Introduction

In this lab you will explore the nasal cavity, oral cavity, pharynx and larynx. The nasal cavity is the first part of the upper respiratory tract. It contains structures that swirl and condition the air before it moves on the next respiratory tract structures. The oral cavity is the first part of the digestive system. Its structures allow for mechanical digestion by chewing, chemical digestion by the products of salivary glands, and taste. The oral cavity is also part of the respiratory system, as, of course, we can take in air through the oral cavity. The larynx is part of the respiratory system, and it contains the vocal cords and other structures required for producing sound in speech. The pharynx sits posterior to the nasal cavity, oral cavity, and larynx. It contributes to the respiratory system by providing a passageway for air to travel from the nasal or oral cavities to the larynx. It also contributes the digestive system by connecting the oral cavity to the esophagus, and it contains muscles that function in swallowing.

Lab Activity 1: Slideshow Images

Go through the slideshow images displayed on the computers in lab and explore the structures on the Terms to Know. All of the regions you are examining in this lab are in close proximity. Therefore, you will see parts of the oral cavity, nasal cavity, larynx, and/or pharynx on the same image. There will also be structures labeled on some of the images that we have talked about in other labs. Within these images you will be able to identify all of the structures in the list of terms. The following section describes some of these structures in more detail (and you are responsible for knowing this information):

Oral Cavity

• The oral cavity can be divided into two parts. The oral vestibule is the portion of the oral cavity between the teeth and the lips. The oral cavity proper is the portion of the oral cavity between the teeth and the pharynx, where the tongue is located.
• Palate: The palate is the roof of the oral cavity. The most anterior portion is the hard palate. This is formed by part of the maxilla and the palatine bone. The soft palate is composed of skeletal muscle. At the posterior portion of the soft palate is the uvula, which closes off the entrance from the oropharynx to the nasopharynx during swallowing so that food does not enter the nasopharynx and nasal cavity.
• Arches: The oral cavity opens into the oropharynx through paired muscular folds: The palatoglossal arch and the palatopharyngeal arch. The palatoglossal arch is formed by the palatoglossus muscle and the membrane covering it, while the palatopharyngeal arch is formed by the palatopharyngeus muscle and the membrane covering it. Between these arches sits the palatine tonsils. These are aggregations of lymphatic tissue that trap foreign antigens entering the body via the mouth to mount an early immune response. The palatine tonsils can sometimes become very inflamed with illness, which is called tonsillitis.
• Tongue: The tongue plays important roles in both the mechanical digestion of food and sound production (articulation). The tongue itself is composed of several different intrinsic muscles (muscles completely within the tongue), and it also has several extrinsic muscles that act on it. Three of these muscles can be observed in one of the images: The styloglossus, genioglossus, and hyoglossus. The names of these muscles help you to identify them based on their origins. The styloglossus originates from the styloid process of the temporal bone. The genioglossus originates under the chin (genio- means chin). The hyoglossus originates on the hyoid bone. All of these muscles insert into the tongue.
• Muscles of Mastication: The muscles of mastication act on the mandible and function in chewing our food. The temporalis muscle runs from the temporal bone to the coronoid process of the mandible. It elevates and retracts the mandible. The masseter originates on the zygomatic arch and inserts on the mandible. It is the prime mover of elevation of the mandible (clenching the teeth), and it also protracts the mandible. The lateral and medial pterygoids originate on the sphenoid bone and insert onto the mandible. They protract the mandible and to move it side to side, as we do when we grind our food between our back teeth when chewing. All of these muscles are innervated by the trigeminal nerve (CN V).
• Salivary glands: The salivary glands produce saliva, which contains substances that help with the chemical digestion of food, moisten the oral cavity and ingested food, and dissolves food materials for taste. The parotid gland is the largest salivary gland, and it is located in the posterior cheek region, just anterior to the ear. The parotid duct pierces the buccinator muscle and enters the oral cavity. Production of saliva from the parotid gland is controlled by the glossopharyngeal nerve (CN IX). The submandibular glands sit just inferior to the body of the mandible on each side, and they produce the majority (60-70%) of our saliva. The submandibular ducts carry the saliva from this gland to the floor of the mouth. The sublingual glands are smaller and sit just inferior to the tongue, anterior to the submandibular glands. They secrete their saliva into the floor of the oral cavity. Secretion from the submandibular and sublingual glands are controlled by the facial nerve (CN VII).
• Temporomandibular joint (TMJ): This joint is the articulation between the condyle of the mandible and the temporal bone. This hinge joint allows us to open and close our mouth.

Nasal Cavity

• Nasal bones: The nose is formed by both cartilage and bone, with the nasal bones forming the bridge of the nose more superiorly and posteriorly.
• Nasal septum: Divides the nasal cavity into right and left halves. It is partially formed by bone and partially formed by cartilage
• Nasal conchae: The nasal conchae condition the air that enters through the nasal cavity. They cause the air to swirl, and the membranes that cover them help to warm and moisten the air before it travels further down the respiratory tract. The superior and middle nasal conchae are part of the ethmoid bone, while the inferior nasal conchae is its own bone. The space below each conchae is called a meatus, and it is named for the conchae above it.
• Paranasal sinuses: The sinuses are air-filled spaces in four bones of the skull. They function to lighten the skull, humidify and warm inhaled air (via their mucous lining), and provide resonant chambers for sound production. The frontal sinuses sit just superior to the orbits’ medial aspect, while the large maxillary sinuses sit just lateral to the nose. The ethmoid bone contains many small sinuses sitting just superior to the nasal cavity, and these are called the ethmoid air cells. The sphenoid sinus sits just superior to the nasopharynx.
• Olfactory structures: An important function of the nose is olfaction, or smell. The mucous lining at the superior portion of the nasal cavity contains the receptors of the olfactory nerves. The olfactory nerves run through the foramina of the cribriform plate of the ethmoid bone and synapse in the olfactory bulb. The axons of the neurons from the olfactory bulbs travel posteriorly through the olfactory tract to the primary olfactory region of the brain.

• Nasopharynx: Portion of the pharynx posterior to the nasal cavity.
• Oropharynx: Portion of the pharynx posterior to the oral cavity.
• Laryngopharynx: Portion of the pharynx posterior to the larynx.
• Pharyngeal constrictors: The superior, middle, and inferior pharyngeal constrictors contract sequentially during the swallowing process to move food towards the esophagus. It can be difficult to define each visually, so we will refer to them together as the pharyngeal constrictors. These are skeletal muscles, and they are innervated by the vagus nerve (CN X).
• Piriform recess (Pyriform sinus): This region is located within the laryngopharynx on either side of the entrance into the pharynx. It is a common place for food to become trapped while swallowing. Though this is not really a significant problem, it can make us feel like something caught in our throat.

• Thyroid cartilage: This is the largest laryngeal cartilage and is only located anteriorly and laterally. It does not form a complete ring around the larynx. The laryngeal prominence of the thyroid cartilage protrudes anteriorly, forming our Adams apple.
• Cricoid cartilage: Inferior to the thyroid cartilage. It is thin anteriorly and taller posteriorly.
• Epiglottis: This is the spoon-shaped flap of cartilage that folds over the opening to the larynx during swallowing to prevent food from entering the airway.
• Arytenoid cartilages: These are small, L-shaped cartilages involved in sound production. The vocal cords are attached to the thyroid cartilage anteriorly and the ends of the arytenoid cartilages posteriorly. As the arytenoids rotate within the larynx, the tension on the vocal cords changes, resulting in changes in sound production.
• Vocal folds: The vocal folds contain the vocal ligaments, or vocal cords. When viewing a midsagittal section of the larynx, you can observe two folds, one on top of the other, with a small space between them. The superior fold is the vestibular fold, also known as the false vocal fold. The true vocal folds are the inferior fold in this view. Sound production occurs as a result of movement of the vocal cords within the vocal fold.
• Several muscles act on the larynx during sound production, and most can be identified based on their names, which indicate their attachment points. The cricothyroid muscle runs from the cricoid to the thyroid cartilages. The transverse arytenoid muscle runs horizontally between the right and left arytenoids, while the oblique arytenoid muscles form an “X” shape on top of the transverse arytenoid muscle. The posterior cricoarytenoid muscles run from the cricoid to the arytenoid cartilages. Muscles acting on the arytenoid move these cartilages to change the tension on the vocal cords in sound production.
• Recurrent laryngeal nerve: This branch of the vagus nerve innervates most muscles of the larynx. If this nerve is damaged, the patient will have a hoarse voice or be unable to produce sound. This nerve is vulnerable because it travels down into the thorax near the heart (even wrapping around the arch of the aorta on the left) before it travels back up to the larynx.

Lab Activity 2: The Navigator – Muscles of Mastication, The Tongue and Salivary Glands

Use the Navigator to observe the muscles of mastication, the tongue and the salivary glands. This tool can be very helpful for viewing the structures of these regions from different angles as well as for isolating the and identify the structures listed above. DO NOT save any pre-sets. Preset 1 has already been created for you specifically for this lab.

**Note: If you are having difficulty seeing the various structures, you can change the background color of the Navigator screen. Click on File and Preferences. Here you can choose a lighter background color.

Lab Activity 3: Plastic Nose with Nasal Sinuses Model

We have one plastic nose with nasal sinuses model for you to observe in this lab. Please be gentle when looking at the model, there are parts that come apart and can be damaged when trying to replace them or if they are dropped.

• Review the model as well as the laminated images and key to identify structures from the terms to know list above. (the terms on the key in light gray are numbered on the laminated images, but you are NOT responsible to know them for lab, although they might help you for the lecture course)

Lab Activity 4: Plastinated Tissue – Oral & Nasal Cavity, Pharynx, Larynx

Begin with the respiratory dissection plastinated specimen:

• Nasal Cavity: The nasal septum has been removed, and you can observe the superior, middle, and inferior nasal conchae as well as the spaces below them: the superior, middle, and inferior nasal meatus. You can observe a small portion of the frontal sinus in the fontal bone as well as the sphenoid sinus more posteriorly, deep in the skull. You can also see the location of the ethmoid air cells, just anterior to the sphenoid sinus, though there is bone in front of these air cells in this specimen.
• Oral Cavity:  The oral vestibule and oral cavity proper can be challenging to discern here, as the teeth have been lost. However, you can somewhat see where the teeth would have been and understand generally where these two regions are located on this plastinate. You can easily observe the hard palate, soft palate, uvula and tongue. You can also see the submandibular gland inferior to the mandible. The other salivary glands have been removed. Finally, observe the masseter on this specimen.
• Larynx: Observe the thyroid cartilage, laryngeal prominence, cricoid cartilage, and thyrohyoid and cricothyroid muscles.  Also observe the epiglottis. 
• Pharynx:  Observe the nasopharynx and oropharynx. You can look down into the laryngopharynx, but this region has not been dissected in a midsagittal section.

Now look at the head and neck plastinated specimen:

• Muscles of mastication and temporomandibular joint: On the specimen’s left you can see the temporalis and masseter muscles. On the right, these muscles have been cut so that you can observe the medial and lateral pterygoid muscles. On both sides you can observe the temporomandibular joint.

Lab Activity 5: Visible Body Digital Atlas

Oral Cavity

• To see the oral cavity, click on the search box, now type in “Oral Cavity.” If you hide the gingiva, you can see the oral cavity proper. In this view, you can rotate the image around and see: hard palate, soft palate, uvula, sublingual glands, and submandibular glands.
• Next, click on “Menu.” To see the tongue, you can click on 1. Upper Digestive System under the Digestive System View. If you hide the mandible, gingiva and the teeth, you can see the tongue, styloglossus, genioglossus, and hyoglossus when you rotate the image around.
• Now click on “Menu” to return to systems view, under Muscular Systems View, now click on 2. Mastication. You will see the temporalis and masseter on a lateral view of this image. To see the lateral and medial pterygoids you will need to hide the zygomatic, mandible and maxilla as well as the masseter, the pterygoid muscles sit deep to all of these structures.

Nasal Cavity

• First, click on Respiratory System Views, then 1. Upper Respiratory. Hide the skin of the face and head. Now you can see the nasal cavity and the sinuses. You will have to rotate the model around, but you can see the ethmoidal air cells, the maxillary, frontal and sphenoid sinuses.
• Click on “Menu” to return to systems view, now click on 2. Nasal Cavity. In this view you can easily see the nasal conchae (superior, middle, inferior) and if you remove the cartilage on the nose, you can also see the nasal septum (septal cartilage).

Pharynx and Larynx

• First click on “Systems,” then under Respiratory System Views, click on 4. Pharynx and Larynx. Explore the structures of the pharynx and larynx here, specifically you can see: the pharyngeal constrictors (superior, middle, inferior).
• Click on “Menu” to return to the systems view, now click on 6. Laryngeal Muscles. Identify the structures listed under the larynx here: thyroid cartilage, cricoid cartilage, epiglottis, arytenoid cartilages, vocal folds and the muscles of the larynx; cricothyroid, transverse arytenoid and oblique arytenoid.