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Neuronal Function. Goal: electrochemical communication Requirement: Electrochemical signal generation Electrochemical signal propagation Electrochemical signal transmission. Neuronal Function. Neuronal Function. Electrochemical Signal generation. Establishing Membrane Potential ( V m ). - PowerPoint PPT Presentation
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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
epsp
threshold
depo
lari
zatio
nhy
perp
olar
izat
ion
Time
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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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