5.1

(a)

(b)

(c)

Sea anemone Jelly fish Hydra

A B C D

E F G 50 mV

20 ms

5.2

Helminthoida

Helminthopsis

Gyrolithes

Cochlichnus

Gordia

Regular meandering without crossing

Planolites

Irregular meandering without crossing

Spiraling

Meandering sinusoidally

Irregularly meandering and crossing

Simple straight

Second-order meanders

First-order meanders

Irregular

Straight

Ear

ly

Cam

bria

n

Pre

cam

bria

n

5.3

Water pik

Siphon nerve

Abdominal ganglion

Genital nerve

Pericardial nerve

Branchial nerve

Gill

Siphon

Stimulating and recording electrodes

5.4

SiphonMantle shelf

Gill

Int. II

L22

L23

L16

Polysynaptic

Monosynaptic

SN1 SN2 SN3 SN4 SN5 SN6 SN7 SN8

L7 LDG1 LDG2 L9G1 L9G2 RDG

5.5

(a)

(b)

(c)

(d)

(e)

(f)

5.6

Antenna tap

Do-si-do

Retreat

Strike/Rip

Meral spread

No agonistic behavior

Wresling

5.7

Reflex Chain

Motorneurons

Stretchreceptors

contracted relaxed

Antagonist muscles

Central Pattern Generator

CNS

CPG

contracted relaxed

Antagonist muscles

CNS

5.8

M CPGs

CPGs

CPGs

M

M

Buccal ganglion Cerebral ganglion

Buccal mass

Lip muscles

5.9

0

2

4

6

8

10

12

0 3 6 9 12 15

Res

pons

e S

tren

gth

0

2

4

6

8

10

12

0 1 2 3 4 5 6 7 8 9 100

2

4

6

8

10

12

0 1 2 3 4 5

Strong

Weak

0

2

4

6

8

10

12

0 1 2 3 4 5

Res

pons

e S

tren

gth

ISI = 60 s

ISI = 10 s

0

2

4

6

8

10

12

0 1 2 3 4 5 6 7 8

Res

pons

e S

tren

gth

600 Hz

200 Hz

400 Hz

600 Hz

0

2

4

6

8

10

12

0 1 2 3 4 5 6 7 8 9 10 11 12

(1)(2)

(3)

(2)

(4) (5)

(6)

(7)(8)

(9)

DS DS

Habituation Trials

Resting period

Resting period

Resting period

5.10

0

20

40

60

80

0 5 10 15 20

Trials

Me

an

Re

spo

nse

Sco

reWith DS

Without DS

DS

5.11

Stimulus generator

Time-date generator

Video cassette recorder

Petri plate holder

Micromanipulator stand

Microscope

C. elegans

Video monitor

Antagonistic reflex systems mediate forward and backward locomotion in response to a tap stimulus.

Head Tail

Before habituation:ALM and AVMPLM

AVM and ALMBackward motion

PLMForward motion

(a)

(b)

5.12

Siphon Head

SNSN

IN

IN

L7

Gill

5.13

Interneuron

Serotoninand other

neurotransmitters

Axo-axonic synapse

L7

Sensory neuron from siphon

Membrane proteins

Adenylate cyclase

cAMP

PKC

PKA

Closes K+ channels

Opens Ca++ channels

Mobilization of vescicles

Spike broadening

Short-term sensitization

Dishabituation

5.14

One-day retention

0

50

100

150

200

250

300

0 2 4 6 8 10

Trials

Me

dia

n D

ura

tion

of

Sip

ho

n W

ithd

raw

al (

s).

One-week retention

0

50

100

150

200

250

300

0 2 4 6 8 10

Trials

Sensitization

Control

Three-week retention

0

50

100

150

200

250

300

0 2 4 6 8 10

Trials

5.15

Dolabrifera

Bursatella

Dolabella

Aplysia

Akera

BullaIncreased

excitability

Spike broadening

Loss of both:Increased excitability

Spike broadening

5.16

Bodysurface

Bodysurface

Bodysurface

Effector

Effector

Effector

Lower invertebrates

Higher invertebrates

Vertebrates

Plastic Excitatory