Descartes View
K&W 4-1
Luigi Galvani (1737-1798)
Electrified Frogs
• Luigi Galvani
• Frog legs attached to
wire in market
• Electrical storm made
legs move
• Early idea of electrical
properties of nervous
system
Electrical Stimulation
K&W 4-2
Neural Communication
The journey of nerve message
As message passes
along the nerve,
Electrode indicates
a shift from
negative to positive
and then back to
negative again
K&W 4-4
Neural Communication
Cell body end
of axon
Direction of neural impulse: toward axon terminals
Hodgkin and
Huxley
Two Cambridge profs and a
squid get together (1939)
Squid and axon
K&W 4-5
Microelectrodes
KW 4-7
Recording from an axon
K&W 4-6
Reversal of
charges
K&W 4-15
Ions
Ions on the move
Concentration gradient: move from area of higher concentration to
area of lower concentration
K&W 4-8
Ions meet a barrier
No pores = No
movement of ions
With pores, ions
can move.
Charge develops
Electrical Gradient: opposite charges attract (+ --)
like charges repel (+
+)
K&W 4-9
Ions of the axon
KW 4-10
Resting Cell Recording
KW 4-10
Resting Cell Charges
KW 4-10
Depolarization
A Graded Potential
KW 4-11
Hyperpolarization
KW 4-11
A Graded Potential
Axons get polarized
K&W 4-11
When an action potential occurs,
Na+ and K+ work together
KW 4-13
Fig. 2-17, p. 43
Phases of the action potential
K&W 4-14
Fig. 2-15, p. 39
Neural Communication
Reversal of Charges
Cell body end
of axon
Direction of neural impulse: toward axon terminals
Falling
dominos
K&W p. 131
Ion flow
K&W 4-15
Properties of Action Potentials
•
•
•
•
•
All or none: fires completely or not at all
Self-propagates: recreates itself
Does not degrade: doesn’t lose power
Full strength to the end of axon
Axon can be any length
Analogies for Action Potentials
• Band of Fire moving down tube
• Ring sliding down a string
• Doing “the wave” in stadium
End of segment one
Naked Neurons
• Neurons without
myelin sheath
• Slower
• Shorter
• Can’t carry messages
long distances
• What does myelin
sheath provide?
Louis-Antoine Ranvier
• French physician
discoverer of the
myelin sheath.
• 1835-1922
• In 1878 he discovered
myelin and the famous
nodes which received
his name
Nodes of Ranvier
K&W 4-16
Saltatory
conduction
K&W 4-17
Multiple Sclerosis
•
•
•
•
Jacqueline Du Pre
1945-1987
MS diagnosis in 1971
Hilary and Jackie
(1998 movie)
Neuronal Integration
• To fire or not to fire, that is the question
• All or none principle: all or nothing at all
• Why important?
Firing
Line
Threshold
Sherrington
• Sir Charles Scott
Sherrington
• (1857-1952)
• Withdrawal reflex
• Principle of
summation
• Nobel prize in
medicine 1932
Withdrawal Reflex in Dogs
• One mild pinch
between toes 
no response
• Two pinches quickly
in same spot 
withdraw paw
• Temporal Summation
• Temporal = over time
Paw reflex: part 2
• One mild pinch in one
location 
no response
• Two pinches in
different locations 
withdraw paw
• Spatial Summation
• Spatial = over space
Temporal: one location
Postsynaptic cell
Excitatory
Postsynaptic
Potential
Presynaptic cell
KW 4-19
synapse
Temporal EPSP
KW 4-19 top
Spatial:
more than
one location
K&W 4-20
Spatial EPSP
KW 4-19
Importance of EPSP
•
•
•
•
Excite cells
Bring about activity
Sensation felt
Muscle moved
Excitation must be balanced
• Nervous system can’t
run on just excitation
• Sometimes better not
to respond
• Role on inhibition
• Calm down the
nervous system
Role of Inhibition
• Provides break for the
nervous system
• Lowers activity levels
• Keeps the brain from
over-excitation, as in
epilepsy
EPSP vs IPSP
Temporal IPSP
KW 4-19
Temporal Combos
Spatial Combos
A cell
decides to
fire
Democracy of Cells
K&W 4-21
Emotional Arousal
Autonomic nervous system controls
physiological arousal
Sympathetic
division (arousing)
Parasympathetic
division (calming)
Pupils dilate
EYES
Pupils contract
Decreases
SALIVATION
Increases
Perspires
SKIN
Dries
Increases
RESPIRATION
Decreases
Accelerates
HEART
Slows
Inhibits
DIGESTION
Activates
Secrete stress
hormones
ADRENAL
GLANDS
Decreases
secretion of
stress
hormones
Control over heart
• Sympathetic 
excites
• Parasympathetic 
inhibits
• Work together to
control heart