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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.
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