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