9 Oral Cavity | Nasal Cavity | Pharynx | Larynx
Learning Objectives:
- Identify the structures of the nasal cavity and the sinuses and describe their functions
- Identify the contents of the oral cavity, including the salivary glands.
- Describe and identify the muscles of mastication and muscles that act on the tongue.
- Identify the cartilage and muscles of the larynx and explain how the vocal cords function.
- Describe the parts of the pharynx.
Terms to Know
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Nasal Cavity and Smell
Larynx
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Oral Cavity
Pharynx
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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 to the digestive system by connecting the oral cavity to the esophagus, and it contains muscles that function in swallowing.
Lab Activities
Activity 1: Slideshow Images
Go through the slideshow images on Canvas 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 we have discussed or will be discussing in other labs. Within these images, you will 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 sit 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 mouths.
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.
Pharynx
- 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: 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.
Larynx
- 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 Adam’s 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 the 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.
Activity 2: VIdeos and Model Slideshows
Observe the structures above in the videos and model slideshows on Canvas. The videos and model slideshows cover:
- Plastinated tissue from lab, including a midsagittal view and lateral views
- Video walk-throughs from the digital atlas
- Video walk-throughs of the slideshow referenced in Activity 1
- Slideshow of the sinus and nasal cavity model
Wrap up and clinical connection
The clinical connection for this lab reviews the anatomy of the oral cavity, pharynx, and larynx. The first video shows all the structures working together during singing. The second video looks further at the vocal cords during singing. In the final video, a barium swallow test is shown. The anatomy of the pharynx and larynx are reviewed, and you can observe normal swallowing and abnormal swallowing(dysphagia). It is amazing to see the anatomy in action in these videos and even more impressive to see when the anatomy is dysfunctional.