๐ Structure-Nervous Systems
Structure-Nervous Systems.
This lesson explains the core concepts from this topic for BSc Agriculture entomology preparation.
STRUCTURE AND FUNCTIONS OF NERVOUS SYSTEMS
The basic component in the nervous system is the nerve cell or neuron, composed of a
cell body with two projections (fibres) - the dendrite that receives stimuli and the axon that
transmits information, either to another neuron or to an effector organ such as a muscle. Axon
may have lateral branches called Collateral and terminal arborization and synapse . Insect
nuerones release a variety of chemicals at synapses either to stimulate or to inhibit effector
neurones or muscles. Acetylcholine and catecholamines such as dopamine are the important
neurotransmitters involved in the impulse conduction. Neurones are of following types based on
structure and function.
A. Structural basis
i. Monopolar : neurone with a single axon
ii. Bipolar : neurone with a proximal axon and a long distal dendrite.
iii. Multipolar : neurone with a proximal axon and many distal dendrites.
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This lesson explains the core concepts from this topic for BSc Agriculture entomology preparation.
STRUCTURE AND FUNCTIONS OF NERVOUS SYSTEMS
The basic component in the nervous system is the nerve cell or neuron, composed of a
cell body with two projections (fibres) - the dendrite that receives stimuli and the axon that
transmits information, either to another neuron or to an effector organ such as a muscle. Axon
may have lateral branches called Collateral and terminal arborization and synapse . Insect
nuerones release a variety of chemicals at synapses either to stimulate or to inhibit effector
neurones or muscles. Acetylcholine and catecholamines such as dopamine are the important
neurotransmitters involved in the impulse conduction. Neurones are of following types based on
structure and function.
A. Structural basis
i. Monopolar : neurone with a single axon
ii. Bipolar : neurone with a proximal axon and a long distal dendrite.
iii. Multipolar : neurone with a proximal axon and many distal dendrites.
B. Functional basis
i. Sensory neurone: It conducts impulse from sense organs to cennervoussystem(CNS).
ii. Motor neurones: It conducts impulse from CNS to effector organs
iii. Inter neurones:(association neurone: It interlinks sensory and motor neurones.
The cell bodies of interneurones and motor neurones are aggregated with the fibres inter
connecting all types of nerve cells to form nerve centres called ganglia.
Mechanism of impulse conduction
Impulses are conducted by the neurones by two means.
A. Axonic conduction: Ionic composition varies between inside and outside of axon resulting in
excitable conditions, which leads to impulse conduction as electrical response.
B. Synaptic conduction: Neuro chemical transmitters are involved in the impulse conduction
through the synaptic gap. Neuro transmitters and the type of reactions helping in the impulse
conduction is as follows.
Acetyl CO-A + Choline (choline acetylase ) ๏ฎ Acetyl choline
Acetyl choline + Water (Acetyl choline esterase ) ๏ฎ Choline + Acetic acid
NERVOUS SYSTEM
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 centres (ganglia). These nerve centres (ganglia) are
connected by longitudinal tracts of nerve fibres called connectives and transverse tracts of nerve
fibres called commissures . Central nervous system is made up of the following.
(i).Brain: Formed by the fusion of first three cephalic neuromeres.
Protocerebrum : Large, innervate compound eyes and ocelli.
Deutocerebrum : Found beneath protocerebrum, innervate antennae.
Tritocerebrum : Bilobed, innervate labrum.
Functions: i. Main sensory centre controls insect behaviour.
ii. Ventral nerve cord : Median chain of segmental ganglia beneath oesophagus.
iii. Sub esophageal ganglia: Formed by the last three cephalic neuromeres. Innervates
mandible, maxillae and labium.
iv. Thoracic ganglia: Three pairs found in the respective thoracic segments, largest ganglia,
innervate legs and muscles.
v. Abdominal ganglia: 8 pairs, number varies due to fusion of ganglia, innervate spiracles.
vi. Thoraco abdominal ganglia: Thoracic and abdominal ganglia are fused to form single
compound ganglia. Innervate genital organs and cerci.
II. Visceral nervous system
The Visceral ( sympathetic ) nervous system consists of three subsystems: (i) the
stomodeal or stomatogastric, which includes the frontal ganglion; (ii) Ventral visceral and (iii)
the caudal visceral . 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.
III. Peripheral nervous system
The peripheral nervous system consists of all the motor neurone axons that radiate to the
muscles from the ganglia of the CNS and stomodeal nervous system plus the sensory neurones
of the cuticular sensory structures (the sense organs) that receive mechanical, chemical, thermal
or visual stimuli from an environment.
Summary Cheat Sheet
- Covers the core definitions, classifications, and exam-relevant points from this lesson.
- Focus on key terms, distinguishing characters, and practical relevance in agricultural entomology.
References
2 sources โข [1] [2]
References
Fundamentals of Entomology
Insect Morphology and Systematics
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