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)