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Neurons:
Anatomy &
Physiology
Review: Chapter 2 of textbook.
Information from prerequisite
classes, that I assume you know.
Neurons
Basic functional unit of N.S.
 Specialized cell

All

cells have same basic properties
information processing
Transmits
 Integrates
 Stores


Regulation of behavior ~

Dendrites & soma
Receive & Integrate information ~
Stimuli


Axon carries information away from soma
 Electrical signal
Axon terminal releases chemical message
neurotransmitter (NT) ~
Neuronal Membrane
Common Cellular Properties
 Compartmentalization
 Semipermeable
 Fluid Mosaic Model
 Phospholipids
 Proteins ~

Phospholipid Bilayer
Hydrophilic
heads
Hydrophobic
tails
Membrane Proteins: Ionophores
Ions Channels
 Nongated

Gated

mechanically -gated

electrically-gated (voltage-gated)

chemically -gated ~
Membrane Proteins
NT
INSIDE
OUTSID
E
Membrane is polarized

More negative particles inside than out
unequal

distribution of ions
Bioelectric Potential
like

a battery
Potential for ion movement
current
~
Resting Membrane Potential
+
Na
Cl
outside
+
+
+
+
+
+
+
+
+
+
+
Membrane
- - - - - - - - - - inside
A
+
K
Forces That Move Ions
Concentration (C)
 particles in fluid move from area of
high to area of low concentration
 diffusion, random movement
 Electrostatic
(E)
 ions = charged particles
 like charges repel
 opposite charges attract ~

Organic anions Membrane impermeable
Opposing electrical force not required
Vm = -65 mV
A
C
Chloride ion
Cl
C
Vm = -65 mV
E
ECl- = - 65 mV
 Concentration gradient equal to
electrostatic gradient.
 *No net movement at resting potential ~

Potassium ion
E
Vm = -65 mV
+
K
C
EK = - 75 mV
 Concentration gradient greater than
electrostatic gradient.
 Leaks out neuron ~

+
Na
Sodium ion
C
Vm = -65 mV
ENa+ = +55 mV
 Concentration gradient and
electrostatic gradient into neuron. ~

E
Neural Communication
Neural Signaling



Inside neuron
 Electrical signal
 2 types of current
Postsynaptic potentials
 dendrites & soma
Action potential (AP)
 carries information down axon
 triggers NT release into synapse ~
Postsynaptic Potentials - PSPs
Chemically-gated ion channels
 Graded
 Summation
 Passive current (electrotonic)
 Fast
 Decremental
 Relatively long-lasting
 10 - 100 msec ~

EPSPs
Excitatory Postsynaptic Potential
 Depolarization (+)
 Em becomes more positive
 more likely to trigger AP
 Na+ influx ~

IPSPs
Inhibitory Postsynaptic Potential
 similar to EPSPs
 EXCEPT opposite
 hyperpolarization (-)
 Em becomes more negative
 less likely to trigger AP
 K+ efflux ~

Integration
EPSPs & IPSPs summate
 become stronger
 or cancel each other
 Net stimulation
 determines message

excitation
or
inhibition ~
Postsynaptic Potentials






Soma & Dendrites
Chemically-gated channels
Passive current
Graded
Summation
EPSP
Excitatory
Depolarization
Na+ influx
AP more likely

IPSP
Inhibitory
Hyperpolarization
K+ efflux
AP less likely
Action Potentials
Large and rapid change in membrane
potential
 Occurs in axon only
 voltage-gated channels
 triggered by EPSPs
 at axon hillock
 threshold potential ~

+40
0
Vm
-60
-70
-80
Time
+40
0
Vm
Depolarization
Na+ influx
-60
-70
-80
Time
+40
0
Repolarization
K+ efflux
Vm
-60
-70
-80
Time
+40
Afterhyperpolarization
0
Vm
K+ efflux
-60
-70
-80
Time
AP Characteristics
Voltage-gated channels
 All or none
 Self-propagated

regenerated
Non-decremental
 Slow
 Short-lived change in Em
 1-2 msec ~

Frequency Code
Pattern = Intensity of stimulus
 # APs per second
 Place = type of stimulus
 Visual, auditory, pain, etc.
 Brain area that receives signal ~

Injected
Current
0 mV
-65 mV
Time 
Subthreshold
stimulus
Moderate
stimulus
Strong
stimulus
PSPs
Graded
Summation
chemical-gated
longer duration
10-100 msec
passive spread
instantaneous
decremental
vs
APs
All-or-none
voltage-gated
short
1-2 msec
propagated
slow
nondecremental