The Nervous System of The Nervous System of ArthropodsArthropods

Insect (arthropod) vs. HumansInsect (arthropod) vs. Humans

ArthropodArthropod

• Background InfoBackground Info– Arthropods are the largest phylum of Arthropods are the largest phylum of

animals and include insects, animals and include insects, crustaceans, and arachnids.crustaceans, and arachnids.

– They have a segmented body and They have a segmented body and usually have many appendages on each usually have many appendages on each segment.segment.

– All arthropods have a strong outer All arthropods have a strong outer exoskeleton made of chitin.exoskeleton made of chitin.

Pictures ExamplesPictures Examples

• Crustacean Crustacean

• ArachnidArachnid

• InsectInsect

Arthropod vs. Human• Insect Nervous system not centralized• Behaviors like feeding, locomotion, and

mating is controlled by segmental ganglia instead of the brain.  

• arthropod nerve cells tend to be much larger and fewer in number than those of vertebrates

• Invertebrates have neurons that are unipolar and vertebrates have neurons that are multipolar

• For fast conduction speed, invertebrates have myelin sheaths while invertebrates have giant axons.

• Sometimes the brain may innervate or inhibit activity in the segmental ganglia. These signals aren’t necessary for survival

– A headless insect can survive for days or weeks until it dies of starvation or dehydration if only it’s neck is sealed to prevent the loss of blood!

Arthropod Nervous Arthropod Nervous SystemSystem

• Arthropods have a nervous system which is Arthropods have a nervous system which is composed of ganglia. It is connected by the composed of ganglia. It is connected by the ventral nerve cord. ventral nerve cord. – The ventral nerve cord has segmented ganglia The ventral nerve cord has segmented ganglia

which is connected by nerve fibers.which is connected by nerve fibers.– A ganglion is a dense group of interconnected A ganglion is a dense group of interconnected

neurons neurons • Their purpose is to process sensory information and Their purpose is to process sensory information and

control motor functions. control motor functions.

• Most commonly, each body segment of the Most commonly, each body segment of the arthropod will have one ganglion on each side. arthropod will have one ganglion on each side.

• Some ganglia are fused and form the brain Some ganglia are fused and form the brain

Arthropod BrainArthropod Brain

• The arthropod’s brain is composed The arthropod’s brain is composed of six ganglia which are fused of six ganglia which are fused together. They are located near the together. They are located near the backside within the head capsule.backside within the head capsule.– There are three parts of the brain and There are three parts of the brain and

each controls certain activities in the each controls certain activities in the body: body:

ProtocerebrumProtocerebrum

• Protocerebrum: This is the first pair Protocerebrum: This is the first pair of ganglia which are responsible for of ganglia which are responsible for vision; they stimulate the nerves that vision; they stimulate the nerves that react with the ocelli.react with the ocelli.– The ocelli are like miniture eyes that The ocelli are like miniture eyes that

are capable of sensing light. They are are capable of sensing light. They are also photoreceptor organsalso photoreceptor organs

– Arthropods generally have two ocelli, Arthropods generally have two ocelli, the lateral ocelli and dorsal orcelli.the lateral ocelli and dorsal orcelli.

DeutocerebrumDeutocerebrum

– Deutocerebrum:The deutocerebrum is Deutocerebrum:The deutocerebrum is the second pair of ganglia which is the second pair of ganglia which is responsible for processing the sensory responsible for processing the sensory information that is collected by the information that is collected by the antennae. antennae.

TritocerebrumTritocerebrum

• Tritocerebrum: The tritocerebrum is Tritocerebrum: The tritocerebrum is the third pair of ganglia which the third pair of ganglia which integrates the sensory inputs from integrates the sensory inputs from the protocerebrum and the the protocerebrum and the deutocerebrums. deutocerebrums.

• The tritocerebrum also links and The tritocerebrum also links and connects the brain to the rest of the connects the brain to the rest of the ventral nerve cord. ventral nerve cord.

Other important gangliaOther important ganglia

• Subesophageal ganglionSubesophageal ganglion– Located in the headLocated in the head– Stimulates the madibular nerves which are Stimulates the madibular nerves which are

partly responsible for sensations of the face.partly responsible for sensations of the face.– Also stimulates the pharynx, salivary glands, Also stimulates the pharynx, salivary glands,

and neck muscles.and neck muscles.– Thoracic GangliaThoracic Ganglia

• Controls movement for traveling by innervating the Controls movement for traveling by innervating the legs and wingslegs and wings

– Abdominal gangliaAbdominal ganglia• Controls the movement of the abdominal musclesControls the movement of the abdominal muscles

The Stomodeal Nervous The Stomodeal Nervous SystemSystem

• The internal organs are stimulated by the The internal organs are stimulated by the Stomodeal Nervous SystemStomodeal Nervous System–     There are a pair of frontal nerves near There are a pair of frontal nerves near

the base of the tritocerebrum that link the base of the tritocerebrum that link the brain with the frontal ganglion on the brain with the frontal ganglion on the anterior wall of the esophagus.   the anterior wall of the esophagus.   • This ganglion activates and stimulates the This ganglion activates and stimulates the

pharynx and muscles associated with pharynx and muscles associated with swallowing.   swallowing.  

• The gut and the heart get activatedThe gut and the heart get activated

PicturesPictures

The End