Nervous System: Part 1By Taylor Barnhill, Julia Bogiages, Bridget

Brown, and Ellen Kitsos

Nervous System Overview

• Animation

Motor Neuron Structure• Dendrites: Input zones where the neuron

receives information• Nucleus: the powerhouse of the neuron• Cell body: Cell membrane containing organelle• Trigger Zone: Plasma membrane where

protein pumps and gated ion channels are located. Between the cell body and axon.

• Axon: Conduction zone, pass on signals from the trigger zone

• Axon endings: the output zone where messages are sent to other cells

• *Myelin Sheath: fatty substance that wraps around the dendrites catalyst that enhances rate of action potential and speeds up gate openings

Sodium Potassium Protein Pumps• Gradients determine the direction of diffusion.• Pumps require ATP to distribute against the

gradient.• Gradients reverse during an action potential

and sodium-potassium pumps correct them.• Moves in a 3:2 ration, pumping more

potassium ions on the outside. Positive ions entering and leaving, this is why the cell is negative voltage (at resting potential: -70 volts)

• Sodium Potassium Protein Pump Animation

Gated Ion Channels• Protein pumps and channel proteins allow potassium

and sodium ions to pass through.

• Gated ion channels are types of channel proteins, they facilitates diffusion but can close off at a certain voltage.

• Sodium ions rush in when a certain voltage is reached.

What is Action Potential?-A reversal in voltage differences across the

plasma membrane of the neuron (input zone)

-Triggered by a strong signal stimulus.

-Causes change in ion concentration and a voltage spike (graph peak)

Action Potential Sequence1) Stimulus hits the input zone2) Signals spread form input zone into the

trigger zone, where many sensitive, volted channels for Na+ ions are present

3) Certain amount of change in voltage difference across plasma membrane is called threshold level and triggers action potential

4) Positively charged Na+ ions flow into the neuron, causing more gates to open, more sodium to enter (positive feedback)

5) Neuron becomes more positive on the inside

Action Potential Sequence Cont.6) Influx of Na+ ions causes voltage spike7) Gated Na+ channels close 8) Halfway through the reversal, K+ channels

open, causing K+ to flow out9) This restores original voltage difference

across the membrane10) Na+/K+ pumps restore ion gradients

Sources1)http://www.google.com/imgres?

q=neuron+diagram&um=1&hl=en&client=safari&sa=X&rls=en&biw=1202&bih=629&tbm=isch&tbnid=yq3fWGAwg973GM:&imgrefurl=http://webspace.ship.edu/cgboer/theneuron.html&docid=BhtVqrZnXJW4QM&imgurl=http://webspace.ship.edu/cgboer/neuron.gif&w=700&h=500&ei=Mt6XUNzgJtGH0QHOr4GYBA&zoom=1&iact=hc&vpx=155&vpy=328&dur=984&hovh=190&hovw=266&tx=150&ty=102&sig=114060480899373829760&page=1&tbnh=144&tbnw=246&start=0&ndsp=12&ved=1t:429,r:4,s:0,i:146

2) Starr, Cecie. Biology: The Unity and Diversity of Life. Ninth ed. Pacific Grove: Brooks/Cole, 2001. Print.

3) http://www.youtube.com/watch?v=i-NgGKSNiNw&feature=player_embedded