The Nose

• The nose is the superior part of the respiratory tract and contains the peripheral organ of smell.
• It is divided into right and left nasal cavities by the nasal septum.
• The nasal cavity is divided into the olfactory area and the respiratory area.

Nerve Supply of the Muscles of the Orbit (pp. 715-6)

• Three cranial nerves supply the muscles of the eyeball; the oculomotor (CN III), trochlear (CN IV) and abducent (CN IV) nerves.
• All three enter the orbit via the superior orbital fissure.

• The trochlear nerve supplies the superior oblique muscle.
• The abducent nerve supplies the lateral rectus muscle.
• The oculomotor nerve supplies everything else.

• A mnemonic that is used is this formula for this strange sulfate: SO₄(LR₆)₃

The Meatus of the Nose

Sphenopalatine Recess

• This space is posterosuperior to the superior concha.
• The sphenoidal sinus opens into this recess.

Superior Meatus

• This is a narrow passageway between the superior and middle nasal conchae.
• The posterior ethmoidal sinuses open into it by one or more orifices.

Middle Meatus

• This is longer and wider than the superior one.

• The anterosuperior part of this meatus lead into a funnel-shaped opening, called the infundibulum, through which the frontonasal duct leads to the frontal sinus.
• There is one duct for each frontal sinus and since there may be several, there may be several frontonasal ducts.

• When the middle concha is removed, rounded elevation called the ethmoidal bulla (L. bubble), is visible
• The middle ethmoidal air cells open on the surface of the ethmoidal bulla.

• Inferior to this bulla is a semicircular groove called the hiatus semilunaris.
• The frontal sinus opens into this hiatus anterosuperiorly.
• Near the hiatus are the openings of the anterior ethmoid air cells.
• The maxillary sinus also opens into the middle meatus.

Inferior Meatus

• This is a horizontal passage, inferolateral to the inferior nasal concha.
• The nasolacrimal duct opens into the anterior part of this meatus.
• Usually, the orifice of this duct is wide and circular.

Innervation of the Pharynx

• The motor and most of the sensory supply of the pharynx is derived from the pharyngeal plexus of nerves on the surface of the pharynx.
• The plexus is formed by pharyngeal branches of the vagus (CN X) and glossopharyngeal (CN IX) nerves, and by sympathetic branches for the superior cervical ganglion.

• The motor fibres in the pharyngeal plexus are derived from the cranial root of accessory nerve (CN XI), and are carried by the vagus nerve to all muscles of the pharynx and soft palate.
• The exceptions are stylopharyngeus (supplied by CN IX) and the tensor veli palatini (supplied by CN V3).

Walls of the Tympanic Cavity or Middle Ear

• This cavity is shaped like a narrow six-sided box that has convex medial and lateral walls.
• It has the shape of the biconcave lens in cross-section (like a red blood cell).

The Roof or Tegmental Wall

• This is formed by a thin plate of bone, called the tegmen tympani (L. tegmen, roof).
• It separates the tympanic cavity from the dura on the floor of middle cranial fossa.
• The tegmen tympani also covers the aditus ad antrum.

The Floor or Jugular Wall

• This wall is thicker than the roof.
• It separates the tympanic cavity from the superior bulb of the internal jugular vein. The internal jugular vein and the internal carotid artery diverge at the floor of the tympanic cavity.

• The tympanic nerve, a branch of the glossopharyngeal nerve (CN IX), passes through an aperture in the floor of the tympanic cavity and its branches form the tympanic plexus.

The Lateral or Membranous Wall

• This is formed almost entirely by the tympanic membrane.
• Superiorly it is formed by the lateral bony wall of the epitympanic recess.
• The handle of the malleus is incorporated in the tympanic membrane, and its head extends into the epitympanic recess.

The Medial or Labyrinthine Wall

• This separates the middle ear from the membranous labyrinth (semicircular ducts and cochlear duct) encased in the bony labyrinth.
• The medial wall of the tympanic cavity exhibits several important features.

• Centrally, opposite the tympanic membrane, there is a rounded promontory (L. eminence) formed by the first turn of the cochlea.
• The tympanic plexus of nerves, lying on the promontory, is formed by fibres of the facial and glossopharyngeal nerves.

• The medial wall of the tympanic cavity also has two small apertures or windows.

• The fenestra vestibuli (oval window) is closed by the base of the stapes, which is bound to its margins by an annular ligament.
• Through this window, vibrations of the stapes are transmitted to the perilymph window within the bony labyrinth of the inner ear.

• The fenestra cochleae (round window) is inferior to the fenestra vestibuli.
• This is closed by a second tympanic membrane.

The Posterior or Mastoid Wall

• This wall has several openings in it.
• In its superior part is the aditus ad antrum (mastoid antrum), which leads posteriorly from the epitympanic recess to the mastoid cells.

• Inferiorly is a pinpoint aperture on the apex of a tiny, hollow projection of bone, called the pyramidal eminence (pyramid).
• This eminence contains the stapedius muscle.
• Its aperture transmits the tendon of the stapedius, which enters the tympanic cavity and inserts into the stapes.

• Lateral to the pyramid, there is an aperture through which the chorda tympani nerve, a branch of the facial nerve (CN VII), enters the tympanic cavity.

The Anterior Wall or Carotid Wall

• This wall is a narrow as the medial and lateral walls converge anteriorly.
• There are two openings in the anterior wall.

• The superior opening communicates with a canal occupied by the tensor tympani muscle.
• Its tendon inserts into the handle of the malleus and keeps the tympanic membrane tense.

• Inferiorly, the tympanic cavity communicates with the nasopharynx through the auditory tube.

The Inferior Wall of the Orbit

• The thin inferior wall of the orbit or the floor is formed mainly by the orbital surface of the maxilla and partly by the zygomatic bone, and orbital process of the palatine bone.

• The floor of the orbit forms the roof of the maxillary sinus.

• The floor is partly separated from the lateral wall of the orbit by the inferior orbital fissure.