DR 6 - Neck and Oral Cavity DEMO COPY(1) PDF

Module 202: Neuroscience and Behaviours: Neck and Oral Cavity. 202 DR6: Neck and Oral Cavity Learning Outcomes: By the end of the module you should be able to: • Identify the anatomy of the mouth • Locate the components of the tongue and its innervation (cranial nerves 5,7,9) • Locate the main...

Module 202: Neuroscience and Behaviours: Neck and Oral Cavity. 202 DR6: Neck and Oral Cavity Learning Outcomes: By the end of the module you should be able to: • Identify the anatomy of the mouth • Locate the components of the tongue and its innervation (cranial nerves 5,7,9) • Locate the main structures of the larynx • Locate the main structures of the pharynx • Identify the triangles of the neck and the strap muscles • Identify the main neurovascular structures that transverse the neck • Apply clinical examples to anatomical principles In this practical session you will study the anatomy of the neck, and oral cavity. For this session, you will be examining a range of prosected specimens as well as the anatomical models available within the dissecting room. As with all your other practical sessions in the dissecting room make sure you work through this handout, answer the questions and complete the checklist. Orbital and Nasal Cavity Prof. Claire Smith 9/30/2020 1 Module 202: Neuroscience and Behaviours: Neck and Oral Cavity. Workstation 1. Mouth In this workstation you will examine the oral cavity, floor of the mouth and tongue. A. Oral Cavity The oral cavity is located inferior to the nasal cavities and is continuous with both the nasal cavities superiorly and the pharynx inferiorly, as well as opening onto the face. The oral cavity has key boundaries. The roof of the mouth is formed by the hard and soft palate, the walls by the muscular cheeks, a floor formed by the tongue and other muscles and the posterior boundary is continuous with the oropharynx. The oral cavity functions as part of the digestive system and in manipulating the sounds produced by the larynx. The oral cavity opens onto the face through the oral fissure. The oral cavity is divided into an outer oral vestibule and inner oral cavity • The outer oral vestibule includes the lips and cheeks • The inner oral cavity is enclosed by the teeth. • The roof includes the hard and soft palate. • Muscles of the soft palate create the arches of the oral cavity. • • Palatoglossal arch • Palatopharyngeal arch – including the uvula The floor of the cavity is formed by muscles (mylohyoid and geniohyoid) and the tongue and contains the submandibular and sublingual glands. Using the mirrors and your own face • Examine the lips and inside the mouth to identify the boundaries formed. • Locate the palatoglossal (Pga)and palatopharyngeal arch (Ppa). • Identify the uvula (Uv). Use the image on the next page to check your findings. Orbital and Nasal Cavity Prof. Claire Smith 9/30/2020 2 Module 202: Neuroscience and Behaviours: Neck and Oral Cavity. The image above depicts the oral cavity. Lift up your tongue and locate the: • Frenulum of the tongue (FTo) • Openings of the sublingual glands and the submandibular glands (OSLG, OSMG) The image above depicts the sublingual region of the oral cavity. Orbital and Nasal Cavity Prof. Claire Smith 9/30/2020 3 Module 202: Neuroscience and Behaviours: Neck and Oral Cavity. B. Floor of the mouth. The digastric muscle is superficial to the muscles you will examine. The anterior belly of the digastric muscle (innervated by CN V3), is attached to the mandible in the digastric fossa and has a fascial sling attachment to the hyoid bone (identify the hyoid bone on a skeleton). The posterior belly is supplied by the facial nerve (CN7). Digastric helps to open the jaw when the masseter and temporalis muscles are relaxed. The floor of the mouth is made up of the mylohyoid, geniohyoid and tongue. Two mylohyoid muscles form a muscular diaphragm that defines the inferior limit of the floor of the oral cavity. They are attached to medial side of the mandible body, and run inferiorly to the midline where fibres join with the contralateral fibres in a raphe. • Trace the digastric muscle across its anterior and posterior bellies. • Turn the prosection over so that on the inferior aspect you can examine the floor of the mouth, locate the mylohyoid muscle. mylohyoid anterior digastric hyoid The image above depicts muscles of the floor of the mouth. • Examine the geniohyoid muscles that lie on either side of the midline and run from the mandibular symphysis to the body of the hyoid (try using a skull to see these attachment sites). The geniohyoid muscles main role is to pull the hyoid and larynx superiorly and anteriorly during swallowing. What is the innervation of the geniohyoid muscles? Orbital and Nasal Cavity Prof. Claire Smith CNXII Hypoglossal nerve 9/30/2020 4 Module 202: Neuroscience and Behaviours: Neck and Oral Cavity. C. On the head examine the tongue The tongue is a muscular structure that sits in the floor of the mouth. The tongue is divided in the midline by a septum, which means all the muscles of the tongue are paired. The extrinsic muscles have origins outside the tongue and insert into it. The four extrinsic muscles are the genioglossus, hyoglossus, styloglossus and palatoglossus. You will easily be able to identify genioglossus on the medial surface of your bisected head as it is the large fan shaped muscle that makes up a great deal of the bulk of the muscle. Genioglossus muscle fibres originate immediately superior to the origin of geniohyoid (from the genial tubercle on the internal aspect of the mandible) and run into the tongue where they blend with the intrinsic muscles. Genioglossus is innervated by the hypoglossal nerve and acts to protrude the tongue. • Locate genioglossus Hyoglossus is a key landmark in the floor of the mouth as the lingual artery enters the tongue deep to hyoglossus and the hypoglossal and lingual nerves enter the tongue on the external surface of the hyoglossus. Hyoglossus is innervated by the hypoglossal nerve and acts to depress the tongue. • Locate hyoglossus. Styloglossus takes its origin on the styloid process of the temporal bone (use a skull to identify this structure). Styloglossus runs inferiorly and medially between the constrictor muscles of the pharynx to enter the lateral surface of the tongue. Styloglossus is innervated by the hypoglossal nerve and acts to elevate and retract the tongue • Locate styloglossus (It may be difficult to see clearly). Palatoglossus originates from the aponeurosis of the soft palate and passes anteriorly and inferiorly to the tongue. It is innervated by the vagus nerve (CN 10). Palatoglossus acts to depress the palate and elevates the back of the tongue. • Locate palatoglossus. Use the image on the next page to check your findings. Orbital and Nasal Cavity Prof. Claire Smith 9/30/2020 5 Module 202: Neuroscience and Behaviours: Neck and Oral Cavity. palatoglossus styloglossus genioglossus hyoglossus The image above depicts muscles of the tongue. • Using the MRI image, locate the genioglossus and geniohyoid muscles - note the relaxed position of the tongue in the mouth. The image above depicts an MRI sagittal section of the head. Orbital and Nasal Cavity Prof. Claire Smith 9/30/2020 6 Module 202: Neuroscience and Behaviours: Neck and Oral Cavity. Unlike the extrinsic muscles of the tongue, the intrinsic muscles are less visible mainly because they originate and insert in the substance of the tongue. The muscles are the superior and inferior longitudinal muscles and the transverse and vertical muscles. These muscles act together to alter the shape of the tongue by changing the length, curling the edges and rounding and flattening the surface. The major artery of the tongue is the lingual artery, which originates from the external carotid artery and travels anteriorly from an inferior position to the apex of the tongue. Drainage of blood from the tongue is achieved via the lingual vein and its tributaries. The innervation of the tongue involves five cranial nerves: • The glossopharyngeal nerve carries general and taste sensation from the pharyngeal (posterior third) tongue. • The lingual nerve (V3) supplies general sensation to the anterior two thirds. • The facial nerve via the chorda tympani nerve supplies taste from the anterior two thirds of the tongue, the fibres travel in the lingual nerve. • The hypoglossal and accessory (using the vagus nerve) nerves innervate the muscles of the tongue. If you are able to reflect the mandible away from the lateral surface of the oral region you will notice how the lingual nerve loops under the submandibular duct and ascends into the tongue. The hypoglossal nerve is also often near the lingual vein. lingual artery lingual nerve Submandibular duct hypoglossal nerve lingual vein The image above depicts the lingual nerve, artery and vein. Apart from eating and swallowing, why are precision movements of the tongue required? Speech Orbital and Nasal Cavity Prof. Claire Smith 9/30/2020 7 Module 202: Neuroscience and Behaviours: Neck and Oral Cavity. Clinical Context Squamous cell carcinoma of the mouth As the oral cavity is lined by non-keratinizing squamous epithelium, 95% of malignant tumours in the oral cavity are squamous cell carcinomas which usually occur in old age and with a clear male predominance (90% to 10%). Their main risk factors are alcohol and tobacco use, especially when combined which raises risk by x15. HPV and EBV infection is also a likely contributing factor. Interestingly, fruit and vegetable consumption appear to reduce risk of squamous neoplasia in the mouth. Many sites in the oral cavity, the larynx or the pharynx may harbour a neoplasm and treatment is dependent on site and stage primarily. Surgery or radiation therapy are the main treatment options and in young patients, survival rate is up to 75% in early stage tumours. Metastasis is mainly seen in local neck lymph nodes and the lungs. Acute epiglottitis Sepsis originating from a dental or pharyngeal origin can spread to the epiglottis, causing oedema of the glottis and asphyxia. The enlarged epiglottis can occlude the laryngeal inlet causing stridor and this often necessitates urgent airway intervention. • Using the MRI scan of a sagittal section of the head and neck identify the epiglottis Orbital and Nasal Cavity Prof. Claire Smith 9/30/2020 8 Module 202: Neuroscience and Behaviours: Neck and Oral Cavity. Workstation 2. Larynx and Pharynx In this workstation you will examine the larynx, pharynx and strap muscles of the neck. A. On the model and prosections examine the larynx. The larynx is the organ responsible for voice production. It is located in the neck inferior to the hyoid bone and superior to the trachea at the vertebral level C3-C6. The larynx is responsible for producing phonation and acts to guard the air passages. It is comprised of a series of cartilages including a single thyroid cartilage, epiglottis, and cricoid cartilage and paired arytenoid, corniculate and cuneiform cartilages. • Locate the laryngeal cartilages (thyroid, epiglottis and cricoid, arytenoid, corniculate and cuneiform) • Locate the vocal folds. The interior of the larynx is comprised of a cavity and the vocal folds. You will be able to see the vocal fold on the model. You will also note there is another fold; this is the vestibular fold or false vocal fold. The vocal fold attaches to the arytenoid cartilages and muscles surround the larynx create change in the tone and the pitch of the sound emitted. These muscles are controlled by the inferior and superior laryngeal nerves which are branches of the vagus nerve. epiglottis thyroid cartilage vocal fold cricoid cartilage The image above depicts cartilages of the larynx. Orbital and Nasal Cavity Prof. Claire Smith 9/30/2020 9 Module 202: Neuroscience and Behaviours: Neck and Oral Cavity. Pharynx The pharynx is the superior expanded portion of the nasal and oral cavities. The pharynx extends inferiorly past the larynx to become continuous with the oesophagus. The pharynx is divided into three portions; nasopharynx, oropharynx and laryngopharynx. • Locate the nasopharynx posterior to the nose and superior to the soft palate • Locate the oropharynx posterior to the mouth • Locate the laryngopharynx posterior to the larynx Aggregations of lymphoid tissue is found in the pharynx and forms an incomplete tonsillar ring. The lymphoid tissue forms in groups known as tonsils. In the nasopharynx the pharyngeal tonsil (adenoid) is located in the mucus membrane of the roof and posterior wall of the pharynx. The palatine tonsils are located in the oropharynx, at the interval between the palatine arches. • Locate on the prosection where the tonsils would be- it is not always possible to see them. The wall of the pharynx is comprised of voluntary muscle (unique for the GI tract). The muscles are arranged with an inner longitudinal layer and an outer circular layer (opposite to the rest of the GI tract). The external circular layer is formed by three muscles; the pharyngeal constrictors- superior, middle and inferior, which are supplied by CN10. • Locate the three constrictor muscles on the prosection What happens to the vocal fold during a Valsalva manoeuvre? They close to prevent the passage of air out of the trachea, increasing the intrathoracic pressure. Orbital and Nasal Cavity Prof. Claire Smith 9/30/2020 10 Module 202: Neuroscience and Behaviours: Neck and Oral Cavity. Clinical Context Laryngoscopy Laryngoscopy is the procedure used to examine the internal surfaces of the larynx. The tongue normally covers the epiglottis, and so needs to be gently pulled aside. The vestibular folds normally appear pink, whereas the vocal folds are whiter. The image above depicts the internal view of the larynx as seen by laryngoscopy. Why might this procedure be performed? When direct visualisation is needed, extraction of foreign bodies. Heimlich manoeuvre A foreign object e.g. food may be inhaled into the vestibule of the larynx, this causes the muscles of the larynx to go into spasm and no air enters the tract. The individual becomes speechless and asphyxiation occurs, death occurs in approximately 5 minutes from lack of oxygen. The individual may cough in an attempt to dislodge the object. Emergency action must be taken to remove the blockage. This may take the form of sudden compression of the abdomen (Heimlich manoeuvre). This procedure elevates the diaphragm and compresses the lungs forcing air into the larynx to assist in removing the blockage. Orbital and Nasal Cavity Prof. Claire Smith 9/30/2020 11 Module 202: Neuroscience and Behaviours: Neck and Oral Cavity. Emergency Airway Opening Cricothyrotomy Emergency procedure for when the airway is obstructed above the level of the vocal cords. The median cricothyroid ligament can be perforated and a small tube inserted. • Locate this point on a specimen or model at your station. Tracheostomy Emergency procedure for when the larynx is obstructed secondary to foreign body, oedema (eg anaphylaxis) or neck trauma at the level of 2nd,3rd or 4th tracheal ring. If first ring is included it could cause subglottic stenosis later. • Using the MRI scan identify the: thyroid cartilage and cricoid cartilage of the larynx and the vocal fold. Identify where a tracheostomy might be placed. The image above depicts an MRI sagittal section of the head and neck. Orbital and Nasal Cavity Prof. Claire Smith 9/30/2020 12 Module 202: Neuroscience and Behaviours: Neck and Oral Cavity. Workstation 3. Triangles and blood supply to the neck In this workstation you will examine the muscles, arteries and nerves associated with the triangles of the neck and the major veins and arteries of the neck. A. Muscles of the neck. Superficial neck The most superficial muscle of the neck is platysma, a thin broad sheet. Underneath the platysma on the anterior aspect is a series of ‘strap’ muscles of the neck. The neck is divided into an anterior and posterior triangle by the sternocleidomastoid muscle. • Locate platysma • Locate sternocleidomastoid Muscles in the anterior triangle of the neck are described in relation to their position to the hyoid bone. They are therefore suprahyoid (above the hyoid bone) and include: mylohyoid, geniohyoid, stylohyoid and digastric. Muscles which are ‘infrahyoid’ (below the hyoid) are the: sternohyoid, omohyoid, sternothyroid and thyrohyoid and are known as the strap muscles. • Locate the strap muscles of the neck (sternohyoid, omohyoid, sternothyroid and thyrohyoid) Use the image to the right for reference Orbital and Nasal Cavity Prof. Claire Smith 9/30/2020 13 Module 202: Neuroscience and Behaviours: Neck and Oral Cavity. Triangles of the neck The neck is divided into an anterior and posterior triangle by the sternocleidomastoid muscle. • Trace the sternocleidomastoid and identify the anterior and posterior triangles. The anterior triangle is further sub-divided into four smaller triangles; - Carotid - Submandibular - Submental - Muscular Carotid triangle Bounded by the posterior belly of digastric, superior belly of omohyoid and superior anterior border of sternocleidomastoid. The carotid triangle contains: the carotid artery, internal jugular vein and vagus nerve, in addition to other nerves like the hypoglossal nerve. Submandibular triangle Bounded by the anterior and posterior bellies of digastric and the surface of the mandible. The submandibular triangle contains: the submandibular gland, branches of the external carotid artery and branches of the facial nerve. Submental triangle Located under the chin, bounded by the anterior belly of digastric and continuous with the submental triangle on the opposite side. The submandibular triangle contains lymph nodes and small veins. Muscular triangle Bounded by the superior belly of omohyoid, sternohyoid and the lower borders of sternocleidomastoid. The muscular triangle, as its name suggests, contains the strap muscles of the neck discussed earlier. Orbital and Nasal Cavity Prof. Claire Smith 9/30/2020 14 Module 202: Neuroscience and Behaviours: Neck and Oral Cavity. The image to the left depicts the triangles of the neck. • Examine the larger muscles of the neck involved in movement: sternocleidomastoid, omohyoid, trapezius and the scalene muscle group. • Trace out on the prosection each of the triangles, ensuring to identify the borders and the contents. Orbital and Nasal Cavity Prof. Claire Smith 9/30/2020 15 Module 202: Neuroscience and Behaviours: Neck and Oral Cavity. B. Blood supply and drainage of the neck. Arteries The arterial supply to the head and neck is derived from the common carotid and vertebral arteries. Both ascend in the neck. The common carotid artery is located within the carotid sheath and around vertebral level C4, divides into internal and external. The internal artery ascends without giving off any branches and supplies the brain and spinal cord. The external artery gives off several branches: superior thyroid, ascending pharyngeal, lingual, facial, occipital, posterior auricular, maxillary and superficial temporal. • You will have already come across some of these arteries before, but now bring the flow of arterial blood to the whole head together and trace out each of these arteries, using prosection and the figure below. The above image depicts the arterial supply to the head and neck. Orbital and Nasal Cavity Prof. Claire Smith 9/30/2020 16 Module 202: Neuroscience and Behaviours: Neck and Oral Cavity. Veins Veins of the head and neck drain into the internal and external jugular veins. The internal jugular vein starts at the jugular foramen, then joins the subclavian vein to form the right and left brachiocephalic veins. The external jugular vein is formed from the posterior auricular and retromandibular vein at the angle of the mandible and will join the subclavian vein. The position of veins can vary, as can the size. • Ensure you can locate the following vessels: internal jugular vein, external jugular vein, retromandibular vein. The image above depicts venous drainage of the head and neck. Orbital and Nasal Cavity Prof. Claire Smith 9/30/2020 17 Module 202: Neuroscience and Behaviours: Neck and Oral Cavity. Clinical Context Neck Trauma The neck is divided into three zones to clinically assess neck trauma. Zone 1 Includes the root of the neck to the clavicles. Structures at risk in this region are the apices of the lungs, thyroid and parathyroid glands, trachea, oesophagus, common carotid arteries and jugular veins. Zone 2 Extends from the cricoid cartilage to the angle of the mandible. Structures at risk include the superior part of the thyroid gland, thyroid and cricoid cartilages, larynx, carotid arteries, jugular veins and oesophagus. Zone 3 Is from the angle of the mandible to the top of the head. Structures at risk include the salivary glands, oral and nasal cavities. This image illustrates the zones used to classify neck trauma by zone. Orbital and Nasal Cavity Prof. Claire Smith 9/30/2020 18 Module 202: Neuroscience and Behaviours: Neck and Oral Cavity. Benign enlargement of the thyroid May compress nearby structures e.g. oesophagus and the trachea. • How might this affect the patient? Difficulty swallowing and breathing respectively Carcinoma of the thyroid Unlike benign enlargements of the gland, a carcinoma will invade nearby structures, causing more severe complications such as haemorrhage. If the recurrent laryngeal nerve is involved, the patients present with voice changes; if the cervical sympathetic chain is involved, the patients present with Horner’s syndrome. Central Line Patients requiring central venous access, e.g. on ITU, will have lines placed into the internal jugular vein approximately 3cm above the clavicle. This is undertaken using guided ultrasound. These are usually performed on the right side, as it is a straight line from the jugular vein into the brachiocephalic vein, into the superior vena cava. • Explore this area using Complete Anatomy to see this relation Orbital and Nasal Cavity Prof. Claire Smith 9/30/2020 19 Module 202: Neuroscience and Behaviours: Neck and Oral Cavity. CT angiogram Having covered the arterial supply to the head, use the CT angiogram to locate the: • Anterior cerebral arteries • Middle cerebral arteries • Posterior cerebral arteries (these are difficult to see in this particular image) • Internal carotid artery • External carotid artery and a few of its branches. The image above depicts a CT angiogram of the head and neck. Orbital and Nasal Cavity Prof. Claire Smith 9/30/2020 20 Module 202: Neuroscience and Behaviours: Neck and Oral Cavity. Workstation 4: Pathology of the Neck and Oral Cavity Cleft palate Sagittal CT Coronal CT A gap in which structure allows communication between the oral and nasal cavities? Hard palate Referencing the image on the right, which structures of the nasal cavity have also been compromised in this individual’s case? Ethmoid, vomer, conchae - meatuses What functional issues might this individual experience if their condition went untreated? Communication between oral and nasal cavities – mucous and food/drink Infection Difficulty breathing through the nose. Using your knowledge of the anatomy of the oral and nasal cavities, why might an individual with a cleft palate be more likely to experience ear infections? Close relation of the eustachian/pharyngotympanic/auditory tube. Orbital and Nasal Cavity Prof. Claire Smith 9/30/2020 21 Module 202: Neuroscience and Behaviours: Neck and Oral Cavity. Lingual thyroid Sagittal CT Axial CT Ectopic thyroid is a congenital abnormality more commonly seen in females resulting from the failure of normal caudal migration of the thyroid gland. Lingual thyroid represents more than 90% of ectopic thyroid cases. Where does the thyroid migrate to in more commonly seen anatomy? Into the neck, sitting atop the thyroid cartilage of the larynx What symptoms might a patient experience due to a lingual thyroid? Difficulty swallowing (dysphagia), difficulty speaking (dysphonia) How does thyroid function differ in cases of ectopic thyroid such as the above? Largely asymptomatic – little to no difference What treatments are normally undertaken for those with lingual thyroid? If asymptomatic, no treatment needed. Surgery can be considered, but needs to then be balanced to ensure patient does not then suffer from massive hypothyroidism. Orbital and Nasal Cavity Prof. Claire Smith 9/30/2020 22 Module 202: Neuroscience and Behaviours: Neck and Oral Cavity. Neck fracture Axial CT Sagittal CT The two CT scans above are an example of a “Hangman Fracture”, named so as it was normally seen in those executed by hanging. Today this kind of fracture is seen in injuries with massive hyperextension of the neck, such as motor vehicle accidents. Which vertebrae is fractured in a “Hangman Fracture”? C2 Which portions of the vertebrae are fractured? Pedicles / pars interarticulares What closely related neurovascular structures are at risk of damage during this type of fracture? Spinal cord What might the consequences of injury to these structures be? Death Orbital and Nasal Cavity Prof. Claire Smith 9/30/2020 23 Module 202: Neuroscience and Behaviours: Neck and Oral Cavity. Checklist Review all the structures you have examined today and ensure that you are satisfied that you have completed the check list below before you leave the dissecting room: • Identify the anatomy of the mouth • Locate the components of the tongue and its innervation (cranial nerves 5,7,9) • Locate the main structures of the larynx • Locate the main structures of the pharynx • Identify the triangles of the neck and the strap muscles • Identify the main neurovascular structures that transverse the neck Orbital and Nasal Cavity Prof. Claire Smith 9/30/2020 24