Nervous System
The nervous system is the part of an animal body that coordinates its behavior and transmits signals between different body areas.
A nervous system can be thought of as an organized collection of neurons that interact at points of contact called synapses.
Nervous system and brain have dual functions:
1. Maintenance of inner vital functions of the organism.
Control of behavior of that organism within a given environment.
Neurons
Neurons are electrically excitable cells whose membrane can generate and transmit changes of voltage that form a signal. These changes in voltage can be graded in amplitude in all or nothing events of fixed amplitude called action potentials.
Synapses
Synapses are point where the membranes of two or more neurons come very close together, associated with specialized features of the membranes.
Electrical signals in one cell may be passed directly to other cells at electrical synapses or more often are converted into chemical signals that diffuse across a tiny synaptic gap that remain between the membrane.
Invertebrate Nervous System
The cellular component of an invertebrate nervous system include:
1. Sensory neurons which convert physical variables into electrical signals.
2. Motor neurons which make synapses with muscles or other effector organs
3. Interneurons which transmit information between other neurons and glia.
In invertebrates, unlike vertebrates, the somata of motor neurons and interneurons are not important sites of synaptic input.
Instead they give rise to a single primary neurite that enter the core of the ganglion and divide into dendritic and axonal regions.
The distinction between input and output regions is often quite blurred, and in most cases it is possible to find input and output synapses adjacent to one another.
Lower invertebrates have simple nervous system such as circular nerve net or a chain of segmentally organized ganglia.
Nervous Human System
Human nervous system is divided into
1. Central Nervous System
The CNS include the brain and the spinal cord and is the site of information processing and control.
2. Peripheral Nervous System
The PNS comprises of all the nerves of the body associated with the CNS.
The nerve fiber of the PNS are of two types : Afferent fibers and Efferent fibers
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