Schedule

Lab 24 - Bisected Head II

Suggested readings from
Gray's Anatomy for Students, 2nd ed.
Ch. 8, 985-1012
Suggested readings from Langman's Medical Embryology:
11th ed - Ch. 16 (Head & Neck): pp. 265-287
12th ed - Ch. 17 (Head & Neck): pp. 260-282

Primary Lab Objectives and Goals:

  1. Examine the dorsal surface of the tongue, and carefully dissect the extrinsic and intrinsic tongue muscles. Consider how they work with each other to shape the tongue.

  2. Examine the muscles that form the floor of the mouth and support the tongue.

  3. Examine the mucosa, nerves, and blood vessels of the hard palate.  

  4. Distinguish the components of the nasal septum.

  5. On the lateral wall of the nasal cavity, locate the three conchae (turbinates) and their associated meatus. Find the openings of the nasolacrimal duct and the paranasal sinuses.

 

Dissection Instructions

1. DORSAL SURFACE OF THE TONGUE 

  1. Examine the dorsal and midline surface of the tongue.
  2. Note the various types of mucosal papillae covering the dorsal surface.  Try to identify vallate, filliform, foliate, and fungiform papillae 
  3. Identify the terminal sulcus.
 

 

NOTE: The intrinsic muscles of the tongue attach to each other, more than they attach to bone, and can work “against” each other.  As one portion becomes rigid, a portion that attaches to it can contract and shorten.  Thus the tongue functions as a muscular hydrostat.  You will want to dissect these carefully and consider the different directions of the fibers in order to appreciate this arrangement. You will look at the extrinsic muscles first and then look at the intrinsic and see how they all interact.

  1. Identify the extrinsic muscles of the tongue:
    • Styloglossus - attaches the tongue to the skull
    • Genioglossus - attaches the tongue to the anterior of the mandible
    • Hyoglossus – attaches the tongue to the hyoid bone
  2. You will look at these muscles now, and then examine them again with their innervation in the lab associated with masticatory muscles. 
 

 

 

2. ROOT OF THE TONGUE

  1. Look at the tongue in sagittal section.  Examine the genioglossus muscle.  Look at the way it radiates from its attachment on the mandible. 
  2. Note that the lower portion of the genioglossus muscle is considered the root of the tongue.
  3. Immediately inferior to the genioglossus, identify the geniohyoid muscle. The geniohyoid muscle runs from the inside of the jaw at the midline to the hyoid.  Its fibers run anteroposteriorly.
  4. Below the geniohyoid, identify the mylohyoid muscle.  Its fibers run mediolaterally. 

Thus, two muscles at right angles to each other (the geniohyoid and mylohyoid), support the floor of the mouth.

  1. Note the intrinsic muscle fibers in the substance of the tongue running in three mutually perpendicular directions.   
  2. At the moment you can see the superior longitudinal band running under the mucous tissue of the tongue over the genioglossus muscle. 
  3. Remove some mucous tissue to expose the intrinsic muscle.
  4. To see the remaining intrinsic muscles, make a coronal slice through the tongue on one side above the insertion of the genioglossus muscle, but not all the way down to it.

You can now see the transverse bands of the intrinsic fibers running from the median fibrous septum laterally, and the vertical intrinsic muscle fibers extending superiorly and blending with the superior longitudinal fibers.

The inferior longitudinal band running longitudinally between the genioglossus and hyoglossus muscles is hard to see and may be seen in the next lab associated with the masticatory muscles.

Atlas Image:

 

 

3. HARD PALATE

  1. Using a probe, remove the mucosa from the hard palate on the inferior surface where it was cut during the head bisection.
  2. Grasp the mucosa with your fingers and peel it off from medial to lateral.
  3. Detach the mucosa along the medial side of the alveolar process of the maxilla.
  4. Identify the greater and palatine nerves and the greater palatine vessels where they emerge from the greater palatine foramen.
  5. Use blunt dissection to follow the greater palatine nerve anteriorly.

FUNCTIONAL ANATOMY: The palatine nerves are branches of the maxillary nerve that pass through the pterygopalatine ganglion (which you will explore next lab).  The greater palatine nerve emerges from greater palatine foramen to the roof of the mouth. There are also lesser palatine nerves passing through the small foramina and going to the soft palate. The nasopalatine nerve supplies the mucosa over the anterior part of the hard palate, passing through the incisive foramen.  The palatine nerves carry parasympathetic, general sensory, and some taste fibers.

  1. Posterior to the greater palatine nerve, identify the lesser palatine nerve.
  2. Use blunt dissection to follow the lesser palatine nerve to the soft palate. 
  3. All three of these nerves (greater palatine, nasopalatine, and lesser palatine) are branches of CN V2.

Atlas Images:

 

 

 

4. NASAL SEPTUM

  1. Note the uvula (which you already sectioned) hanging down from the back edge of the soft palate. 
  2. Distinguish the bony and cartilaginous portions of the nasal septum:  
    • Vomer
    • Perpendicular plate of the ethmoid
    • Septal cartilage
  3. Identify the olfactory epithelium at the top of the nasal fossa by its distinctive yellow pigmentation.
 

 

 

 

5. NASAL CAVITY

When you bisected the head, you should have gone slightly off the midline such that the nasal septum is intact on one side. Go through the steps below on the OPPOSITE site (the side that does not have the nasal septum).

  1. Examine the lateral wall of the nasal cavity.   
  2. Identify the bony scroll-like structures called conchae on the lateral wall of the fossa (there are usually three conchae but sometimes there can be four of them)
  3. Place a probe into the space overhung by each concha. Each space is called a meatus.
 

FUNCTIONAL ANATOMY:
The upper two conchae are processes of the ethmoid bone. It is into their meatus that the ostia (mouths) of the ethmoidal, frontal, and maxillary air sinuses open. The sphenoid sinus opens through a hole in the sphenoid bone and into the posterior nasal cavity. The inferior conchae are their own separate bones. The nasolacrimal duct opens below the inferior concha.  Consider these turbinates (conchae) in cross-section, and note how they influence the airflow for clearing debris, cooling/warming, and humidifying/dehumidifying.

 

  1. Remove the inferior and middle conchae by gently fracturing them off with upward leverage

In the middle meatus, you will now be able to see openings to the paranasal sinuses.

  1. Probe the openings of the paranasal sinuses into the middle meatus.  Follow the semilunar hiatus that allows a connection between the middle meatus and the frontal, ethmoid, and maxillary sinuses.
  2. Locate the opening of the nasolacrimal duct into the inferior meatus.
 

 

CLINICAL CORRELATIONS

Septal deviation
In some cadavers you will see a deviated nasal septum. Plastic deformation of septal cartilage can occur from trauma or be “congenital.  In the former, deformation occurs in the anterior septal cartilage.  In the latter, deviations occur in all septal components as a result of pressure on the face and skull of the neonate during pregnancy and parturition.

Greater palatine nerve block
The greater palatine nerve can be anesthetized by injecting anesthetic into the greater palatine foramen. The nerve emerges approximately between the second and third molar teeth. The nerve block anesthetizes, on the side concerned, all the palatal mucosa and lingual gingivae posterior to the maxillary canine teeth and the underlying bone.

Cancer of the base of the tongue
Tumors at the base of the tongue are increasing in frequency in United States and Europe possibly as a result of human papillomavirus (HPV).   Because this type of tumor is so far back in the oral cavity it is often hard to see at early stages of diagnosis and provides little discomfort to patients (unlike tumors on the side of the tongue which are often felt as the tongue moves around.  But at later stages, because of its anatomical location, tumors of the base of the tongue can cause difficulty swallowing and also difficulties in speech and even breathing at very late stages.

 

 

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