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

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

Neuronal Structure Spinal Motor Neuron

Variations on a Theme Golgi Type II (Cortex) Basket Cell (Cerebellum)

Sensory Neurons Bipolar (Vision) Unipolar (Pain/Touch)

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

Dendritic Spines

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

Cell Assemblies

Signaling in the 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 Distribution

Ion Concentrations 1: Cl A- 1: Ca++ 1:946050Na++ 40:110400K+ RATIOOUTSIDEINSIDEION 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 Active 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 Spinal Motor Neuron AXON HILLOCK

Axon 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 Structure Spinal Motor Neuron AXON HILLOCK

Myelin Sheath Act as an insulator – Prevents things from moving in and out of the cell Including Ions

Oligodendrocytes

Nodes of Ranvier

Gaps in the sheath High concentration of Na+ channels – Reenergizes the signal so it can reach the axon terminal

Neuron: Axon Terminal

Axon Terminal: Synaptic Vesicles

Synaptic Transmission

Cell Assemblies

Synaptic Transmission: Caveat

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)