Deglutition: Anatomy, Physiology, and Neural Innervations

Overview

• The anatomy and physiology of Deglutition will be discussed
• Oropharyngeal structures and neural innervations will be reviewed

Oropharyngeal Structures

• Structures includes face, oral cavity, nasal cavity, and pharyngeal cavity

Neural Innervations

• Neural innervations includes cranial nerves: CN V, CN VII, CN VIII, CN IX, CN X, CN XI, CN XII

Face

• The facial skeleton is made up of the frontal, nasal and zygomatic bones, the maxillae and the mandible
• The frontal bone and the maxillae contain air-filled sinuses that develop after birth and contribute to facial growth
• Muscles on the face control facial expression
• Lip muscles are important for speech production and are innervated by the facial nerve
• Sensory nerve supply to the face is from the trigeminal nerve, which is vital for controlling facial muscle movements
• The arterial supply to the outside of the head comes from branches of the external carotid artery, as well as branches of the facial, superficial temporal and occipital arteries
• Venous drainage of the face is mainly from veins that share the same names, draining into the internal and external jugular veins, with some blood draining into the vertebral veins

Lips

• The skin covering the lips is very thin and is continuous with the mucosa of the oral cavity internally
• Lips do not have direct bony attachments
• Lips are suspended by a number of muscles, making them very flexible
• Sensory innervation includes the infra-orbital and mandibular nerves
• Motor innervation includes the facial nerve (VII)
• Superior and inferior labial arteries provide blood supply
• Lips function as sensory organs to control food and drink intake, which contribute to facial expression and speech

Oral Cavity

• Oral cavity divided into an oral cavity proper internal to the teeth, and vestibule region between lips and cheeks
• The roof of the oral cavity is formed by the hard and soft palates
• Lateral walls are the cheeks, formed mainly of the buccinator muscles
• The mylohyoid muscle lies on the floor of the mouth and the tongue sits on top of it
• The lips surround the interlabial space

Maxilla

• The maxilla forms the roof of the mouth
• The parts include the palatine process, palatine bone, velum, and uvula

Velum

• The velum is attached to the free border anteriorly to the hard palate
• Laterally muscles are continuous with the superior pharyngeal constrictors
• It moves posteriorly and hangs in the oral cavity when relaxed
• Five muscles move the velum - Glossopalatine, Pharyngopalatine, Levator palati, Uvular, Tensor palatini

Mandible

• The mandible or jaw is the only moveable bone of the skull
• The body is horizontal and horseshoe-shaped
• Mental protuberance is a median triangular prominence on the front of the body that forms the chin
• Alveolus forms the superior margin of the body and houses the lower teeth
• Sublingual and submandibular fossae are depressions on the medial surface of the body for the sublingual and submandibular glands
• The angle is where the ramus meets the body with attachments for the masseter, medial pterygoid, and stylomandibular ligament
• Ramus is a vertical plate, possessing the coronoid and condylar processes superiorly
• Coronoid process is triangular and flat, projecting upwards from the front of the superior border of the ramus, serves as an attachment point for temporalis
• The condylar process is a broad head projecting upwards from the back of the superior border of the ramus
• Mandibular condyle is a convex articular surface on top of the condylar process
• The mandibular notch separates the coronoid and condylar processes

Temporomandibular Joint

• The condylar process articulates with the temporal bone at the temporomandibular joint (TMJ)
• Alveolus articulates with the roots of the lower teeth
• Foramina exist
• The mandibular foramen is in the center of the medial surface of the ramus and transmits the inferior alveolar nerve and vessels
• The mental foramen is found in the lateral surface of the body and transmits the mental branch of the maxillary nerve and vessels

Floor of the Mouth

• The submandibular gland is a salivary gland in the floor of the mouth medial to the mandible, which wraps around the posterior free edge of mylohyoid dividing it into superficial and deep parts
• The sublingual gland is the smallest of the major salivary glands
• The sublingual gland is located anterior to the submandibular gland; small ducts empty into the floor of the mouth
• The blood supply to the facial arteries
• Parasympathetic Innervation from the facial nerve (VII)

Tonsils

• Palatine tonsils are located in the tonsillar fossae lateral to the root of the tongue
• The medial surfaces of the tonsils are visible within the oropharynx
• The tonsil consists of lymphatic material, being of variable size and larger in children
• The tonsils guard against inhaled and ingested pathogens
• Blood supply is from branches of the external carotid artery
• Innervation includes the glossopharyngeal nerve and maxillary nerve

Tongue

• Tongue formed of skeletal muscle and covered by oral mucosa
• The two groups of tongue muscles included are intrinsic and extrinsic
• Extrinsic muscles have one attachment outside the tongue, forming the bulk
• Extrinsic muscles change the tongue's position within the oral cavity
• Attachments of intrinsic muscles are within the tongue, responsible for changing its shape
• Projections called papillae form the oral mucosa on the surface to increase surface area and house taste buds
• A shallow sulcus terminalis on the dorsal surface divides the tongue into anterior two-thirds and posterior one-third

Buccal Cavity

• Oral mucosa: buccal sulci
• Reflection of alveolar mucosa to buccal/labial mucosa forms a deep recess called the sulci
• Buccal sulci posteriorly between the buccal and alveolar mucosa, running from the buccal frenulum to the hamular notch
• Oral mucosa: thin, non-keratinized mucosa lining the inside of the cheek (buccinator muscle) that is continuous with adjacent mucosal layers

Concha

• The superior nasal concha is a curved plate of bone, hanging down from the ethmoid bone
• The space beneath it is known as the superior meatus
• The walls of the nasal cavity, along with the three conchae and adjoining paranasal sinuses, are covered with a respiratory mucosa of high vascularity
• The conchae increase the surface area of the nasal mucosa, warming and moisturizing the air, while airborne particles adhere to it

Nasal Mucosa

• A large convoluted space located behind the nose
• It separates from the oral cavity below by the hard and soft palates, and extends sagittally by the nasal septum
• The space beneath each is known as a meatus
• The walls of the nasal cavity along with the three conchae and adjoining paranasal sinuses are covered with a highly vascular respiratory mucous membrane
• A dense network of hairs in the vestibule filters the air entering the nasal cavity
• Air is warmed and moistened passing over the mucosa, causing any remaining airborne particles to adhere
• Nasal mucosa: inferior meatus- the space beneath the inferior nasal concha, where the nasolacrimal canal opens into it

Pharynx

• The pharynx is a muscular tube with constrictor muscles connecting the nasal and oral cavities with the esophagus and larynx
• When food is swallowed, the soft palate moves backwards, blocking the nasal cavity and epiglottis
• The epiglottis moves downwards to block the entrance to the larynx and the constrictor muscles push the food safely into the esophagus

Nasopharynx

• The pharynx has three parts overall, and the nasopharynx is the highest, located posterior to the nasal cavities
• Pharyngeal mucosa: nasopharynx is lined with mucosa that protects it from the friction caused by swallowing food
• When food is swallowed, the soft palate blocks the nasal cavity, and the epiglottis blocks the larynx, so that constrictor muscles can then push food safely into the esophagus

Oropharynx

• The pharynx can be described in three parts, and the oropharynx is located posterior to the oral cavity as the middle part
• Oropharynx lined with mucosa that protects it from friction

Hypopharynx

• The hypopharynx, also called the laryngopharynx, is the lowest part of the pharynx posterior to the larynx
• It is lined with mucosa that protects it from friction
• When food is swallowed, the soft palate blocks the nasal cavity, and the epiglottis blocks the larynx, so that constrictor muscles can then push food safely into the esophagus
• Pharyngeal mucosa: Pyriform recesses
• Vertically oriented mucosal lined recess located in the laryngopharynx anteriorly, between the lamina of the thyroid cartilage (laterally) and the cricoid cartilage (medially)

Thyroid Cartilage

• The shield-like thyroid cartilage makes up most of the anterior and lateral walls of the larynx
• Important landmarks:
• Two flattened, quadrilateral plates of cartilage that are united in the front, separating in the back called Laminae
• Laryngeal prominence is the vertical midline prominence ('Adam's apple') that unites the two laminae anteriorly
• A deep V-shaped notch superior to the laryngeal prominence which separates the laminae, called the Thyroid notch
• A long thin superior projection from the posterior border of the Lamina, called the superior horn
• A thin inferior projection from the posterior border of the Lamina, which articulates with a facet on the cricoid arch, called the Inferior horn

Epiglottis

• The epiglottis is a thin, flexible leaf-shaped piece of cartilage located posterior to the thyroid membrane and body of the hyoid
• Its attached is in the midline to the hyoid and thyroid, and to the arytenoid cartilages by folds of mucous membrane
• The epiglottis closes off the larynx when swallowing, which directs food/liquid into the esophagus, protecting the airways

Cricoid Cartilage

• The cricoid cartilage is the only complete cartilaginous ring in the air passages, forming the most inferior part of the larynx which supports the entrance to the trachea
• It lies below the thyroid cartilage and on top of the 1st tracheal cartilage
• Articulates with the thyroid cartilage and the arytenoid cartilages

Tracheal Cartilage

• The trachea begins with the first tracheal cartilage, at the lower border of the cricoid cartilage at the level of C6, and ends in the mediastinum superiorly by dividing into the right and left principal bronchi.
• Functioning to keep the trachea open, the cartilages are C-shaped.
• The trachea is a tube composed of cartilages and membranes belonging to the respiratory system
• Begins at the lower border of the cricoid cartilage (at the level of the C6) and ends in the superior mediastinum by dividing into the right and left principal bronchi
• The patency of the trachea is maintained by a series of C-shaped rings of hyaline cartilage, united by fibro-elastic membranes.
• Trachealis muscle lies posteriorly across the gap of each cartilage, contracting the tracheal lumen

Muscles of Mastication

• This include intrinsic and extrinsic muscles.

Intrinsic Muscles

• Superior longitudinal
• Inferior longitudinal
• Transverse
• Vertical

Extrinsic Muscles

• Genioglossus
• Styloglossus
• Palatoglossus
• Hyoglossus

Muscles of the Tongue

• Four pairs of extrinsic muscles which have origins on bones of the skull or mandible, with insertions in the tongue
• These muscles change the position of the tongue including its shape
• Intrinsic muscles run entirely within the tongue vertically, transversely and horizontally altering its shape
• The extrinsic tongue muscles initiate movement of prepared food from the mouth to the pharynx
• Both sets of tongue muscles are very important in speech articulation

Facial Muscles

• Obicularis oris
• Transverse: Buccinator and Risoius
• Levator labii superior
• Zygomatic minor
• Zygomatic major
• Quadratus labii inferior
• Mentalis
• Depressor anguli oris
• Levator anguli oris
• Incisivus labii superior and inferior
• Platysma

Facial Expression

• The muscles are relatively small and attach skin of face and scalp to the bones of the skull
• The configuration of facial skin is changed altering our facial expression
• Facial expression is very important in non-verbal communication
• Muscles play a role in verbal communication, especially altering the shape of the upper/lower lips during articulation of many vowel and consonant phonemes
• Facial expression muscles are innervated by the facial nerve (7th cranial nerves)

Muscles of Swallowing

• Swallowing is a complex coordinated neuromuscular activity
• It involves eight groups of muscles in the head and neck
• Includes muscles of mastication, facial expression, tongue, soft palate, pharynx, larynx and suprahyoid and infrahyoid muscles

Taste

• Taste buds on the tongue are associated with specialized areas called lingual papillae
• Three include taste buds
  • Vallate papillae: eight to twelve large vallate papillae are positioned in a v-shaped line just anterior to the terminal sulcus, with glossopharyngeal nerve (9th) innervation
  • Foliate papillae: located on the lateral surface of the tongue close to the termination of the sulcus terminalis, with glossopharyngeal nerve (9th) innervation
  • Fungiform papillae: located on the anterior part of the dorsal surface of the tongue with chorda tympani branch of the facial nerve (7th) innervation
• Filiform papillae are numerous on the surface of the anterior two thirds of the tongue but do not contain taste buds

Cranial Nerves

The following nerves are critical for neural innervation

• CN V: Trigeminal
• CN VII: Facial
• CN IX: Glossopharyngeal
• CN X: Vagus
• CN XI: Spinal Accessory
• CN XII: Hypoglossal

CN V: Trigeminal

• Sensory innervation to the face, scalp, teeth, tongue, membranes of the mouth, palate, nose, and nasal sinuses.
• Motor to the muscles of mastication, lower jaw, palatal elevators

CN VII: Facial

• Sensory for taste to the anterior 2/3 of tongue while providing sensory input to the middle ear
• Motor to the muscles of the face, including the buccinator, stylohyoid, and posterior belly of the digastric

CN IX: Glossopharyngeal

• Sensory to the pharynx, posterior 1/3 of the tongue for taste and carotid sinus
• Motor to the pharynx

CN X: Vagus

• Sensory input to the pharynx, larynx, trachea, and lungs
• Motor activity for the pharynx, layrnx, and esophagus

CN XI: Spinal Accessory

• Motor function and joins the Vagus in motor the pharynx & larynx
• Motor to sternocleidomastoid and trapezius

CN XII: Hypoglossal

• Motor to the tongue

Explore the anatomy and physiology of deglutition, covering oropharyngeal structures and neural innervations. Key structures include the face, oral cavity, nasal cavity, and pharyngeal cavity. Cranial nerves such as CN V, CN VII, CN VIII, CN IX, CN X, CN XI, and CN XII are vital for this process.