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Function of the Nervous system.
• Organism responds to changes in the environment for survival.
• Changes occur in the internal and external environment.
• Responses can be reflex or planned.
• Function of the human nervous system is highly sophisticated and it is
very difficult to understand.
• Experiments on animals cannot give full understanding as in other
systems.
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Phylogeny (evolution) of the Nervous system.
• In one cell organism all activities have to be carried out by the same
cell.
• When multicellular animals evolved, some cells evolved as receptor
cells and some as effecter cells with nerve net.
• Next stage led to symmetrical nerve net.
• When the animal became more complex, segmentation occurred.
Each segment had a pair of collection of nerve cells- ganglions.
• Ganglions functioned as coordinating bodies at the segmental level
between receptors and effecters.
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Phylogeny of the Nervous system.
• When the body structure needed movement of effectors from one segment to
another, the structure dragged its nerve supply with it.
• When activity in certain segment became more specialized, the ganglion also had
to develop more than the others.
• This occurred especially in the cephalic end and led to encephalization.
• Certain receptors were pooled in strategic places and developed as special sense
organs.
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Formation of the neural tube.
A. Embryonic disc.
B. Formation of neural plate and neural
crest in ectoderm.
C. Neural grove formation by
depression.
D. The edges of the neural plate comes
together to form neural tube. Introduction to nervous System 7
• Development of the nervous system in human embryo goes through
the stages in evolution.
• Understanding this helps to understand the structure and function of
the Nervous system.
Ontogeny (embryology) of the Nervous System.
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Development of Spinal cord
• The neural tube develops into inner
Ependymal layer and outer mantle layer.
Marginal layer develops as nerve fibers
grow.
• Dorsal or posterior part is named Alar
lamina and anterior or ventral part Basal
lamina.
• Alar lamina performs sensory function
and the Basal lamina moto functions.
• Lateral or intermediate portion performs
autonomic function.
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Encephalization.
• Cranial part enlarges – brain: and the rest remains tubular – spinal cord.
• Three dilations become visible- Prosencephalon, mesencephalon and
Rhombencephalon.
• Telencephalon and diencephalon from forebrain.
• Metencephalon and Myelencephalon from hind brain.
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Organization of brain
• Telencephalon- cerebral cortex and
corpus striatum.
• Diencephalon- thalamus, hypothalamus
and neurohypophysis.
• Mesencephalon- midbrain.
• Metencephalon- pons and cerebellum.
• Myelencephalon- medulla oblongata.
Introduction to nervous System 10
