🔑 Key Definitions

• Oral cavity: First part of digestive tract bounded by lips, cheeks, palate, tongue, and teeth.
• Tongue: Muscular organ involved in taste, speech, swallowing, and food manipulation.
• Papillae: Surface projections on tongue responsible for taste and friction.
• Intrinsic muscles: Muscles that change the shape of tongue.
• Extrinsic muscles: Muscles that change the position of tongue.
• Lingual nerve: Nerve supplying general sensation to anterior two-thirds of tongue.
• Aphthous ulcer: Painful superficial ulcer of oral mucosa.

Muscles of the tongue are skeletal muscles responsible for movement and shape control.

Intrinsic muscles — shape change:

• Superior longitudinal
• Inferior longitudinal
• Transverse
• Vertical

Extrinsic muscles — position change:

• Genioglossus
• Hyoglossus
• Styloglossus
• Palatoglossus

Intrinsic muscles change the shape of the tongue, allowing precise articulation and food manipulation. Extrinsic muscles move the tongue in different directions, helping in swallowing, speech, and maintaining airway patency.

Hypoglossal nerve injury can cause tongue paralysis. The tongue deviates toward the injured side, leading to speech difficulty and swallowing problems.

• Hypoglossal nerve CN XII → all tongue muscles except palatoglossus.
• Palatoglossus → vagus nerve CN X.

Sensory supply:

• Anterior 2/3 general sensation → lingual nerve CN V3.
• Anterior 2/3 taste → chorda tympani CN VII.
• Posterior 1/3 general sensation and taste → glossopharyngeal nerve CN IX.
• Posterior-most part → vagus nerve CN X.

Different parts of the tongue have different embryological origins. This explains why the anterior two-thirds and posterior one-third have different sensory and taste nerve supply.

• Lingual nerve injury: loss of general sensation from anterior tongue and risk of unnoticed tongue biting.
• Chorda tympani injury: loss of taste from anterior two-thirds of tongue.
• Glossopharyngeal nerve injury: impaired taste and sensation from posterior one-third; may also affect gag reflex.
• Hypoglossal nerve injury: tongue weakness, deviation, speech difficulty, and swallowing difficulty.

• Primary arterial supply → lingual artery.
• Parent artery → external carotid artery.
• Major branches → dorsal lingual, deep lingual, and sublingual arteries.
• Venous drainage → lingual vein to internal jugular vein.

• Anterior 2/3 develops mainly from the first pharyngeal arch.
• Posterior 1/3 develops mainly from the third pharyngeal arch.
• Posterior-most part develops from the fourth arch.
• Tongue development begins around the 4th week and is completed by the 8th week.
• Tongue muscles migrate from occipital somites.

The different arch origins of the tongue explain the different cranial nerve supply of its anterior and posterior regions. This is a high-yield embryology-anatomy integration point.

• Ankyloglossia: short lingual frenulum causing restricted tongue movement.
• Macroglossia: enlarged tongue.
• Bifid tongue: failure of fusion.
• Microglossia: small tongue.

These anomalies may cause feeding difficulty, speech difficulty, and swallowing problems.

• Skin layer
• Vermilion zone
• Oral mucosa
• Stratified squamous epithelium
• Skeletal muscle
• Sebaceous glands

The vermilion zone has rich blood supply, giving lips their red color. Thick epithelium protects the lips against mechanical stress.

• Enamel: hard outer protective layer and hardest tissue in the body.
• Dentin: supportive layer containing tubules.
• Pulp: nutritive and sensory core containing vessels and nerves.
• Cementum: anchors tooth to periodontal ligament.

• Longitudinal section: helps identify crown, root, enamel, dentin, pulp cavity, cementum, and periodontal attachment.
• Transverse section: helps understand circular arrangement of enamel/dentin/pulp and relation of tooth layers.
• Clinical relevance: enamel loss exposes dentin and may lead to sensitivity or caries progression.

Loss of enamel exposes dentin and causes tooth sensitivity. Deep caries may involve pulp, producing pain and infection risk.

• Filiform
• Fungiform
• Circumvallate
• Foliate

The tongue contains taste buds, stratified squamous epithelium, connective tissue, and skeletal muscle arranged in different planes.

Papillae increase surface area and help in taste sensation. Taste buds contain gustatory cells that detect taste stimuli. Filiform papillae are most numerous and mainly mechanical, while other papillae are more involved in taste.

• Trauma
• Infection
• Vitamin deficiency
• Autoimmune disease
• Stress

Persistent oral ulceration should not be ignored because it may require evaluation for serious pathology, including malignancy.

Aphthous ulcers are small, painful ulcers of the oral mucosa.

Treatment options:

• Topical steroids
• Vitamin supplementation when deficiency is present
• Pain relief gels
• Maintenance of oral hygiene

Taste Perception

1. Food dissolves in saliva.
2. Taste molecules bind to receptors on taste buds.
3. Sensory impulse is generated.
4. Signals travel through cranial nerves.
5. Brain interprets taste.

Taste Pathway Summary

1. Taste buds are stimulated by dissolved chemicals in saliva.
2. Impulses are carried mainly through cranial nerves VII, IX, and X.
3. Signals reach the nucleus tractus solitarius in the brainstem.
4. Information is relayed to the thalamus.
5. Signals project to the gustatory cortex for conscious taste perception.

• Tongue muscles → movement → speech clarity.
• Papillae → taste detection → food selection.
• Teeth → mechanical breakdown → digestion efficiency.
• Nerve supply → sensation and motor control → coordinated swallowing.
• Embryological origin → nerve supply pattern → clinical examination findings.

• Aphthous ulcers: painful but usually benign oral ulcers.
• Tongue paralysis: commonly linked with hypoglossal nerve injury.
• Ankyloglossia: restricted tongue movement due to short frenulum.
• Glossitis: inflammation of tongue, often associated with deficiency states or infection.
• Lingual nerve injury: loss of general sensation from anterior tongue.
• Chorda tympani injury: loss of taste from anterior two-thirds of tongue.
• Glossopharyngeal nerve injury: impaired posterior tongue sensation, taste, and gag reflex.

• Hypoglossal nerve supplies all tongue muscles except palatoglossus.
• Palatoglossus is supplied by vagus nerve.
• Anterior 2/3 taste is carried by facial nerve through chorda tympani.
• Posterior 1/3 sensation and taste are carried by glossopharyngeal nerve.
• Tongue develops from pharyngeal arches.
• Different embryological origins explain different nerve supply.
• Enamel is the hardest tissue in the body.
• Filiform papillae are the most numerous papillae.
• Ankyloglossia can cause speech difficulty.
• Aphthous ulcers are painful but usually benign.
• Tongue deviation suggests hypoglossal nerve injury.
• Persistent oral ulcer requires clinical evaluation.