Overview
This module details the anatomy and physiology of the pharynx, larynx, nasal cavity, and olfactory system, focusing on their structure, function, and significance in respiration, digestion, sound production, and olfaction. Key structures, pathways, and muscle actions involved in swallowing, speech, and smell are emphasized.
The Pharynx
- The pharynx is a muscular tube lined with mucous membrane, running from the posterior oral and nasal cavities to the openings of the esophagus and larynx.
- is a short tube of skeletal muscle
- Involved in both digestion (food passage) and respiration (air passage).
- receives food and air from mouth
- receives air from nasal cavities
- Involuntary muscle contractions close airways during swallowing.
- The pharynx has three regions, each with distinct structure and function:
- Nasopharynx: <u>Superior</u>, <u>only for breathing and speech</u>. Contains pharyngeal tonsils (adenoids) and auditory (Eustachian) tubes.
- contains pharyngeal tonsils (adenoid tonsils): aggregates of lymphnoid reticular tissue similar to lymph node that lies at superior portion of nasopharynx
- contains a rich supply of lymphocytes and is covered with ciliated epithelium that traps and destroys invading pathogens that enter during inhalation
- large in children â> regress with age and may even disappear
- uvula is a small bulbous, teardrop-shaped structure located at the apex of the soft palate
- Both the uvula and soft palate move like a pendulum during swallowing, swinging upward to close off the nasopharynx to prevent ingested materials from entering the nasal cavity
- auditory (Eustachian) tubes: connect to each middle ear cavity open into the nasopharynx
- connection is why colds often lead to ear infections
- Oropharynx: <u>Middle</u>, <u>serves for both respiration and digestion</u>. Contains palatine and lingual tonsils.
- bordered superiorly by the nasopharynx and anteriorly by the oral cavity
- wall of the oropharynx = similar to oral cavity
- mucosa includes a stratified squamous epithelium that is endowed with mucus-producing glands
- nasopharynx becomes the oropharynx, the epithelium changes from pseudostratified ciliated columnar epithelium to stratified squamous epithelium
- contains two distinct sets of tonsils:
- palatine tonsils: one of a pair of structures located posterolaterally in the oropharynx
- lingual tonsils: located at the base of the tongue
- BOTH â> composed of lymphoid tissue and trap and destroy pathogens entering the body through the oral or nasal cavities
- Laryngopharynx: <u>Inferior</u>, serves respiration and digestion; connects anteriorly to larynx for air passage to bronchial tree and posteriorly to esophagus for food.
- continues the route for ingested material and air until its inferior end, where the digestive and respiratory systems diverge
- stratified squamous epithelium of the oropharynx is continuous with the laryngopharynx
- Anteriorly = opens in larynx
- posteriorly = enters esophagus
- does not directly connect to trachea
Divisions of the Pharynx
| Region | Function(s) | Key Structures |
|---|
| Nasopharynx | Air passage, speech | Pharyngeal tonsils (adenoids), auditory tubes |
| Oropharynx | Air and food passage | Palatine tonsils, lingual tonsils |
| Laryngopharynx | Air and food passage, divergence | Opens to esophagus (posterior), larynx (anterior) |
- Epithelial lining:
- Nasopharynx: pseudostratified ciliated columnar epithelium
- Oropharynx and laryngopharynx: stratified squamous epithelium (with mucus glands)
Lymphoid Tissue in Pharynx
- Pharyngeal tonsils: At the roof of the nasopharynx; lymphoid tissue with ciliated epithelium traps and destroys pathogens from inhaled air. Large in children, regress or disappear with age.
- Palatine tonsils: Located posterolaterally in oropharynx.
- Lingual tonsils: At base of tongue.
- Both palatine and lingual tonsils trap pathogens entering through oral or nasal cavities.
Muscles Involved
- Palatal muscles: Levator veli palatini, tensor veli palatini (elevate soft palate during swallowing)
- Pharyngeal constrictors: Superior, middle, and inferior (propel bolus downward)
- Laryngeal elevators: Palatopharyngeus, stylopharyngeus, salpingopharyngeus (raise pharynx during swallowing)
Deglutition (Swallowing)
- Movement of food from mouth to stomach (swallowing); takes about 4â8 seconds for solids/semisolids, 1 second for very soft food/liquids.
- Involves skeletal muscles of tongue, and muscles of pharynx and esophagus.
- Aided by: Saliva and mucus.
- Controlled by: Voluntary and involuntary muscle actions (latter by autonomic nervous system).
| Phase | Type | Events |
|---|
| Voluntary (oral/buccal phase) | Conscious | Tongue pushes bolus against hard palate into oropharynx. |
| Pharyngeal (controlled by autonomic nervous system) | Involuntary | Soft palate and uvula rise, closing nasopharynx. Laryngeal muscles constrict to prevent aspiration (epiglottis covers glottis). Pharyngeal constrictors move bolus. Breath held briefly (deglutition apnea). |
| Esophageal (controlled by autonomic nervous system) | Involuntary | Bolus enters esophagus. Peristalsis (muscular contractions) moves bolus toward stomach; sphincters open/close appropriately. Mucus secretion lubricates bolus. |
- Key events:
- Elevator muscles contract to receive bolus, relax as constrictors contract to force bolus down into esophagus and initiating peristalsis.
- Epiglottis folds downward to cover glottis during swallowing, preventing aspiration (access to trachea and bronchi) (food in trachea triggers cough reflex).
- during swallowing â> soft palate + uvula rise reflexively to close off entrance of nasopharynx
The Larynx
- A cartilaginous structure, inferior and anterior to the laryngopharynx, connecting the pharynx to the trachea.
- Plays roles in regulating airflow, producing sound, and protecting the lower respiratory tract during swallowing.
- prevents food and drink from entering the trachea, conducts air, and produces sound
- <u>Lined superiorly by stratified squamous epithelium (protects from abrasion)</u> and <u>below transitions to pseudostratified ciliated columnar epithelium (with goblet cells for mucus production).</u>
- Mucus traps and removes debris/pathogens; cilia move mucus upward toward pharynx for swallowing.
- 3 large cartilage pieces:
- thyroid cartilage (anterior), epiglottis (superior), and cricoid cartilage (inferior
Laryngeal Cartilages
| Cartilage | Location | Key Features |
|---|
| Thyroid cartilage | Anterior, largest | Contains laryngeal prominence (Adamâs apple; more prominent in people with high levels of testoterone). |
| Cricoid cartilage | Inferior | Complete ring, wide posteriorly, narrow anteriorly. |
| Epiglottis | Superior | Flexible, elastic cartilage attached to thyroid cartilage, covers trachea during swallowing. |
| Arytenoid cartilages | Paired, posterior | Attach to vocal cords, move cords during speech. |
| Corniculate, cuneiform cartilages | Paired, accessory | Support vocal structures. |
Vocal Structures
- Glottis: composed of vestibular folds, vocal folds, and intervening space.
- inhaled air leaves the pharynx passing through this structure
- Vestibular folds (false vocal cords): Folds of mucous membrane superior to true cords, protect true vocal cords.
- Vocal folds (true vocal cords): White, membranous, attached to thyroid (anterior) and arytenoid (posterior) cartilages. inner edges are free = oscillation for sound production.
- Pitch/voice: Determined by size/tension of vocal folds; larger folds (usually in males) â deeper voice.
- Glottis opening controls airflow and sound; tension/position adjusted by intrinsic laryngeal muscles (names not required).
Larynx during Swallowing
- Pharynx and larynx lift upward.
- Epiglottis folds down to cover the glottis, blocking trachea and preventing aspiration.
- Movements enlarge passage for food and keep airways protected.
Musculature
- Extrinsic muscles: Supra- and infrahyoid muscles position and stabilize larynx.
- Intrinsic muscles: Move laryngeal cartilages to change vocal fold length/tension (do not memorize individual names).
pathway of swallowing
- 1. tongue moves up and back towards soft palate, pushing bolus towards oropharynx
- 2. stimulation of receptors in the oropharynx cause the uvula and soft palate to elevate and seal off the nasopharynx
- 3. contraction of the pharyngeal constrictors moves the bolus through the oropharynx and laryngopharynx
- 4. bolus enters the esophagus and peristaltic contractions propel the bolus toward the stomach
The Nasal Cavity
- nasal cavity: function as part of respiratory system
- nasal bones: lie under root and bridge of nose
- articulates superiorly with frontal bone and laterally with maxillary bones
- alar cartilage: forms apex (anterior portion) of nose surrounding nares (nostrils)
- Entry point for air; involved in air filtration, warming, humidification, and olfaction.
- External nose: Root and bridgeâbone (nasal, frontal, maxillary). Protruding portionâcartilage (including alar cartilage at apex around nostrils).
- Nasal septum: Separates right and left nasal cavities.
- Anterior: formed by septal cartilage
- Posterior: formed by perpendicular plate of ethmoid bone and thin vomer bone
- Floor: formed by maxillary and palatine bones
- Posterior wall: formed by sphenoid bone
Conchae and Meatuses
- Lateral walls: Superior, middle, and inferior nasal conchae (superior/middleâethmoid bone; inferiorâa separate bone).
- 3 bony projections of nasal cavity in each lateral wall
- inferior nasal conchae = separate bones
- superior + middle conchae = portions of ethmoid bone
- superior, middle, and inferior meatuses: Spaces beneath each conchaâsuperior, middle, and inferior nasal meatus.
- Function: Conchae/meatuses <u>increase surface area</u> and <u>disrupt airflow, causing air to swirl/bounce along mucosaâair is cleaned, warmed, and humidified</u>.
Paranasal Sinuses
- Air-filled cavities within the frontal, maxillary, sphenoid, and ethmoid bones.
- Lined with nasal mucosa; all communicate with nasal cavity.
- Functions: reduce bone mass = lighten skull, condition and warm air, enhance voice resonance.
| Sinus | Location | Notes |
|---|
| Frontal | Frontal bone, above eyebrows | Most anterior sinus |
| Maxillary | within maxillary bones, just below orbits | Largest, prone to infection; drains poorly; paired |
| Sphenoid | within body of sphenoid bone, single midline | Most posterior |
| Ethmoid air cells | located in right and left sides of ethmoid bone, between orbit & nasal cavity | Multiple small spaces |
Olfaction (Sense of Smell)
- Olfaction (sense of smell) detects chemical stimuli in the air; closely linked with the nasal cavity.
- Olfactory epithelium: Small patch in superior nasal cavity.
- Olfactory receptor neurons: Bipolar sensory cells with apical dendrites (olfactory hairs/cilia) extending into mucus layer surface.
- located in small region within superior nasal cavity
- Odorant molecules dissolve in mucus and bind receptors on olfactory cilia.
Olfactory Pathway
- Olfactory receptor neuron axons pass through cribriform plate foramina (ethmoid bone) and into brain.
- Synapse in olfactory bulb (above cribriform plate).
- Second-order neurons form the olfactory tract running posteriorly along the inferior surface of the frontal lobe.
- Most fibers travel to the primary olfactory cortex (superomedial temporal lobe), where smell is consciously perceived.
Key Points about Olfaction
- Only sense that does not relay through thalamus before reaching cortex (see source notes).
- Functions alongside mucus for trapping/solubilizing odorants for detection.
Key Terms & Definitions
- Nasopharynx: Superior pharyngeal region for breathing and speech; contains pharyngeal tonsils and auditory tubes.
- Oropharynx: Middle pharyngeal region; for both air and food, contains palatine and lingual tonsils.
- Laryngopharynx: Inferior pharyngeal region; split of air (larynx) and food (esophagus).
- Deglutition: Swallowing process; includes voluntary and involuntary phases.
- Glottis: Opening of larynx; includes vestibular folds, vocal folds, and space between.
- Laryngeal promi00nence: Adamâs apple; thyroid cartilage projection.
- Paranasal sinuses: Air-filled cavities that lighten skull, condition air, and add resonance to voice.
- Olfactory epithelium: Nasal region with olfactory receptor neurons for smell.
- Cribriform plate foramina: Holes in ethmoid bone for passage of olfactory nerve axons.
Essential structures and concepts from each section are listed; focus study on their locations, functions, associated muscles, major processes (like swallowing), and the major pathways for olfaction and sound production.