A&P of Speech - SLH 371 - Spring 2025

Speech System

  • Contains 5 main components:
    • Respiration
    • Phonation
    • Resonance
    • Articulation
    • Prosody

Respiration

  • Provides subglottic air pressure to drive phonation.
  • Inhalation:
    • Active: Contract diaphragm and chest muscles, lung space expands, air goes in.
  • Exhalation:
    • Passive or Active: Diaphragm and chest muscles relax, lung space contracts, air goes out.

Phonation

  • Created by periodic opening and closing of the vocal folds.
  • Provides speech sound source.

Resonance

  • Quality imparted onto sounds by vibrating in its resonating chamber.
  • In English, /m/, /n/, and /ŋ/ are the only nasal consonants.
  • Nasal co-articulation of vowels that precede a nasal consonant.
  • Speech-related airflow, passing through oral or nasal cavities.

Articulation

  • Shaping of the airstream through precisely coordinated movement of the articulators.
  • Key articulators include:
    • Alveolar ridge
    • Blade of the tongue
    • Tip of the tongue
    • Lip
    • Teeth
    • Hyoid bone
    • Nasal cavity
    • Larynx (thyroid cartilage)
    • Palate
    • Oral cavity
    • Front of the tongue
    • Nasopharynx
    • Velum
    • Back of the tongue
    • Uvula
    • Root of the tongue
    • (Oro)pharynx
    • Epiglottis
    • Laryngopharynx
    • Esophagus
    • Vocal folds
    • Trachea
  • Place-Voice-Manner (PVM) Chart:
    • PLACE:
      • LABIAL: Bilabial, Labiodental
      • CORONAL: Interdental, Alveolar
      • DORSAL: Palatal, Velar, Glottal
    • MANNER:
      • Stop: Voiced, Voiceless
      • Fricative: Voiced, Voiceless
      • Affricate: Voiced, Voiceless
      • Nasal: Voiced
      • Lateral: Voiced (LIQUID)
      • Rhotic: Voiced
      • Glide: Voiced
    • VOICING: Includes examples such as:
      • Bilabial: p (voiceless), b (voiced)
      • Labiodental: f (voiceless), v (voiced)
      • Interdental: θ (voiceless), ð (voiced)
      • Alveolar: t (voiceless), d (voiced), s (voiceless), z (voiced)
      • Palatal: ʃ (voiceless), ʒ (voiced), tʃ (voiceless), dʒ (voiced)
      • Velar: k (voiceless), g (voiced), ŋ (voiced)
      • Glottal: h (voiceless)
      • Sonorants: includes m, n, ŋ, l, r, w, j

Prosody

  • Use of phrasing, pitch, loudness, tempo, or rhythm to convey meaning.
  • Requires coordination of:
    • Respiration
    • Phonation
    • Resonance
    • Articulation
    • Cognitive & pragmatic understanding of the needs of the communication partner.

Knowledge Check - Speech Subsystem Deficits

  • Respiration deficit: Possible harsh voice, soft voice, flat affect, reduced intelligibility, hypernasality.
  • Phonation deficit: Possible harsh voice, soft voice, flat affect, reduced intelligibility, hypernasality.
  • Articulation deficit: Possible harsh voice, soft voice, flat affect, reduced intelligibility, hypernasality.
  • Resonance deficit: Possible harsh voice, soft voice, flat affect, reduced intelligibility, hypernasality.
  • Prosody deficit: Possible harsh voice, soft voice, flat affect, reduced intelligibility, hypernasality.

The Motor System

Motor Hierarchy (Simplified)

  • Desire to Move.
  • Association Cortex.
  • Basal Ganglia.
  • Thalamus.
  • Cerebellum.
  • Primary Motor Cortex:
    • Responsible for all voluntary motor activity involving striated muscle.
  • Extrapyramidal System.
  • Pyramidal System.
  • Cranial and Spinal Nerves.
  • Neuromuscular Junction.

Structure of Motor Control

  • Higher-level linguistic processes.
  • Motor commands are issued.
  • Motor actions are planned.
  • Movements are executed.

Primary Motor Cortex (M1)

  • Main motor execution area.
  • Main origin of corticospinal & corticobulbar tracts.
  • Cell bodies of most upper motor neurons (UMN) live here.
  • Takes voluntary movement patterns formulated elsewhere and transmits to lower motor neurons (LMN).

Premotor Cortex (PMC)

  • Input from multiple sensory areas, M1, basal ganglia, & cerebellum.
  • Output to M1, brainstem, & spinal cord.
  • Planning, Initiation, Maintenance, Inhibition, and Learning of complex movements.

Supplementary Motor Area (SMA)

  • Main output is to other cortical regions (including M1).
  • Inputs from: basal ganglia, cerebellum, M1, PMC, prefrontal cortex, Broca’s area.
  • Preparation, Initiation, Timing, Monitoring, and Task-Switching.

Broca's Area

  • Active during movement planning, movement imitation, and understanding others' movements.

Motor Speech Programmer

  • Broca’s area, PMC, SMA, somatosensory cortex, supramarginal gyrus, auditory cortices, insula, basal ganglia.
  • Hypothetical entity that establishes motor plans/programs for speech.
  • Within language-dominant hemisphere.

Basal Ganglia

  • Includes:
    • Caudate nucleus
    • Putamen
    • Globus pallidus
    • Substantia nigra
    • Thalamus

Basal Ganglia Functions

  • Facilitating voluntary movement.
  • Suppressing unwanted movement.
  • Movement.
  • Posture/tone regulation.
  • Movement selection/learning.
  • Scaling.

Cerebellum

  • Control circuit.
  • Afferent to efferent ratio: 40:1.

Cerebellar Functions

  • Coordinate movement.
  • Movement scaling and timing.
  • Balance agonist/antagonist muscle activity.
  • Error detection.
  • Motor learning.

Descending Motor Tracts

  • Pyramidal: Voluntary control for skilled movements.
    • Corticospinal, corticobulbar.
  • Extrapyramidal: Subconscious, automatic muscle activities.
    • Rubrospinal, reticulospinal.

Corticospinal and Corticobulbar Tracts

  • Corticospinal:
    • Originates in the precentral gyrus of the cerebrum.
    • Passes through the genu of the internal capsule.
    • Descends through the midbrain and pons.
    • Decussates (crosses over) at the pyramidal decussation in the lower medulla.
    • Forms the lateral corticospinal tract and anterior corticospinal tract.
    • Connects to muscles via ventral root fibers in the spinal cord.
  • Corticobulbar:
    • Originates in the precentral gyrus of the cerebral cortex.
    • Passes through the internal capsule.
    • Connects to the nuclei of cranial nerves (III, IV, V, VI, VII, X, XI, XII) in the brainstem (midbrain, pons, medulla).
    • These cranial nerves then connect to muscles.

Lower Motor Neurons

  • Cranial nerves: CN V, VII, IX, X, XII.
  • Spinal nerves: Cervical plexus (C3-C5), innervate diaphragm, abdominal, and intercostal muscles.
  • Go from brainstem/spinal cord to muscle.

Lower Motor Neurons: Final Common Pathway

  • Last link in the chain that causes movement.
  • Involves:
    • Cell body
    • Axon
    • Schwann cells
    • Bouton
    • Neuromuscular junction
    • Acetylcholine (neurotransmitter)
    • Synaptic cleft

Neuromuscular Junction

  • Axonal terminal of a motor neuron.
  • Contains mitochondria.
  • Synaptic cleft separates the neuron from the muscle fiber (sarcolemma).
  • T tubules and junctional folds of the sarcolemma at the motor end plate.
  • Involves the release of acetylcholine (ACh).
  • Acetylcholinesterase breaks down ACh in the synaptic cleft.
  • Binding of ACh to receptors opens Na+/K+Na^+/K^+ channels.

Speech Motor Control

  • Higher-level linguistic processes.
  • Motor commands are issued.
  • Motor actions are planned.
  • Movements are executed.

Importance for SLPs

  • Knowledge of motor control will help us understand how and why our patients’ speech is altered.
  • Potentially help with a differential diagnosis.

Knowledge Check - Neural System Impact on Articulation

  • Primary motor cortex/UMN.
  • PMC/SMA.
  • Basal ganglia.
  • Cerebellum.
  • LMN.

Summary

  • Speech is a skilled, precise movement that requires coordination of respiration, voice, resonance, articulation, and prosody.
  • Multiple CNS/PNS structures are responsible for carrying out these skilled, precise movements.
  • Motor control of speech requires feedback and feedforward control.