NERVOUS RESPO

NSE

RESPON

SES OF T

HE

EARTHW

ORM

INTR

ODUCTIO

N

EARTHWORMS

Phylum Annelida

InvertebrateFluid-filled chambers to maintain its structure (hydroskeleton like)

Closed circulatory system (many "hearts" -- pump blood)

Hermaphrodites

NERVOUS SYSTEM OF

EARTHWORMS

Incomplete centralization and Cephalization

Cephalization is accumulation of neural tissue in the head/anterior end Brain: Dorsal Ganglion found in the head

SENSORY RECEPTORS

Sensory receptors can be classified into 4 groups

1. Stimulus Ampullae of Lorenzini - electric fields, salinity, temperature

Baroreceptors - pressure in blood vessels Chemoreceptors - chemical stimuli

2. Location Cutaneous - sensory receptors found in dermis/epidermis

Muscle spindles - have mechanoreceptors that detect stretch in muscles

SENSORY RECEPTORS

3. Morphology Free nerve endings - terminal branches of neuron have no myelin sheath - found throughout the dermis/epidermis

Encapsulated receptors - specialized functioning

4. Rate of adaption Tonic receptor - receptor that adapts slowly to stimulus

Phasic receptor - adapts rapidly to stimulus - ex. Pacinian corpuscle

MOVEMENT

1. Tropic Movement/Tropism Response that result in curvatures of whole plant organs or single part of the body of an organism toward or away from a stimulus

2. Taxic Movement/Taxis Automatic movement of the whole body of an organism directed toward or away from a stimuli

More finely tuned response to environmental stimuli than a change in speed or turning of a random movement

Efficient way of finding food or locating a mate

PREFIXES FOR TAXIS AND TROPHISM

Chemo – Chemical Thigmo – Touch Photo – Light Thermo – Temperature Geo – Gravity

RESPONSE

1. Positive attracts the organism

2. Negative makes the organism move

away

METHODOLO

GY

CONTACT: DIFFERENT

POINTS

CONTACT: ONEPOINT

LIGHT

HEAT

MOISTURE

XYLENE

RESULTS

LIGHT

The reaction to the light was negative

It avoided the light sourceThe reaction only applied to the

“head” or anterior part of the earthworm. The other parts did not respond to the light.

Earthworms do not have eyes. They contain photosensitive cells scattered at the skin of their bodies mostly at the head portion which cause them to retreat from light.

MOISTURE

After 20 minutes, the earthworms were all found at the moist side of the set-up.

SUMMARY OF RESULT

Stimuli Negative or Positive

Contact – different points

Negative Thigmotaxis

Contact – one point

Negative Thigmotaxis

Light Negative Phototaxis

Heat Negative Thermotaxis

Moisture Positive Chemotaxis

(or Hydrotaxis)

Chemical Negative Chemotaxis

CONCLUSION

The earthworm avoids light, heat, and exposure to chemicals but favors a moist environment. It also avoids contact but after constant continuous exposure, it becomes desensitized from the pressure.