SPPA 2050 Speech Anatomy & Physiology

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Neuronal Function

Goal: electrochemical communication

Requirement:

• Electrochemical signal generation

• Electrochemical signal propagation

• Electrochemical signal transmission

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Neuronal Function

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Neuronal Function

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ElectrochemicalSignal generation

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Establishing Membrane Potential (Vm)

• Intracellular space• Cell membrane• Extracellular space

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Establishing Membrane Potential (Vm)

• Na: Sodium• K: Potassium• Cl: Chloride• Ca: Calcium• +: positive ion• -: negative ion

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Establishing Membrane Potential (Vm)

Active Transport: Na-K pump

• Transports 3 Na+ ions out of the cell

• Transports 2 K+ ions into the cell

• Net effect– Electrostatic gradient– Concentration gradient

• Requires energy

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Resting membrane potential (Vm)

Vm = ~ -70 millivolts

Vm more positive → depolarization

Vm more negative → hyperpolarization

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Changing VmReceptor mediated

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Changing Vm

Voltage Gated Channels

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Changing VmPhysical change in permeability

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Postsynaptic Potentials (EPSP & IPSP)

• Local• Passive• Graded

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Summation of PSP

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Temporal Summation Spatial Summation

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Reaching a Threshold

-70 mVepsp

ipsp

epsp

epspepsp

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threshold

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Time

SPPA 2050 Speech Anatomy & Physiology

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Electrochemical Signal Propagation

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Time course• ↑ depolarization

(~ +100 mV)• Brief (~ 1 msec)• Repolarization• Hyperpolarization• Return to Vm

Other features• Active• All-or-none• Refractory period

– Absolute– Relative

Action Potential

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Action Potential: Propagation

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Action Potential: Propagation

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Action potential: Saltatory Conduction

• Conduction velocity• Conduction velocity

increased by presence of – Myelin - insulates the axon – nodes of Ranvier – AP

“skips” from node to node

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Clinical Note

• Multiple Sclerosis – a demyelinating disease

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Electrochemical Signal Transmission

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The Synapse

• Secretory potential• Pre synaptic neuron• Post synaptic neuron• Synaptic cleft• Synaptic Vesicles• Neurotransmitters• Receptors• Neuromuscular

junction

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Neurotransmitters

Features• Excitatory• Inhibitory• Direct• 2nd Messenger

Common NT• Acetylcholine• Dopamine• Serotonin• Glutamate• GABA• Glycine

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Receptor Action

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Synaptic Modulation: Glutamate

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Clinical Note: Parkinson’s Disease

• Loss of dopamine• Causes movement disorder• Can cause dysarthria

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Clinical Note: Botulinum Toxin (BOTOX)

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Clinical Note: Botulinum Toxin (BOTOX)

• Spasmodic dysphonia

• Excess contraction of laryngeal muscles

• BOTOX temporarily paralyzes the muscles

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Stretch Reflex: Simple Neuromuscular Circuit

• Also known as– Patellar tendon reflex– Knee-jerk reflex

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Stretch Reflex: Components

• Sensory receptor (muscle spindle)

• Afferent nerve fibers

• CNS neurons (interneurons)

• Efferent nerve fibers

• Muscle

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Stretch Reflex

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