Anatomy & Physiology of the Speech Mechanism I

COMSDIS 210: Survey of Communication Disorders

The Speech Chain

• Speech is produced as a result of a series of complex , coordinated movements of the speech mechanism.

– The speech mechanism consists of the structures of the head, neck and thorax*.

– Hundreds of muscles and other structures are involved. Their movements are some of the fastest, most coordinated, most subtle associated with human movement.

• Thorax = the skeleton of the chest that creates a cavity to house the structures of the heart and lower respiratory system.

– Lower respiratory system: lungs, bronchi and alveoli

– Upper respiratory system: trachea, larynx, oral cavity and nasal cavity

Location of thorax

• Consists of the rib cage in the front (anterior/dorsal view), which is connected to the vertebral column in the back (posterior/ventral view).

• Trachea from the top (superior view) to diaphragm from the bottom (inferior view).

• Anatomy : “structures” – Study of the structures of the body & the

relationship of those structures to one another.

• Physiology: “function” – Study of the functions of bodily structures and

systems.

• Anatomy and physiology are interrelated; one affects the other.

• However, a person can have normal anatomy that does not function appropriately. A person’s anatomy can function appropriately even if the structures are abnormal.

Speech scientists

• Specialize in understanding the anatomical and physiological processes involved in speech production.

– Often work in labs, alongside specialists from the fields of medicine, engineering and computer science.

Modification of the definition of speech production

• The anatomical and physiological processes involved with the production, modification and shaping of speech sounds; processes used for the purpose of communication via oral language.

Systems/processes involved in speech production

System Process• Respiratory system “respiration”• Phonatory system “phonation”• Resonatory system “resonation”• Articulatory system “articulation

Speech disorders

• Speech disorders result from impairment(s) in one or more of the processes involved in speech production.

Classification of speech disorders

• Phonatory (voice) disorders• Resonatory (resonance) disorders• Articulatory (articulation) disorders• Fluency disorders

• Motor speech disorders: “mixed” disorders caused by impairments affecting the respiratory, phonatory, resonatory and articulatory systems.

Respiration

• The processes involved with breathing (draw O2 from the air, exchange it with CO2).

• The energy or power source for speech

• Speech requires a strong energy source: impaired respiration results in impaired speech production.

• Respiration directly controls vocal intensity/ loudness.

• Persons need both a strong respiratory system AND good respiratory control to generate and maintain adequate loudness, as well as to modify levels of loudness.

Simplified view of the anatomy and physiology of respiration

• Inhalation must bring adequate supply of air into lungs.

• Exhalation must be strong enough to propel the air upward and outward.

• Primary function of respiration = to sustain life

(quiet/passive breathing/tidal respiration). – Primary muscles of respiration involved with tidal

respiration.

• Secondary function of respiration = to generate air needed to created sound (speech breathing).– Secondary “accessory” muscles of respiration needed

for speech breathing and active forced inspiration (lifting, pushing, athletics).

How speech breathing is different from quiet breathing

1. Time spent inhaling decreases; time spent exhaling increases.

(Respiratory cycle = 1 inhalation + 1 exhalation)

Quiet breathing: duration of inhalation & exhalation roughly equivalentOne cycle = 40% inhalation + 60% exhalation

Speech breathing: One cycle = 10% inhalation + 90% exhalation

2. Inhale greater volume of air (2+ liters) when speaking; inhale lower volume of air (0.5 liter) when resting. Exhale greater volume of air when speaking than when resting.

3. Greater voluntary control over breathing during speech. (Respiration is a reflexive behavior controlled by the brain stem.)

Primary muscles of respiration

1. Intercostal muscles (fill the spaces between the ribs, sitting on the outside and inside of the rib cage in 3 layers)– External intercostals – Internal intercostals – Innermost intercostals

• Contraction of the intercostals causes the ribcage to expand both sideways and from front to back. This increases volume of the thoracic cavity.

2. Diaphragm (large muscle that contracts & expands when breathing)

• Responsible for 75% of the respiratory effort.

• When it contracts, it flattens which increases the thoracic volume.

• When it relaxes, it is pushed up by the underlying abdominal organs into a dome shape, decreasing thoracic volume.

Inhalation/inspiration• Contraction of the inspiratory muscles (external

intercostals & diaphragm) causes the thorax and lungs to expand. The rib cage elevates.

• Expansion of the lungs increases lung volume.

• Air pressure within the lungs drops below atmospheric pressure.

• Air rushes into the lungs equalizing lung pressure with atmospheric pressure.

Exhalation/expiration• Thorax decreases in size, reducing lung volume.

• Air pressure within the lungs elevates to levels that are above atmospheric pressure. Air rushes out of lungs.

• Does not require active contraction of expiratory muscles. Gravity acts on the elevated rib cage; elasticity of lung tissue returns lungs & thorax to relaxed state. Internal intercostal muscles also pull the rib cage down.

Whenever volume increases, pressure decreases.

• In inspiration thoracic volume increases so air pressure decreases. (Created by contraction of respiratory muscles)

• In expiration, thoracic volume decreases so air pressure increases. (Created by gravity, elasticity of lungs & action of certain parts of the internal intercostals which pull the ribs downward.

• During respiration there are two areas of unequal pressure connected by tubing (bronchi, trachea). Air from the area of higher pressure will always diffuse into the area of lower pressure.

• Atmospheric air drawn to area of lower pressure during inspiration. (Converse is true during expiration.)

Phonation (voice)• Exhaled air is sent upward through the upper

respiratory system, which includes the trachea, larynx, oral cavity and nasal cavity.

• As the air passes through the larynx it passes through the vocal folds.

• When stimulated, the vocal folds vibrate.

• Vibrations of the vocal fold transforms the air into sound.

Anatomical terms used when discussing phonation

• Pharynx: muscular tube running from nasal cavity, through the oral cavity to the entrance of both the trachea (respiratory system) and the esophagus (digestive system). – nasopharynx, oropharynx (throat), laryngopharynx

• Trachea (windpipe): muscular tube through which air passes from the oral cavity to the lungs.

• Esophagus: tube behind the trachea through which food passes to the stomach.

• Larynx (voicebox): composed of five cartilages connected by membranes, ligaments and muscles . Contains the vocal folds (vocal cords). – Sits above the trachea. Protects the trachea by

keeping out everything but air. The vocal folds close tightly to form protective seal over top of trachea. The larynx is protected by the epiglottis, which drops and covers the laryngeal opening during swallowing.

Functions of the larynx

1. To protect the lungs from foreign bodies by forming a protective seal over the trachea.

2. To create sound through the action of the vocal folds on exhaled air.

Voice = creation of sound through vocal fold vibration

Cartilages of the larynx3.9 p. 98

• Thyroid cartilages (1)

• Cricoid cartilage

• Arytenoid cartilages (2)

• Epiglottis

• The left and right laminae of the thyroid cartilage meet in the midline (laryngeal prominence/ Adam’s apple)

• The larynx is suspended in the neck from the hyoid bone, a horse-shoe shaped bone that floats horizontally at the base of the neck.

• The movements of the larynx and vocal folds are controlled by two sets of muscles.

• Extrinsic laryngeal muscles (3.10-11, p. 98-99)– 4 Suprahyoids (laryngeal elevators)

• Elevate the larynx during swallowing and speech• Include the digastricus, stylohyoid, geniohyoid and

mylohyoid muscles.

– 4 Infrahyoids (laryngeal depressors)• Lower the larynx • Include the omohyoid, sternohyoid, sternothyroid, and

thyrohoid muscles

• Intrinsic laryngeal muscles– Situated in the larynx– Control the movements of the vocal folds.– Include the cricothryoid muscle, posterior

cricoarytenoids (2), lateral cricoarytenoids (2), arytenoids* (2), and the thyrohoid muscle (vocalis).

Vocal Folds• Two thin sheets of tissue (mucosa-lined

ligaments), connected on their outer edge to the inside of the thyroid cartilage.

• Horizontally, they stretch from the arytenoid cartilages (posterior) to the thyroid cartilage (anterior).

• A thin layer of muscle (vocalis muscle) lies within the tissue of the vocal folds.

V.F. movements controlled by movements of the arytenoid cartilages

• Close (approximated/adducted) tightly to protect the trachea and lungs from foreign bodies.

• Open (abducted) during breathing and close (adducted) to initiate a cough;

• Open and close rapidly during vocal fold vibration. Caused by movements of the arytenoid cartilages.

• The number of times the v.f. vibrate = pitch of voice

Average pitch values

Adult female = 240 Hz (Hertz/cycles per second)

Adult male = 130 Hz

Differences relate to mass of the v.f.

Female v.f. are smaller and shorter, therefore they vibrate faster.

• Glottis = space between vocal folds when open

SummaryHow is speech produced?

1. A person inhales and then exhales air. The exhaled air is sent upward through the larynx, where it passes through the vocal folds.

2. As the air passes through the vocal folds, they are set into rapid vibration, which transforms the air into sound.

3. The sound is modified by the shape and configuration of an individual’s vocal tract. (particularly the oral and nasal cavities)

4. The sound is shaped into specific speech sounds created by manipulations of the speech articulators.