The Nervous System Feeling nervous? By: Conor Chinitz, Kelvin Chen, Nathan Bolton, Jack Clifford

What is the Nervous System? The Nervous System - a network of specialized cells responsible for organizing and transmitting electrochemical signals throughout the body (2). Composed of excitable cells called neurons (nerve cells) Neurons "fire" electrical signals to send messages " I thought I fired you! Why are you still working? " " Because I'm a neuron. "

"No matter how inherently lazy you feel, you are never really doing nothing... " —Kelvin

Neuron Structure Source: mhhe.com

The Axon Axons are output zones where messages are sent to other cells 1.Trigger Zone - junction between cell body and axon (2) 2.Nodes of Ranvier and Myelin Sheaths - conduction and insulation zones along axon, respectively (2) 3.Axon Terminal - end of axon (2)

Summary of Major Structures StructureFunction SomaCell body; contains nucleus; processes signals Dendrites Receives electrical signals from neighboring neurons and directs to soma (input) AxonsTransmits signals to neighboring neurons (output) Myelin SheathBead-like lipid structures that wrap around axons to facilitate signalling Axon: "Let's connect. " Dendrite: "On Facebook? " Axon: "No! With each other! " Sources: 2,3

Neurons at Rest In order for neurons to fire, they store electrical energy in the form of Na + and K + ions (2,3) Neurons at rest maintain a constant charge (voltage difference) o Resting Potential - the inherent voltage difference across the plasma membrane of an axon at rest (-70 millivolts) (2,3) Voltage difference caused by imbalance of Na + and K + ions across axon membrane (2,3)

Ion Distribution in Neurons At "rest," ions are still constantly entering and leaving the membrane through transport proteins(2) Facilitated ion transport happens actively and passively: 1.Passive transport: Na + and K + seep through channel proteins 2.Active transport: sodium-potassium pumps use ATP to move ions against concentration gradient (2 K + enter: 3 Na + exit) (2) Resting potential is a misnomer as the cell is not at rest but constantly working to maintain this ratio (2)

Ion distribution at rest Source:

Action Potential When the neuron is at rest, it has a negative charge (2) Action Potential occurs when stimulus overcomes the threshold (>-70mV) (2) o at action potential, there is a reversal of Na + and K + ions in membrane (2) o sudden ion influx results in a reversal of charge (membrane becomes positive in respect to extracellular fluid) (2) Neuron 1: "Girl, what happened to you?" Neuron 2: "Your stimulus carried me over my threshold!"

Ion Behavior during Action Potential Stimulus overcomes threshold of excitation is reached and initiates action potential (stimulus > -70 mV) Ion permeability changes: 1.Voltage-gated Na + channel open, allowing Na + to rush in 2.axon interior is now positively charged in respect to extracellular fluid (polarity reversal) 3.Voltage-gated K + channel open, allowing K + to rush out 4.axon interior is now back to being negatively charged in respect to extracellular fluid Sodium-Potassium pump then restores resting-potential distribution of Na + to K + Source: 2

Source: library.thinkquest.org

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Myelin Sheath Insulates electrical signal traveling along the axon o Prevents electrical signal from dispersing (2) Enhances rate of action potential propagation (2)

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Thank you! We hope this presentation excited your neurons.

Bibliography 1 ) Abedon, Stephen T. "Transport Across Membranes." Home. Ohio State University, 28 Mar Web. 24 Oct ) Starr, Cecie, and Ralph Taggart. Biology: The Unity and Diversity of Life. 5 th ed. Belmont, Calif.: Wadsworth Pub. Co., Print. 3) Campbell, Neil, and Heyden Robin. Biology: Exploring Life. Florida: Pearson Education, Inc., Print.

Further Exploration Interactive Program for Action Potential: o f Applications of Neurons: o mans/ o