1. Neural Basis of Speech
2/29/00

2. Neuron Neuron = Nervous system cell
Neuron cell body (contains nucleus)
Nucleus (contains genetic material)
Dendrites (projections; communication from 1 neuron to another)
Axon (single long process which conducts nerve impulses to muscles, glands or other neurons)
Rarely can be replaced
Cannot regenerate

3. Neuron Structure
Nucleus
Dendrites
Nucleolus
Axon

4. Neuron Three basic types: Sensory Neurons Motor Neurons Interneurons
Conduct nerve impulses from sensory receptor (eye or ear) to the brain & spinal cord
Travel from periphery to central site
Direction of travel is afferent
Motor Neurons
Carry neural instructions from the brain to muscles or glands
Travel from central nervous system to the periphery
Direction of travel is efferent
Interneurons
Most numerous of all types
Constitute neural tissue of brain & spinal cord

5. Neuron Three primary structure types: Monopolar Bipolar Multipolar
Cell body located in a collateral section that connects to transmitting zone of dendrite & axon
Cell of somatic sense (sense of touch & pressure)
Bipolar
Cell body along the main structure of the neuron with the dendrite extending in one direction from body and the axon in the other direction
Found in special senses (vision, audition, olfaction)
Multipolar
Multiple dendrites project from cell body
Neuron of the CNS & motor neuron innervating muscle

6. Types of Neurons
CB= Cell Body
Bipolar
Unipolar
Multipolar
Axons

7. Neural Connections
Communication between neurons is achieved by the release of neurotransmitters
Synapse= Tiny gap between 2 neurons
Presynaptic Neuron= Transmits impulse
Postsynaptic Neuron= Receiving impulse
Excitation (promoting neural activity)
Inhibition (reducing neural activity)
Neurotransmitter=Chemicals involved in neural communication
Released from terminal boutons of one neuron into cleft of synaptic junction
Contained in synaptic vesicles

8. Synapse Vesicles PRESYNAPTIC NEURON Lock & Key Synaptic Cleft
POSTSYNAPTIC
NEURON

9. Neurotransmitters 100 different kinds Major: Slower Neurotransmitters:
Glutamate
Aspartate
Gamma-aminobutyric acid (GABA)
Glycine
Relatively simple & fast action
Central to basic life processes
Slower Neurotransmitters:
Seratonin
Norepinephrine
Dopamine

10. Synaptic
Connections
Neuron B
Neuron C
Synapses
Myelin
Neuron A

11. Myelin & Glia Larger axon insulated with fatty coating- Myelin
Increases speed of neural transmission
Reduces interference with the neural message
Multiple sclerosis- dymyelinating
Neurons outnumbered by glial cells
Hold neurons in place & provide nutrients
Oligodendroglia (form myelin in CNS)
Schwann (form myelin in the PNS)

12. Neural Impulse
Neurons generate electrical impulse traveling the length of the nerve fibers
Neural activity= electrical & chemical activity
Neuron is like a battery
Stores electrical potential by accumulating positive charge in one terminal & excessive negative at the other terminal
An electrical potential across the membrane is created
Extracellular positive compared to intracellular
Ions carry charges
positive: sodium (Na+ ) & potassium (K+)
Negative: chlorine (CL=)

13. Neural Impulse Positive ions- concentrated outside the cell (sodium)
Negative ions- concentrated inside the cell
Resting membrane potential (-70 millivolts) created due to excessive positive outside cell
Maintained through sodium-potassium pump
act to exchange sodium ions found inside the cell with potassium ions found outside the ell
Neuron at rest= polarized
Neural activity= depolarization

14. Sodium-Potassium Pump
Sodium (Na+)
Extracellular fluid
Sodium
Channel
Potassium
Channel
Potassium (K+)
Intracellular fluid

15. Neural Impulse Action potential occurs= Wave of depolarization
Depolarization occurs when an action in another neuron momentarily lowers the voltage of a region of a membrane
Causes voltage-controlled gates to open that regulate sodium channels
Sodium floods into the cell
Polarity reverses from -70 to +30 mV
Cell returns to rest (sodium-potassium pump)

16. Neural Impulse
Depolarization effects tiny portion of membrane at a time.
Causes a wave down the entire membrane by causing voltage gated channels to open
Wave continues until the axon terminal
Synapse with other neuron
Transmitted to next neuron

17. Na+ Na+ B A D Na+ C A B C D CL- K+ K+ K+ K+ A= resting state;
ionic imbalance
Na+
CL- B A K+
B= depolarization;
Sodium
channels open; potential positive D
Na+ K+ C K+ K+
C= Opening of potassium
channels; potential returns negative
D= return to rest as
sodium-potassium
pump works A B C D

18. Neuroanatomy of the Vocal Mechanism

19. Neuroanatomy of the vocal Mechanism
Volitional control of muscles of the larynx resides in the brain.
Connecting points in brain that have a role in control of phonation: cortex, subcortical areas, midbrain & medulla.
Next slides will briefly review phonation neuroanatomy & neurophysiology.

20. Cortical Mechanisms of Phonatory Control
The cerebral cortex is responsible for:
conceptualization, planning, and execution of speech , including phonation.
Three major areas of the cortex responsible for vocalization:
a) Precentral & postcentral gyrus,
b) Anterior (Broca’s) area,
c) Supplementary motor area.

21. Cortical Areas Involved in Speech Movement Control
Primary Motor Cortex
Premotor & Supplementary
Cortex
Somatosensory
Cortex
Broca’s Area
-Stimulation of these areas can initiate, stop or distort vocalization.
-These behaviors occur in dominant & nondominant hemispheres.

22. Speech and Phonation are complex motor acts
Involves simultaneous activation and control of many muscles.
Control of these motor acts occurs primarily in the cortex.
Control of individual muscles occurs lower in the brain.
No evidence that cortical stimulation produces a response in a single solitary muscle.
Higher brain function = idealization of the event, integration of sensory information, feedback control, and coordination of various muscles.

23. Subcortical Mechanisms
Motor cortex has connections to the Thalamus ( egg shaped in the middle of the cerebral cortex),
A major portion of the diencephalon or interbrain.
Contain nuclei for language & speech
Relay station from cortical to subcortical brain
Thalamus has major pathways to the motor cortex & Broca’s area.
Parts of the diencephalon: a) hypothalamus, b) metathalumus, c) epithalumus, d) subthalumus, & e) third ventricle.

24. Thalamus: What Does it Do?
Projections to Cerebral Cortex
Acts as a relay for impulses in lower areas of the brain.
Integrates emotion into a complex motor act.
Plays a major role in:
coordinating out-going information from cortex,
integrating incoming sensory information
adding emotionality to speech
Thalamus
Diencepahalon
Midbrain
Projections
to Cerebellar
Cortex
Pons

25. Nuclei in thalamus that project to parts of the cerebral cortex
to & from
Sup. Parietal Lobule
Motor area receives its projections from the ventrolateral nucleus.
1971- ventrolateral nucleus shown to be responsible for initiation of speech movements & control of loudness, pitch, rate & articulation.
Broca’s area- receives connections from dorsomedian nuclei.
to & from Prenucleus
to & from
Parietal Lobe
Massa
Intermedia
Dorsal
Median
Lateral
Dorsal
Ventral
Lateral
Ventral posterior
Lateral

26. Midbrain Structures
Midbrain (mesencephalon) lies beneath the thalamus.
Cerebral peduncles lie on anterior surface of the midbrain and connect the cerebrum with the brainstem and spinal cord.
Posterior side has four colliculi: Superior (visual function), inferior (audition).
Within midbrain lies the cerebral aqueduct of Sylvius, surrounded by periaqueductal gray.

27. Periaqueductal Gray: What does it do?
Stimulation of dorsal and ventrolateral areas of periaqueductal gray = activity in some laryngeal muscles.
1985- Larson reported some cells in ventrolateral area stimulate muscle activity, whereas some suppress activity.
Periaqueductal gray is an intermediate area between recognition of a stimulus and the production of a motor act.

28. Brainstem
Bilateral structures in brainstem implicated in the neural control of phonation:
Nucleus ambiguus
Nucleus tractus solitarii
Nucleus parabrachialis
How do we know these structures are involved in phonation?

29. Yoshida, Mitsumasu, Hirano Study
Traced connections among brainstem structures.
Injected tracer chemical into one nucleus ambiguus.
Found evidence of tracer throughout the contralateral nuclei, nuclei tractus solitarri bilaterally, in nucleus parabrachialis and bilaterally in the lateral and ventrolateral parts of the periaqueductal gray area, with a predominance ipsilaterally.
Conclusion: Many interconnections bilaterally among the nucleus ambiguous, nucleus tractus solitarri, and motor roots of vagus.

30. Cerebellum Structure lying posterior to the midbrain area.
Implicated in the control of movement.
Three main portions: a) vermis, b) pars intermedia, c) hemispheres
Consists of many traverse folia- increases surface area.
Fissura prima- fissure separating anterior & posterior lobes.

31. References:
Colton, R.H. & Casper, J.K.,(1990), Understanding Voice Problems: A physiological perspective for diagnosis and treatment,, Williams & Wilkins.
Bhatnager, S.C. & Andy, O.J., (1995), Neuroscience for the study of communicative disorders, Williams & Wilkins.
Kuehn, D.P., Lemme, M.L. & Baumgartner, J.M., (1989), Neural basis of speech, hearing, and language, College- Hill Press.
Lieberman, M., (1991), Neuroanatomy made easy and understandable, Aspen Publishers.
Netsell, R., (1985), Speech and language evaluation in neurology-adult disorders, Grune & Stratton.
Poritsky, R., (1992), Neuroanatomy: a functional atlas of parts & pathways, Mosby-Year Book.