plate 523; Grant p. 691; Netter 3e 34-35, 4e 38-39):

• Anterior part: slope of the nasal bones
• Intermediate part: cribriform plate of ethmoid bone
• Posterior part: anterior and inferior aspects of the body of the sphenoid bone.

Nasal septum (Clemente plate 524 fig. 829; Grant p. 691; Netter 3e 35, 4e 39):

• The perpendicular plate of the ethmoid bone and the vomer bone may articulate with each other posteriorly.
• The septal cartilage intervenes between bony elements of the septum, forming support for the midline ridge of the nose, tip and columella (between nares from tip of the nose to anterior nasal spine of the maxilla).
• Deviation of the nasal septum is most frequent between the vomer and the septal cartilage.

Lateral wall (Clemente plate 525; Grant p. 691; Netter 3e 34, 4e 38)

• Superior, middle and inferior nasal conchae and their corresponding meatuses.
• Sphenoethmoid recess lies superior to the superior concha.
• Vestibule, just inside each naris, is lined by skin.
• Atrium, inferior to nasal bones, is lined by mucoperiosteum.

The inferior concha

• is a separate bone articulating with maxilla, lacrimal and palatine bones on the lateral wall of the nasal cavity (Clemente plate 523; Grant p. 691; Netter 3e 34, 4e 38).
• Its meatus contains the opening of the nasolacrimal duct draining tears from medial aspect of the orbit into the nasal cavity (Clemente plate 507 fig. 798; Grant p. 695; Netter 3e 34, 78, 4e 37-38, 82 ).

The posterior extent of the nasal cavity is adjacent to the opening of the auditory tube in the nasopharynx (Clemente plate 525; Grant p. 695; Netter 3e 33, 4e 37).

The middle concha is a process of the ethmoid bone (Clemente plate 523; Grant p. 691; Netter 3e 33, 4e 38) and it overlies the middle meatus.

Paranasal air sinuses open into this meatus: the hiatus semilunaris (Clemente plate 522 fig. 826; Grant p. 695; Netter 3e 33, 4e 37) opens on the wall of the middle meatus between the unciform process of the ethmoid bone and the ethmoid bulla.

• Frontal sinus drains into the superior aspect of the hiatus semilunaris (Clemente plate 522 fig. 826; Grant p. 695; Netter 3e 33, 4e 37).
• Anterior and middle ethmoidal air sinuses drain through openings of the ethmoidal bulla on superoposterior aspect of the hiatus semilunaris.
• Maxillary air sinus has its ostium directly inferior to the ethmoid bulla within the hiatus semilunaris.

The superior concha is also a process of the ethmoid bone (Clemente plate 523; Grant p. 691; Netter 3e 34, 4e 38).

• It overlies the superior meatus receiving the opening of the posterior ethmoidal air cells (Clemente plate 525 fig. 832; Grant p. 695; Netter 3e 32, 33, 4e 38).

Superior to the superior concha is the spheno-ethmoidal recess where the sphenoid air cells drain into nasal cavity.

NERVE SUPPLY TO THE NASAL CAVITY

The mucosa of upper nasal cavity is innervated by the olfactory (I) and trigeminal (V1; anterior ethmoidal) nerves (Clemente plate 524 fig. 830; Grant p. 692; Netter 3e 38-39, 4e 42-43).

The anterior ethmoidal nerve carries general sensation (pain, temperature, touch and pressure).

Most of the general sensation of the lateral wall and nasal septum is mediated by V2, which is associated with the pterygopalatine ganglion (Clemente plate 526; Grant p. 692; Netter 3e 39, 4e 43).

• The pterygopalatine ganglion receives the preganglionic parasympathetic fibers of the superficial (greater) petrosal nerve (VII; Clemente plate 527; Grant p. 692, 700, 831; Netter 3e 39, 117, 4e 43, 123).
• The postganglionic parasympathetic neurons send secretomotor fibers to glands above the floor of the mouth.

Terminal branches of the infraorbital nerve (Grant p. 692; Netter 3e 38, 4e 42) also enter the vestibule of the nose from the skin covering the nares.

A small branch from the anterior superior alveolar nerve also innervates the anterior nasal mucosa of the inferior meatus (Grant p. 692; Netter 3e 38, 4e 42).

The mucosa on the lateral wall of the nose is innervated by branches of the descending greater palatine nerve from the inferior pole of the pterygopalatine ganglion.

Superior and inferior posterior lateral nasal nerves run in the mucoperiosteum covering the conchae and the meatus.

The nasal septum mucosa is innervated by the nasopalatine nerve (Clemente plate 524 fig. 830; Grant p. 692; Netter 3e 39, 4e 43).

• It enters the nasal cavity from the pterygopalatine fossa through the sphenopalatine foramen
• and descends on the median nasal septum.
• The terminal branch leaves the nasal cavity via the incisive foramen (Clemente plate 524 fig. 830; Grant p. 692; Netter 3e 39, 4e 43).

The sympathetic innervation of the nasal cavities comes from the superior cervical ganglion. These postganglionic fibers reach the nose via the nerve of the internal carotid artery (Clemente plate 527; Grant p. 701; Netter 3e 40, 4e 44) and the deep petrosal nerve of the pterygoid canal. In the pterygopalatine fossa, they join with terminal branches of the maxillary artery and are vasomotor to blood vessels in the nasal cavity and palate.

BLOOD SUPPLY OF THE NASAL CAVITY

The sphenopalatine artery

• arises from the maxillary artery in the pterygopalatine fossa (Clemente plate 526; Grant p. 693; Netter 3e 36-37, 4e 40-41).
• It enters the nasal cavity with the nasopalatine nerve and supplies upper 2/3 of the nasal septum.
• It then anastomoses with the greater palatine artery ascending through the incisive foramen.

The site of anastomosis is a frequent area of hemorrhage (epistaxis or nosebleed).

The lateral walls of the nasal cavity are supplied by blood vessels accompanying the terminal branches of the anterior ethmoidal nerve and the greater palatine nerve and they have the same name (Clemente plate 526; Grant p. 693; Netter 3e 37, 4e 41).

The venous drainage of the nose parallels the arterial supply and forms a network overlying the inferior and middle conchae.

The erectile tissue overlying the conchae humidifies and warms the inspired air in the upper respiratory passage.

PARANASAL AIR SINUSES

• The sphenoid (Clemente plate 522 fig. 826; Grant p. 694; Netter 3e 44, 4e 48-49), ethmoid (Clemente plate 528; Grant p. 696; Netter 3e 44-45, 4e 48-49), frontal (Clemente plate 529; Grant p. 696; Netter 3e 44, 4e 48-49) and maxillary are paired but asymmetrical.
• They are lined with respiratory epithelium which becomes converted to stratified squamous epithelium with chronic respiratory irritation. This may lead to chronic sinusitis.

Sinus drainage

Sphenoid air sinuses drain into the sphenoethmoidal recess (Clemente plate 525 fig. 832; Grant p. 696; Netter 3e 45, 4e 37). A surgical approach to the pituitary may be done through these air sinuses and the nasal cavities.

Ethmoidal air sinuses (anterior, middle and posterior).

• Anterior and middle drain into middle meatus by openings of the ethmoidal bulla (Clemente plate 522 fig. 826; Grant p. 695; Netter 3e 34, 4e 37).
• Posterior ethmoidal air cells drain into the superior meatus.

Frontal sinus drains via the infundibulum into the superior extension of the hiatus semilunaris (Clemente plate 525 fig. 832; Grant p. 695; Netter 3e 45, 4e 37).

Maxillary sinus drains into the middle meatus through the hiatus semilunaris. The air sinus has a floor at the level of the hard palate (Clemente plate 529; Grant p. 698; Netter 3e 45, 4e 49) and since the ostium is more superiorly located (Clemente plate 525 fig. 832; Grant p. 696, 698; Netter 3e 45, 4e 49), there is often drainage problems. The nerve supply is by the posterior and middle superior alveolar nerves (V2; Clemente plate 527 fig. 836; Grant p. 700; Netter 3e 41, 4e 45).

Mastoid air sinuses (Clemente plate 527 fig. 836; Grant p. 710; Netter 3e 89, 4e 94) drain into the nasal cavity via the middle ear and auditory tube.

updated 11/09/2008

THE ORAL CAVITY AND CONTENTS

The VESTIBULE

• is bounded by lips and cheeks,
• is lined with non-keratinized stratified squamous epithelium.
• the parotid papilla is in the superior vestibule, opposite the 2nd upper molar tooth (Netter 3e 47, 4e 51).
• is vascularized by the superior and inferior labial arteries from the facial artery (Clemente plate 474; Grant p. 632; Netter 3e 32, 4e 36) . These arteries anastomose freely with their contralateral counterparts. Because of these profuse anastomoses, lip bleeding is controlled by grasping the injured lip between the fingers to stop the blood flow.

Nerve supply of the vestibule:

• The orbicularis oris and buccinator muscles are innervated by cranial nerve VII (facial nerve; Clemente plate 469; Grant p. 629; Netter 3e 21, 4e 25).
• The skin and mucosa of the upper lip, cheek and vestibule are innervated by the anterior, middle and posterior superior alveolar nerves from V2 (Clemente plate 527; Grant p. 700; Netter 3e 42, 4e 45).
• The skin and mucosa of lower lip and adjacent anterior vestibule are innervated by the mental nerve (V₃; Clemente plate 476; Grant p. 630-631, 671; Netter 3e 42, 4e 46).
• The mucosa of the inferior vestibule adjacent to the cheek is innervated by the long buccal (buccinator; Grant p. 630, 668; Netter 4e 46) nerve from the anterior division of V₃.

ORAL CAVITY

• The roof is formed by the hard and soft palates with the midline uvula (Clemente plate 530 fig. 843; Grant p. 682; Netter 3e 48, 52; 4e 51).
• The posterior border is formed by the pillars of the fauces (Clemente plate 530; Grant p. 676; Netter 3e 54, 4e 51, 58)
• The floor is formed by the tongue divided into anterior 2/3 and posterior 1/3 by the palatoglossal arch, the V-shaped sulcus terminalis and circumvallate papillae (lying anterior to the sulcus; Clemente plate 539; Grant p. 676; Netter 3e 54, 4e 58).
• The lingual frenulum (Clemente plate 532 fig. 847; Grant p. 680; Netter 3e 47, 4e 51) is found on the undersurface of the tongue with openings of the ducts of the submandibular gland (Clemente plate 533 fig. 850; Grant p. 680; Netter 3e 47, 4e 51).

In examination of the tongue, grasp the tip of tongue with gauze and pull the tongue out of the mouth. Examine the lateral aspects of the anterior 2/3 of the tongue. This is a common site for cancer of the tongue.

FLOOR OF THE MOUTH (SUBLINGUAL REGION)

The sublingual gland (Clemente plate 532 fig. 847, plate 543; Grant p. 680-681; Netter 3e 57, 4e 61):

• lies on the lingual aspect of the body of the mandible, deep to the plica sublingualis (sublingual fold), which is the posterolateral continuation of the lingual frenulum.
• It has a row of 15 or 16 ("middle-teens") ducts that empty into the floor of the mouth on the plica sublingualis.
• The duct of the submandibular gland and the lingual nerve lie on the medial surface of the sublingual gland.
• The mylohyoid muscle lies inferior to the sublingual gland.
• The sublingual gland is innervated by postganglionic parasympathetic fibers reaching the gland via its sensory nerve, the lingual nerve (V₃). Preganglionic parasympathetic fibers run with the chorda tympani (VII) synapsing in the submandibular ganglion (Clemente plate 479; Grant p. 831; Netter 3e 41, 4e 46).

The lingual nerve

• provides the general sensory (pain, touch and temperature) modality to the anterior 2/3 of the tongue and the floor of the mouth (Clemente plate 532 fig. 848; Grant p. 680-681, 829; Netter 3e 55, 4e 59).
• also carries chorda tympani which has special taste fibers and secretomotor fibers of VII.
• enters the floor of the mouth on the medial mandible next to the 3rd molar tooth (Clemente plate 533 fig. 850; Grant p. 680-681; Netter 3e 42, 4e 46). It is thus vulnerable in extraction of the wisdom teeth.
• Preganglionic parasympathetic fibers leave the lingual nerve to synapse in the submandibular ganglion (Clemente plate 535 fig. 855; Grant p. 680, 840; Netter 3e 42, 4e 133). Postganglionic parasympathetic fibers rejoin the lingual nerve to reach the sublingual salivary gland. The submandibular ganglion is thus suspended from the main trunk of the lingual nerve.

The lingual nerve is:

• superior to the mylohyoid muscle in the floor of the mouth (Clemente plate 479; Grant p. 681; Netter 3e 42, 4e 46).
• lateral to the submandibular duct (Clemente plate 479; Grant p. 680-681, 780; Netter 3e 42, 4e 46),
• and medial to the sublingual gland (Clemente plate 479; Grant p. 680; Netter 3e 56, 4e 60).
• Subsequently, it passes inferior and then medial to the submandibular duct to ascend into the body of the tongue (Clemente plate 533 fig. 850; Grant p. 680-681; Netter 3e 55, 4e 59).

The chorda tympani provides taste fibers which supply the anterior 2/3 of the tongue. The cell bodies are in the geniculate ganglion in the middle ear (Clemente plate 573; Grant p. 709, 831; Netter 3e 117, 4e 135).

The hypoglossal nerve enters the floor of the mouth on the lateral aspect of the hyoglossus muscle, above the hyoid bone and the mylohyoid muscle (Clemente plate 535 fig. 855; Grant p. 681, 780; Netter 3e 55, 4e 59). Cranial nerve XII lies inferior to the lingual nerve and is purely motor to the muscles of the tongue.

Test cranial nerve XII by protrusion of the tongue. Deviation is toward the side of the lesion.

The tongue

• allows for mastication, swallowing, speech and taste.
• The anterior 2/3 (body or oral part) is derived from the ectodermal stomodeum.
• The posterior 1/3 (pharyngeal part or root) is derived from the endodermal foregut.
• These 2 parts are separated by the sulcus terminalis posterior to the circumvallate papillae (Clemente plate 539; Grant p. 676; Netter 3e 52, 4e 58).
• The sulcus terminalis is oriented posteriorly and the foramen cecum can be found at the tip of the V-shaped sulcus terminalis. This is the point of origin of the thyroid gland.
• Lingual tonsils are located posterior to the sulcus terminalis.

Mucous membrane of the tongue:

• The papillae (filiform, fungiform, circumvallate and foliate) are innervated by cranial nerve VII via the chorda tympani (anterior 2/3) and by IX (posterior 1/3; (Clemente plate 539; Grant p. 676; Netter 3e 54, 4e 58).
• The taste buds in the epiglottis and the pharyngeal walls are innervated by X.
• The taste buds in the palate are innervated by cranial nerve VII via the greater petrosal nerve. Branches from the latter are distributed by the greater and lesser palatine nerves (Clemente plate 532 fig. 849; Grant p. 683, 831; Netter 3e 48, 4e 52).

Muscles of the tongue

1) The 3 extrinsic muscles of the tongue change the position of the tongue.

• The genioglossus attaches to the superior genial tubercles and protrudes the tongue (Clemente plate 540; Grant p. 679-680; Netter 3e 59; 4e 63).
• The hyoglossus depresses the tongue.
• and the styloglossus retracts the tongue.

2) The intrinsic (longitudinal, transverse and vertical) muscles change the shape of the tongue.

The lingual artery:

• is a branch from the external carotid artery and supplies the tongue.
• courses anteriorly on the middle constrictor (Clemente plate 460 fig. 724; Grant p. 763, 781; Netter 3e 53, 4e 59, 69) parallel with cranial nerve XII.
• The hyoglossus muscle intervenes between cranial nerve XII (lateral) and the lingual artery (medial). The lingual artery is the only major structure medial to the hyoglossus muscle (Clemente plate 535 fig. 855; Grant p. 679-680, 780-781; Netter 3e 55, 4e 59).
• Dorsal lingual branches from the lingual artery are given to the dorsum of the tongue
• and deep lingual arteries are given to the body of the tongue.
• Other terminal branches supply the genioglossus muscle and the sublingual gland.
• Lymphatics follow arteries and drain to both right and left jugular lymphatic trunks of the neck (Clemente plate 455; Grant p. 676, 716; Netter 3e 68, 4e 73).

TEETH

In each adult jaw (Clemente plates 544, 545; Grant p. 685-689; Netter 3e 52-53, 4e 56-57):

• 4 incisors
• 2 canines
• 4 premolars
• 6 molars

Nerve supply of teeth and gums (Clemente plate 542 fig. 866; Grant p. 687; Netter 3e 41, 42, 4e 45-46):

V2 supply the teeth and gums of the maxillary arch.

• The molar teeth are supplied by the posterior superior alveolar nerve from the pterygopalatine fossa.
• The bicuspids (premolars) are innervated by the middle superior alveolar nerve from the infraorbital nerve.
• The canines and incisors are innervated by the anterior superior alveolar nerve from the infraorbital nerve
• The gums on the palatal surface are innervated by the nasopalatine nerve (incisors) and greater palatine nerve (bicuspids and molars; Clemente plate 527; Grant p. 683; Netter 3e 39, 4e 52).

V3 supplies teeth and gums of mandibular arch.

• The inferior alveolar (dental) nerve innervates all the teeth in the mandible.
• The gums of the molars and bicuspids are innervated by the long buccal nerve
• The gums of the incisors are innervated by the mental nerve.
• The lingual gums are innervated by the lingual nerve.

THE EAR AND THE TEMPORAL BONE

The EXTERNAL EAR

is formed by the:

• Auricle (Clemente plate 564; Grant p. 703; Netter 3e 87-88, 4e 92-93): is made of elastic cartilage and is continuous with the cartilage of the external acoustic meatus and the lobule (which is formed by loose connective tissue).
• External acoustic meatus (Clemente plate 566 fig. 921; Grant p. 703; Netter 3e 87, 4e 92)

The innervation of the skin of the ear:

• The superior portion is innervated by V₃ via the auriculotemporal nerve (Clemente plate 468; Grant p. 627, 703; Netter 3e 20, 4e 24);
• The inferior portion including lobule is innervated by fibers of the great auricular nerve from the cervical plexus (C 2, 3);
• The external acoustic meatus and the skin surrounding the opening (concha) are innervated by the vagus nerve (X) for general sensation (Clemente plate 468; Grant p. 703; Netter 3e 20, 4e 24).

Neurological examination of the skin of ear can determine the status of the upper spinal cord (great auricular nerve, C 2, 3), the medulla (vagus X) and the pons (trigeminal V).

The external acoustic meatus (Clemente plate 566 fig. 921; Grant p. 703, 705; Netter 3e 87, 4e 92):

• extends from the concha to the tympanic membrane.
• Lateral cartilaginous 1/3 (lined with hair, sebaceous glands and ceruminous glands)
• Medial bony 2/3 (thin stratified squamous epithelium, also lining external surface of tympanic membrane).
• The auricular branch of the vagus (X) provides the sensory innervation (Clemente plate 479; Grant p. 703; Netter 3e 20, 120, 4e 24, 126).

The MIDDLE EAR or TYMPANUM

Sound waves create vibrations on the tympanic membrane moving the 3 bony ossicles (malleus, incus and stapes) which in turn vibrate the oval window (fenestra vestibuli) on the medial wall of the middle ear: this is an amplification system (Clemente plate 566; Grant p. 704; Netter 3e 88, 4e 93, 95).

The middle ear is a modified bony sinus in the petrous portion of the temporal bone. It communicates with the mastoid air cells through the aditus to the mastoid antrum(Clemente plate 569; Grant p. 710, 713; Netter 3e 89, 4e 94) and with the nasopharynx through the auditory tube (pharyngotympanic tube; Clemente plate 566; Grant p. 704-705; Netter 3e 87, 4e 92, 94).

The tympanic cavity and its walls:

• The roof is a thin layer of petrous temporal bone (Clemente plate 566; Grant p. 708-709; Netter 3e 87, 4e 92) separating the middle cranial fossa from the middle ear.
  • The space below the roof is the epitympanic recess (Clemente plate 566; Grant p. 708; Netter 3e 88-89, 4e 92-93) for the articular joint of the head of the malleus and body of the incus.
   
• The floor of the tympanic cavity rests upon the superior jugular bulb (Clemente plate 569 fig. 928, plate 573 fig. 935; Grant p. 710-711; Netter 3e 87, 4e 92).
  • Where the internal carotid artery (moving anteriorly) diverges from the internal jugular vein (moving posteriorly), the cranial nerves IX and X send branches into the bony tympanic floor (Clemente plate 571 fig. 932; Grant p. 710; Netter 3e 89, 4e 94, 125).
  • Roof and floor converge anteriorly to form the auditory tube which is divided by the processus cochlearis (Clemente plate 569; Grant p. 711; Netter 3e 88-89, 4e 92-94) into:
    • a superior compartment containing the tensor tympani muscle. The tensor tympani inserts into the handle of the malleus.
    • and a lower compartment which joins with the cartilaginous portion of the auditory tube.
   
• The lateral wall of the tympanic cavity is closed by the tympanic membrane.
• The ascending carotid artery is associated with the anterior wall of the tympanic cavity, separated by a thin layer of bone (Clemente plate 571, fig. 932; Grant p. 710; Netter 3e 89, 4e 94).
  • Pulsations may be heard by the patient in some clinical disorders.
   
• The posterior wall of the tympanic cavity contains a tunnel, the aditus, connecting to the mastoid antrum.
  • Fluid from the mastoid air cells drain via the aditus into the tympanic cavity and then into the auditory tube and the nasopharynx.
  • Fluid may collect within the tympanic cavity if the auditory tube is obstructed due to an upper respiratory airway infection.
  • The VIIth cranial nerve enters the posterior wall below the aditus (Clemente plate 569 fig. 928; Grant p. 708, 710; Netter 3e 89, 4e 94) and exits from the base of the temporal bone via the stylomastoid foramen (Clemente plate 571 fig. 932; Grant p. 616, 712-713; Netter 3e 89, 4e 94).
  • The chorda tympani arises from the facial nerve within the posterior wall of the middle ear, courses over the eardrum along the lateral wall (Clemente plate 569; Grant p. 708, 711; Netter 3e 89, 4e 94), and exits via the petrotympanic fissure into the infratemporal fossa.
  • The pyramid is also located in the posterior wall. The apex of the pyramid has an orifice through which the tendon of the stapedius passes to insert on the neck of the stapes (Clemente plate 570; Grant p. 708; Netter 3e 89, 4e 93-94).
    • The stapedius acts to retract the stapes from the oval window and reflexively attenuates loud sound. It is innervated by cranial nerve VII and Bell's palsied patients may complain of sensitivity to loud sounds (hyperacusis).
     
• The medial wall of the tympanic cavity faces the inner ear contained within the petrous portion of the temporal bone.
  • It has the promontory at its center, overlying the first turn of the cochlea. Within the mucosa covering the promontory is the tympanic plexus where fibers of VII, IX and X intermingle (Clemente plates 570, 571; Grant p. 708, 710; Netter 3e 89, 4e 93). Through this plexus will pass:
    • sensory fibers to the external and middle ear
    • and preganglionic parasympathetic fibers for the greater (Clemente plate 571 fig. 932; Grant p. 834-835; Netter 3e 89, 4e 123, 125) and lesser petrosal nerves.
• Posterior and superior to the promontory are the oval window for the foot of the stapes, the canal for the facial (VIIth cranial) nerve and the prominence of the lateral semicircular canal (Clemente plates 570, 571; Grant p. 708, 710; Netter 89).
• The shape of the oval window matches the footplate of the stapes.
• The canal of facial nerve is horizontal and connects the internal auditory meatus to the descending canal of VII in the posterior wall.

Posterior and inferior to the promontory is the round window or fenestra cochleae (Clemente plate 570 fig. 930; Grant p.710; Netter 89-91), closed by a membrane (Netter 4e 94).

The tympanic membrane

• is circular (Clemente plate 567; Grant p. 706; Netter 3e 88, 4e 93-94)
• is set in a sulcus in the tympanic bone
• is oriented laterally, anteriorly and inferiorly ("catches sounds from the ground as one advances").
• is lined with epidermis (ectodermal) laterally and mucous membrane (endodermal) medially.
• The handle of the malleus is attached to the tympanic membrane.
• The superior pars flaccida of the eardrum attaches to the lateral process of the malleus.
• The chorda tympani lies posterior to this pars flaccida and must be avoided in puncturing the eardrum to drain the middle ear.

3 bony ossicles

(Clemente plate 568; Grant p. 707; Netter 3e 88, 4e 93-94)

2 synovial joints (between malleus and incus; between incus and stapes; may be affected by otosclerosis resulting in deafness):

• Malleus has a head, neck, manubrium with lateral process and an inferior tip. The anterior process of the malleus is attached to a stabilizing ligament (Clemente plate 568 fig. 926; Grant p. 708; Netter 3e 88-89, 4e 93-94).
• Incus: The body of the incus articulates with the malleus at the malleoincudal (incudomalleolar) joint (Clemente plate 568 fig. 926; Grant p. 707; Netter 3e 88, 4e 93-94).
  • Short crus (process) attaches via a ligament to the posterior wall of the epitympanic recess (Clemente plate 568 fig. 925; Grant p. 709; Netter 3e 89, 4e 94).
  • Long crus is vertically oriented and descends into the tympanic cavity. It has a lenticular process, which articulates with the head of the stapes.
  • Stapes has a head, neck, posterior and anterior limbs and footplate attached to the oval window by an annular ligament.

The role of the middle ear is to transfer vibratory sounds from the air to a fluid (perilymph):

• Vibratory surface of eardrum is 55 mm2 .
• Footplate is 3.2 mm2 .
• Hydraulic ratio between membrane and footplate is 17:1.

Muscles of the ossicles: the contraction of either of these muscles attenuate sound by decreasing the movement of ossicles.

1) The tensor tympani (Clemente plates 569, 570; Grant p. 708; ; Netter 3e 88-89, 4e 93-94) in the auditory canal runs around the processus cochleariformis to attach to the handle of the malleus: the contraction tenses the eardrum by pulling medially. It is innervated by a branch of V₃ as it exits foramen ovale.

2) The stapedius in the pyramid of the posterior wall, inserts into the neck of the stapes. The contraction pulls the foot plate away from the oval window to dampen the sound. It is innervated by VII.

The INNER EAR

is a bony labyrinth (Clemente plates 574-575; Grant p. 704-705, 714; Netter 3e 90-91, 4e 95) containing a membranous labyrinth.

The bony labyrinth consists of:

• the cochlea,
• the vestibule
• and the semicircular canals.

1) The cochlea is shaped like a snail shell with 2.5 turns. Vibrations from the perilymph of the vestibule is communicated to the fluids of the cochlea stimulating the hearing receptors of the inner ear.

2) The vestibule lies between the cochlea and semicircular canals, communicating with both chambers. It communicates with the tympanic cavity via the oval window (fenestra vestibuli).

3) The 3 semicircular canals: anterior (superior), posterior and lateral (horizontal). They lie in 3 planes like the corner of a room. Their function is to maintain balance.

The membranous labyrinth (Clemente plate 575; Grant p. 704, 714; Netter 3e 90, 4e 95-96) is surrounded by perilymph and is formed by the cochlear duct, saccule, utricle and 3 semicircular canal ducts.

The ductus endolymphaticus passes from saccule and utricle through a canal in the petrous bone, the vestibular aqueduct, to a fissure lateral to the internal auditory meatus. It acts as a safety expansion, the endolymphatic sac being placed extradurally.

Fluid waves from the perilymph are communicated to the endolymph of the cochlear duct for hearing.

Angular acceleration of endolymph in semicircular canals shifts the endolymph in the semicircular ducts and stimulate the vestibular receptors in the ampulla of the semicircular canal.

The utricle (for detecting movements in the sagittal plane) and the saccule (for detecting movements in the coronal plane) are for head movements detection. This is based on gravitational forces acting on their receptor mechanisms.

VIIIth cranial (Vestibulocochlear) nerve

(Grant p. 715; Netter 3e 118, 4e 124):

Test hearing by using a tuning fork placed against the mastoid process:

• If the eardrum and bony ossicles are impaired, then the bony conduction should be heard normally. But if VIII is impaired then total deafness is the result.
• Test balance by having patient stand with feet together and eyes closed. If the vestibular portion of VIII is defective then the patient will fall to the lesioned side.

The blood supply of the inner ear enters the internal acoustic meatus with VII and VIII: This labyrinthine artery is a branch of the anterior inferior cerebellar artery (Clemente plate 493, 574-575; Grant 647; Netter 3e 132-133, 4e 136, 139). It may be affected by strokes in the vertebral arterial system.

VIIth cranial (Facial) nerve:

• is the nerve of the 2nd pharyngeal arch to the muscles of facial expression, stylohyoid, posterior belly of the digastric and stapedius.
• also carries the fibers of the nervus intermedius (intermediate nerve) for taste (special sensory) and preganglionic parasympathetic fibers to all glands of the face, except the parotid gland.

The facial (VIIth cranial) nerve:

• runs through the internal auditory meatus with VIII (Clemente plate 574; Grant p. 709; Netter 92),
• lies above VIII in the canal, above the vestibule of the bony labyrinth,
• bends on the medial wall of the middle ear and forms the genu with the geniculate ganglion,
• and courses to the posterior wall to descend through the facial canal and exit through the stylomastoid foramen (Clemente plate 573; Grant p. 710-711; Netter 3e 89, 4e 94).

The geniculate ganglion contain the cell bodies for the taste fibers. There is no synapse in the geniculate ganglion.

The greater (superficial) petrosal nerve (Clemente plates 574-575; Grant p. 709-710; Netter 3e 89, 4e 94) branches from the geniculate ganglion, pierces the anterior wall of tympanic cavity, enters the middle cranial fossa. It carries taste fibers for the palate, and secretomotor fibers for glands in the roof of the oral cavity, the nasal cavity and the orbit.

The descending part of VII gives off a motor branch to the stapedius and the chorda tympani (Clemente plate 572 fig. 934; Grant p. 831; Netter 3e 89, 4e 94).

The chorda tympani runs between the handle of the malleus and the vertical process of the incus (Clemente plate 569; Grant p. 708; Netter 3e 89, 4e 94) to exit into the infratemporal fossa (Clemente plate 479; Grant p. 669; Netter 3e 42, 4e 46) via the petrotympanic fissure. It carries taste fibers from the anterior 2/3 of the tongue and secretomotor fibers to the submandibular ganglion.

Unilateral facial muscles paralysis

Test:

1) for loss of taste in the an