S11 Nasal Cavity, Sinuses and Ear - LabLink

Click here for a condensed, step-by-step dissection summary.

Examine the nasal septum

Find these structures:

  • Vomer
    • Ala
  • Ethmoid
    • Perpendicular plate
  • Septal nasal cartilage
  • Olfactory nn. (CN I)
  • Ophthalmic a.
    • Anterior ethmoidal a.
      • Anterior septal brs.
    • Posterior ethmoidal a.
  • Maxillary a.
    • Third (pterygopalatine) part
      • Sphenopalatine a.
        • Posterior septal brs.
  • Facial a.
    • Superior labial br.
      • Nasal septal br.
  • Anterior ethmoidal n. (V1)
    • Internal nasal brs.
      • Medial nasal brs.
  • Maxillary n. (V2)
    • Nasopalatine n.

Note: Depending on how the donor’s head is sectioned, it may or may not have an intact nasal septum.

1.) Remove the nasal mucosa from the nasal septum to reveal the three portions of the nasal septum & the neurovasculature of the septum. Nasal septum is comprised of: anteriorly, the septal nasal cartilage, posteroinferiorly, the vomer, and posterosuperiorly, the perpendicular plate of the ethmoid.

Note: The nasal septum receives vasculature from three general sources:

  • superiorly, from the anterior ethmoidal a. (via anterior septal brs.) and the posterior ethmoidal a.,
  • posteriorly from the sphenopalatine a. (via posterior septal brs.), and
  • anteriorly from the superior labial a. (via nasal septal brs.) and greater palatine a.
  • These arteries come from the ophthalmic a. (anterior & posterior ethmoidal aa.), maxillary a. (sphenopalatine & greater palatine aa.), and the facial a. (superior labial a.). The arteries of the nasal septum anastomose on the anterior aspect of the septum, an area known as the Kiesselbach’s area/plexus. A preponderance (>90%) of episodes of epistaxis originate in Kiesselbach’s area.

Photo 1. Nasal septum

Photo 2. Nasal septum vasculature

Note: The nasal septum is innervated by branches of V1 and V2.

V1 supplies the septum through:

  • medial nasal brs. (from internal nasal brs. of the anterior ethmoidal n.), whereas

V2 supplies the septum through:

  • nasopalatine n., and the
  • posterior superior medial nasal brs.

Note: Most of the nasal septum is innervated by nasopalatine n. A small part of the nasal roof and superior portion of the septum is innervated by the posterior superior medial nasal brs. The anterior portion of the nasal septum is innervated by medial nasal brs. (of internal nasal brs. of the anterior ethmoidal n.).

Note: One of the more obvious contributions of neurovasculature to the nasal septum is the collection of olfactory nn. (CN I). The olfactory nn. can be located descending inferiorly from the cribriform foramina of the ethmoid bone.

Photo 3. Nerves of the nasal septum

Observe the osteo-mucosal structures of the lateral nasal wall

Find these structures:

  • Nares
  • Nasal vestibule
  • Choanae
  • Spheno-ethmoidal recess
    • Opening - sphenoidal sinus
  • Superior nasal concha
  • Superior nasal meatus
    • Opening - posterior ethmoidal cells
  • Middle nasal concha
  • Middle nasal meatus
    • Ethmoidal bulla
    • Opening - middle ethmoidal cells
    • Ethmoidal infundibulum
      • Opening - frontonasal duct
    • Semilunar hiatus
      • Opening - anterior ethmoidal cells
      • Opening - maxillary sinus
  • Inferior nasal concha
  • Inferior nasal meatus
    • Opening of nasolacrimal duct

2.) Turn the hemisected head so that the medial portion is facing up. Locate components of the external nose and nasal cavity: nares, nasal vestibule, and choanae.

Note: The nares (external nasal apertures) are often referred to as nostrils and are parts of the external nose. Just posterior to the nares are nasal vestibules. The posterior edge of the vestibule serves as an important transition area between hair-bearing skin and mucous membrane, which lines the rest of the nasal cavity. The nares are separated by a nasal septum (septal cartilage, vomer, and perpendicular plate of the ethmoid) that divides the nasal cavity. The nasal cavity continues distally into the nasopharynx through the choanae (posterior nasal apertures).

Photo 4. Components of nose

3.) Observe the nasal conchae, maintaining the mucosal coverings.

Note: The superior and middle nasal conchae (turbinates) are scroll-shaped components of the ethmoid bone located in the nasal cavity. The superior nasal concha is the smallest with the middle concha of intermediate size. The inferior nasal concha is the largest and most substantial of the nasal conchae, and are not components of another bone. Occasionally, there are highest (supreme) nasal conchae, within the sphenoethmoidal recess. The nasal conchae are thickly lined with nasal mucosa, and serve several functions: increase surface area of nasal cavity, humidification and filtration of inspired air, and direction of airflow.

Photo 5. Nasal conchae

4.) With scissors, remove the nasal conchae from the nasal cavity to expose the spheno-ethmoidal recess, and superior, middle, and inferior nasal meatuses. Observe the ethmoidal bulla, semilunar hiatus, and ethmoidal infundibulum in the middle nasal meatus. Within the nasal meatuses, there are openings (ostia, orifices) to sinuses, air cells, and ducts. Locate openings to the: sphenoidal sinus, posterior ethmoidal cells, middle ethmoidal cells, frontal sinus, maxillary sinus, anterior ethmoidal cells, and nasolacrimal duct.

Note: With embalming, nasal mucosa may become edematous (swollen) and impliable (stiff), thus small openings may not always be obvious or locatable.

Note: There are four meatuses or recesses associated with the nasal conchae, the:

  • spheno-ethmoidal recess is located superior to the superior nasal concha,
  • superior nasal meatus can be found between the superior and middle nasal conchae,
  • middle nasal meatus is located between the middle and inferior nasal conchae,
  • inferior nasal meatus can be identified below the inferior nasal concha.

Photo 6. Nasal meatuses and spheno-ethmoidal recess

Note: The spheno-ethmoidal recess is located above the superior nasal concha, and the opening of the sphenoidal sinus is located here.

Photo 7. Spheno-ethmoidal recess and ethmoidal bulla

Note: The superior nasal meatus is located between the superior and middle nasal conchae. The openings of the posterior ethmoidal cells are located in the superior nasal meatus.

Note: The middle nasal meatus is located between the middle and inferior nasal conchae. The openings of several sinuses are found in the middle nasal meatus (middle ethmoidal cells, frontal sinus, maxillary sinus, and anterior ethmoidal cells).

Note: Within the middle nasal meatus, there are several important structures. The ethmoidal bulla is a noticeable projection just inferior to the middle nasal concha, caused by the middle ethmoidal cells. Inferior to the bulla is a slit-like opening, the semilunar hiatus. The anterosuperior portion of the semilunar hiatus expands into a funnel-shaped opening, the ethmoidal infundibulum. The frontonasal duct of the frontal sinus typically drains into the ethmoidal infundibulum, while the semilunar hiatus hosts openings for the anterior ethmoidal cells and maxillary sinus.

Photo 8. Middle nasal meatus

Photo 9. Middle nasal meatus

Note: The inferior nasal meatus can be identified below the inferior nasal concha, and contains the opening of nasolacrimal duct, which conducts tears from the orbit.

Photo 10. Inferior nasal meatus

Examine the sub-mucosal neurovasculature of the lateral nasal wall

Find these structures:

  • Ophthalmic a.
    • Anterior ethmoidal a.
      • Anterior lateral nasal brs.
    • Posterior ethmoidal a.
  • Maxillary a.
    • Third (pterygopalatine) part
      • Sphenopalatine a.
        • Posterior lateral nasal aa.
  • Facial a.
    • Lateral nasal brs.
  • Anterior ethmoidal n. (V1)
    • Internal nasal brs.
      • Lateral nasal brs.
    • External nasal n.
  • Maxillary n. (V2)
    • Posterior superior lateral nasal brs.
    • Greater palatine n.
      • Posterior inferior nasal nn.
    • Anterior superior alveolar n.
      • Nasal br.
    • Infra-orbital n.
      • Internal nasal br.

5.) Remove the lateral nasal mucosa, and locate the the neurovasculature.

Note: The lateral nasal wall is served by branches of the same arteries which serve the nasal septum, namely the:

  • anterior ethmoidal (via anterior lateral nasal brs.) & posterior ethmoidal aa.,
  • sphenopalatine a. (via posterior lateral nasal aa.), and the
  • facial a. (via lateral nasal br.).

Photo 11. Lateral nasal wall arteries

Note: The lateral nasal wall is innervated by branches of V1 and V2 that also serve the nasal septum.

V1 supplies the lateral wall through:

  • lateral nasal brs. (from internal nasal brs. of the anterior ethmoidal n.), whereas

V2 supplies the lateral wall through:

  • posterior superior lateral nasal brs.,
  • posterior inferior lateral nasal brs. (from greater palatine n.),
  • nasal brs. of the anterior superior alveolar n., and
  • internal nasal br. of the infra-orbital n.

Note: The mid- to posterior aspects of the lateral nasal wall are innervated by posterior superior lateral nasal brs. and posterior inferior lateral nasal brs. (from greater palatine n.). Posterior superior lateral nasal brs. innervate the superior and middle nasal meatuses, whereas the posterior inferior lateral nasal brs. innervate the middle and inferior nasal meatuses. The anterior aspect of the lateral wall is innervated superiorly by lateral nasal brs. (from internal nasal brs. of the anterior ethmoidal n.) and inferiorly by nasal brs. (of the anterior superior alveolar n.) and internal nasal brs. (of the infra-orbital n.).

Photo 12. Lateral nasal wall nerves

Photo 13. Lateral nasal wall nerves

EAR - DEMO & PHOTOS

Dissection of the middle and inner ear is difficult and time consuming, thus there will be no student dissection for this component of the lab. Observe the structures listed below in the Demo Lab as well as through provided visuals.

Find these structures:

Middle ear

Structures visible on the medial wall (labyrinthine wall)

  • Tympanic cavity
    • Oval window
    • Promontory
    • Round window
    • Tensor tympani m.
    • Stapedius m.
    • Stapes

Structures visible on the lateral wall (membranous wall)

  • Tympanic cavity
    • Tympanic membrane
    • Malleus
    • Incus
  • External acoustic meatus
  • Internal acoustic meatus
  • Stylomastoid foramen
  • Carotid canal
  • Jugular fossa
  • Jugular foramen
  • Petrous part of temporal bone
  • Mastoid cells
  • Pharyngotympanic (Eustachian, auditory) tube

Internal ear

  • Semicircular canals
  • Cochlea

Nerves of middle and internal ear

  • Facial n. (CN VII)
    • Chorda tympani
  • Vestibulocochlear n. (CN VIII)
  • Glossopharyngeal n. (CN IX)
    • Tympanic n.
      • Tympanic plexus

6.) Investigate the relevant structures of or near the lateral wall of the tympanic cavity: pharyngotympanic (Eustachian, auditory) tube, malleus, incus, tympanic membrane, and chorda tympani.

Note: The tympanic membrane (eardrum) divides the external (external acoustic meatus) and middle ear (tympanic cavity). The manubrium of the malleus attaches to the deep (internal) surface of tympanic membrane. It is considerably larger (15-20x) than the base of the stapes, which inserts on the oval window. The tympanic membrane is principally innervated by the auriculotemporal n.

Note: There are three, small ear ossicles within the middle ear: malleus, incus, and stapes. The malleus is attached to the tympanic membrane and articulates with the incus, incus articulates with both the malleus and stapes, and the stapes base attaches to the oval (vestibular) window, which leads into the inner ear. All joints between the bones are synovial. The ear ossicles transfer sound waves from the external ear to the inner ear. Interestingly, these ossicles have a well-corroborated (embryological, paleontological, and comparative anatomical) history as posterior jaw bones in ray-finned fishes and non-mammalian amniotes.

Note: The chorda tympani (a branch of facial n.) is located in the middle ear region traversing between the malleus and incus. Chorda tympani branches from the facial n. in the facial canal, just proximal to the stylomastoid foramen, and exits the skull through the petrotympanic fissure to join the lingual n. in the infratemporal fossa. Chorda tympani carries preganglionic parasympathetic fibers to the submandibular ganglion and taste to the anterior 2/3rds of the tongue.

Photo 14. Lateral wall of left tympanic cavity, medial

7.) Investigate the relevant structures of or near the medial wall of the tympanic cavity: tensor tympani m., oval window, round window, stapedius m., stapes, stylomastoid foramen, promontory, tympanic n., tympanic plexus, pharyngotympanic (Eustachian, auditory) tube, and mastoid cells.

Note: The tensor tympani m. tendon is often visible on the lateral wall of the middle ear cavity. This muscle spans between the cartilaginous portion of the pharyngotympanic tube and the malleus, and plays a role in tempering the vibrations of the tympanic membrane. Like the tensor veli palatini m., the tensor tympani m. is innervated by a branch of V3 (a branch of the nerve to the medial pterygoid m).

Note: The oval window (fenestra vestibuli/ovalis) is located posterosuperior to the promontory. It is an entrance to the inner ear, and the footplate of the stapes occupies this space. The round window (fenestra cochleae/rotunda) is located inferior to the promontory. During life, this space is closed by a secondary tympanic membrane.

Note: The pharyngotympanic tube connects the middle ear to the nasopharynx, and is typically closed but can open slightly in order to equalize pressure (the Valsalva maneuver). The tube is cartilaginous on the pharyngeal end (2/3rds of the tube), and bony (1/3rd of the tube) at the tympanic portion.

Note: The tendon of the stapedius m. is visible on the medial wall of the middle ear (the muscle belly is completely surrounded by bone). The tendon attaches to the neck of the stapes, and when contracted, the stapedius m. dampens vibrations of this ossicle. It is innervated by a small branch of the facial n. (CN VII).

Note: The promontory of the cochlea is located on the medial wall of the middle ear cavity. This structure presents as a bulging of bone caused by the deep cochlea. The tympanic plexus is located under the mucosal covering of the promontory. The tympanic plexus is composed of fibers from the tympanic n. (branch of glossopharyngeal n.) and caroticotympanic nn. (postganglionic sympathetic fibers). These branches supply mucosa of mastoid air cells, pharyngotympanic tube, and the tympanic cavity.

Note: Mastoid cells are located within the mastoid process of the temporal bone, and are connected to the tympanic cavity and mastoid antrum. Infection may spread from the tympanic cavity to air cells and areas surrounding, leading to mastoiditis.

Photo 15. Medial wall of left tympanic cavity, lateral

Photo 16. Medial wall of left tympanic cavity, lateral

8.) Investigate visible structures of the inner ear and related structures: semicircular canals, cochlea, facial n. (CN VII), and vestibulocochlear n. (CN VIII).

Note: The vestibulocochlear n. (CN VIII) enters the temporal bone through the internal acoustic meatus, where it quickly divides into cochlear (hearing) and vestibular (proprioception/balance) nerves.

Note: The cochlea (auditory) and semicircular canals (balance and equilibrium) are components of the inner ear. There are three semicircular canals: anterior (superior), lateral (horizontal), and posterior.

Photo 17. Temporal cavity, posterior