Module 25: Oral Cavity and Taste

Oral cavity

Mouth framed by cheeks, tongue, and palate

Lips or labia

At the entrance of the mouth, outer covering is skin that transitions to a mucous membrane in the oral vestibule, very vascular with a thin layer of keratin, covers the orbicularis oris muscle, confine food between the teeth so food is chewed evenly

Orbicularis oris

Regulates what comes in and goes out of the mouth

Labial frenulum

Midline fold of mucous membrane that attaches the inner surface of each lip to the gum

Cheeks

Make up the oral cavity’s sidewalls, inner covering is mucous membrane made up of non-keratinized stratified squamous epithelium, connective tissue, and buccinator muscles, confines food between teeth so food is chewed evenly

Gingivae (gums)

Cover alveolar processes of the upper and lower jaws and surrounds the necks of the teeth

Oral vestibule

Pocket-like part of the mouth framed on the inside by the gums and teeth and the outside by the cheeks and lips

Fauces

Opening between oral cavity and throat

Oral cavity proper

Mouth’s main open area running from the gums and teeth to the fauces

Palate

Arched shaped and allows us to handle both digestion and respiration at the same time, anterior region is the hard palate

Hard palate

Anterior region of the palate that serves as a wall between the oral and nasal cavities and a rigid shelf against which the tongue can push food, created by maxillary and palatine bones, ends in the posterior oral cavity

Soft palate

Fleshier tissue after the hard tissue ends, mainly composed of skeletal muscle, moves upward with uvula to help keep foods and liquids from entering the nasal cavity

Uvula

Drops down from the center of the soft palate’s posterior edge, moves upward with soft palate to help keep foods and liquids from entering the nasal cavity, contributes to sound produced by snoring

Palatoglossal arch

Muscular fold extending downward from the soft palate on either side of the uvula where the oral cavity opens into the oropharynx next to the base of the tongue, palatoglossus muscle

Palatopharyngeal arch

Muscular fold extending downward from the soft palate on either side of the uvula where the oral cavity opens into the oropharynx and forms the superior and lateral margins of the fauces, palatopharyngeus muscle

Palatine tonsils

Clusters of lymphoid tissue in between palatoglossal and palatopharyngeal arches that protect the pharynx

Lingual tonsils

Located at the base of the tongue and posterior 1/3 of the tongue in the oropharynx

Tongue

Attached to the mandible, styloid processes of the temporal bones, and the hyoid bone to be positioned over the floor of the oval cavity, facilitates ingestion, mechanical digestion, chemical digestion, sensation, swallowing and vocalization, lined with stratified squamous epithelium

Medial septum

Extends along entire length of the tongue, dividing it into symmetrical halves

Intrinsic muscles

Change tongue’s size and shape to manipulate food for swallowing, inserts into the tongue from origins within it

Extrinsic muscles

Move the tongue in space, originate outside the tongue and insert into connective tissues within the tongue, help position food for optimal chewing, gather food into a bolus, and position food so it can be swallowed

Papillae

Extensions of lamina propria on the mucosa on the top and sides of the tongue, contains structures for gustatory transduction, includes circumvallate, foliate, filiform, and fungiform

Fungiform papillae

Mushroom-shaped and cover a large area of the tongue, tend to be larger toward the rear of the tongue and smaller on the tip and sides, contain taste buds

Filiform papillae

Short and bristle-like, contain touch receptors that help the tongue move food around the mouth, create an abrasive surface, distributed over anterior 2/3 of the tongue

Lingual glands

In the lamina propria, secrete mucus and water serous fluid that contains lingual lipase to break down triglycerides once it is activated in the stomach

Lingual frenulum

Fold of mucous membrane on the underside of the tongue and tethers the tongue to the floor of the mouth

Palatoglossus function

Elevates posterior tongue

Hyoglossus function

Pulls tongue down and back

Styloglossus function

Pulls tongue up and back

Genioglossus function

Pulls tongue forward

Intrinsic salivary glands

Unicellular glands housed within the mucous membrane of the mouth and tongue, constantly secreting saliva directly into the oral cavity or indirectly through ducts

Extrinsic salivary glands

Multicellular

Salivary glands function

Moistens ingested food, cleanses, lubricates, chemical digestion, salivary amylase for carbs and lingual lipase for lipids, anterior bacterial action through lysozyme, dissolves materials for taste receptors, neutralizes acids by secreting saliva

Labial glands

Secrete small amounts of saliva in the lips

Buccal glands

In the cheeks, ensure all areas are supplied with adequate saliva

Palatal glands

In the palate, ensure all areas are supplied with adequate saliva

Lingual glands

Ensure all areas are supplied with adequate saliva

Major salivary glands

Submandibular glands, sublingual glands, parotid glands

Submandibular glands

On floor of the mouth, secrete saliva into the mouth through submandibular ducts, innervated by CN VII

Sublingual glands

Lie below the tongue, secrete saliva into the interior surface of the oral cavity through lesser multiple sublingual ducts, innervated by CN VII

Parotid glands

Largest glands between the skin and masseter muscle, anterior to the ears, secrete saliva into the mouth through the parotid duct, innervated by CN IX

Parotid duct

Near the second upper molar tooth and runs parallel to the zygomatic arch and pierces the buccinator

Regulation of salivation

Regulated by ANS, parasympathetic stimulation keeps saliva flowing at just the right level in the absence of food, sympathetic stimulation reduces salivation during times of stress

Salivation process

Food contains chemicals that stimulate taste receptors on the tongue, which send impulses to the superior and inferior salivatory nuclei in the brain stem. These send parasympathetic impulses through the fibers in the glossopharyngeal and facial nerves, stimulating salivation. Salivation is increased after you swallow to cleanse the mouth and water down or neutralize chemical remnants, but most saliva is swallowed along with the food and reabsorbed.

Teeth

Organs similar to bones that you use to tear, grind, and mechanically break down food

Deciduous teeth

Baby teeth, 20

Permanent teeth

Adult teeth, 32, 8 incisors, 4 cuspids, 8 premolars, 12 molars

Incisors

Sharp front teeth for biting into food

Cuspids

Flank the incisors and have a pointed edge to tear up food

Premolars

Posterior to the cuspids and have an overall flatter shape with two rounded cusps for mashing food

Molars

Most posterior and largest, several pointed cusps for crushing food

Wisdom teeth

Third set of molars, eruption delayed until early adulthood, may fail to erupt and remain impacted

Alveolar processes

In maxilla and mandible where teeth are secured

Periodontal ligament

Connective tissue holding teeth in their sockets

Crown

Portion of tooth projecting above the gum line, contains inner pulp cavity with loose connective tissue where nerves and blood vessels run

Root

Portion of tooth embedded within the maxilla and mandible, contains inner pulp cavity with loose connective tissue where nerves and blood vessels run

Root canal

Region of the pulp cavity that runs through the root of the tooth

Dentin

Bone-like tissue surrounding the pulp cavity

Cementum

Covers dentin in the root of each tooth

Enamel

Covers dentin in the crown of each tooth, susceptible to mechanical and chemical erosion

Taste buds

Sense food in the mouth and sense taste

Temporomandibular joint

Connects temporal bone and mandible in a synovial, diarthrotic hinge joint with an articular disc and ligaments that provide stability

Muscles of mastication

Create movement of the TMJ, must exert enough pressure ot bite through and chew before swallowing

Masseter

Main muscle used for chewing, elevates the mandible to close the mouth and protracts the mandible, originates at the maxilla arch and inserts onto the mandible

Temporalis muscle

Elevates and retracts the mandible, originates at the temporal bone and inserts onto the mandible

Lateral pterygoid

Assists in chewing and moving food within the mouth, protrudes, depresses, and moves the mandible medially, originates at the pterygoid process of the sphenoid bone and inserts onto mandible

Medial pterygoid

Assists in chewing and moving food within the mouth, elevates, protracts, moves the mandible medially, originates at the sphenoid bone and maxilla, inserts onto mandible and TMJ

Motor innervation

All intrinsic and extrinsic muscles are innervated by CN XII except for the palatoglossus muscle, which is innervated by CN X

General sensation innervation

Somatic sensation to the anterior 2/3 is innervated from a branch of CN V3, visceral sensation to the posterior 1/3 is innervated by CN IX, visceral sensation to the root is innervated by CN X

Taste innervation

Taste to the anterior 2/3 is innervated by branch of CN VII, taste to posterior 1/3 is innervated by CN IX, taste perception is performed by epiglottis and tongue’s epiglottic region innervated by branch of CN X

Foliate papillae

On lateral and posterior tongue, contains taste buds

Vallate papillae

Least numerous but the largest, in an inverted V shape on the posterior dorsal surface, most taste buds are here

Taste process

Specialized gustatory receptor cells in papillae taste buds can transduce taste stimuli, sensitive to the chemicals contained within foods ingested. They release neurotransmitters based on the amount of chemical in the food onto the dendrites of sensory neurons in the facial, glossopharyngeal, and vagus nerve. Sensory pathway travels along facial and glossopharyngeal nerves and synapses with neurons of the solitary nucleus in the brain stem. Axons from solitary nucleus project to ventral posterior nucleus in the thalamus to project to the gustatory cortex of the insular cortex, where taste is processed.