Nervous System: Part 1
By Taylor Barnhill, Julia Bogiages, Bridget
Brown, and Ellen Kitsos
Nervous System Overview
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Animation
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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
Sodium Potassium Protein Pumps
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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
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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 Sequence
1) Stimulus hits the input zone
2) 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 spike
7) Gated Na+ channels close
8) Halfway through the reversal, K+ channels
open, causing K+ to flow out
9) This restores original voltage difference
across the membrane
10) Na+/K+ pumps restore ion gradients
Sources
1)http://www.google.com/imgres?q=neuron+diagram&um=1&hl=en&client=safa
ri&sa=X&rls=en&biw=1202&bih=629&tbm=isch&tbnid=yq3fWGAwg973GM:
&imgrefurl=http://webspace.ship.edu/cgboer/theneuron.html&docid=BhtVqr
ZnXJW4QM&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=1140604808993
73829760&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