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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
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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 • 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 Assemblies • Groups of connected neurons that perform certain functions
Cell Assemblies: The Neuron • A specialized cell that receives, processes and/or transmits information • Modulatory 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 Modulatory Characteristics
Neuronal Structure Spinal Motor Neuron
Variations on a Theme Basket Cell (Cerebellum) Golgi Type II (Cortex)
Sensory Neurons Unipolar (Pain/Touch) Bipolar (Vision)
Neuronal Structure Spinal Motor Neuron
Soma • Contains the nucleus and machinery • Life Processes
Neuronal Structure: Dendrites Spinal Motor Neuron
Dendrites (Tree) • Highly Aborized • Receive “messages” from other neurons • Some have dendritic “spines” • Input sites • Separated from neighbor by a synapse (space) • Caveat: They can transmit signals as well
Neuronal Structure: Axon Spinal Motor Neuron
The Axon • Tube-like structure • Micrometers to meters • Covered by the “Myelin Sheath” Axon
The Axon • Tube-like structure • Carries a signal from the soma to the terminal buttons • Signal = Action Potential (AP) (electrical/chemical event) Axon
Myelin Sheath • Surrounds many (but not all) axons • Formed by Oligodendrocytes (CNS) and Schwann Cells (PNS) • There are gaps between adjacent cells • Several micrometers • Called “Nodes of Ranvier” • Internode region
Neuronal Structure: Terminal Buttons Spinal Motor Neuron
Terminal Buttons • Found at the end of the axon • When an AP reaches the terminal • Release chemical into the synapse • Neurotransmitter (NT)
Neurotransmitters • This Info can be excitatory or inhibitory to a neighboring neuron
Electrical Potentials • Most work done with the Giant Squid Axon • Neurons work by electrical and chemical activity
Electrical Potential • Inside is more negative than the outside • -70 mv • Membrane resting potential
Ions • 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 INSIDE OUTSIDE RATIO K+ 400 10 40:1 Na++ 50 460 1:9 Cl- 40 540 1:13 A- 400 ------ ------ Ca++ 0.4 10 1:25 Ion Concentrations The number is not as important as the ratio
Ion Concentration • More positive charge on the outside then on the inside of the neuron
The Action Potential (AP) • Its hard to know what’s going on • Difficult to isolate ions • Everything is occurring at once • The charge is changing • Impacts ion movement
Reaching 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
Caveat • Takes many excitatory inputs to reach thresholds • Temporal summation • Spatial summation
Repolarization • After time • The Na+ channels automatically close • K+ channels begin to open • K+ leaves the cell carrying with it the positive charge • Repolarization
Overshoot • Too much K+ leaves causing the cell to be hyperpolarized
Back to Resting State • The Na+/K+ pump restores the normal ion concentrations and distributions
Axonal Conduction • This measurement takes place at one point on the giant squid axon • The signal must travel distances to reach its destination
Signal Decrement Weak depolarization = loss of signal
AP Propagation Strong depolarization = strong signal
Neuronal Structure AXON HILLOCK Spinal Motor Neuron