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Neuro INeuro I
Or:
What makes me do that Voodoo that I Do so Well!
Neurons and More NeuronsNeurons and More Neurons
The root of it all…...
The BrainThe Brain
Responsible for all behavior
Sensation– Sensory (Afferent)
Neurons
Movement– Motor (Efferent) Neurons
Integration of info– Interneurons
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
Cell AssembliesCell Assemblies
Groups of connected neurons that perform certain functions
Cell Assemblies: The NeuronCell Assemblies: The Neuron
A specialized cell that receives, processes and/or transmits information– Modulatory Characteristics
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
Neuronal StructureNeuronal Structure
Spinal Motor Neuron
Variations on a ThemeVariations on a Theme
Golgi Type II(Cortex)
Basket Cell(Cerebellum)
Sensory NeuronsSensory Neurons
Bipolar(Vision)
Unipolar(Pain/Touch)
Neuronal StructureNeuronal Structure
Spinal Motor Neuron
SomaSoma
Contains the nucleus and machinery– Life Processes
Neuronal Structure: DendritesNeuronal Structure: Dendrites
Spinal Motor Neuron
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
Dendritic SpinesDendritic Spines
Neuronal Structure: AxonNeuronal Structure: Axon
Spinal Motor Neuron
The AxonThe Axon
Tube-like structure– Micrometers to meters– Covered by the
“Myelin Sheath”
Axon
The AxonThe Axon
Tube-like structure– Carries a signal from
the soma to the terminal buttons
Signal = Action Potential (AP) (electrical/chemical event)
Axon
Myelin SheathMyelin Sheath
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
Neuronal Structure: Terminal Neuronal Structure: Terminal ButtonsButtons
Spinal Motor Neuron
Terminal ButtonsTerminal Buttons
Found at the end of the axon– When an AP reaches the terminal
Release chemical into the synapse– Neurotransmitter (NT)
NeurotransmittersNeurotransmitters
This Info can be excitatory or inhibitory to a neighboring neuron
Cell AssembliesCell Assemblies
Signaling in the NeuronSignaling in the Neuron
Electrical PotentialsElectrical Potentials
Most work done with the Giant Squid Axon– Neurons work by electrical and chemical
activity
Electrical PotentialElectrical Potential
Inside is more negative than the outside
-70 mv Membrane resting
potential
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
Ion DistributionIon Distribution
Ion ConcentrationsIon Concentrations
1:1354040Cl-
------------400A-
1:25100.4Ca++
1:946050Na++
40:110400K+
RATIOOUTSIDEINSIDEION
The number is not as important as the ratio
Ion ConcentrationIon Concentration
More positive charge on the outside then on the inside of the neuron
The Active NeuronThe Active Neuron
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
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
CaveatCaveat
Takes many excitatory inputs to reach thresholds– Temporal summation– Spatial summation
RepolarizationRepolarization
After time– The Na+ channels automatically close– K+ channels begin to open
K+ leaves the cell carrying with it the positive charge
– Repolarization
OvershootOvershoot
Too much K+ leaves causing the cell to be hyperpolarized
Back to Resting StateBack to Resting State
The Na+/K+ pump restores the normal ion concentrations and distributions
Axonal ConductionAxonal Conduction
This measurement takes place at one point on the giant squid axon– The signal must travel distances to reach its
destination
Signal DecrementSignal Decrement
Weak depolarization = loss of signal
AP PropagationAP Propagation
Strong depolarization = strong signal
Neuronal StructureNeuronal Structure
Spinal Motor Neuron
AXON HILLOCK
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
Neuronal StructureNeuronal Structure
Spinal Motor Neuron
AXON HILLOCK
Myelin SheathMyelin Sheath
Act as an insulator– Prevents things from moving in and out of the
cell Including Ions
OligodendrocytesOligodendrocytes
Nodes of RanvierNodes of Ranvier
Nodes of RanvierNodes of Ranvier
Gaps in the sheathHigh concentration of Na+ channels
– Reenergizes the signal so it can reach the axon terminal
Neuron: Axon TerminalNeuron: Axon Terminal
Axon Terminal: Synaptic Axon Terminal: Synaptic VesiclesVesicles
Synaptic TransmissionSynaptic Transmission
Cell AssembliesCell Assemblies
Synaptic Transmission: Synaptic Transmission: CaveatCaveat
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)