Speech

Cortical Motor Areas for Speech Production

  • Pre-motor cortex:

    • Role in planning movement.

  • Broca’s area:

    • Role specifically in planning speech movement.

  • Supplementary motor area:

    • Programming movement sequences.

    • Feeds correct motor instructions in correct sequence to the primary motor cortex.

  • Primary motor cortex:

    • Responsible for the EXECUTION of the movement (after plans have been checked).

  • The sequence of speech motor control:

    1. Plan

    2. Program

    3. Execute

Terminology

  • Motor Plan:

    • Considered the highest level of the motor system.

    • Specifies what motor goals are (i.e. what needs to happen).

    • 'Big Picture' i.e. identifies destinations and steps, but not details.

    • Example: To say “cat”:

      • Inhale (respiratory support for speech).

      • Move articulators (e.g. lips and tongue) to make the sounds.

      • Phonate on exhalation.

  • Motor Program:

    • Considered the lower level of the motor system relative to motor planning.

    • Relies on the higher-level motor plan to dictate what needs to be done.

    • Specifies motor procedures (i.e. how will a goal be achieved).

    • Identifies the spatial and temporal elements of the ‘journey’

    • Are adaptable in response to feedback

    • Example: To say “cat”:

      • In order to inhale (as identified in the motor plan) I need to activate respiratory muscles including the diaphragm, internal intercostals, and external intercostals.

      • In order to move my lips and tongue I need to activate specific muscles of the lips and tongue: orbicularis oris, genioglossus, hyoglossus, styloglossus, palatoglossus, superior longitudinal muscle, inferior longitudinal muscle, verticalis, transversus.

      • Think about the timing, force, duration, intensity of movements.

Cranial Nerves for Speech

  • Peripheral nerves extend from the brainstem.

  • 12 pairs of cranial nerves – motor/sensory/mixed.

  • 5 of these pairs are involved in the neural process of speech.

Cranial Nerves for Speech Production

  • CN V = trigeminal nerve:

    • Muscles of mastication.

    • Jaw movement and articulation/speech intelligibility.

  • CN VII = facial nerve:

    • Movement of facial muscles.

    • Lip movement and articulation of bilabial sounds e.g. “m” or rounding of the lips in vowels.

  • CN IX = glossopharyngeal nerve:

    • Can aid in velopharyngeal closure and possible abnormal nasal airflow/resonance.

  • CNX = vagus nerve:

    • Primarily responsible for the elevation of the soft palate during velopharyngeal closure and possible abnormal nasal airflow/resonance.

    • Responsible for vocal folds and vocal quality.

  • CNXII = hypoglossal nerve:

    • Muscles of the tongue and articulation of lingual sounds e.g. “l” and “k”

Integration of Speech Motor System

  • Cortical speech planning and programming:

    • premotor cortex; supplementary motor area; Broca’s area; primary motor cortex.

  • Control circuits:

    • subcortical structures including the basal ganglia control circuit and cerebellar control circuits (they have no direct link to the final common pathway/LMN).

  • Direct activation pathway/UPPER MOTOR NEURONES:

    • corticobulbar tracts (CNs).

  • Final common pathway/LOWER MOTOR NEURONES:

    • cranial nerves (CNs: V, VII, IX, X, XII).

The Corticobulbar Tract (CBT)

  • Arises from the primary motor cortex/M1

  • Passes through the Internal Capsule

  • For voluntary control of muscles for speech

  • Known as upper motor neurons (UMNs)

  • Synapses to lower motor neurons (LMNs) in CN nucleus in the brainstem

  • LMNs then innervate muscles for speech: face, tongue, pharynx, and larynx.

  • To summarise:

    • The CBT arises from the primary motor cortex and projects to the motor cranial nerve nuclei located in the brainstem and then onto muscles for speech production.

Outcomes of Lesions on the CBT

  • UMN/direct activation pathway:

    • Lesion in the Primary motor cortex or Internal capsule, e.g., stroke or traumatic brain injury.

  • LMN/final common pathway:

    • Lesion/pathology from the brainstem, e.g., stroke, to muscle function, e.g., myasthenia gravis (a problem with the transmission of messages from the peripheral nervous system to the muscles – neuromuscular junction problem).

Upper Motor Neuron Lesion vs Lower Motor Neuron Lesion

Feature

Upper Motor Neuron Lesion

Lower Motor Neuron Lesion

Paralysis/paresis

Muscle groups, especially voluntary, skilled movements

Paralysis

Reflexes

Hyperreflexia – increased reflex response

Hyporeflexia - Loss of reflexes

Atrophy

Some atrophy generally due to disuse

Pronounced atrophy -70-80%

Tone

Hypertonia (increased tone)

Hypotonia (decreased or no tone)

Paralysis Type

Spastic paralysis

Flaccid paralysis

Disorders Causing UMN and LMN Speech Disorders

  • Stroke (UMN, LMN)

  • Motor neurone disease:

    • Amyotrophic lateral sclerosis - ALS (UMN and LMN)

  • Cerebral Palsy - CP (UMN, LMN)

  • Tumors (UMN, LMN)

  • Trauma/s (UMN, LMN)

  • Multiple Sclerosis - MS (UMN, LMN)

  • Myasthenia Gravis (LMN)

  • Bell’s palsy (LMN)

  • Guillain-Barré Syndrome (LMN)

Types of Motor Speech Disorders

  • Motor speech disorders occur because of damage to the nervous system.

  • Depending on the type and location of damage, the different stages of planning, programming, control, or execution of speech can be impacted.

  • DYSARTHRIA

    • An umbrella term referring to speech movement disorders.

    • There are different types of dysarthria depending on the location of damage in the nervous system.

  • DYSPRAXIA/APRAXIA OF SPEECH

    • Refers to impairment with the capacity to plan or program speech.

Dysarthria

  • Results in an abnormality in different aspects of movement including: strength, range, tone, accuracy of movement.

  • Can impact any of the muscles utilized in speech production: breathing; phonation (voice production), resonance (refers to airflow through oral or nasal cavities); articulation (production of speech sounds); and/or prosody (refers to features of speech such as intonation, stress pattern, loudness variations, pausing, and rhythm).

  • Spastic dysarthria vs. flaccid dysarthria (refer to slide no. 14).

Spastic Dysarthria

  • Features of speech to listen for:

    • Strained/strangled/harsh vocal quality

    • Slow speaking rate

    • Monopitch

    • Monoloudness

  • Overall, can impact speech intelligibility from mild to severe.

  • Severity will depend on the type, location, and extent of neural damage.

  • It will vary from person to person.

  • Some people with have minimal affect on speech intelligibility while others may require the use of AAC systems.

Flaccid Dysarthria

  • Features of speech to listen for:

    • Breathy voice

    • Short phrases

    • Increased nasal resonance

    • Imprecise articulation.

  • Overall, can impact speech intelligibility from mild to severe.

  • Severity will depend on the type, location, and extent of neural damage.

  • It will vary from person to person.

  • Some people with have minimal affect on speech intelligibility while others may require the use of AAC systems.

Dyspraxia

  • Impairment with the capacity to plan or program speech.

  • Inconsistent speech sound errors on consonants and vowels, in repeated productions of syllables and words.

    • This means there is variability in how they say words: they may say it correctly and then at a later time be unable to produce the word correctly.

  • The person may make several attempts to say a word before saying it correctly.

  • Disrupted and/or lengthened co-articulatory transitions between sounds and syllables.

  • Impaired prosody (or rhythm of speech)

  • Can see groping movements with the jaw, lips, or tongue to make the correct movement for speech sounds.

  • Overall, can impact speech intelligibility from mild to severe.

  • Severity will depend on the type, location, and extent of neural damage.

  • It will vary from person to person.

  • Some people with have minimal affect on speech intelligibility while others may require the use of AAC systems.

Functional Outcomes to Speech

  • Speech features will depend on the type of motor speech disorder the person has.

    • E.g., flaccid/spastic dysarthria vs. dyspraxia.

  • Some people will present with 2 motor speech diagnoses: that is, both a dysarthria and a dyspraxia.

  • Different speech subsystems can be affected: one, several, or all: breathing; phonation (voice production), resonance (refers to airflow through oral or nasal cavities); articulation (production of speech sounds); and/or prosody.

  • Overall impact will be on speech intelligibility.

  • Consider impact on participation in activities that involve speaking: talking to family; making phone calls, ordering food, discussing rehabilitation with allied health team.