Saturday, 30 June 2018

The nervous system of all vertebrates is similar. Bilateral symmetry, a notochord, and a tubular nerve
cord characterize the evolution of vertebrate nervous systems.
The notochord is a rod of mesodermally tissue that encased a notochord in a firm sheath that lies
ventral to the neural tube. It first appeared in marine chordates and is present in all vertebrate embryos,
but it is reduced or absent in adults. In most vertebrate species, when embryo develop than vertebrae
serially arranged into a vertebral column that replace the notochord. This vertebral column help the
development of strong muscles, allowing vertebrates to become fast-moving, predatory animals. Some
other bones developed into powerful jaws, which facilitated the predatory nature of these animals.
A related character in vertebrate evolution was the development of a single, tubular nerve cord above
the notochord. During early evolution, the nerve cord underwent , regional modification, and
specialization into a spinal cord and brain. Over time, the anterior end thickened variably with nervous
tissue and functionally divided into the hindbrain, midbrain, and forebrain. In the sensory world of the
fast-moving and powerful vertebrates, the anterior sensory receptors became more complex and
bilaterally symmetrical. For example, paired structures, such as eyes and ears, developed to better
gather information from the outside environment.
The nervous system of vertebrates has two main divisions (see figure).

Central nervous system
The central nervous system is consist of the brain and spinal cord and those site where information
Peripheral nervous system
The peripheral nervous system is consist of all the nerves of the body that outside the brain and spinal
cord. These nerves are commonly divided into two groups:
Sensory (afferent) nerves
Sensory (afferent) nerves, transmit information to the central nervous system.
Motor (efferent) nerves
Motor (efferent) nerves, which take away commands from the central nervous system. The motor nerves
further divide into the voluntary (somatic) nervous system, which extend commands to skeletal
muscles, and the involuntary (visceral or autonomic) nervous system, which stimulates other muscles
(smooth and cardiac) and glands of the body.
The nerves of the autonomic nervous system divide into sympathetic and parasympathetic systems.
Nervous system pathways are consist of individual neuronal axons bundled like the strands of a telephone
Difference between central and peripheral nervous system
In the central nervous system, bundles of nerve fibers are called tracts. In the peripheral nervous
system bundle of nerve fiber, are called nerves. The cell bodies from which the axons extend often
cluster into groups than these groups are called nuclei if they are present in the central nervous system
and ganglia if they are present of the peripheral nervous system.


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