The oral cavity

•  Oral cavity

  There is a fold of tissue called a frenulum that attaches to the upper lip and also one under the tongue. The uvula of the soft palate hangs down at the back of the mouth and either side of the uvula there are tissue folds called arches. The anterior folds are the palatoglossal arches and the posterior folds are the palatopharyngeal arches.  These arches are created by muscles of the palate that pass to the tongue and pharynx.

  
•  Oral cavity

  In between these folds is a collection of lymphoid tissue called the palatine tonsils. Healthy palatine tonsils are usually small, but they can become very swollen and easily seen if they become infected. The fauces is another name for the opening of the oral cavity (mouth).

  
• Muscles

  The lateral walls of the oral cavity are formed by buccinator.  Mylohyoid forms a diaphragm in the floor of the mouth and has the anterior belly of digastric inferior and geniohyoid muscle superior. ‘Genio’ refers to the mandible and ‘glossus’ refers to the tongue. Mylohyoid attaches to the mylohyoid line of the mandible, geniohyoid attaches to the inferior genial tubercle of the mandible and genioglossus attaches to the superior genial tubercle.

  
• Supra-hyoid muscles

  The posterior belly of digastric attaches to the mastoid process, and stylohyoid attaches to the styloid process of the temporal bone. So, they sit either side of the stylomastoid foramen that allows the facial nerve to exit the skull – therefore the facial nerves innervates both of these muscles. The mandibular division of the trigeminal nerve innervates the lower teeth and gums and the muscles of mastication, so it also supplies the mylohyoid nerve to innervate mylohyoid and the anterior belly of digastric both of which attach to the mandible.

  
• Salivary glands

  The sublingual gland lies entirely in the floor of the mouth, under the tongue. The parotid gland has a duct that opens at the upper second molar (on each side) and the submandibular glands have a duct that opens between the 1st and 2nd incisors either side of the frenulum in the floor of the mouth (one each side). The sublingual gland has many small ducts that open directly into the floor of the mouth. The slide shows the nerves that supply the parasympathetic secretomotor fibres to each gland.

  
• Floor of the mouth

  The lingual nerve is a branch of the mandibular division of the trigeminal nerve that supplies sensory innervation to the anterior 2/3rds of the tongue, and carries taste and parasympathetic fibres from the facial nerve. The hypoglossal nerve is the main motor supply to the tongue musculature.

  
• Tongue

  The surface of the tongue is roughened by small papillae, many of which are associated with fibres that detect taste (taste buds). The largest papillae form a line 2/3rds of the way along the tongue – they are the vallate papillae.The surface of the posterior third has a bumpy appearance due to the presence of the lingual tonsil which is embedded into this part of the tongue. The lingual and palatine tonsils effectively guard the entrance to the oropharynx and there is further lymphoid tissue to protect the nasopharynx.

  
• Nerves

  The anterior 2/3rds receives general sensation from the lingual nerve (CNV3). The special sense of taste to the anterior 2/3rds is carried to the tongue within the lingual nerve but the fibres originate in the facial nerve. The chorda tympani branch of the facial nerve carries these fibres and joins the lingual nerve in the infratemporal fossa. The sensory innervation to the posterior third is more straightforward with general sensory and special sense of taste from the glossopharyngeal  nerve. 

  
• Tongue – intrinsic muscles

  •Change the shape of the tongue

  •Fibres in different orientations

  •All fibres within the tongue

  •Hypoglossal nerve CN XII

  The intrinsic muscles lie entirely within the tongue and act to change the shape of the tongue to help mold the food into a bolus. Cranial nerve XII is the primary MOTOR supply to the tongue as it innervates all of the instrinsic and most of the extrinsic muscles of the tongue.

  
• Tongue – extrinsic muscles

  •Change the position of the tongue in the mouth

  •Originate outside the tongue and insert into the tongue

  •Hypoglossal nerve CN XII EXCEPT palatoglossus = vagus nerve CN X in the pharyngeal plexus

  They are called extrinsic as the originate from structures outwith the tongue (hyoid bone, styloid process, palate, mandible) and insert into the tongue. Palatoglossus is the odd one out here as it is not supplied by CN XII but instead shares the innervation of many of the other muscles of the soft palate – CN X in the pharyngeal plexus.

  
• Blood supply

  The lingual artery is the 2nd anterior branch of the external carotid artery

  The arterial supply to the tongue is from the lingual artery. It is crossed by the hypoglossal nerve, passes under hyoglossus and enters the floor of the mouth. It supplies the floor of the mouth, the extrinsic muscles and sends a deep branch into the body of the tongue.

  
• Venous drainage

  The tongue drains blood mainly to the lingual vein which communicates with the internal jugular vein.

  
• Nerve supply

  
• Lingual nerve

  lingual nerve descending to the tongue from the infratemporal fossa, whereas the hypoglossal nerve passes from the hypoglossal canal at the base of the skull and passes over hyoglossus but under mylohyoid to enter the floor of the mouth.

  
• Lymphatic drainage

  The tip of the tongue drains into nodes under the chin (submental). The lateral edges of the tongue pass lymph into nodes around the submandibular salivary gland (submandibular). The central and posterior parts of the tongue drain to deep nodes in the neck (deep cervical).

  
• Hard Palate

  The roof of the oral cavity is formed by the hard and soft palates. The hard palate is composed mainly from the palatine parts of the maxilla but there are also 2 palatine bones that complete the posterior part of the hard palate. In life, the bones are covered with the mucous lining of the oral cavity and the soft palate hangs from the posterior border.

  
• Glands of the palate

  There are also small glands embedded into the mucosa covering the hard palate, they produce mucous and are innervated by the facial nerve.

  
• Nerves and vessels

  The palate is supplied by the greater palatine vessels and nerves. The greater palatine artery arises in the pterygopalatine fossa as a branch of the 3rd part of the maxillary artery. it descends in the palatine canal to enter the palate via the greater palatine foramen. The nerves are branches of the maxillary division of the trigeminal nerve from the pterygopalatine ganglion that also descend in the palatine canal and enter the greater palatine foramen. Remember that CNV2 only has sensory nerves.

  
• Palatine nerves and vessels

  The lesser palatine vessels and nerves are branches of the greater palatine but pass posteriorly to supply the soft palate.

  
• The soft palate has a muscular core covered in mucous lining. It hangs from the hard palate and the uvula hangs down between the arches at the posterior part of the oral cavity. The palatine aponeurosis attaches to the hard palate, it is tough connective tissue and helps to strengthen the soft palate and provide a site for muscle attachment. There are 5 muscles that move the soft palate. The soft palate hangs at the back of the mouth. If not expecting the soft palate to be touched the sensory response will elicit the gag reflex.

  
• Soft palate

  The muscles of the soft palate are:

  Levator veli palatini - from the petrous temporal bone and cartilage of the auditory tube to the palatine aponeurosis. Acts to raise the soft palate.

  Tensor veli palatini – from the cartilage of the auditory tube, wraps a tendon around the pterygoid hamulus (small bony point of the medial pterygoid plate) to  thepalatine aponeurosis. Tenses the soft palate.

  
• Soft palate

  Musculus uvulae – the muscle core of the uvula, from the palatine bones to the palatine aponeurosis. Elevates and retracts the uvula.

  Palatoglossus – from the palatine aponeurosis to the tongue (forms the anterior arch in the oral cavity). Elevates the tongue and helps to close the oral cavity from the oropharynx.

  
• Soft palate

  Palatopharyngeus -  from the wall of the pharynx to the palatine aponeurosis. Elevates the pharynx and moves the pharyngeal wall forwards towards the soft palate.

  All muscles are innervated by the cranial part of the accessory nerve running in the vagus nerve in the pharyngeal plexus EXCEPT tensor veli palatini (CNV3).

  
• Palatine nerves

  Blood from the greater palatine artery and the ascending palatine branch of the facial artery. Veins drain to the pterygoid venous plexus and lymph mainly passes to the deep cervical nodes. Sensory nerves are branches of the greater/lesser palatine (CNV2) and also from the CN IX.

  
• Facial nerve

  the facial nerve sends fibres into the pterygopalatine ganglion (via greater petrosal and nerve of the pterygoid canal) which join with the CNV2 nerves to supply the small glands of the palate.

  
• Teeth

  teeth missing = the alveolar bone that supported the tooth is absorbed, leading to reduced bone in that area (blue arrow).

  If all of the teeth are lost = all of the supporting alveolar bone is also lost.

  
• Nerve supply

  CNV2 which supply the upper teeth and gums and CNV3 which supplies the lower teeth and gums.

  
• Vessels

  The teeth and gums also requires a blood supply – from alveolar branches of the maxillary artery.