The nervous system is a complex network of nerves and cells that carry messages to and from the brain and spinal cord to various parts of the body.The functional unit of the nervous system is a highly specialized cell called the neuron. Neurons are specialized to produce signals that can be communicated over short to relatively long distances, from on part of an animal's body to another The nervous system includes both the Central nervous system and Peripheral nervous system. The Central nervous system is made up of the brain and spinal cord and The Peripheral nervous system is made up of the Somatic and the Autonomic nervous systems.

The nervous systems of invertebrates are smaller and contain fewer neurons than those of vertebrates, yet they generate the great diversity and complexity of behavior that has contributed to the incredible success of these animals.

CNIDARIANS

The cnidarians (hydras, jellyfishes, and sea anemones)

have the simplest form of nervous organization. These animals called a nerve net.

Nerve net– a latticework that conducts impulses

from one area to another. Impulse conduction by neurons is bidirectional.

Coral and sea anemones contain the simplest form of a nervous system. There is no centralization of the nervous system; therefore they don't have a brain. Neurons communicate with one another whenever they cross the path of another. This is called en passant synapse. The neurons send the information in almost every direction and lay between the two layers of each the coral and sea anemone.

Green Anemone

JELLYFISHES

JELLYFISHES

Jellyfish, also, do not have a specialized nervous system, but they do have a nerve net. The nerve net is found in the epidermis. The rhopalial lappet located around the jellyfish’s body sends information from the nerve rings. Jellyfish are sensitive to light, but they cannot see images. They use the ocelli to help determine which way is up by detecting sunlight. The nerve net helps the jellyfish know when the prey or a predator touches it on their oral arms.

MEDUSA

• Jellyfish are made up of 95% water.

• Jellyfish can have tentacles of more than 100 feet long.

• Large species of jellyfish can eat crustaceans.

• "A group of jellyfish is often called a 'smack.' Many species of jellyfish

are also capable of congregating into large swarms or 'blooms'

consisting of hundreds or even thousands of individuals".

Additional Facts…

Animals, such as flatworms and roundworms that move in a forward direction have sense organs concentrated in the body region that first encounters new environmental stimuli.

Thus, the second trend in nervous system evolution involves cephalization.

Cephalization– is a concentration of receptors and

nervous tissue in the animal’s anterior end.

For example: a flatworm’s nervous system contains “Ganglia” .

Ganglia - are distinct aggregations of

neuron cell bodies in the head region.- Ganglia function as primitive

“brains”.

Flatworm Anatomy

Hexopoda Anatomy

Echinoderm

The nervous system of Sea Star or Starfish is primitive and poorly developed. However, they have eye spots that can detect light and help with orientation. However, they lack the advanced nervous system of chordates.

• Sea Stars have two stomachs, a cardiac and pyloric stomach, and the eversion

of the cardiac stomach occurs when the Sea Star wants to feed. They push their

stomach out of their body and over the prey, where digestive enzymes break

down the break and make transport into the sea star’s body easier.

• Sea Stars can regenerate lost limbs through asexual reproduction. Fisherman

used to just chop Starfish into pieces, hoping to kill them and stop them from

eating up the oyster beds, and then throw them back into the ocean. However,

they were unaware that Echinoderms can regenerate lost limbs, and this would

just increase their population even more, making the issue worse.

•Brittle Stars can be found at depths as great as 6000 m.

•The anus of a Sea star is located on top of its body.

•Echinoderms only live in salt water, and are very sensitive in changes of salinity.

If a sea cucumber were placed in fresh water, it would swell up and explode.

Additional Facts…

Echinoids, also known as sea

urchins.

Sea urchins, sea cucumbers, and sand dollars are all part of the Phylum Echinodermata.

There is little knowledge of the nervous system of echinoderms. Without a brain, the nervous system coordinates the movement of the tube feet and spines. The defense mechanisms of echinoderms give evidence that the nervous system must be more complex than it looks.

Sea Cucumbers Sand Dollars

Scientists can age sand dollars by counting the number of growth

rings on the plates of the exoskeletons.

An urchin's teeth can drill through steel pilings by flaking away the

rust that coats them.

Sometimes sand dollars chew their food for 15 minutes before

they swallow.

It can take up to two days for a sand dollar to digest its food.

In fast-moving water, young sand dollars my swallow heavy sand

grains in order to weigh themselves down. Adults fight the currents

by growing heavier skeletons.

The redlined sea cucumber from Papua New Guinea can grow up to

2 meters in length.

Additional Facts…

Snail

The center of the nervous system of snails is more towards the head because that’s where all of the animal’s sensory organs are located.Snails have two pairs of tentacles; the upper pair serve as two eyes.Snails have a cerebral ganglia that is divided into 5 sections and that serves as a primitive brain that makes snails capable of associative learning and these different sections of the ganglia are connected.Limpets central nervous system is coiled and cephalized.

Cepaea hortensis

Most bivalves can perceive light by their late larval stages through their eyespots.photoreceptors are reported in the pallial nerve.Cilia perceive touch and vibrations through the water. Cells along the edge of the mantel respond to light and touch (photoreceptors). Ganglia are located above the mouth, in the digestive system, and in the foot. It’s connected by two pairs of long nerve cords.

Bivalves are simple. They have 3 pairs of ganglia and two pairs of long nerve cords. The cerebrophleural ganglia is located near the esophagus. It is connected to two nerve cords, located closely to visceral ganglia that are located under the posterior adductor muscle. Then they are connected to a second pair of nerve cords that carry nerve signals to a pair of pedal ganglia near the foot.

Lobster

LOBSTERS: Lobsters have highly developed systems of both smell and taste. The first

antennae, act as the "nose" of the lobster. Hundreds of fine hairs cover the antennules

and are the actual organs of smell. In order for a lobster to be able to smell something,

or to be able to walk towards a smell, it has to constantly sample the chemicals in the

water to determine their changing concentration. Lobsters do this in the same way that

humans do - - they sniff. Sniffing is accomplished by flicking the antennules downward

quickly - - this removes the old water and replaces it with new water and a new odor

sample. Because lobsters have two antennules, they can determine the direction of the

smell by comparing the difference in concentrations between the two antennules.

The legs and mouthparts possess the taste organs, which are also hairs, but of different

shapes from those found on the antennules. Legs probe the sediment for food items and

pass these items to the mouthparts which provide the final determination of whether

something should be swallowed or not.

SHRIMPS

SHRIMPS: Nerves carry impulses from their eyes, antennules, and antennae to their brain. Two nerve trunks run from the brain forming a singular ventral nerve cord.

CRAB

True Crabs:

True crabs have a massive amount of ganglia, which can also be identified as the “brain.” They also have another mass of ganglia that passes down their body. True crabs don’t have a true brain but ganglia which are in control of all of their body functions.

Atlantic Ghost Crab Calico Crab

Horseshoe Crabs:

Horseshoe crabs have a brain the is around the mouth. This brain controls the eyes and many different other functions.

Scorpions are invertebrates in the class Arachnida. Within the cephalothorax they have a "head" which includes a brain. Because they are invertebrates, they do not have a spinal column or spinal cord. They do have sensory organs which connect to the brain through neurons and nerves and nerve chords.

REFERENCES:

 

http://www.els.net/WileyCDA/ElsArticle/refId-a0003637.html

http://www.snow.edu/allans/biology1320/nervoussystem.html

http://www.news-medical.net/health/What-is-the-Nervous-System.aspx

http://w3.shorecrest.org/~Lisa_Peck/MarineBio/syllabus/ch7invertebrates/

Invertwp/2007/tj/nerv.html

http://w3.shorecrest.org/~Lisa_Peck/MarineBio/syllabus/ch7invertebrates/

Invertwp/2007/jillian1/Nerv.html