Lec. 20 nervous system.ppt
- 1. R K PANSE Assistant Professor Entomology
- 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
- 12. Insect Brain protocerebrum hypocerebral ganglion recurrent nerve subesophageal ganglion tritocerebrum deutocerebrum frontal ganglion
- 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)