Anatomy and Physiology of Speech and Hearing – Comprehensive Study Notes

Introduction to Speech and Hearing Anatomy and Physiology

  • Objective overview: after reading the chapter, students should be able to identify major anatomical structures related to speech, language, and hearing; describe physiological functions; name historical contributors; describe essential physiological processes for speech production and hearing; understand how impairments in structures relate to communication disorders.
  • Key terms introduced: Anatomy; Dissection; Physiology; Gross Anatomy; Cellular Anatomy and Physiology; Upper/Lower Respiratory Tract; Nasal Cavity; Cilia; Mouth; Breathing; Adenoids; Pharynx; Esophagus; Bronchial Tubes; Bronchitis; Bronchioles; Alveoli; Lungs.

Anatomy and Physiology Foundations

  • Anatomy: study of the structure of the body and its parts.
    • Etymology: Greek ana = up/through, tomie = cutting.
    • Historical approach: dissection of cadavers; modern living-body examination via endoscopy, CT, MRI.
  • Physiology: study of the functions of the body and its parts.
    • Etymology: Greek physis = nature, logia = to speak.
  • Gross anatomy vs Cellular anatomy (histology):
    • Gross: parts visible to naked eye.
    • Cellular: microscopic structures.
  • Importance for audiology and SLP: understanding speech/hearing mechanisms is essential for normal communication and disorders.

Three Subsystems of Speech Anatomy

  • Respiratory system
  • Laryngeal system
  • Articulatory system
  • Speech uses the same anatomy as non-speech tasks (breathing, swallowing, coughing).

Respiratory System: Overview and Function

  • Major components: lungs, diaphragm, rib cage, trachea, pharynx, oral and nasal passages.
  • Two tracts: upper (oral/nasal cavities and pharynx) and lower (trachea, bronchi, lungs).
  • Air entry: inhaled primarily through nostrils into nasal cavity; nasal cavity lined with mucous membranes and cilia to warm, moisten, and filter air.
  • Mouth breathing: potential negatives (less filtration and warming; more irritation; linked to higher URIs, possible asthma exacerbation); often due to nasal obstruction (e.g., enlarged adenoids).
  • Adenoids: paired tissue at the back of the nasal cavity; filters debris from nasal air.
  • Pharynx: approx. 5 in (12.7 cm) long; hollow tube behind nose to trachea/esophagus; muscles encircle the throat; directs food to the esophagus during swallowing; during breathing, air goes from nose to pharynx to trachea/lungs.
  • Breathing rates (typical):
    • Rest: ~14–16 breaths/min.
    • Post-exercise: >60 breaths/min.
    • Newborns at rest: ~40–50 breaths/min.
    • By age 5: ~25 breaths/min.
  • Trachea: main airway to/from lungs; elastic tissue with ~20 cartilage rings; flexible for head/neck movements while breathing.
  • Bronchial tubes: two main tubes branching from trachea to each lung.
  • Bronchioles: progressively narrower airways beyond the bronchi.
  • Alveoli: tiny air sacs at ends of airways where gas exchange occurs; surrounded by capillaries; oxygen into blood; CO₂ removed from blood.
  • Lungs: paired, cone-shaped organs occupying most of chest space; left lung slightly smaller to accommodate the heart.
  • Rib cage and diaphragm: protected by 12 rib pairs; diaphragm is the principal inspiratory muscle; diaphragm moves downward during inhalation; rib cage expands; air fills lungs.
  • Primary function: gas exchange to sustain life; inhaled air contains O₂, N₂, CO₂; O₂ used for cellular metabolism; CO₂ expelled.
  • Respiratory cycle in speech: inhalation is ~10% of cycle; exhalation ~90% to sustain speech on one breath.
  • Balloon analogy for expiratory resistance: inhaling a large volume, then expelling air through resistance prolongs expiratory airflow; relates to vocal fold vibration and oral cavity resistance during speech.
  • Respiratory protection and pathology context:
    • Lung cancer: second most common cancer; ~130,000 US deaths in 2023 (≈70,000 men, ≈60,000 women).

Laryngeal System: Structure and Function

  • Major structures: cartilage, muscles, and bone forming the larynx (not a single structure).
  • Thyroid cartilage: central laryngeal structure; contains laryngeal prominence (Adam’s apple); not directly related to the thyroid gland.
  • Epiglottis: leaf-shaped cartilage above the laryngeal prominence; important for swallowing to direct food away from the airway (not a primary speech structure).
  • Hyoid bone: horseshoe-shaped bone high in the neck; attachment point for tongue muscles (from above) and laryngeal muscles (from below); often described as a “floating bone.”
  • Cricoid cartilage: ring-shaped structure at the base of the larynx; sits atop the trachea.
  • Laryngeal framework: hyoid bone, thyroid cartilage, cricoid cartilage.
  • Vocal folds (thyroarytenoid muscles): paired structures within the larynx; attached anteriorly under the Adam’s apple; attached posteriorly to the arytenoid cartilages; arytenoids swivel to open/close and lengthen/shorten folds.
  • Glottis: space between the open vocal folds.
  • Phonation (voice production): during exhalation, air pressure builds under closed vocal folds; folds vibrate to produce sound; vibration is phonation.
  • Fundamental Frequency (F0): basic rate of vocal fold vibration; perceived as pitch.
    • Children: ≈ F0≈350 extHzF_0 \approx 350 \, ext{Hz}
    • Women: ≈ F0≈240 extHzF_0 \approx 240 \, ext{Hz}
    • Men: ≈ F0≈120 extHzF_0 \approx 120 \, ext{Hz}
    • Reason for lower F0 in men: larger, bulkier vocal folds that vibrate more slowly.
  • Visuals referenced: relation between vocal fold size and pitch; sequential steps of vocal fold vibration (frontal view).

Ar tic ul at or y Syst em: Speech Articulators

  • Articulation: movement of one structure against another to produce speech sounds.
  • Vocal tract: extends from larynx to lips; includes cavities, muscles, and bones; three cavities:
    • Oral cavity (mouth)
    • Nasal cavity (nose)
    • Pharyngeal cavity (throat)
  • Movable articulators: lips, tongue, soft palate (velum), pharynx, mandible.
  • Fixed articulators: hard palate, alveolar ridge, teeth.
  • Lips: essential for several consonants (e.g., /p/, /f/, /m/); ventriloquism as an exception (speech without visible lip movement).
  • Tongue: most important speech articulator; not a single muscle but a complex muscular arrangement; essential for all vowels and many consonants (e.g., /s/, /l/, /θ/ in “th”).
  • Soft palate (velum): soft tissue at the back of the roof of the mouth; tip is the uvula; function: velopharyngeal closure to separate oral and nasal cavities; most sounds require oral articulation except for /m/, /n/, /ŋ/ which involve nasal resonance.
  • Velopharyngeal closure: necessary to prevent nasalization of most sounds; pharyngeal muscles assist with closure.
  • Pharynx as articulator: muscular walls move to assist velopharyngeal closure.
  • Mandible (jaw): hinge with temporal bones; provides fine-tuning of speech; can impact articulation quality; “pipe speech” illustrates how jaw constraints affect clarity when the jaw is restricted (e.g., with a pipe in the mouth).
  • Fixed articulators details:
    • Hard palate: bony front roof of mouth; base for certain sounds (e.g., /ʃ/ in “shoe”).
    • Alveolar ridge: ridge behind the upper teeth; contact point for sounds like /t/, /d/, /z/.
    • Teeth: upper and lower incisors for /v/, /f/, /θ/ (“vie” and “faith”).
  • Glossectomy: surgical removal of all or part of the tongue; partial glossectomy common; many individuals still able to communicate effectively post-procedure.
  • Masseter muscle: strongest jaw muscle; can exert up to ~200 pounds of force during chewing.

The Process of Speech Production: S * T = P

  • Concept: speech production converts aerodynamic energy (source) into acoustic energy (product) via transfer function.
  • Formula: SimesT=PS imes T = P where:
    • S = source (respiratory system as driving energy for speech)
    • T = transfer function (laryngeal and articulatory system shaping the sound)
    • P = product (acoustic speech signal)
  • Brain involvement: speech starts with language centers in the brain generating a message; neural commands drive respiratory, laryngeal, and articulatory mechanics.
  • Role of the brain in speech: essential for coordinating respiratory, laryngeal, and articulatory systems; detailed brain anatomy and nervous system discussed in later chapters.

Hearing (Audition) Overview

  • Hearing (audition) consists of two major components:
    • Peripheral auditory system: outer ear through the auditory nerve.
    • Central auditory system: beyond the auditory nerve to auditory centers in the brain.
  • Basic flow: sound waves are collected by the outer ear, transmitted through the middle ear, converted to mechanical energy, transferred to the inner ear, transduced into neural impulses, and processed by brain centers.
  • Peripheral Auditory System overview (Figure references in text): outer ear, middle ear, inner ear structures; functional roles are described below.

Peripheral Auditory System: Outer Ear

  • Outer ear components:
    • Auricle (pinna): visible part; made of elastic cartilage; landmarks include helix, tragus, lobule.
    • External auditory meatus (ear canal): about 2.5 cm; outer third is elastic cartilage; inner two-thirds lie in temporal bone; lined with skin and fine hairs; ceruminous (cerumen) glands secrete earwax to protect canal and prevent drying.
  • Functions:
    • Funnels sound toward the eardrum.
    • Slightly boosts high-frequency sounds due to canal resonance, aiding localization and perception.
  • Common notes: ears are sometimes cupped behind the ear to aid sound localization; cotton swabs are discouraged for cleaning ears due to risk of impaction and damage.
  • Figures referenced: cross-sectional view of outer, middle, inner ear structures.

Middle Ear

  • Location: air-filled space within the temporal bone.
  • Key components: tympanic membrane (eardrum); three ossicles (malleus, incus, stapes); two auditory muscles (tensor tympani and stapedius); Eustachian tube.
  • Tympanic membrane: thin, tough, fibrous membrane vibrating with sound pressure waves.
  • Ossicular chain: malleus (connected to eardrum), incus, stapes (connected to the oval window of the cochlea).
  • Acoustic reflex: involuntary contraction of middle ear muscles (tensor tympani and stapedius) to stiffen the ossicular chain in response to loud sounds (typically >90 dB), protecting the inner ear.
  • Eustachian tube: connects middle ear to the pharynx; functions to protect, aerate, drain; equalizes middle ear air pressure with environmental pressure; normally closed and opens with pressure changes (e.g., airplane cabin changes cause a “pop”).
  • Distance/angles: adult Eustachian tube ~35 mm long; ~45-degree angle; in children, shorter (~17 mm) and more horizontal, increasing risk of middle ear infections due to poorer drainage.

Inner Ear

  • Location: housed within the temporal bone; fluid-filled space (unlike middle ear).
  • Two main structures:
    • Vestibular apparatus (balance): includes semicircular canals; helps sense and maintain balance; dizziness often linked to vestibular issues; higher risk in certain populations (e.g., diabetics show increased vestibular dysfunction).
    • Cochlea (hearing): snail-like structure with ~2.75 turns in humans; basal (high-frequency) to apical (low-frequency) gradient; three fluid-filled compartments: scala vestibuli (upper), scala tympani (lower), scala media (cochlear duct) in middle.
  • Organ of Corti: located in the scala media on the basilar membrane; contains ~4 rows of hair cells (≈20,000 total) that transduce mechanical energy into neural impulses; each hair cell has a connection to auditory nerve fibers.
  • Basilar membrane and tonotopy: different regions respond to different frequencies; basal end responds to high frequencies, apical end to low frequencies; tonotopic organization is preserved from cochlea to auditory cortex.
  • Auditory nerve: bundle of >30,000 fibers carrying auditory (hearing) and balance information; comprises cochlear (hearing) and vestibular (balance) branches; fibers project to brainstem nuclei such as the cochlear nucleus, then upward through pons and midbrain to the temporal lobe.
  • Hearing range: normal human hearing approx. 20 extHzextto20,000 extHz20 \, ext{Hz} ext{ to } 20{,}000 \, ext{Hz}; humans typically cannot hear below 20 extHz20 \, ext{Hz}.
  • Auditory pathway summary: auditory nerve -> cochlear nucleus (brainstem) -> crossings/decussations -> brainstem nuclei -> thalamus (medial geniculate body) -> auditory cortex (Heschl's gyrus) in the temporal lobe; sound from left ear tends to be processed in right hemisphere and vice versa.

Central Auditory System

  • Beyond the cochlear nerve: neural pathways cross the brainstem midline; pathway passes through multiple brainstem nuclei and ascends to temporal lobe.
  • Final processing center: auditory cortex (Heschl’s gyrus) in the temporal lobe.

The Process of Hearing (Audition) in Stages

  • Step-by-step:
    1) Outer ear collects and channels sound toward the eardrum.
    2) Middle ear transforms acoustic energy into mechanical energy via the tympanic membrane and ossicular chain.
    3) Stapes transfers mechanical vibrations into the fluid of the inner ear via the oval window, creating a traveling wave inside the cochlea.
    4) Hair cells along the organ of Corti transduce mechanical energy into neural impulses that reflect original sound frequencies.
    5) Nerve impulses travel along the auditory nerve to the brainstem, then to the auditory cortex for perception.
  • Important concept: energy is preserved through successive energy transformations from airborne sound to neural signals, enabling faithful perception of the original sound's physical characteristics.
  • Figural references: process diagrams illustrate the flow from S (source) to T (transfer function) to P (product) for speech production, and analogous flow for hearing.

Historic and Cultural Context in Anatomy and Physiology

  • Historic figures in anatomy/physiology:
    • Henry Gray (1827–1861): author of Gray’s Anatomy, foundational medical anatomy text (1830s–1850s edition; expanded later).
    • Henry Vandyke Carter (1831–1897): illustrated Gray’s Anatomy.
    • Bartolomeo Eustachi (1510–1574): early anatomist; described tensor tympani and stapedius muscles and the tuba auditiva (eustachian tube).
    • Antoine Ferrein (1693–1769): coined the term vocal cords; described laryngeal muscles as the vibrating bands producing sound; terminology shift to ‘vocal folds’.
    • Alfonso Corti (1822–1876): described the organ of Corti in the cochlea; foundational for cochlear hearing science.
    • Anna Morandi Manzolini (1714–1774): anatomist/artist who created wax models; contributed to anatomical visualization.
    • Sir Victor Negus (1887–1974): laryngologist; influential in detailing laryngeal anatomy; his work supported cross-species comparisons.
    • Willard R. Zemlin (1929–1998): authored a classic textbook on Speech and Hearing Science; early comprehensive education text for the field;
      highlighted anatomy/physiology of speech and hearing.
  • The two-tube vocal tract theory (Lieberman & Crelin, 1971): humans have separate oral and pharyngeal tubes – enabling a broad range of sounds; contrasts with other animals having a single-tube tract; two-tube anatomy reduces bi-directional eating/breathing efficiency and increases choking risk; infant laryngeal position starts high (single-tube) and descends with growth to enable diverse speech.
  • Anthropometry: study of body measurements; origin in criminology via Alphonse Bertillon (1853–1914); modern uses include assessing variations in body structure for clinical evaluation and equipment design; note historical misuse (Nazi era) highlighting ethical considerations.
  • Contemporary relevance of anthropometry: helps in understanding variations related to disabilities, hearing aid fitting, oral-peripheral speech mechanisms; informs accommodations and design.
  • Biological and clinical implications: anatomical/positional differences affect speech/hearing function and device fitting; autistic-related morphological observations noted as area of research (Ali et al., 2022).
  • Miscellaneous: echolocation (biosonar) described for comparative context of auditory processing in animals (bats, dolphins, etc.).

Cultural and Practical Implications in Anatomy and Physiology

  • Anthropometry and disability: recognition that body measurements vary; critical in designing accessible environments and devices; helps characterize syndromes and variation ranges.
  • Ethical considerations: historical misuse (e.g., Nazi racial classifications) underscores the importance of ethical use of anatomical data and respect for diversity.
  • Clinical relevance: variations in ear anatomy influence audiology practices (e.g., fitting hearing aids); variations in oral-peripheral structures influence speech-language pathology assessments.

Anatomy and Physiology on the World Wide Web (Additional Resources)

  • Gray’s Anatomy (Bar tleby edition) – foundational text.
  • Zemlin Memorial Website – resources on Zemlin’s contributions.
  • How the Ear Functions – video resource (classic)
  • Larynx and the Voice – video resource (classic)
  • URLs provided as helpful supplementary materials for visualization and deeper study.

Connections to Prior Lectures and Foundational Principles

  • The S * T = P framework links physical energy generation (source) to transfer through the vocal tract (transfer function) to acoustic output (product), mirroring fundamental principles of signal processing where a source is filtered by a system to yield an output.
  • Auditory processing follows a pathway from peripheral reception to central interpretation, illustrating a classic sensory-neural cascade from receptor to cortex.
  • The three subsystems (respiratory, laryngeal, articulatory) align with the modular view of speech production: energy supply (breathing), sound generation (voice), and sound shaping (articulation).
  • The two-tube vocal tract concept complements historical models by explaining how humans achieve a wide range of articulatory configurations while enabling safe swallowing and breathing.

Study Questions (Summary from Chapter 33)

  • List and describe the three subsystems of speech anatomy.
  • Name pioneers who contributed to our understanding of hearing and speech anatomy/physiology.
  • List and describe the two main components of hearing anatomy.
  • Explain the processes of speech production.
  • Explain the process of hearing.

Key Takeaways and Practical Implications

  • Speech production relies on integrated respiratory, laryngeal, and articulatory systems, coordinated by brain activity and expressed through the S \, T \, P framework.
  • The vocal folds’ vibration (phonation) and F0 govern voice pitch; anatomical differences in the larynx explain gender/age-related pitch variations.
  • Articulatory precision depends on movable and fixed articulators; jaw movement (mandible) contributes significantly to speech clarity; limitations (e.g., pipe speech) illustrate how structural constraints affect articulation.
  • The nasal passages and velopharyngeal mechanism play a crucial role in determining nasal vs. oral resonance; most speech sounds require oral resonation, with nasal sounds relying on nasal cavity coupling.
  • Hearing is a multi-stage process involving outer/middle/inner ear structures; hair cell transduction preserves spectral details; tonotopy organizes frequency-to-place mapping in the cochlea.
  • The central auditory pathway processes and localizes sound, with hemispheric processing patterns (e.g., left ear → right auditory cortex, etc.).
  • Historical and ethical contexts enrich understanding of anatomy/physiology and remind us to apply knowledge responsibly in clinical settings.

Quick Reference: Selected Numerical and Factual Details

  • Respiratory cycle: inhalation ≈ 10110extofcycle10\frac{1}{10} ext{ of cycle}, exhalation ≈ 90110extofcycle90\frac{1}{10} ext{ of cycle} for speech.
  • Resting breathing rates:
    • Adults: 14$–$16 ext{ breaths/min}
    • Post-exercise: >60extbreaths/min60 ext{ breaths/min}
    • Newborns: 40$–$50 ext{ breaths/min}
    • By age 5: ≈ 25extbreaths/min25 ext{ breaths/min}
  • Trachea: about 20extcartilagerings20 ext{ cartilage rings}.
  • Eustachian tube length: adult ≈ 35extmm35 ext{ mm}; child ≈ 17extmm17 ext{ mm}; angle ~45exto45^ ext{o} in adults; more horizontal in children.
  • Lungs: left lung smaller than right; 12 pairs of ribs; diaphragm as principal inspiratory muscle.
  • Lung cancer deaths in 2023: ≈ 130,000130{,}000 (≈ 70,000extmen, 60,000extwomen70{,}000 ext{ men}, \, 60{,}000 ext{ women}).
  • Hearing range: 20extHzextto20,000extHz20 ext{ Hz} ext{ to } 20{,}000 ext{ Hz} (normal hearing).
  • Organ of Corti: ~20,000 hair cells across four rows; tonotopic organization along basilar membrane.
  • Normal auditory nerve fiber count: >30,00030{,}000 fibers.
  • Two-tube vocal tract evolution suggests modern humans uniquely combine oral and pharyngeal tubes for broader speech sounds.

Summary of Core Concepts

  • Speech anatomy uses three subsystems: respiratory (energy source), laryngeal (sound source), articulatory (sound shaping).
  • Speech production is a transformation of aerodynamic energy into acoustic energy via the S \, T \, P framework.
  • Hearing involves peripheral reception and central processing, with a well-characterized pathway from outer ear to auditory cortex.
  • Historical figures and ethical considerations shape our understanding of anatomy, with anthropometry illustrating both clinical utility and ethical pitfalls.
  • The content emphasizes both the anatomical details (bones, cartilages, muscles) and the physiological processes (phonation, velopharyngeal closure, traveling waves in the cochlea) essential for communication sciences.

References and Suggested Further Reading

  • Robb, Michael P. INTRO: a Guide to Communication Sciences and Disorders, Plural Publishing, 2023. ProQuest Ebook Central.
  • Related figures and diagrams referenced: Figures 2–1 through 2–22 (respiratory, laryngeal, articulatory systems; auditory anatomy; historic portraits).
  • External resources listed in the chapter for supplementary visuals (Gray’s Anatomy edition; Zemlin Memorial site; ear function and larynx videos).