Our sense organs 45

The cells
– our body’s 100 million
million building blocks
Did you know that the human body consists of
approximately 100 million million cells, each of
which contains 10,000 times as many molecules
as there are stars in the Milky Way? Note that the
Milky Way comprises at least 100,000 million
stars.
The smallest building blocks of the human body,
as well as of plants and animals, are the cells.
Body structures consist of cells, along with intercellular
material. In the case of unicellular organisms
(protozoa), the cell is the entire organism. A
cell is the smallest possible morphological entity
capable of independent life. In metazoa (manycelled
creatures) the cells are the basic functional
organic units, or building blocks, which make up
the whole organism. Cells differ widely in regard
to size, shape, and function.
Cell membrane
Section of
a dendrite
Cytoplasm with
mitochondria
and endoplasmic
reticulum
Nucleus with
nucleolus
Post-synaptic
unit
Synaptic vesicles
Node of Ranvier
Myelin sheath
Pre-synaptic
nerve terminal
Schematic diagram of a neural (nerve) cell.
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