K&W 4-1 Descartes View
Jan 15, 2016
K&W 4-1
Descartes View
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
K&W 4-4
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
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
K&W 4-8
Concentration gradient: move from area of higher concentration to area of lower concentration
Ions meet a barrier
K&W 4-9
No pores = No movement of ions
With pores, ions can move.
Charge develops
Electrical Gradient: opposite charges attract (+ --)like charges repel (+ +)
Ions of the axon
KW 4-10
Resting Cell Recording
KW 4-10
Resting Cell Charges
KW 4-10
Depolarization
KW 4-11
A Graded Potential
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
KW 4-19
Excitatory
Postsynaptic
Potential
Presynaptic cell
Postsynaptic cell
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
K&W 4-21
Democracy of Cells
Emotional ArousalAutonomic nervous system controls
physiological arousal
Sympatheticdivision (arousing)
Pupils dilate
Decreases
Perspires
Increases
Accelerates
Inhibits
Secrete stresshormones
Parasympatheticdivision (calming)
Pupils contract
Increases
Dries
Decreases
Slows
Activates
Decreasessecretion of
stress hormones
EYES
SALIVATION
SKIN
RESPIRATION
HEART
DIGESTION
ADRENALGLANDS
Control over heart
• Sympathetic excites• Parasympathetic
inhibits• Work together to
control heart