Unit 6 in Entomology
Unit six. Reception and Integration: The Insect Nervous System.
In this unit, you'll need to describe the origin of the insect nervous system, identify the major structures of
the insect nervous system and describe their function, compare and contrast the physical structure and
functions of compound eyes and simple eyes, differentiate between the two types of simple eyes and
describe the four types of mechanical receptors insects possess.
Have you ever thought about how insects receive information from their environment?
We use all of our
five senses, but what about insects?
Think about this.
Do they have eyes?
have a nose?
The answer may seem obvious to you: insects don't have noses, but have you ever
thought about how they smell or do they even smell?
Well, yes, they do. They have receptors on their
antenna and other parts of their body to pick up scents.
In order to understand how an insect picks up a
scent, let's first look at how humans do it.
Someone is baking luscious bread in the kitchen.
As you walk by the kitchen, chemical molecules mixed
with the steam waft up from the cooking food and enter your nose.
The molecules then bind to tiny hairs
in the nasal cavity.
These hairs are extensions of olfactory nerve cells.
Nerve cells are also called
The binding of the chemical causes your olfactory nerves to fire and send a message to your
brain. There, the brain interprets the message and fires another nerve cell in response that stimulates
your salivary glands.
You begin to salivate and you're ready to eat.
Insects smell in a similar way.
Their olfactory neurons are not enclosed in a nasal cavity, but within their
antennae, mouthparts or even their legs.
When a female moth sends out a chemical to attract a mate,
the male moth picks up the chemical molecules with his antennae, where his olfactory neurons are
These neurons fire a message to his brain which interprets the signal and stimulates neurons
that cause the male to fly, migrating towards the female's scent.
If you take a look at the diagram below,
you can see the moth.
Male moths usually have very large antennae and these antennae have small
projections on the sides you can see where they can pick up of lots and lots of scent.
If you look at
diagram C, you can see an enlargement of the tip of one of the branches showing all of the olfactory hairs
on the end of the antenna.
The insect nervous system arises during embryonic development from cells called neuroblasts, located in
These neuroblasts first developed into a mass of nerve called a ganglion.
form in each segment and they begin to connect with each other as neuron fibers grow out from each
If you take a look at the diagram on the right, you see a representation of nervous system
At the top you see the neuroblast formation.
In the middle the neuroblasts form ganglia
and then the ganglia interconnect.
And then by C, you have ganglia fusion.
So, as insects become