neuro i
DESCRIPTION
Neuro I. Or: What makes me do that Voodoo that I Do so Well!. Neurons and More Neurons. The root of it all…. The Brain. Responsible for all behavior Sensation Sensory (Afferent) Neurons Movement Motor (Efferent) Neurons Integration of info Interneurons. The Brain. Donald Hebb - PowerPoint PPT PresentationTRANSCRIPT
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Neuro INeuro I
Or:
What makes me do that Voodoo that I Do so Well!
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Neurons and More NeuronsNeurons and More Neurons
The root of it all…...
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The BrainThe Brain
Responsible for all behavior
Sensation– Sensory (Afferent)
Neurons
Movement– Motor (Efferent) Neurons
Integration of info– Interneurons
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The BrainThe Brain
Donald Hebb Proposed that the
brain is not merely a mass of tissue– but a highly integrated
series of structures that perform specific functions
cell assemblies
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Cell AssembliesCell Assemblies
Groups of connected neurons that perform certain functions
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Cell Assemblies: The NeuronCell Assemblies: The Neuron
A specialized cell that receives, processes and/or transmits information– Modulatory Characteristics
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Modulatory CharacteristicsModulatory Characteristics
Depolarize– Make a neighbor more
likely to be active
Hyperpolarize– Make a neighbor less
likely to fire
Change the dynamics of a receptor– Make it less receptive
to a signal (NT)
Affect synthesis, movement and release of NT to another neuron
Moduation
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Neuronal StructureNeuronal Structure
Spinal Motor Neuron
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Variations on a ThemeVariations on a Theme
Golgi Type II(Cortex)
Basket Cell(Cerebellum)
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Sensory NeuronsSensory Neurons
Bipolar(Vision)
Unipolar(Pain/Touch)
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Neuronal StructureNeuronal Structure
Spinal Motor Neuron
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SomaSoma
Contains the nucleus and machinery– Life Processes
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Neuronal Structure: DendritesNeuronal Structure: Dendrites
Spinal Motor Neuron
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Dendrites (Tree)Dendrites (Tree)
Highly AborizedReceive “messages” from other neurons
– Some have dendritic “spines” Input sites
– Separated from neighbor by a synapse (space)
Caveat: They can transmit signals as well
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Dendritic SpinesDendritic Spines
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Neuronal Structure: AxonNeuronal Structure: Axon
Spinal Motor Neuron
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The AxonThe Axon
Tube-like structure– Micrometers to meters– Covered by the
“Myelin Sheath”
Axon
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The AxonThe Axon
Tube-like structure– Carries a signal from
the soma to the terminal buttons
Signal = Action Potential (AP) (electrical/chemical event)
Axon
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Myelin SheathMyelin Sheath
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Myelin SheathMyelin Sheath
Surrounds many (but not all) axonsFormed by Oligodendrocytes (CNS) and
Schwann Cells (PNS)There are gaps between adjacent cells
– Several micrometers– Called “Nodes of Ranvier”– Internode region
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Neuronal Structure: Terminal Neuronal Structure: Terminal ButtonsButtons
Spinal Motor Neuron
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Terminal ButtonsTerminal Buttons
Found at the end of the axon– When an AP reaches the terminal
Release chemical into the synapse– Neurotransmitter (NT)
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NeurotransmittersNeurotransmitters
This Info can be excitatory or inhibitory to a neighboring neuron
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Cell AssembliesCell Assemblies
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Signaling in the NeuronSignaling in the Neuron
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Electrical PotentialsElectrical Potentials
Most work done with the Giant Squid Axon– Neurons work by electrical and chemical
activity
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Electrical PotentialElectrical Potential
Inside is more negative than the outside
-70 mv Membrane resting
potential
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IonsIons
Molecules that have given up or taken on an electron– Gives the molecule a charge– Some move more readily across the membrane
then others Dependent on circumstances
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Ion DistributionIon Distribution
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Ion ConcentrationsIon Concentrations
1:1354040Cl-
------------400A-
1:25100.4Ca++
1:946050Na++
40:110400K+
RATIOOUTSIDEINSIDEION
The number is not as important as the ratio
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Ion ConcentrationIon Concentration
More positive charge on the outside then on the inside of the neuron
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The Active NeuronThe Active Neuron
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The Action Potential (AP)The Action Potential (AP)
Its hard to know what’s going onDifficult to isolate ions
– Everything is occurring at once– The charge is changing
Impacts ion movement
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Reaching ThresholdReaching Threshold
Excitatory Input (Depolarization)– Causes the influx of positive ions (Na+) into
the cell by opening Na+ channels Voltage gated channels
– Great variety in threshold level
– If enough positive charge comes in The threshold is reached
– More NA+ channels open– Making the cell more positive– All or none
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CaveatCaveat
Takes many excitatory inputs to reach thresholds– Temporal summation– Spatial summation
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RepolarizationRepolarization
After time– The Na+ channels automatically close– K+ channels begin to open
K+ leaves the cell carrying with it the positive charge
– Repolarization
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OvershootOvershoot
Too much K+ leaves causing the cell to be hyperpolarized
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Back to Resting StateBack to Resting State
The Na+/K+ pump restores the normal ion concentrations and distributions
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Axonal ConductionAxonal Conduction
This measurement takes place at one point on the giant squid axon– The signal must travel distances to reach its
destination
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Signal DecrementSignal Decrement
Weak depolarization = loss of signal
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AP PropagationAP Propagation
Strong depolarization = strong signal
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Neuronal StructureNeuronal Structure
Spinal Motor Neuron
AXON HILLOCK
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Axon HillockAxon Hillock
Has a high concentration of low threshold Na+ Channels– Very sensitive to changes in ion movement– Activation results in a autocataclysmic response
All Or none
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Neuronal StructureNeuronal Structure
Spinal Motor Neuron
AXON HILLOCK
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Myelin SheathMyelin Sheath
Act as an insulator– Prevents things from moving in and out of the
cell Including Ions
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OligodendrocytesOligodendrocytes
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Nodes of RanvierNodes of Ranvier
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Nodes of RanvierNodes of Ranvier
Gaps in the sheathHigh concentration of Na+ channels
– Reenergizes the signal so it can reach the axon terminal
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Neuron: Axon TerminalNeuron: Axon Terminal
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Axon Terminal: Synaptic Axon Terminal: Synaptic VesiclesVesicles
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Synaptic TransmissionSynaptic Transmission
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Cell AssembliesCell Assemblies
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Synaptic Transmission: Synaptic Transmission: CaveatCaveat
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In conclusion:In conclusion:
Neurons are good.They excite or inhibit.They produce 1 neurotransmitter (in
mammals).Transmission is essential.Neuromodulators can change everything
(more on that later)