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Speech Science Primer
Chapter 3: The Raw
Materials—Neurology
& Respiration
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Neurology
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Neuromotor events in speech production
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Basic divisions of nervous system
• Central nervous system (CNS): Brain and spinal cord
• Peripheral nervous system (PNS): All other components,
including:
– Cranial nerves (exit CNS from brainstem)
– Spinal nerves (exit CNS from spinal cord)
• Efferent neurons: Nerve impulses from CNS to peripheral
parts of the body (motor functions)
• Afferent neurons: Nerve impulses from peripheral parts
of the body to CNS (sensory functions)
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Basic divisions of the brain
• Brainstem: Atop spinal cord
– Upper brainstem includes thalamus, basal ganglia
– Lower brainstem includes pons and medulla
oblongata
• Cerebellum: Posterior to brainstem
• Cerebral hemispheres: Wrap around the brainstem;
include areas for higher cognitive function and language
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Anatomy & physiology of neurons
• Individual neurons contain a cell body plus projections
(dendrites, axons)
• Axons carry information away from the cell body
(efferent)
• Dendrites receive information from incoming axons
• Firing is “all or nothing”: Stimuli above threshold always
generate same response strength
• Stronger signals yield more frequent firing (amplitude
doesn't change)
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Neuronal firing: The action potential
• Neuron at rest:
– Has negative internal charge
• Neuron during firing:
– Potassium (K+) exits the neuron
– Sodium (Na+) floods into the neuron
– Cell interior briefly gains positive charge
• Resting negative potential (charge) restored soon after
firing
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The synapse
• At the synapse, the axons of adjacent neurons branch
into terminal arbors
• The terminal arbors meet the dendrites of the nerve cell
receiving incoming stimulation
• Neuronal firing releases chemicals (neurotransmitters)
into synaptic cleft
• Neurotransmitters can either facilitate or inhibit firing in
the next neuron(s)
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Neurons at the synapse
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Speech & the CNS
• Cortical damage may yield speech or language problems:
– Aphasia: Language impairment
– Apraxia of speech: Deficits in speech motor
programming
– Dysarthria: Difficulty with speech movements
• Language and speech mainly controlled by left cerebral
hemisphere:
– Broca's area: Third convolution of left frontal lobe
– Wernicke's area: First convolution of left temporal
lobe
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Motor & sensory areas of the cortex
• Motor strip: Frontal lobe
• Sensory strip: Parietal lobe
• Sensory and motor strips separated by Fissure of
Rolando
• Representation of the body is upside down in motor and
sensory strips
• Large amounts of cortex are devoted to the hands and
oral (speech) structures
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Motor strip
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Cortical areas for speech & language
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More on laterality
• Wada testing:
– Used to test for laterality prior to brain surgery
– Paralyzes one side of the brain and the side of the
body it controls (contralateral)
• Language laterality and handedness:
– Right-handers: About 96% are left-lateralized for
language
– Left-handers: About 70% are left-lateralized for
language
– Some speakers show bilateral organization for
language
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"You've hissed my mystery lectures"
• Spoonerisms: Units of speech/language are exchanged in
production (“damp towel” becomes “tamp dowel”)
• Errors follow rules:
– Consonants only exchange with consonants
– Vowels only exchange with vowels
– First sounds and syllables are most prone to
reversals
• Provide evidence that speech is not programmed one
word, syllable, or sound at a time
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Speech & the peripheral nervous system
• Oral and laryngeal structures are innervated mainly by
cranial nerves
• The respiratory system is innervated by spinal nerves
• Efferent impulses interface with muscles in motor units:
– An action potential at the motor unit stimulates
muscle fibers
– Muscle contraction may cause movement of speech
structures/articulators or change in muscle tone
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Respiration
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Respiration & speech
• All English speech sounds require airflow from the lungs
• Airflow forces the vocal folds to vibrate in voiced sounds
(phonation)
• Obstructing airflow in the upper vocal tract yields
supraglottal sound sources (e.g., bursts, frication noise),
especially for consonants
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Respiratory system as power supply
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Physics of breathing
• Expansion of the chest and lungs creates negative
pressure (Boyle's law)
• Air flows in to equalize the pressure (inhalation)
• Contraction of the chest and lungs creates positive
pressure
• Air flows out (exhalation)
• Exhaled airflow is modified for speech production
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Support structure of respiratory system
• Vertebral column
• Sternum
• Ribs:
– Join to vertebral column at back (bony connections)
– Upper ribs join sternum at front via cartilage
– Lower (floating) ribs connect to vertebrae only
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Structure of thoracic cavity
• Encircled by bone (ribs, sternum, vertebrae)
• Diaphragm forms floor of the thoracic cavity
• Pleural linkage connects lungs to rib cage and
diaphragm:
– Costal (rib) pleura lines rib cage
– Pulmonary (visceral) pleura surrounds lungs
– Fluid holds the pleural layers together but allows
sliding movement
– The lungs respond to the expansion and contraction
of the rib cage and diaphragm movements
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External intercostal muscles
• Superficial to internal intercostal muscles
• Connect osseous portions of ribs to each other
• Run downward toward sternum
• Contraction raises and expands rib cage: Inhalation
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Internal intercostal muscles
• Deep to external intercostal muscles
• Run downward away from sternum
• Connect both osseous and cartilaginous portions of ribs:
– Interosseous portions: Lower and compress rib cage:
Exhalation
– Interchondral portions: Raise and expand rib cage:
Inhalation
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Inhalation in quiet breathing
• The medulla oblongata sends commands to the
respiratory muscles
• The diaphragm contracts:
– The thoracic cavity expands vertically downward
• The external intercostals, interchondral portions of
internal intercostals, contract:
– The thoracic cavity expands up and out
• Lung volume increases because of pleural linkage
• Air pressure within the lungs decreases
• Air flows in through the nose and mouth
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Speech breathing: Overview
• More air is typically inhaled than in quiet breathing
(especially for loud or long utterances)
• Accessory muscles of neck, chest, abdomen, and back
may assist in expanding rib cage
• Control is more voluntary and conscious than in quiet
breathing
• Exhalation is slower and takes up more of the respiratory
cycle
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Passive expiration in quiet breathing
• Relaxation of the respiratory muscles with air in the
lungs:
– Allows the lungs and rib cage to recoil
– Respiratory system collapses
– Air pressure within the lungs increases
– Air flows out
– Lungs return to resting volume
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Respiratory quantities
• Tidal volume: Amount of air exchanged (in and out)
during a cycle of quiet breathing
• Vital capacity (VC): Amount of air exchanged in
maximum inspiration-maximum expiration:
– Respiratory volumes often expressed as a
percentage of VC (e.g., tidal volume is about 10% of
VC)
• Resting volume: The respiratory system relaxes at about
40% of VC
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Respiratory volumes
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Active expiration (speech & singing)
• Above resting volume:
– Muscles counteract passive collapse of lungs
– Inspiratory muscles maintain lungs in expanded state
– Slow expiration early during exhalation phase
• Below resting volume:
– Muscles force respiratory system into compressed
state
– Expiratory muscles compress thorax and abdomen
– Maintain expiration longer
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Muscle use in speech breathing
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Details of muscle activation for speech
• During breathing, both inspiratory and expiratory
muscles are active most of the time
• The balance between inspiratory and expiratory muscle
action changes continuously
• The respiratory system maintains fairly constant pressure
during speech
• Small variations occur to change intensity (e.g., for
stressed syllables)
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The respiratory system & syllable stress
• Increasing subglottal pressure (Ps) yields an increase in
intensity (I):
– I = Ps3 or Ps4
– Small increases in Ps cause large increases in I
• Abdominal and internal intercostal muscles probably raise
Ps for stressed syllables
• Higher Ps may contribute to other features of syllabic
stress:
– Higher f0
– Increased duration
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Speech breathing & phrasing
• Inspirations usually occur at major linguistic boundaries
(phrases, sentences)
• Long utterances require muscle control to maintain
subglottal pressure (Ps) throughout
• Utterance requirements affect both inspiratory and
expiratory muscle use
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Respiratory control in clinical populations
• Voice disorders: Improper laryngeal valving may waste
exhaled air
• Hearing impairment: Poor laryngeal control may again
waste air
• Motor speech disorders: May affect respiratory muscle
coordination
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