Neurology for Speech Pathology: UMNs, LMNs, & Cranial Nerves

Neurology for Speech Pathology

Lecture Learning Outcomes

• Explain the importance of neurology for speech pathology:
  • Theoretical understanding of normal structure and function.
  • Clinical application in understanding and treating disorders.
• Describe areas/structures of the brain involved in speech and language processes:
  • Focus on specific structures.
  • Detailed study of cranial nerves.
• Define and explain the role of Broca’s and Wernicke’s areas for speech and language.
• Cranial Nerves:
  • Name and number of each of the 12 cranial nerves.
  • General function of each cranial nerve.
• Describe the role of Upper Motor Neurons (UMNs) and Lower Motor Neurons (LMNs).
  • Describe implications of damage to UMNs compared with LMNs.
  • Explain the implications of facial nerve damage.

Readings

• Webb (2017):
  • Chapter 2: Organisation of the Nervous System I.
  • Chapter 1: Introduction to Speech-Language Neurology.

Understanding the Brain

• Theoretical Importance:
  • Informs about normal structure and function.
  • Explains how the brain controls processes for speech and language.
  • Helps in understanding and remediating/treating speech and language disorders.
• Clinical Importance:
  • Understanding what happens when something goes wrong.
  • Considering both developmental (genetic) and acquired causes (early or later stages of neural development).

Underlying Mechanisms

• Clinicians with a deep understanding of disorders are more efficient and make more appropriate decisions.
• Importance of understanding the client’s needs and wants.
• Understanding general information about a disorder and its characteristics, including how it progresses.
• Importance of specific information about each client, requiring effective communication skills to gather necessary information.
• Understanding the underlying mechanisms of speech and language production to assess a client’s strengths and weaknesses.
• Knowledge of neurology, theoretical models, and normative data is crucial in supporting the understanding of disorders and conditions.
• Interpretation of a client’s strengths and weaknesses guides the next steps, including treatment options based on evidence-based practice (EBP).
• The SLP must understand the results of speech and language assessment in terms of the underlying neurologic mechanisms.

Speech Pathology

• Speech pathologists may encounter clients with any condition impacting communication and/or swallowing.
• Difficulties can be developmental or acquired, and can be related to:
  • Communication.
  • Cognitive abilities.
  • Structural issues.
  • Neurological factors.
  • Psychological factors.
• Paediatric population:
  • Disability.
  • Speech and language delay and disorder, including stuttering.
• Adult population:
  • Post stroke, traumatic brain injury (TBI).
  • Neurodegenerative diseases.

Speech Pathology Related Models Incorporating Neurological Information

• Van der Merwe’s Model of Sensorimotor speech production.
  • Addresses which areas of the brain are required for speech and language production.
  • Revisited in the context of neurogenic motor speech disorders and fluency.
• Levelt’s Model of Speech Production.
• Locke’s Neurolinguistic Model.
  • Revisiting this lecture
• van der Merwe’s will be revisited more closely in the next session.

The Developing Brain

• Consideration of language across the lifespan, language analytical frameworks, and evidence-based practice in speech pathology.
• Focus on what a child learns in the first two years of life regarding communication.
• Exploration of how this information is learned.
• Consideration of whether language learning is innate (Chomsky), implying a biological, neurologic, and genetic basis for language.
• How brain mature affects the ability to learn language and other cognitive skills

Locke’s Phases in Development of Linguistic Capacity

• Vocal Learning.
• Utterance Acquisition.
• Analysis and Computation.
• Integration and Elaboration.
• All phases in the induction of linguistic capacity are affected by interactions between neuromaturational events and social stimulation.
• The model claims the existence of a ‘critical’ or ‘sensitive’ period for language learning.
• Eric Lenneberg maintained that the acquisition of syntax was paced by the rate of cerebral maturation and the lateralization of language mechanisms.
  • Rapid acquisition of language starts at approximately 2 years of age, as the brain begins to grow rapidly, and slows at puberty (approximately 12 years of age), when cerebral growth reaches a plateau.
  • Rate of cerebral maturation affects the acquisition of syntax

Understanding the Brain

• The majority of what we learn about brains and how they work is from studies of adults.
• Emerging studies of the developing brain.
• Historically, studies focused on brains of adults when something had gone ‘wrong.’
• Now, there are ways to study the normal brain too.

Brain Dynamics

• Consideration of whether the brain is dynamic or modular.

Speech Production and Brain Areas

• Supplementary motor area
• Primary motor cortex
• Posterior parietal cortex
• Area 5 Area 7
• Premotor cortex
• Dorsolateral prefrontal associative cortex
• Somatosensory cortex

Speech, Language, Cognition and The Lobes

• Frontal Lobe:
  • Executive functions, thinking, planning, organising and problem solving, emotions and behavioural control, personality.
• Motor cortex:
  • Movement
• Sensory cortex:
  • Sensations
• Parietal lobe:
  • Perception, making sense of the world, arithmetic, spelling.
• Temporal lobe:
  • Memory, understanding, language.
• Occipital lobe:
  • Vision.

Speech, Language, Cognition and the Lobes details

• Parietal lobe:
  • Perception, spatial awareness, manipulating objects, spelling
• Wernicke's area:
  • Understanding language
• Broca's area:
  • Expressing language
• Frontal lobe:
  • Planning, organising, emotional and behavioural control, personality, problem solving, attention, social skills, flexible thinking and conscious movement
• Occipital lobe:
  • Vision
• Temporal lobe:
  • Memory, recognising faces, generating emotions, language

Sensory Motor Homunculus Map

• Motor cortex (precentral gyrus)
• Sensory

Broca’s and Wernicke’s Areas

• Location of each area.
• Major functions of each area.
• Connected by the arcuate fasciculus.
  • Bundle of nerve fibres.
  • Connects phonological recognition to phonological production.

Broca’s and Wernicke’s Areas – Some History

• Broca:
  • Pierre Paul Broca (1824-1880), French physician.
  • First to identify aphasia.
  • Localised human language to a definite circumscribed area of the left hemisphere.
  • Observed that the 2 hemispheres of the brain were asymmetric in function.
  • Determined that the Left hemisphere is where language is located.
  • Proposed the Localisation of function in the nervous system.
  • Identified Broca’s area in the frontal lobe as an expressive speech center.
  • Associated Broca’s aphasia with non-fluent aphasia, expressive aphasia.
• Wernicke:
  • Carl Wernicke (1848-1905).
  • Identified an auditory speech center in the temporal lobe associated with comprehension of speech (1874).
  • Emphasized the importance of cortical language centers associated with the various language modalities.
  • Stressed the importance of association fiber tracts connecting areas or centers.
  • Associated Wernicke’s aphasia with fluent aphasia, receptive aphasia.

Relevance to Practice

• Consideration of which areas covered in neurology are most relevant to practice.
  • Voice.
  • Swallowing.
  • Fluency.
  • Speech.
  • Language.
  • Multi-modal communication.
• Thinking about normal structure and function, and then pathology relating specifically to the brain.
• Reference:
  • Bhatnagar, S. C. (2008). Neuroscience for the study of communicative disorders. Philadelphia: Lippincott Williams and Wilkins.

Lower Motor Neurons and Upper Motor Neurons

• Understanding consequences of damage to each type.
• Upper Motor Neurons:
  • Controls, innervates, plans.
• Lower Motor Neurons:
  • Executes the plans to move the muscles.
• Brain cells involved in voluntary movement.

Lower Motor Neurons and Upper Motor Neurons details

• UMN – Upper Motor
  • CNS – Central Nervous System
  • Brain
  • Brainstem Nuclei
  • Spinal Cord
  • Inside the CNS – Can’t leave the CNS
  • Synapse only with a LMN
• LMN – Lower Motor
  • PNS – Peripheral Nervous System
  • Cranial Nerves
  • Spinal Nerves
  • Spinal Cord
  • Brainstem Nuclei
  • Cranial Nerves
  • Cranial and Spinal Nerves
  • Cell bodies in the brainstem but axons can leave CNS and synapse with muscles of the body.

LMN and UMN additional resources

• 1° motor neuron
• MI = primary motor cortex
• Decussation in the medulla
• Hemisection
• 2° motor neuron in the spine

Brain Stem UMN and LMN

• Motor corlax
• Dilateral innervation
• Lower motor neurons
• form the mole group of cranial nerve nuclei
• Motor pathways

UMNs and LMNs: Implications

• UMNs:
  • Originate in the cerebral cortex, synapse and innervate LMNs.
  • Control and provide the strategy for movement.
• LMNs:
  • Originate in the brainstem and innervate muscles in the face and body.
  • Cranial nerves are LMNs.
  • Execute the commands received from the UMNs.
• (Duffy, 2013, p.39)

Cranial Nerves

• Lower Motor Neurons

Cranial Nerves Importance

• Cranial nerves are particularly important for speech and swallow functions.
• Spinal nerves are not covered in detail (relevant to physio, exercise physiology, chiro).
  • Though there are still functions like respiration that involve spinal nerves.

Innervation

• Some CNS are purely sensory and cannot be called LMN (as LMN is a motor function) (CN I, II and VIII).
• All the muscles of speech production are innervated by the cranial nerves except the muscles relating to breathing.
• Cranial nerves are part of the PNS and are composed of lower motor neurons.
• Spinal nerves are also part of the PNS and are composed of lower motor neurons.
• Innervation of the cranial nerves (lower motor neurons) by upper motor neurons are mostly bilateral and contralateral.
• There are some exceptions.

Peripheral and Central Nervous System

• Peripheral Nervous System:
  • 12 Cranial nerves
  • 31 Spinal nerves
• Central Nervous System:
  • Spinal cord
  • Brain

Cranial Nerves Information

• For each of the 12 cranial nerves:
  • The name and number of the nerve.
  • The site of the cranial nerve nuclei, i.e., where on the brainstem does it come from.
  • Whether it is a motor or sensory nerve or both.
  • The general function of the cranial nerve.
  • One way you could test the nerve’s function.

Cranial Nerves (Bhatnagar, 2008)

Cranial Nerve Nuclei Origins

Clinical Signs

• What clinical signs may be indicated if a cranial nerve is damaged?
• How do you think a clinician/medical practitioner can assess/test/observe for clinical signs?
• Which cranial nerves relate to functions of communication and swallowing?

Facial Nerve VII

• Raising the eyebrows (frontalis).
• Closing the eyes (orbicularis oculi).
• Frowning (corrugator).
• Open mouth smiling (zygomaticus).
• Closed mouth smiling (risorius).
• Pouting (orbicularis oris).
• Lifting top lip (levator labii).
• Pulling lower lip down (depressor labii).
• Sticking bottom lip out (mentalis).
• Pulling jaw and corners of mouth gently down (platysma).
• Wrinkling nose (procerus/nasalis).

Clinical Signs of Facial Nerve Damage

• Can give us clues about whether or not damage was sustained at the upper motor neurons or the lower motor neurons.
• UMN facial palsy.
• Or
• LMN facial palsy.

Corticobulbar Innervation

• Facial Nerve

Facial Musculature Paralysis

• Lower Motor Neuron lesion:
  • Paralysis of ipsilateral upper & lower facial musculature (unable to raise eyebrow or smile on affected side).
• Upper Motor Neuron lesion:
  • Paralysis of contralateral lower facial musculature (unable to smile on affected side, but can raise both eyebrows).

UMNs and LMNs: Implications for Facial Palsy Details

• UMN lesion:
  • Lower part of the face is impaired contralateral (opposite side).
  • Can’t smile.
  • Upper part of the face is preserved because this receives innervation from both (bilateral) UMNs.
  • Can raise eyebrows.
• LMN lesion:
  • Paralysis/impairment of the ipsilateral facial muscle.
  • Both top and bottom of the face – can’t smile or raise eyebrows on the same side of the lesion.

Differences Between Upper Motor Neuron and Lower Motor Neuron Type Facial Palsy

Stroke Vignette (Brian)

• Brian is 77-years-old. he was cooking in the kitchen when he collapsed onto the floor. his daughter called an ambulance and he was taken to the emergency room. he had a stroke, and slowly regained consciousness over the next two days. however, when he woke up, he had the following signs and symptoms:
  • Paralysis of the right face and arm
  • Loss of sensation to touch on the skin of the right face and arm
  • Inability to answer questions but ability to understand what was said to him
  • Ability to write down his thoughts more easily than to speak them
• Based upon the Brian's symptoms, which cerebral artery was blocked? (be specific)
• Why was he paralysed in the right face and arm?
• What is the name of his language disorder, and what caused it?
• Which cranial nerves have been impaired and why do you think so?