PSYC 170 - Summer 2013 - Professor Claffey
Notes: Neuron
PDF
Stained Florescent
Microscopy
Source: http://phys.org/news175417796.html |
Hand Drawing (Ramon y
Cajal)
Source: http://nobelprizewatch.wordpress.com/2011/12/06/
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Computer Graphic
Source:
http://thetechjournal.com/science/neuron-implantation-can-rewire-brain-itself.xhtml
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Background
Functional unit of nervous system
A cell specialized for the ___________________ and
___________________ of signals
____ billion in adult human brain (
source)
Uses ____________________ and ______________________ systems to
communicate
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In central nervous system
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In peripheral nervous
system
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clusters of cell bodies
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bundles of axons
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Cell basics
Nucleus & DNA
Membrane
Organelles
Mitochondria
Energy metabolism: constant need for ________________ and
________________
Sources: http://en.wikipedia.org/wiki/Neuron#Anatomy_and_histology (left), Pinel (right)
Structures for communication
Source: http://en.wikipedia.org/wiki/Neuron
Types of neurons
http://en.wikipedia.org/wiki/Neuron#Functional_classification
Glial Cells
Support cells
Generally outnumber neurons (as much as 10:1 in some parts of the
brain)
Oligodendrocytes
myelin extensions wrap around axons in central
nervous system
provides myelin to multiple neurons
Schwann cells
provides myelin in peripheral nervous system
1 Schwann cell per axon
can aid in regeneration
Microglia
aid in recovery, part of inflammation process
Astrocytes
historically seen as "glue" or support cells
increasingly recognized for communication
abilities
part of blood-brain-barrier and may regulate
blood flow
recycle neurotransmitters
Resting Potential
Where is this going:
The neuron is going to rapidly move ions across
its membrane
It spends the energy in advance to setup for
this action
Potential
Energy that is available to do work
Ball at top of slope, spring, laptop battery
Chemical gradients
Example of non-charged particles diffusing across barrier to reach
equilibrium
Concentration gradient - the "downhill" change in concentration
Electrical gradients
Ions - molecules that carry a negative or positive charge
Electrostatic pressure - the force pushing molecules down the
gradient (space below is intentionally blank for drawing)
Source:
http://www.anselm.edu/homepage/jpitocch/genbio/nervousnot.html
Sodium-Potassium Pump
A pump that moves ___________________ out and _______________ in
by using __________________
(The brain uses about
20% of your daily calories, this is a major component)
Source:
http://hyperphysics.phy-astr.gsu.edu/hbase/biology/nakpump.html
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Not really a pump, but just a _________________
Source: http://en.wikipedia.org/wiki/Na%2B/K%2B-ATPase |
Channels
Proteins embedded in the membrane that allow molecules to
_____________ diffuse through
Voltage-gated channels - open and close in response to
_________________________________
Ligand gated - open and close in response to
_________________________________
Na+ channel - _________ at negative potentials, slower/faster to
respond
K+ channels - _________ at negative potentials, slower/faster to
respond
Neuron's Resting Potential
Typical resting potential is _____________
Source: http://academic.uprm.edu/~ephoebus/id81.htm |
Sodium (Na+)
Potassium (K+)
Chloride (Cl-)
Organic anion (A-)
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Action Potential
Where we are going:
How does a signal get passed down the neuron
(along the axon)
A sequence of events that disrupts the resting
potential
Post-synaptic potentials
Axon terminals release neurotransmitters
These neurotransmitters react with receptors on
the next neuron
Can cause the neuron to depolarize or
hyperpolarize
Polarization
Source:
http://www.polaris.iastate.edu/NorthStar/Unit1/activity1.htm
Depolarization
Hyperpolarization
Sub-threshold depolarization
Does NOT make membrane potential more positive than threshold
(typically -65 mV)
A little Na+ comes in, making the potential more positive
K+ is pushed out by the incoming Na+ and the NaK pump is still
working, so returns to resting potential
Above-threshold depolarization
DOES make membrane potential more positive than threshold
(typically -65 mV)
As it depolarizes, more and more sodium channels open
Na+ starts coming in faster and faster, creating positive feedback
Full action potential occurs
Total number of ions flowing through membrane is relatively small,
so concentrations do not change much
Stages
Source:
http://www.dummies.com/how-to/content/understanding-the-transmission-of-nerve-impulses.html
Source:
http://www.msdellasantina.com/Files%20AP/Ch%2048%20Neurons%2006_files/slide0078_image046.gif
Depolarization / rising phase
becoming more positive as Na+
channels open
with all channels open, Na+ pushes
potential up to +50 mV
Repolarization
at maximum positive voltage, Na+
channels close & no-longer voltage sensitive
K+ channels eventually fully open
K+ pushes out until voltage goes
negative
Undershoot
With K+ fully open, potential goes
more negative than resting
Once K+ go back to
mostly-closed-but-leaky, returns to resting potential
Refractory Period
Immediately after firing, another
depolarization will not trigger an action potential
absolute refractory period - no
action potential possible
relative refractory period -
action potential requires stronger depolarization
a few milliseconds long
Where in the neuron
Starts at axon hillock (typically)
Travels down axon
Triggers events at axon terminals
Does not automatically pass into next neuron
Source:
http://www.anselm.edu/homepage/jpitocch/genbio/nervousnot.html
Saltatory conduction
Source:
http://psych.hanover.edu/classes/sensation/WebNotes/Class04-2010.html
Myelin covers most of neuron with a few gaps
Ions only exchange across membrane at these
gaps
For reasons related to particle diffusion, this
is faster than continuous conduction
Myelinated neurons (e.g. motor neurons) - 100
m/s
Unmyelinated neurons - 1 m/s
Principles
All-or-none
One directional
Electrical
Fast
Active vs. Passive
Copyright 2012-2013 - Michael Claffey