2. The basic functional unit of nervous system is the nerve
cell or neuron, composed of a cell body (Soma) with two
projections (fibers) the dendrites that receive stimuli and
the axon that transmits information, either to another
neuron or to an effector organ such as a muscle.
3. Axon may have lateral branches called Collateral and
terminal arborization and synapse. Insect neurons
release a variety of chemicals at synapses either to
stimulate or to inhibit effector neurons or muscles.
Acetylcholine and catecholamines such as dopamine are
the important neurotransmitters involved in the impulse
conduction.
4. Neurons are of following types based on
structure and function.
Structural
1) monopolar - a single
projection from the soma,
branching in two (most insect
neurons)
2) bipolar – unbranched
dendrite receives
environmental stimuli, axon
extends to central ganglia
3) multipolar - many branches
off the soma (e.g. strech
receptors)
5. Functional basis
i. Sensory neuron: It conducts impulse from sense organs
to central nervous system (CNS).
ii. Motor neuron: It conducts impulse from CNS to effector
organs (muscles)
iii. Inter neuron (association neuron): It inter-links sensory
and motor neurons.
The cell bodies of inter neurons and motor neurons are
aggregated with the fibers inter connecting all types of
nerve cells to form nerve centers called ganglia.
6. Mechanism of impulse conduction: Impulses are
conducted by the neurons by two means.
Axonic conduction: Ionic composition varies between
inside and outside of axon resulting in excitable conditions,
which leads to impulse conduction as electrical response.
Synaptic conduction: Neurochemical transmitters are
involved in the impulse conduction through the synaptic
gap.
7. What is a synapse and What kinds are there?
A synapse is a space or region between the presynaptic
neuron and the postsynaptic region where the information
(either chemical or electrical is exchanged)
Presynaptic neuron=the
sending or transmitting neuron
Postsynaptic neuron=the
receiving neuron
The diagram to the right
showing the presynaptic
neuron or transmitting neuron
(T) and
The postsynaptic or receiving
(R) neuron.
8. Events at the synapse-The release of the neurotransmitter
occurs when the vesicle moves to the membrane and its
membrane unites with that of the neuron and through
exocytosis is deposited into the synaptic cleft.
9. Neurotransmitters and the type of reactions helping in
the impulse conduction are as follows.
Acetylase
Acetyl CO-A + Choline chloride Acetyl choline
Esterase Acetyl choline
Acetyl Choline Choline + Acetic acid
10. Nervous system can be divided in to
three major
i. Central nervous system (CNS)
ii. Visceral nervous system (VNS)
iii. Peripheral nervous system (PNS)
i. Central nervous system: It contains
double series of nerve centers (ganglia).
These ganglia are connected by
longitudinal tracts of nerve fibers called
connectives and transverse tracts of
nerve fibers called commissures.
Central nervous system includes the
following.
11. Insect Central Nervous System
brain subesophage
al ganglion
thoracic
ganglia
abdominal
ganglia
13. a. Brain: Formed by the fusion of first three
cephalic neuromeres.
Protocerebrum: innervate compound
eyes and ocelli.
Deutocerebrum: innervate antennae.
Tritocerebrum: Bilobed, innervate
labrum.
Brain is the main sensory centre
controlling insect behaviour.
b. Ventral nerve cord: Median chain of
segmental ganglia beneath oesophagus. It
consist by
Ganglion
Longitudinal connectives
Transverse commissures
14. c. Sub esophageal ganglia: Formed by
the last three cephalic neuromeres which
innervate mandible, maxillae and labium.
d. Thoracic ganglia: Three pairs found in
the respective thoracic segments, largest
ganglia, innervate legs and muscles.
e. Abdominal ganglia: Maximum eight
pairs will present and number varies due
to fusion of ganglia. Innervate spiracles.
f. Thoraco abdominal ganglia : Thoracic
and abdominal ganglia are fused to form
a single compound ganglia. Innervate
genital organs & cerci.
15. ii. Visceral nervous system: The visceral (sympathetic)
nervous system consists of three separate systems as
follows: (1) the stomodeal/stomatogastric which includes the
frontal ganglion and associated with the brain, aorta and
foregut; (2) Ventral visceral, associated with the ventral nerve
cord; and (3) Caudal visceral, associated with the posterior
segments of abdomen. Together the nerves and ganglia of
these subsystems innervate the anterior and posterior gut,
several endocrine organs (Corpora cardiaca and Corpora
allata), the reproductive organs, and the tracheal system
including the spiracles.
16. iii. Peripheral nervous system: The peripheral nervous
system consists of all the motor neuron axons that radiate
to the muscles from the ganglia of the CNS and visceral
nervous system plus the sensory neurons of the cuticular
sensory structures (the sense organs) that receive
mechanical, chemical, thermal or visual stimuli from an
environment.
17. FUNCTIONS OF THE NERVOUS SYSTEM
1. To provide for coordination to the other systems
2. To provide for feedback from various parts of the insect
3. To act as the ‘windows’ of the insect by providing
sensory input from the various sense organs, sensilla,
receptors
4. Provides rapid response and feedback from its
peripheral receptors
5. Rapid transfer of information concerning short-term
events and also the coordination of these short-term
events
6. Transfer of messages to the effectors (i.e., muscles and
glands)
