Special Senses - Gustatory

Special Senses ● Sensory receptors are within large, complex sensory organs in the head. ● Smell in olfactory organs ● Taste in taste buds ● Hearing and equilibrium in ears ● Sight in eyes GUSTATORY Taste Receptors Taste buds  Organs of taste  Located on papillae of tongue, roof of mouth, linings of cheeks and walls of pharynx toxin avoidance Umami Glutamate, amino acids T1R1+T1R3 (GPCRs) Evenly Distributed MSG, soy sauce, meat Spicy (pungent) (Not a gustatory taste, but a trigeminal sensation) Capsaicin, heat TRPV1 (Transient ReceptorPotential Vanilloid 1) Throughout the oral cavity Chilli peppers, wasabi Main Structures of the Tongue  Epiglottis: A flap of tissue that prevents food and liquids from entering the trachea during swallowing.  Palatine Tonsil & Lingual Tonsil: Lymphoid tissues that helps in immune defense, protecting against infections.  Terminal Sulcus: A V-shaped groove; separates the oral part from the pharyngeal part.  Midline Groove of Tongue: shallow groove in the middle, divides the tongue into left and right halves. Types of Papillae (Taste and Texture Receptors): 1. Filiform Papillae:  The most numerous papillae, covering most of the tongue’s surface.  Lacks taste buds; provides texture and helps grip food. 2. Fungiform Papillae:  Found mostly on the anterior part of the tongue. Taste/Gustatory Sensations and Receptors  Contains taste buds for detecting sweet, sour, salty, and umami flavors. Taste Detected Receptor/Ion Example 3. Vallate (Circumvallate) Papillae: Sensation Substance Channel/  Large, dome-shaped papillae arranged in a VDistribution shape near the terminal sulcus.  Contains many taste buds and detects bitter Sweet Sugars, T1R2+T1R3(GPC Sugar, honey, tastes. artificial Rs)Throughout the aspartame sweeteners tongue, slightly Other Structures: more at the tip  Palatoglossal & Palatopharyngeal Arches: separate the mouth from the throat; Sour Hydrogen PKD2L1 (Ion Lemon, swallowing and speech. Ions (H+) Channel) vinegar  Median Glossoepiglottic Fold: Connects the Distributed across tongue to the epiglottis, helping with swallowing. the tongue Taste receptors  Chemoreceptors  Taste cells – modified epithelial cells that function as receptors  Taste hairs –microvilli that protrude from taste cells; sensitive parts of taste cells Salty Sodium Ions (Na+) ENaC (Epithelial Sodium Channel)Broadly across the tongue Bitter Alkaloids, toxins T2R (GPCRs) More concentrated at the back for Taste Nerve Pathways 1. Tastants Dissolve in Saliva → Bind to taste receptors on taste buds 2. Activation of taste receptor cells → Neurotransmitter release 3. Signal transmitted via cranial nerves: Caffeine, ● CN VII (Facial) →Anterior ⅔ of tongue quinine (bitter ● CN IX (Glossopharyngeal) → Posterior ⅓ flavor) of tongue Table salt NaCI 4. 5. 6. 7. 8. ● CN X (Vagus) → Epiglottis & Pharynx Cranial Nerves synapse at Nucleus of the solitary tract (NTS) in medulla Signal relayed to Thalamus (Ventral Posteromedial Nucleus, VPM Thalamus send taste signals to Primary Gustatory Cortex (Insula & Frontal Operculum Integration in Orbitofrontal Cortex, Amygdala, & Hypothalamus → Emotional & Autonomic Response (pleasure from sweetness or aversion to bitterness) Perception of taste  Second-order neurons carry taste signals to the thalamus (ventral posteromedial nucleus, VPM). 4. Cortical Processing  From the thalamus, taste information is relayed to the primary gustatory cortex in the insula and frontal operculum.  The orbitofrontal cortex integrates taste with olfaction (smell), texture, and temperature for overall flavor perception. Additional Integration  The amygdala and hypothalamus process emotional and autonomic responses to taste (e.g., pleasure from sweetness or aversion to bitterness). Clinical Application 1. Taste Receptors (Taste Buds) Activation  Taste buds located on the fungiform, foliate, and circumvallate papillae detect chemical stimuli. Tastants (molecules from food) bind to receptors on gustatory cells, activating ion channels or G-protein-coupled receptors.  Depolarization occurs, triggering neurotransmitter release to sensory nerves. Disorder Description Causes Ageusia Complete loss of taste perception Neurological damage (stroke, head trauma) Hypogeusia Reduced ability to taste Zinc deficiency, aging, radiation therapy Dysgeusia Distorted taste perception(e.g., metallic taste) Chemotherapy, medications, oral infections Phantogeusia Perception of taste without stimulus Neurological disorders, UR infections 2. Sensory Nerve Transmission Three cranial nerves carry taste signals from different tongue regions:  Facial nerve (CN VII - Chorda Tympani branch): o Carries taste sensations from the anterior two-thirds of the tongue.  Glossopharyngeal nerve (CN IX): o Transmits taste from the posterior onethird of the tongue, including vallate papillae.  Vagus nerve (CN X - Internal Branch of Superior Laryngeal Nerve): o Conducts taste from the epiglottis and pharynx (minor role in taste perception). Anosmia (loss of smell) Inability to detect odor due to receptor, nerve, or brain damage -Post-viral anosmia (e.g., after COVID19) -Head trauma damaging olfactory pathways -Nasal polyps blocking airflow 3. Brainstem Processing  These nerves synapse at the solitary nucleus (nucleus of the solitary tract, NTS) in the medulla oblongata. Hyperosmia (Heightened smell) Increased sensitivity to odors, often due to hormonal, neurological -Pregnancy-related nausea from strong smell -Migraines causing sme;ll Clinical Application factors or medication effects. hypersensitivity -Addison’s disease leading to heightened olfactory perception Phantosmia (Olfactory hallucinations) Perceiving odors that aren’t present,linked to neurological conditions due to abnormal activity of olfactory cortex. -Smelling burnt toast before a seizure (epilepsy) -Migraines causing phantom floral or metallic scents -Alzheimer’s patients detecting non-existent smoke Synesthesia (Mixed-up senses) Cross-activation of sensory pathways, leading to intertwined perceptions. -Associating names with specific smells (e.g., “Emma” smells like cinnamon –Seeing colors when smelling spices -Tasting flavors when hearing musical notes